CA1290813C - Pacemaker for detecting and terminating a tachycardia - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE

A heart pacemaker detects pace-terminable tachycardia conditions in the atrium of the heart in accordance with selected high rate, rate stability, sudden onset and sustained high rate criteria. When a pace-terminable tachycardia is detected, programmed treatment modalities are applied to attempt to terminate the tachycardia. The tachycardia is treated by applying timed bursts of electrical pulses in formats defined by programmed primary and secondary treatment modalities.
The primary and secondary treatments may be applied in an order which is dependent upon the prior successful treatment of similar tachycardias. The pacemaker may also utilize remembered treatment values which were successfully applied to treat similar tachycardias.
The pacemaker may be programmed to restart the primary and secondary modes of treatment in the event that the modes initially failed to terminate a tachycardia. The pacemaker may also be programmed to limit the rate of burst pulses to avoid overstimulating the heart.

Description

\~

PACEMAKER FOR DETECTING
AND TERMINATING A TACHYCARDIA
TEC~NICAL FIELD
The invention relates to body implantable pacemakers which monitor electrical activity of the heart and stimulate heart tissue as required to revert certain arrhythmias. More particularly, the invention relates a heart pacemaker which detects a pacer-terminable tachycardia and applies electrical stimulat-ing signals in programmed treatment modalities to ter-minate the tachycardia.

BACKGROUND OF THE INVENTION
Implantable cardiac pacemakers have been developed to detect undesirably rapid contractions of the heart which are characterized as tachyarrhythmias or tachycardias. It is known that such pacemakers may terminate or interrupt a detected tachycardia by apply-ing stimulation pulses to the heart which coincide with a termination time period for the tachycardia. Such stimulation pulses may be applied in bursts (one or more pulses). In operation, the time at which a burst begins, the number of pulses in the burst and the time interval between such pulses may be programmed to a fixed value or may be adaptively determined as a per-centage of the detected rate of the tachycardia. ~t

-2-has also been proposed that the tachycardia treatment pulses may have intervals which automatically decrement within the burst. Alternatively, the time at which the burst begins or the intervals between pulses of the burst may be "scanned" by incrementing and/or decrement-ing these values by programmed amounts as bursts are applied to terminate a tachycardia.
Typically, antitachycardia pacemakers attempt to terminate tachycardias when the heart rate exceeds a predefined high rate. Although this means for detecting a tachycardia has the advantage of simplicity, it has the disadvantage that it will detect and attempt to treat high rate sinus rhythms which result from exercise and which the pacemaker should not attempt to terminate.
lS Also, use of the simple high rate detection criterion will result in an attempt to treat other non-pace-terminable conditions.
It is therefore desirable to develop detec-tion criteria which can distinguish and treat only those tachycardias which are susceptible to pacer-termination, such as reentrant tachycar~ias. It has been suggested that a pace-terminable tachycardia may be more accurately identified by detecting the rate of onset of the tachy-cardia. Suddenness of onset often indicates a reentrant tachycardia which may be treated by the pacemaker.
High rate sinus rhythms resulting from exercise will not be detected as pacer-terminable tachycardias, because they do not have the characteristic of sudden onset.
Although the sudden onset detection criterion is useful in distinguishing pacer-terminable tachycardias, it is not capable of discriminating between all such tachycardias. Moreover, a simple sudden onset criterion could mistakenl~ indicate a pacer-terminable tachycardia as a result of transitory cardiac conditions, such as the compensatory pause that normally follows a premature ~1 29~ .3 cardiac contraction occurring during a period of high rate cardiac activity.
It is therefore desirable to provide an improved system for reliably detecting pace-terminable tachycardias and a pacemaker which reliably detects pace-terminable tachycardias in accordance with programmed detection criteria which are defined with respect to the needs of a patient.
It is also desirable to provide a pazemaker which employs the criteria o~ high rate, sudden onset, rate stability and sustained high rate to distinguish pace-terminable tachycardia conditions which may be treated, preferably such a pacemaker wherein the criteria may be selectively combined to maximize the probability of detecting pace-terminable tachycardias for a particular patient.
It is further desirable to provide a pacemaker with ~n improved sudden onset tachycardia detection criterion which distinguishes actual pace-terminable tachycardias from transitory cardiac conditions which may occur as a result of a compensatory pause following a premature cardiac contraction during a period of high rate cardiac activity.
It is further desirable to provide a pacemaker with a rate stability criterion which compares the present high cardiac rate with an average cardiac rate determined from prior rate measurements and diagnoses a pace-terminable tachycardia if the present rate is within a prede~ined range oP the a~erage rate.
It is ~urther desirable to provide a paaemaker with a sustai~ed high rate criterion which will cause a tachycardia to be treated iE a predefined high cardiac rate is sustained Eor a , .;

.3 predetermined period, even if other selected cardiac detection criteria have not been met.
It has been suggested that an antitachycardia pacemaker may treat a tachycardia with treatment parameters which were successfully applied to treat a previou~ tachycardia. Although this general procedure has the advantage, on the average, of reducing the time required to treat succes~ive tachycardia~, it has the disadvantage that it may extend the time for treatment by attempting to treat a tachycardia of one rate with treatment modalities which were previously successful in terminating a tachycardia having a very different rate.
It is therefore also desirable to provide an antitachycardia pacemaker which remembers the valùes of the parameters of treatment modalities which were successfully applied to one tachycardia and which applies these remembered values to treat a similar tachycardia. ~s well, it is desirable to provide an antitachycardia pacemaker which conditions its use of remembered values of treatment modalities on a comparison of the present tachycardia rate with the tachycardia rate of the previous successfully treated tachycardia.
It is further desirable to provide an antitachycardia pacemaker which utilizes primary and secondary methods for treating a tachycardia.
It is further desirable to provide a pacemaker wherein the secondary treatment method may be applied first, if the treatment history indicates that this method has been more successful than the primary method for treating a similar tachycardia.

~ 290~

It is further desirable to provide a pacemaker wherein a detected pace-terminable tachycardia is treated by preselected primary and secondary methods and, if these methods do not terminate the tachycardia, the pacemaker optionally restarts the tr~atment methods to again attempt to terminate the tachycardia.
SUMMARY OF THE INVENTION
The pacemaker of the invention includes a microprocessor which is programmed to detect a pace-terminable tachycardia by using a detection algorithm which selectively includes high rate, rate stability, sudden onset and sustained high rate tests.
The invention provides an antitachycardia pacemaker comprising a means for detecting electrical events occurring in at 'least one chamber of the heart, a means for detecting the events which exceed a predefined tachycardia rate, and in one aspect a means for determining the relative rate stability of the events which exceed the tachycardia rate and a means for detecting a pace-terminable tachycardia when at least a first preselected number of the events exceed the tachycardia rate and a second preselected number of the events have a defined rate stability. In another aspect there is a means for determi,ning the relative suddenness of the onset of events which exceed the predefined tachycardia rate and a means for detecting a pace-terminable tachycardia when a first preselected number of the events exceed the tachycardia rate and the event~ have an onset which exceeds a predefined rate of onset or a sustained high rate number o~ the events exceed the tachycardia rate, the sustained high rate number being greater than the first preselected number. In another aspect there is a means for detecting a pace-terminable tachycardia when at least a preselected number of the events exceed the tachycardia rate; a means for generating a first set of electrical signals having characteristics defining a primary tachycardia treatment modality and a second set of electrical signals having characteristics defining a secondary tachycardia treatment modality; and a means for applying the primary and secondary treatment modalities to interrupt a detected pace-terminable tachycardia in a preqelected order of preference.
In yet another aspect there is a means for detecting a pace-terminable tachycardia when at least a preselected number of said events exceed said tachycardia ra~e; a means for selectively applying at least one burst of electrical signals to terminate a detected pace-terminable tachycardia, the burst starting a pre-defined start delay time following a detected synchronizing event and including a praselecte~ number of electrical pulses, successive pulses being separated by a predefined burst cycle interval; and a means for remembering the values o~ the start delay time, number of burst pulses and burst cycle interval for a successfully terminated tachycardia and for selectively applying these values to terminate a subsequent similar detected pace-terminable tachycardia.
The pacemaker of the invention treats a detected tachycardia by applying electrical stimulating pulses to the heart in programmed treatment modalities. The treatment modalities are deflned in terms of the number of stimulating pulses applied to the heart, the time at which the ~irst of such pulses is applied following a detected tachycardia depolarization and the period between stimulatlng pulses.
The start delay and the pulse~to-pulse interval may be defined as ~ixed program values, or as adaptive values derived as - 5a -a percentage of the detected high cardiac rate. If a burst is generated, the start delay of the pulse or the pulse-to-pulse interval o~ the burst may be "scanned" by incrementing or decrementing the values of these parameters a preselected number of steps or by incrementing and decrementing the parameters in a predefined search pattern. Alternatively, the intervals of the pulses within a burst may be automatically decremented in the autodecremental mode.

- 5b -~6--In adaptive and autodecremental bursting the period between burst pulses may not be decreased below a predefined programmed minimum interval. This pro-grammed limit helps ensure that the heart will not be stimulated by excessively high rate bursts.
The values of successfully applied burst treat-ment parameters may be remembered and applied to termi-nate similar tachycardias which are later detected. At least a primary and an optional secondary treatment modality are employed in an effort to terminate each detected tachycardia. The order of application of the primary and secondary modalities may be reversed if the secondary treatment was the only recorded successful modality for treating a previous similar tachycardia.
If the primary and secondary treatment modali-ties are unsuccessful in treating a tachycardia, the modalities may be tried again if selected conditional restart criteria are met.

BRIEF DESCRIPTION OF THE DRAWINGS
FIGURE 1 illustrates a block diagram of the pacemaker of the invention.
FIGURE 2 illustrates a timing diagram of car-diac signals which satisfy the sudden onset tachycardia criterion of the invention.
FIGURE 3 illustrates other cardiac signals which satisfy the sudden onset criterion of the invention.
FIGURE 4 illustrates cardiac signals which do not satisfy the sudden onset criterion of the invention.
FIGURE 5 illustrates other cardiac signals whlch do not satisfy the sudden onset criterion of the invention.
FIGURE 6 illustrates another set of cardiac signals which satisfy the sudden onset criterion of the invention.

.3 FIGURE 7 illustrates a block diagram of the functional operation of the pacemaker of the invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENT
The pacemaker of the invention employs selec-tive detection criteria to detect the presence of atachyarrhythmia or tachycardia of the heart. When a tachycardia is detected, the pacemaker reacts in a pro-grammed fashion to attempt to terminate the undesirable condition by applying programmed bursts of electrical signals to the heart in accordance with selected treat-ment modalities. If a detected tachycardia is similar to a previously successfully terminated tachycardia, the pacemaker may be programmed to apply the previous successful treatment modality to terminate the present tachycardia.
In principle, the detection and treatment modalities of the invention may be utilized to detect and treat a tachycardia in the atrium and/or ventricle of the heart. However, the detection and treatment modalities have at present been implemented primarily to detect and terminate supra-ventricular tachycardias.
Accordingly, the detection and treatment criteria of the invention will hereafter be described with respect to a single chamber atrial pacemaker. It should be understood that the disclosed single chamber embodiment does not limit the invention to use in the atrium. The invention may be employed to detect and treat tachy-cardias of the ventricle as well as the atrium.
The pacemaker of an embodiment of the inven-tion can detect atrial reentrant tachycardias. Reentranttachycardias occur as a result of a circular conduction of electrical signals within the heart. Such tachycar-dias may be terminated by a properly timed stimulation pulse or set of stimulation pulses which will hereafter be referred to as a "burst". Such tachycardias which 9~8~1~3 r--~

can be treated or terminated with antitachycardia pacing are hereafter referred to as pace-terminable tachycardias. Pace-terminable tachycardias musk be distinguished from non-pace-terminable heart rhythms which occur, for example as a result of exercise.
It should now be understood that the atrial pacemaker of an embodiment of the invention can more reliably distinguish non-pace-terminable tachycardias such as occur as a result of exercise from pace-termin-able tachycardias, for e~ample reentrant tachycardias.If a pace-terminable tachycardia is detected, the pace-maker generates a physician-programmed burst which has previously been efficacious in terminating the tachy-cardia.
The atrial pacemaker of the invention monitors the operation of the heart by detecting electrical sig-nals or "events" which occur in the atrium. If a peri-odic atrial signal is not detected, the pacemaker may be programmed to a bradycardia mode to apply an electri-cal stimulation signal to maintain a predefined pacing rhythm for the heart.
FIGURE 1 illustrates a block diagram of the major functions of an implanted atrial pacemaker in accordance with the invention. As shown in FIG. 1, the pacemaker includes an atrial tip electrode 1 which contacts the heart (not shown) and an associated ring electrode 3 which provides a ground reference with re-spect to the electroda 1. These bipolar electrodes apply electrical stimulating signals to the atrium and detect electrical signals which occur within the atrium.
Signals detected in the atrium are applied by the elec-trodes to a sense amplifier 5 which amplifies the signals by frequency-domain filtering if they are within the expected frequency range of cardiac depolarizations.
The amplified signals are transmitted to a logic and control circuit 7 which includes a microprocessor. The logic and control circuit includes diagnostic data regis-ters which store digital information concerning the treatment of tachycardias and the detected condition of the heart.
The logic and control circuit of the appara-tus of FIG. 1 processes the signals from the sense ampli-fier 5 and uses time-domain analysis to distinguish between valid cardiac signals and extraneous electrical interference, such as noise signals. The logic and control circuit also generates pacing signals and tachy-cardia termination bursts which are applied to an output circuit 9 which converts khe input logic control signals to voltage levels suitable for stimulating the heart.
The pacing or burst signals are applied in accordance with the type of signal that is detected by the sense amplifier 5 and stored treatment information within the microprocessor of the logic and control circuit.
The logic and control circuit implements pro-grammed commands which are received from an external programmer. An implanted antenna coil 11 inductively couples electromagnetic programming pulses from the external programmer to a programming and data trans-mission circuit 13 which applies the data to the logic and control circuit 7. The received data pulses contain programming information in a pulse-position-modulated, binary-coded format. The binary-coded information is demodulated and stored within the logic and control circuit to define the operating characteristics of the pacemaker.
The timing for the microprocessor and digital circuitry of the pacemaker is provided by a crystal oscillator 15 and certain operational modes are ini-tiated by a reed switch 16 which is actuated by an ex-ternally applied magnetic field.
It should generally be understood that the output section 9 of the system of FIG. 1 includes a _g_ pulse generator that may be powered, for example by a single 2.8 volt lithum iodine power cell. The output circuit employs a voltage multiplier and capacitors which are controlled to generate pacing stimuli having a programmed amplitude and timing.
The microprocessor-controlled atrial pacemaker of the invention operates in three bradycardia or atrial pacing modes: AAI, AAT and ~00 (ICHD Code). In addition, the pacemaker may be programmed to an 000 or OAO nonpacing mode.
In the AAI or demand inhibited mode the pace-maker of the invention responds to signals detected by the sense amplifier 5 in three ways. First, if atrial depo].arizations are not sensed within a predetermined period, the pacemaker generates stimulating pulses at the programmed pacing rate. ~econd, if spontaneous atrial depolarizations are sensed at a rate higher than the programmed rate, the atrium is not paced. Third, the logic and control circuitry 7 may identify detected signals as electrical interference or noise and initiate either asynchronous pacing at a programmed rate or non-pacing in the 000 mode, depending upon the programmed noise reversion mode of the pacemaker.
In the AAT or demand synchronous mode, the pacemaker paces the heart at a programmed rate in the absence of sensed cardiac de~olarizations. The pace-maker also paces the heart synchronously when sensed events occur at or above the programmed rate but below a predetermined maximum pacing rate. Consequently, the pacemaker will not be inhibited in response to extraneous noise sources. If atrial sense events occur so rapidLy that the pacemaker would be required to pace faster than its maximum pacing rate, the pacemaker will not pace synchronously with every event. Instead, it will . .
--11~
pace synchronously with some events so that the result-ing pacing rate is equal to or lower than the prede-fined maximum pacing rate.
In the A00 or asynchronous mode, the sense amplifier 5 is not used. The pacemaker continuously generates stimulation signals to the heart at a program-med rate.
In the 000 mode, the pacemaker does not pace or sense the heart. In the OAO mode the pacemaker will not pace the heart but does monitor heart activity.
These modes may be used to check the patient's heart rhythm without stimulating the heart.
The antitachycardia operation of the pace-maker may be activated in the AAI, AAT or 000 modes without affecting the bradycardia or atrial pacing operation in these modes.
The effectiveness of an automatic antitachy-cardia pacemaker is significantly increased iL the device can distinguish between elevated sinus rhythms, for example resulting from exercise, and pace-terminable rhythms which may occur, for example as a result of reentrant mechanisms. Although a high atrial rate is the most characteristic indicator of a tachycardia, its specificity in identifying pace-terminable tachycardias is limited.
It has been found that pace-terminable tachy-cardias frequently exhibit characteristics in addition to a high rate. Thus, pace-terminable tachycardias may often be characterized by an abrupt or rapid onset, a relatively stable rate over time, and a high rate sustained over a relatively long period. While pace-terminable tachycardias may occur without these charac-teristics and sinus rhythm may exhibit them, the charac-teristics are useful criteria for detecting pace-terminable tachycardias in a majority of cases, and particularly when the criteria are used in combination in the programmable pacemaker of the invention.
Thus, the pacemaker of the invention operates with four programmable detection criteria: high rate, sudden onset, rate stability and sustained high rate.
The preferred pacemaker of the invention can combine these criteria in the following nine different combin-ations to detect the presence of a pace-terminable tachycardia:

1. high rate 2. high rate and sudden onset

3. high rate and (sudden onset or sustained high rate)

4. high rate and rate stability

5. high rate and (rate stability or sus-tained high rate)

6. high rate and sudden onset and rate stability

7. high rate and [(sudden onset and rate stability) or sustained high rate]

8. high rate and (sudden onset or rate stability)

9. high rate and (sudden onset or rate stability or sustained high rate) Selection of the appropriate recognition mode for a pace-terminable tachycardia and selection of appropriate numerical values for the parameters of -the mode necessitates a complete electrophysiologic analysis of the specific tachycardias being treated. In addition, a study of the patient's normal sinus rhythm is required to determine how best to discriminate a pace-terminable tachycardia for the particular patient.
The high rate criterion of the pacemaker consists of both an interval between successive atrial events and a number of consecutive intervals at or below that selected interval length. In the present embodiment the high rate interval for detecting a tachycardia may be programmed from 266 to 635 msec and the number of consecutive high rate intervals may be programmed from 5 to 99. The requirement that a number of intervals occur sequentially at the defined high rate helps to prevent the pacemaker from responding to short runs of ectopic beats or short excursions over the programmed high rate which may be caused by emotion, exertion, or changes in posture and which therefore should not be treated as pace-terminable tachycardias.
If the pacemaker detects an atrial event which occurs at an interval with respect to the preceding atrial event that is less than the defined high rate interval, the pacemaker will recognize the atrial event as a high rate event. The pacemaker will then count successive high rate events and, if it reaches the pro-grammed number o~ intervals for the high rate criterion, it will determine that the high rate criterion has been satisfied. However, if the pacemaker detects an interval greater than the programmed high rate interval at any time before having counted the programmed number of high rate intervals, it will begin a new count from zero for the next detected high rate interval.
The sudden onset criterion is programmed for the pacemaker of the invention in terms of the degree of change in successive atrial intervals (i.e., the degree of change in the rate of atrial events~. This degree of change is programmable from 20 to 502 msec.
The selected value of degree of interval change repre-sents the minimum difference that must exist between a detected high rate interval and a preceding sinu.s or low rate interval for the pacemaker to diagnose a sudden onset. With this criterion, it should be understood that the larger the val~le which is selected for the degree of interval change, the more difficult it is to meet sudden onset criterion.
In operation, the pacemaker records the pre-sently detected high rate atrial interval and then checks the preceding three intervals to determine whether the acceleration in atrial rate was abrupt. The acceleration is identified as abrupt if the immediately preceding interval is longer (i.e., slower rate) than the high rate interval by at least the value of the programmed degree of interval change and either of the next pre-ceding two intervals i5 longer than the high rate interval. This relationship for detecting a sudden onset is illustrated in FIG. 2. FIG. 2 shows a succes-sion of atrial events 17a-e and corresponding ventricular events l9a-d which occur in time, with the earliest event occurring on the left and the latest or most recent event occurring on the right. The most recent interval between atrial events 17d and 17e is designated as "S"
to indicate that this interval is shorter than the pre-defined high rate interval and therefore corresponds toan atrial rate that is higher than the predefined hiyh rate. As shown in EIG. ~, the intervals between atrial events 17a and 17b and 17b and 17c are characterized as "L", to designate intervals that are longer (slower rate~ than the predefined high rate interval. The inter-val between the atrial events 17c and 17d is designated as "L+" to indicate that this interval is greater than the program~ed high rate interval by an amount which exceeds the programmed degree of interval change.
With reference to FIG. 2, the most recent atrial event (17d-e) is recognized as a high rate event, because it occurs with an interval S which is shorter than the predefined high rate interval of the pacemaker.
When this high rate interval is detected, the pacemaker checks the next preceding interval and notes that it is longer than the predefined high rate interval by an amount greater than the predefined degree of interval change. The pacemaker then checks the next two preced-ing intervals and determines that they are both longer ("L") than the defined high rate interval. The pacemaker thus recognizes that the event ~17d e) satisfies the high rate criterion of the pacemaker. It should be understood in this regard that the pacemaker would recog-nize this event (17d-e) as a sudden onset event as long as either of the intervals defined bet~,7een the events

10 17a and b or 17b and c was longer than the high rate interval.
FIGURE 3 illustrates an example of another sequence of intervals which would be recognized as a sudden onset condition. FIGURE 3 illustrates a circum-15 stance wherein the interval 22 just preceding the first detected high rate interval 24 does not satisfy the degree of interval change criterion, but the next pre-ceding interval 26 does satisfy this criterion. Under this circumstance, a sudden onset is detected. Thus, 20 with respect to the atrial events 21a-e, the pacemaker notes that the event 21e occurs at an interval 24 shorter than the preclefined high rate interval and therefore recognizes the event 21e as a high rate event. The pacemaker thereafter checks the preceding 25 interval 22 and determines that, although the interval is longer than the defined high rate interval, it does not exceed the high rate interval by the predefined degree of interval change. The pacemaker then checks the next preceding interval 26 and determines that this 30 interval exceeds the high rate interval by at least the defined degree of interval change. The pacemaker thus determines that the high rate event 21e satisfies the sudden onset criteria.
FIGURE ~ ustrates a high rate atrial event 35 23e and preceding events 23a-23d which do not satisfy the sudden onset criteria. Thus, as shown in FIG. 4, a ~15-3~

high rate interval 28 is detected, but the previous two intervals are not sufficiently long to satisfy the prede-fined degree of interval change. Therefore, the high rate event 23e does not satisfy the sudden onset criteria defined with respect to FIGS. 2 and 3.
The sudden onset criteria is necessarily com-plex because it must differentiate a legitimate sudden onset high rate event from transitory events which occur relatively rapidly but which do not indicate a tachycar-dia. For example, a compensatory pause normally followsa premature cardiac contraction. This compensatory pause could appear to indicate a sudden onset of a re-entrant tachycardia if the premature contraction occurs during a period of high rate atrial activity. With reference to Fig. 5, the pacemaker of the invention distinguishes this situation from an actual sudden onset tachycardia, because it finds that the two intervals 30 and 32 preceding such a pause 34, like those following it, are also shorter than the predefined high rate inter-val. This condition does not satisfy the sudden onsetcriterion, because the criterion requires that at least one of the i~tervals 30 and 32 exceed the predefined high rate interval. The pacemaker therefore correctly determines that a compensatory pause amid an ongoing high rate does not satisfy the sudden onset criterion for a reentrant tachycardia.
On the other hand, FIG. 6 illustrates a sitll-ation wherein the sudden onset criterion is satisfied in the presence of a high rate atrial event preceding a tachycardia event 27. In this case, it is assumed that a premature atrial contraction results in an interval 36 that is shorter than the programmed high rate inter-val, followed by an interval 38 that is longer than the programmed high rate interval. If the interval 38 is longer than the programmed high rate interval by at least the value of the defined degree o interval change, this combination satisfies the sudden onset criterion.
Thus, the sudden onset criterion of the pace-maker often is able to distinguish pace-terminable re-entrant tachycardias from sinus tachycardia conditionswhich are not pace-terminable.
Atrial fibrillation or sinus tachycardia can have an onset which is as sudden as that of a pace-terminable tachycardia. Accordingly, it is desirable to provide additional means for distinguishing pace-terminable tachycardias. As mentioned above, it has been found that certain pace-terminable tachycardias are relatively stable in rate. On the contrary, non-pace-terminable tachycardias such as atrial fibrillation and sinus tachycardias resulting from exercise are gener-ally not very stable. Rate stability is therefore a criterion which can be used tc, distinguish a pacP-terminable tachycardia from fibrillation and exercise-related tachycardias. In the pacemaker of the invention, rate stability is programmed as a degree of interval change from 15 to 149 msec; and as a number of intervals from 8 to 250.
In operation, when the pacemaker detects three consecutive high rate intervals, it calculates an average interval length. The average interval length is deter-mined by adding the value of the highest and lowest of the three detected interval values and dividing the sum by 2. Each subsec~ent consecutive high rate interval is then compared with this average. If subsecluent consecutive high rate intervals do not vary by more than th~ programmed degree of interval change from the average, and this stability continues for the programmed number of intervals, the rate stability criterion is satisfied. If at any point a detected high rate interval varies from the average by more than the proc~rammed degree of interval change, the count of stable events .

.3 will be set to zero and the pacemaker will calculate a new average by using the current high rate interval and the two previous high rate intervals. Thereafter the pacemaker will again check for the predefined number of stable intervals. If at any time an interval greater than the predefined high rate interval is detected, the pacemaker will reset its stable rate counter to zero and will compute a new average when three successive high rate events are detected. It should generally be understood that the smaller the programmed degree of interval chanye and the greater the programmed number of intervals, the harder it is for the rate stability criterion to be satisfied.
The pacemaker is also capable of detecting a sustained high rate. This parameter is essentially a backup feature, with a programmable range that begins where the number of intervals for the high rate criter~-ion stops. The sustained high rate criterion is there--fore programmable from between 6 and lO0 (always at least one more than the high rate criterion), up to 250 intervals. The sustained high rate criterion may be programmed only in conjunction with sudden onset and/or rate stability (i.e., combinations 3, 5, 7 and 9 listed above). If a tachycardia is detected and the high rate criterion is satisfied, but the selected sudden onset and/or rate stability criteria are not, satisfaction of the sustained high rate criterion will trigger the tach-ycardia pacing response. This operation generally insures that a pace-terminable tachycardia which con-tinues for an extended period of time (the number ofsustained hiyh rate inte~vals) will be treated by the pacemaker, even if it does not exhibit sudden onset and/or rate stability.
The operation of the pacemaker with the above-identified criteria may be better understood with respect to an example using combination No~ 9 with the follow-ing parameters:

- High rate criterion is 399 msec for 12 intervals ~ Sudden onset degree of interval change is 256 msec - Rate stability criterion is 26 msec for a degree of interval change and lO0 rate stable intervals - Sustained high rate criterion is 200 intervals at the defined high rate When the first high rate interval (i.e., the first interval measured as shorter than 399 msec) is detected, the pacemaker notes in memory that one short high rate interval has occurred. For each subsequent consecutive interval shorter than 399 msec, an addi-tional entry is made. The high rate criterion is satisfied when 12 consecutive short intervals have been counted. If, before that point, an interval longer than 399 msec is measured, the high rate criterion is not satisfied. Counting begins anew with the next interval shorter than 399 msec.
Assessment of sudden onset begins immediately after sensing the first interval shorter than 399 msec.
The pacemaker examines the immediately preceding interval.
If it determines that this interval was 655 msec (399 plus the sudden onset degree of interval change of 256 msec) or more, it considers the initial requirement of the sudden onset criterion to be satisfied. It then examines the next preceding interval; if this interval was longer than 399 msec, the pacemaker considers the sudden onset criterion to be satisfied. If this interval is shorter than 399 msec, the pacemaker then looks at , --19--the next preceding interval. If that interval is longer than 399 msec, the criterion is satisfied.
Alternatively, if the interval immediately preceding the first high rate interval is longer than 399 msec but not longer by an amount at least egual to the sudden onset degree of interval change (i.e., it is shorter than 655 msec), the next preceding interval is examined. If this interval is longer than 399 msec by at least the sudden onset degree of interval change (the interval is 655 msec or longer), the sudden onset criterion is satisfied. Otherwise, a gradual onset tachycardia is diagnosed.
The pacemaker begins to assess rate stability simultaneously with the detection of a high rate event.
If it finds three consecutive high rate intervals, for e~ample 390, 350 and 360 msec, it averages the value of the longest of the three intervals (390 msec) with the value of the shortest (350 msec).
The average (370 msec) is then used as the basis for evaluating subsequent intervals. When 100 consecutive intervals that fall between 345 and 395 msec (i.e., not more than 26 msec variation from the average) have been counted, the rate stability criterion is satisfied.
If, before lOO intervals have been counted, a high rate interval is measured that varies from the average by more than 26 msec, the counter is cleared.
The pacemaker computes a new average using the current high rate interval and the two preceding it. The pacemaker then continues to assess following high rate intervals with respect to the newly computed average.
The sustained high rate counter operates in the same manner as the high rate counter. Sensing of the first interval shorter than 399 msec is registered by both counters. Both then count each consecutive interval of less than 399 msec. The high rate counter stops when 12 intervals have been counted. However, the sustained high rate counter will continue to count intervals until it reaches 200, which satisfies the sustained high rate criterion (like the high rate counter, it is cleared if an interval longer than 399 msec is measured before its programmed number of intervals have been counted). In the event that the criterion or cri-teria with which sustained high rate was programmed are not satisfied, the pacemaker uses the sustained high rate criterion by itself to identify a tachycardia which should be treated.
If all the requirements of programmed tachycardia recognition modes are rnet, the pacemaker enters a diagnosis of pace-terminable tachycardia. Thus, in the example, a pace-terminable tachycardia is diagnosed if the selected criteria of combination No. 9 is satisfied.
When the pacemaker of the invention, detects a pace-terminable tachycardia, it attempts to break the cycle of the tachycardia by applying stimulus pulses to the atrium. The basic therapeutic modality of the pace-maker is a burst which for the purpose of the following discussion is defined as one or more electrical stimulat~
ing pulses applied to the heart and timed to interrupt the tachycardia. The treatment modality of the pacemaker is programmed with respect to three variables. The first of these is the number of pulses from 1 to 25~ in a treatment burst. The second variable is the length of a delay interval which is timed between a sensed synchronizing tachycardia event and the first pulse of the burst. This interval may be programmed from 3 to 653 msec in 2.56 msec steps. The third variable is the burst cycle length which is the pulse-to-pulse interval within a burst. The burst cycle length may be programmed from 10 to 653 msec in 2.56 msec steps.
The initial value of the delay and/or the burst cycle length of the pacemaker may be programmed ~g~ .3 ~22-by fixed or adaptive. In the fixed mode, the delay and burst cycle length are programmed as fixed values in milliseconds. In the adaptive mode, the delay and/or burst cycle length are programmed as a percentage of the interval of the detected tachycardia. In the adap-tive mode, the timing of the treatment modality there-fore depends upon the rate of the detected tachycardia.
As an example, the delay and burst cycle lengths may be programmed as seventy-five percent of the detected tachycardia interval. This provides some adaptability in treating tachycardias which exhibit rate variations over time.
The value of the delay or burst cycle length may be changed in a "scanning" mode wherein the values are incremented or decremented over successive bursts.
In the scanning mode, the value of the burst cycle length or the delay is changed in one of three sequences:
incremental, decremental, or a search pattern which is alternately incremented and decremented. A scanning burst generally increases the effectiveness of the`pace-maker's attempts to locate a characteristic "termination zone" for the tachycardia. If a stimulus is provided in the appropriate termination zone, the tachycardia will be interrupted. In the scanning mode, an initial value of the burst cycle length or delay is thus incre-mented, decremented or alternately incremented and decremented in a search pattern in an effort to apply a stimulus within the termination zone. A scanning burst sequence may be programmed with either fixed or adaptive initial intervals for burst cycle length or delay.
Thus, the initial burst cycle length or delay in a scan-ning mode may be programmed to a fixed value or may be computed as a percentage of the rate interval of the detected tachycardia.
The burst scanning mode is programmed with respect to three parameters: step size, number of `~ 2~s~

steps and number of sequences. The step size for a scanning sequence is the amount by which the burst cycle length or delay are increased or decreased for each successive burst. The pacemaker of the invention may be programmed to a step size of, for example, from 2.56 to 38.4 msec. ~s an example, if a burst is pro-grammed to seven pulses, with a delay of 200 msec and an initial burst cycle length of 251 msec, scanning the burst cycle length incrementally with a step size of 10.2 msec will cause the pulses of the second burst to a have a cycle length of about 261 msec, the pulses of the third burst to have a cycle length of 27~ msec, and so on.
On the other hand, if scanning is programmed to the alternately incremental/decremental se~uence, a further programmable option allows the decremental step to be programmed to one-half the step size of the incre-ment instead of to the same millisecond value as the increment. For example, a burst cycle length initially programmed to 251 msec with incremental/decremental scanning steps programmed to 10.2 msec and one-half step size (i.e. 5.1 msec) respectively, will initially be incremented from 251 to about 261 (251 ~ lO) and will thereafter be decremented from 261 to 246 (251 -5). Thereafter the step size will be again incrementedto 271 and then decremented to 241 and incremented again to 282 msec, and 50 on. The increment/decrement sequence will be carried out for the predefined number of steps for the scan. The number of steps is a scanning variable that defines the number of times that the burst cycle length or the delay will be increased or decreased by the predetermined step size. The number of steps is programmable from 2 to 31.
The final scanning variable is the number of sequences. This i~ the number of times a scan sequence of, for example from 2 to 31 steps, is to be repeated.

The number of sequences is programmable from 1 to 8.
Thus, a predefined scan sequence can be repeated for up to eight times in an effort to locate the termination Yone of a tachycardia and thus terminate the tachycardia.
The physician may supplement or fine tune a basic therapeutic pacing modality by resetting a scan-ning sequence if the rate of the tachycardia changes during the scanning saguence outside an acceptable rate of change. In programming this reset feature, the phy-sician selects a millisecond value for a "difference interval". The scanning sequence will be reset to its initial values if the difference between the rate inter-val of the originally-detected tachycardia which ini-tiated the scan and the rate interval of the presently detected tachycardia during the scan exceeds this selected difference interval. That is, the scanning sequence will be reset if the interval of the tachycardia detected within the scan is either shorter or longer than the tachycardia interval which initiated the scan, by more than the difference interval. It should be appreciated that the reset option is provided to reset a scanning sequence to its beginning point when there is a large change in tachycardia rate, because resetting the scan will increase the probability that the scan will converge on the termination zone of the "new" tachy-cardia. This resetting of the scan sequence should be more efficacious in terminating a tachycardia where the scanned interval is adaptively defined.
If a tachycardia has been successfully termin-ated by a scanning burst, a "use memoryt' function of the pacemaker may be selected to permit immediate reim-plementation of the successful burst parameters when a following similar tachycardia is detected. When the use memory function is selected in conjunction ~ith a scanning sequence, the pacemaker remembers the inter-vals of delay and burst cycle length which were used to .3 successfully terminate a tachycardia. When the next tachycardia is detected, the pacemaker begins with the remembered successful values of delay and burst cycle length. This increases the probability that a minimum S number of bursts will be used to terminate the new tachycardia. If the remembered parameters do not succeed, the pacemaker then scans in an alternating increment/decrement sequence. If this incxement/decre-ment sequence terminates the tachycardia, the new suc-cessful values of delay and burst cycle length arestored in memory. If the increment/decrement sequence fails, the pacemaker will then deliver the full number of burst scan sequences beginning at the programmed values.
The selected use memory function may be re-stricted by electing a related "need interval similarity"
funct,on which restricts the use memory function to tachycardias having an interval similar to that of the last successfully terminated tachycardia. In operation, a difference interval is selected with the programming of the need interval similarity feature to define an interval range within which ~achycardias will be deemed similar. The interval of a newly-detected tachycardia may not vary by more then this difference interval from that of the last successfully terminated tachycardia to qualify as a similar tachycardia. The difference inter-val may be programmed with values of from 15 to 149 msec in lO msec steps.
It should be noted that if the use memory function is selected and the pacemaker applles a burst scan with an alternating increment/decrement se~uence, it is possible that part of the sequence will fall outside of the pacemaker's operational range of from 0 to 653 msec. If this occurs, scanning simply stops when the limit is reached (i.e., incremental: 653 msec;
decremental: 0 (for delay) or minimum cycle length (for -26~
burst cycle length). With a search pattern, scanning may stop in one direction and continue in the other.
The pacemaker will count attempts to pace in the direc-tion in which it is beyond range as well as outputs in the direction in which it is still within range, until the programmed number of steps have been counted.
If an antitachycardia treatment burst is not scanned, it may be programmed in the autodecremental mode. In the autodecremental mode a burst is programmed so that the cycle length (the pulse-to-pulse interval) within the burst will automatically decrement from an initial value by a programmable amount from 2.56 to 38.4 msec. In other words, the interval of the pulses within a burst can be automatically decremented from one pulse to the next. A minimum cycle length variable is defined to limit the interval to which pulses can be decremented within a burst.
The number of attemp-~s for any non-scanned burst is programmable from ~ to 31. If a tachycardia is detected, the pacemaker will apply the selected number of bursts in an effort to terminate the tachycardia.
If scanning is programmed, the selected number of se-guences determines the number of times that the scanning burst is repeated.
Antitachycardia burst treatments, including any programmed scanning sequence, will cease when a tachycardia is terminated. The pacemaker determines whether a tachycardia has been terminated by monitoring the rate of atrial events between bursts. The pacemaker checks only the atrial rate when it is reattempting to treat a tachycardia, other criteria which were employed to initiate the treatment o~ the tachycardia are not rechecked. Thus, when a pace-terminable tachycardia is detected, the pacemaker will apply a burst in a prede-fined treatment modality and will thereafter check therate of atrial events. If the pacemaker detects the ~2~ .3 lesser of the programmed number of high rate intervals or fifteen such intervals, it will again attempt to terminate the tachycardia. If the atrium reverts to a sinus rate lower than the tachycardia rate prior to detecting the required number of consecutive high rate intervals, the pacemaker will record a successful treat-ment of the tachycardia and will return to its brady-cardia mode.
The pacemaker of the invention may be program med to define a primary treatment modality and a secon-dary treatment modality for terminating tachycardias.
Each of the modalities may define a different selected burst se~uence for terminating a tachycardia. In opera-tion, if a tachycardia is detected, the primary modality will initially be applied to terminate the tachycardia.
If the primary modality fails after the programmed number of attempts (or number of secluences if the burst scanning mode is programmed), the pacemaker will attempt the secondary treatment modality for its programmed number of attempts or secluences.
If the programmed primary and secondary pacing modalities both fail to interrupt a tachycardia, the physician must decide ahead of time whether further a~tempts should be made and, if so, under what conditions.
In view of the fact that burst pacing has been found to be effective, a failure of primary and secondary burst pacing treatments might reasonably suggest that the unresponsive tachycardia is sinus or non-pace-terminable in origin. The most conservative course of treatment would therefore be to suspend burst responses-in order to avoid pacing into a sinus rhythm. This conservative treatment mode would be achieved by selecting the "no restart" option. However, if a physician judges that it will be necessary to continue to attempt to terminate a tachycardia after the failure of primary and secondary .3 modes of treatment, he may select one of the following four options to restart treatment:
1. Restart if the high rate criterion is reestablished;
2. Restart if the rate stability criterion is established in addition to the high rate criterion;
3. Restart if a sustained high rate criterion is reestablished; and 4. Restart if either rate stability or sus-tained high rate is reestablished.
The order of application of the primary and ~eondary treatment modalities may be changed in response to information regarding a prior successful treatment of a tachycardia. Thus, if the "can use secondary modality first" ~eature of the pacemaker is selected, the secondary treatment modality will be applied prior to the primary treatment modality whenever an immediately preceding tachycardia was terminated with a history indicating that the primary modality failed and the second modality was successful in treating the tachy-cardia. In operation, when the "can use secondary modality first" feature is elected, the pacemaker auto-matically implements the secondary modality first when it detects a tachycardia condition with a rate that is "similar" to the rate of a previous tachycardia which was successfully treated by only the secondary modality.
If the initial attempt to terminate the tachycardia by the secondary modality fails, the primary modality will be attempted. If the primary modality also fails, further attqmpts will depend upon which of the restart options has been selectad. If restart is selected and satisfied, attempts will continue in the order: primary, secondary, primary, secondary for as long as the high rate criterion is detected.
When the "can use secondary modality first"
feature is programmed, a value for the "interval di~fer-ence" must also be selected to determine a range within which a detected tachycardia will be deemed similar to a previously successfully treated tachycardia. Thus, the pacemaker will use the second modality first only for tachycardias whose rates do not vary by more than the selected interval difference from the previously successfully terminated tachycardia.
The pacemaker of the invention utilizes a series of diagnostic data counters in which it accumu-lates and stores basic ECG data, including the following events:
l. Number of times high rate criterion met;
2. Number of times sudden onset criterion met;
3. Number of times rate stability criterion met;
4. Number of times sustained high rate cri-terion met;
5. Number of times primary modality used;
6. Number of times secondary modality used;
7. Number of times secondary modality used first;
8. Most recent primary burst parameters (tachycardia interval, burst cycle length and delay);
9. Most recent secondary burst parameters (tachycardia int.erval, burst cycle length and delay).
The diagnostic data counters are reset auto-matically whenever the physician changes the pacemaker's operating mode or tachycardia detection/response para-meters.
A minimum burst cycle length is programmed into the pacemaker of the invention in order to insure that the rate of burst pulses applied to the atrium will not exceed a predefined value, reducing the like-lihood of hazardous effects. When the burst cycle length is programmed to a percentage of the tachycardia rate or when the burst is programmed in the autodecre-mental mode, the minimum cycle length parameter i5 pro-grammed to provide a maximum burst rate (i.e. a minimum burst cycle length) which will not be exceeded by the pacemaker. Thus, in burst modalities wherein the rate of burst pulses is automatically increased by the pace-maker, the pacemaker is controlled to insure thatbursts having an undesirably high rate are not applied to the atrium.
The above-described tachycardia detection and treatment functions are implemented in the pacemaker of the invention by a computer program which controls the operation of the microprocessor and associated memory devices to achieve the indicated operations. The com-pute~ code for the microprocessor is described in the attached listing of Appendix A. The listing of Appendix A is not provided in the actual assembly language which is required to operate the microprocessor of the prefer-red embodiment oP the invention. In order to facilitate an understanding of the invention, the listing of Appendix A instead documents and explains the steps of the computer program which operates the microprocessor to achieve the described functions of the invention.
The computer system for the microprocessor will hereafter be generally described with reference to the descriptive program listing and Fig. 7, which illus-trates a block diagram of the functional operation ofthe pacemaker of the invention.
With rePerence to Fig. 7, in bradycardia operation the pacemaker senses atrial events during a sense interval 29. ~f no event is detected within a predefined timed interval (timeout), the atrium is paced at 31 and a refractory interval is started at 33. There-after, program control is passed to an update pacer status routine 35 (see page 17 of program listing) which determines if newly programmed variables have been applied to the pacemaker. If so, the pacemaker stores the newly programmed variables and clears all status flags and diagnostic counters so that the pacemaker can begin carrying out its new instructions. If new programmed variables have not been provided, the update pacer status routine continues with a series of status checks and transfers program control in accordance with the opera-tional status of the pacernaker. Thus, the update pacer status routine will respond to activation of the reed switch 16 (~ig. 1~, a request for transmission of tele-metry or a request for initiation of noninvasive programstimulation when it is desired to evaluate parameters for tachycardia pacing. If the status checks do not initiate a transfer of program control, the pacemaker completes its refractory time at 37 and begins timing a "quiet time" interval at 39. If noise signals are detected during timing of the refractory time or the quiet time, program control will be transferred to a noise reversion routine and eventually control will be returned to update pacer status at 35. If noise is not detected, the pacemaker will again begin sensing atrial events at 29.
If a sense event is detected, the pacemaker will start a sense refractory interval at 41 and will thereafter check the tachycardia detection criteria at 43 to determine if a pace-terminable tachycardia has occurred. If a pace-terminable tachycardia is not detected, control is returned to the update pacer status routine at 35. If a pace-terminable tachycardia is detected, the program determines at 45 if an antitachy-cardia burst should be generated during the presentcycle. If burst parameters have not been calculated, ~9~

program control is transferred from 45 to calculate the burst parameters at 47 and the program then returns to update pacer status at 35. The program thereafter de-tects a sense event at 29, starts timing a sense refrac-tory interval at 41, verifies that a pace-terminable tachycardia has been detected at 43 and determines that a burst must be generated at 45. Thereafter, a synchro-nized burst is generated at 49, a pace refractory inter-val is started at 33 and program control is returned to update pacer status at 35.
With reference to the listing, the deszribed update routine is shown at page 17 and the described "quiet time" routine is shown at page 13. The sense interval function 29 o~ Fig. 7 is generally shown following the label "sense-time" at page 14. The label "start-up" at page 15 generally desi~nates the program entry point when a sense event is detected and a refrac-tory interval must be timed, for example as illustrated at 41 of Fig. 7.
After starting the refractory timed interval, the rate interval for the event is known. Accordingly, program control moves to the point 43 of Fig. 7 to determine if a tachycardia has occurred. The detection of the tachycardia is carried out in the "Check-for-Tach"
routine of page 20 of the listing. In this routine the reed switch 16 is initially interrogated to determine if the switch has been selected to provide an antitachy~
cardia burst regardless of the detected rate. If the switch has been activated for this purpose, program control is transferred to a point which will initiate the delivery of a burst. If the reed switch is not activated, the program determines if the most recent interval is less than the defined tachycardia rate limit interval. That is, the program determines if the most recent interval is an "S" interval whi.ch is shorter than the defined tachycardia rate interval. If a tachy-cardia interval is detected, program control is trans-ferred to a "TACHYl" routine at page 21. Alternatively, if a tachycardia event is not detected, the program S determines if a tachycardia therapy is not in progress, a tachycardia condition is not detected, or if this is not the first detected interval after a burst. If any of these conditions are true, counters which accumulate counts for the detection of a tachycardia are cleared and program control is transferred to the update routine.
In other words, the program has detected a non-tachycardia interval and therefore will begin counting from a zero count if a tachycardia interval is subsequently detected.
On the other hand, if antitachycardia therapy is in progress, a tachycardia condition is detected, or the detected atrial event is the first interval after a burst, a high rate count which counts the number of tachycardia events is incremented. This is done in the case of the first atrial event fo lowing a burst, because such an event is assumed to be a high rate interval.
Following the incrementing of the high rate count, pro-gram control is transferred to the update routine.
With reference to Fig. 7, if a high rate tachy-cardia event is detected at 43 and all programmed hi~h rate criteria are met, burst parameters are set at 47 and program control is returned to the update routine at 35. Thereafter, on the next atrial event, a burst is generated at 49 to attempt to treat the detected tachycardia. Therefore the atrial event which satisfies the tachycardia detection criteria does not synchronize the generation of a burst. Instead, the atrial event following the detection of a tachycardia synchronizes the burst. After the burst a refractory interval is timed at 33 and program control is then passed to the update routine at 35.

.3 As discussed above, th0 "TACHYl" routine at page 21 operates in response to the detection of a high rate atrial event. When such an event is detected, the routine initially interrogates the status of the reed switch and, if the reed switch is set, responds in the appropriate programmed manner. If the reed switch is not set, the program then determines if noise has been detected. If noise was detected, the program transfers control to the update routine. If noise was not de-tected, the program determines if a pace-terminable tachycardia has already been detected. If it has, a burst i5 then generated, synchronized with the following atrial event, as discussed above.
If a pace-terminable tachycardia has not al--ready been detected, the program determines if thestable rate criterion has been satisfied. If this criterion has been satisfied, the program skips around and therefore avoids the stable rate criterion test.
If the stable rate critecion has not previously been satisfied, the program determines if the sense event is stable, that is if the period of the detected high rate event differs from a computed average by less than a predefined maximum interval. Thus, the detected sense event is determined to be unstable if the absolute value of the difference between the computed average and the current interval is greater than the predefined differ-ence interval.
If the sense event is unstable, a new average is computed by calling a "find extremes" routine at page 42 which examines the present and two preceding intervals and generates the average of the sum of the maximum and minimum of these intervals. On the other hand, if the sense event is stable, a rate stability counter is incremented and the counter is then checked to determine if a predefined number of successive high rate atrial events have occurred at the stable rate.

- ~ 2 ~

If the predefined number of events have occurred at the stahle rate, a stable rate detected flag is set to indicate that the stable rate criterion has been met.
After the stable rate flag is set or if it is determined that the preselected stable rate count has not yet been reached, the program determines if the preselected high rate criterion has been satisfied. If the high rate criterion has not been satisfied, the high rate counter is incremented and program control is passed to the program steps of page 21 to determine if the sudden onset criterion is met. If the high rate criterion was detected, the program sXips over the sudden onset test and goes to the "TACHY2" program routine at page 24 to check the program requirements for deducing a reentrant tachycardia against the presently determined conditions.
If, as discussed above, the high rate criterion has not been detected and the high rate count has been incremented, the program at page 23 determines if the sudden onset criterion is met. In operation, the pro-gram determines if therapy is not in progress and ifthe high rate count equals one. If either of these conditions are false, it is unnecessary to test the sudden onset criterion. Accordingly, the program branches to the "TRIG1" routine at page 24 which checks if there have been enough fast beats to consider the detected rhythm a tachycardia. On the other hand, if the conditions are false, the program next determines .if the third most recent interval was a relatively short "S" interval which meets the defined criterion for a high rate tachycardia event. If the third most recent interval was not a high rate interval (e.g., it was not an S) the program next determines if the difference between this third most recent interval and the ~ost recent interval is greater than the variable "ONSET"
which is part of the predefined sudden onset criterion.
If the difference of the indicated intervals is greater .3 than ONSET, tha sudden onset detected flag is set true to indicate that the sudden onset criterion has been met. However, if the difference between the intervals is less than the value of ONSET, the sudden onset detected flag is set false to indicate that the sudden onset criterion has not been met.
If the third most recent interval was a high rate atrial event, the fourth most recent interval is checked to determine if it exceeds the defined high rate interval (i.e., is at "L"). If the fourth most recent interval was not a long interval ~i.e., it was a high rate event), then the sudden onset flag is set false. However, if the fourth most recent interval was a long interval, the program determines if the difference between the second most recent interval and the most recent interval is greater than the value of ONSET.
That is, the program determines if the second most re--cent interval is greater than the most recent interval by at leasc the amount of ONSET. If the difference.
between the intervals is greater than ONSET, the sudden onset detected flag is set to indicate that the sudden onset criterion has been met. However, if the difference of the intervals is less than ONSET, the sudden onset detected flag is set false to indicate that the criterion has not been met. After the sudden onset testing has been completed, the program transfers control to the TRIGl routine of page 24 which checks to see if there have been enough fast beats to consider the atrial rhythm a tachycardia.
In the TRIG1 program routine, the program initially determines if the high rate count equals the preselected required high rate count which defines the high rate criterion. If the required number of counts has been reached to satisfy the high rate criterion, the high rate detected flag is set true. Program control is then passed to the TACHY2 routine of page 25 which !1.3 checks the programmed requirements for deducing a pace-terminable tachycardia against the requirements which have been measured.
If in the TRIG1 routine the high rate criterion has not been met, the program next determines if therapy is in progress and if the high rate count equals the lower of two predetermined numbers, HIGH RATE COUNT or 15. If these conditions have not been satisfied, program control is passed to the UPDATE routine previously de-scribed at page 16. If these conditions are true, itis known that a tachycardia condition has been previously detected and the program is now checking to see i the condition still exists after treatment has been applied.
The program will therefore set the high rate detected flag true, because the HIGH RATE COUNT number or 15 high rate events have been detected after the attempt to treat the tachycardia. Also, the tachycardia detected flag is set true to indicate that a tachycardia has beer. detected following treatment. Program control is ~0 then passed to the antitachycardia therapy routine start~
ing at page 28.
As previously discussed, the TACHY2 routine is entered after the high rate detected flag has been set in TRIGl. In TACHY2, the program first determines if a sustained high rate flag is clear. This flag will be set if the above described sustained high rate criterion has been met. If the sustained high rate flag is clear, the high rate counter is incremented and the program then determines if-the high rate count equals the required count for satisfying the sustained high rate criterion. If the sustained high rate criterion is satisfied, the sustained high rate detected flag is set true.
If the sustained high rate flag was not clear or the hiyh rate count was not equal to the required count for sustained high rate, the program checks to determine if the preselected tachycardia criteria have been met. If the criteria have been met, program control is transferred to the antitachycardia therapy routine starting at page 28 to set up the "burst" treatment in the predetermined modality. I the tachycardia criteria have not been met, the program checks to determine if the primary and secondary therapies have failed. If these therapies have not failed, the program next deter-mines if the detected conditions meet the composite tachycardia detection criteria. If they do meet these criteria, the tachycardia detected flag is set and the tachycardia is treated.
If the primary and secondary therapies failed, the program determines if the restart option has been selected. I~ this option has not been selected, program control is transferred to UPDATE. However, if the re-start option has been selected, the program determines if the detected conditions méet the predefined composite restart detection criteria. If they do not, program control is passed to UPDATE. On the other hand, if the composite restart detection criteria are satisfied, the tachycardia detected flag is set and the tachycardia is treated.
The antitachycardia therapy routine of page 25 is entered after a pace-terminable tachycardia is initially diagnosed or is re-diagnosed in the case of an ineffective burst. The antitachycardia therapy rou-tine and the burst delay calculations routine prepare the pacemaker for producing a burst in accordance with the preselected treatment modality. As previously dis-cussed, the burst is synchronized with respect to the sense event which follows the event at which the pacer-terminable tachycardia is detected.
The antitachycardia therapy routine keeps various flags, for example Burst, Primary Therapy, Secondary Therapy and Both Therapies Failed up-to-date.

3~3~ 3 The routine also clears other flags such as Rate Stability and Persistent High Rate if required and loads the Attempt Counter with either a preselected primary attempt limit or secondary attempt limit to define the number of attempts in the primary and secondary treat-ment modalities which will be carried out before the restart instruction is checked. The routine further decrements and checks the status of the attempt counts to determine whether the treatment therapy should be changed. The routine also determines if the secondary therapy may be performed first. If the secondary therapy can be performed first, the program applies the secondary therapy first if the present tachycardia rate is similar to the rate of the last tachycardia which was success-fully treated by the secondary mode of treatment and is either not similar to the last primary treated tachy-cardia or, if it is similar, the previous similar tachy-cardia was not successfully treated by the primary therapy.
The routine of pages 31 and 32 makes the re-quired calculations for setting up a burst treatment in the required treatment modality. This portion of the program computes S1, the delay from the sense event to the first treatment pulse and S2, the pulse-to-pulse interval in a burst. These values are determined in accordance with selected fixed delay values or delay values derived by adaptive calculations. A Swap flag is ut.ilized to operate the code in the computational manner required for the primary or secondary therapies.
The CALC1 program routine of page 33 performs the necessary calculations for settiny up the parameters for all scanniny therapies. Ayain, the Swap flag, which is set in the burst delay calculations, is used to oper-ate the code to define the parameters for primary and secondary therapies.

The DELIVER BURST routine at page 35 is employed to deliver a burst treatment for a detected pacer-termin-able tachycardia. This routine applies the required number o~ pulses in a defined burst and compares the de~ined pulse-to-pulse burst interval with a selected minimum burst delay. If the defined burst interval is less than the value of the minimum burst delay, the burst interval is set equal to the value of the minimum burst delay to avoid excessively rapid stimulation of the heart when treating the tachycardia.
The remaining program routines of pages 37-46 provide additional features and perform rout.ine program control functions for the pacemaker of the invention.
Thus, the TELE~ routine of page 37 is utilized to perform all telemetry functions for the pacemaker. The Electro-Physiology Study routine of page 39 is employed to set-up the delay and cycle length for the first part of an electrophysiological burst. The EPXTRA routine adds extra stimuli at the end of a burst, if re~uired.
The PACE routine of page 40 operates to deliver the required pacing signals for the pacemaker. The subrou-tine CLEAR of page 41 operates to set initial values for state flags and certain variables of the program.
The subroutine FIN~-EXTREMES of page 42 calculates the interval average which is required to determine the stable rate criter on. The subroutine HR-OVERRIDE at page 43 activates a high rate override feature of a linear integrated circuit of the pacemaker~ The sub-routine UPDATE LI~EAR IC at page 44 updates the linear IC as required. The Shift-Intervals subroutine of page 45 stores the most recent rate interval and associated three preceding rate intervals and updates the intervals by shifting as required. Finally, the SLEEP routine of page 46 allows the microprocessor to operate in a quies-cent or sleep state while timing burst delays.

~40-Although a program and particular ranges of parameter values for detecting and treating pace-texmin-able tachycardias have been particularly described, it should be understood that other programs and parameter values can be employed to implement the desired detection and treatment criteria, without departing from the inven-tion. It should therefore be understood that the inven-tion may be embodied in other specific forms without departing from its spirit or essential characteristics.
The present embodiment is, therefore, to be considered in all respects as illustrative and not restrictive.
The scope of the invention is indicated by the claims rather than by the foregoing description. All chanyes which come within the meaning and range of the equiva-lents of the c}aims are, therefore, intended to be em-braced therein.

APPENDIX A

PA&E 1 INrERrACH PSUE~O CO~E
00~02 ***~******~ **~***********~*********~*
00~03 * - *
00004 * PSVEDO CO~E VERSION OF l~TERTACH *
00005 * *
00006 ***~******~***********************~****
00007 *
00005 * ~EFINITION OF NON-TRI~IAL. VARIABLES
O~OOq *
00010 * CONTROL 1 IS A BIT PAC~ED ~ARIABLE THAT ~EFINES
00011 * THE BRA~YCAR~IA PACING ~O~E OF THE INTERTACH AND
00012 * THE CO~POSIT TACHYCAR~IA ~ETECTIDN CRITERIA. ITS
00013 * BITS ARE ~EFINE~ AS:
00014 *
OOOlS ~ BIT O = NEED ONSET FOR TACHYCAR~IA ~ETECTION
00016 ~ BIT 1 3 MEED RATE STABILIT`f FOR TACHYCARDIA DETECTION
00017 * BIT 2 -~ PERSIST~NT HI~H RATE USE~ AS AN 'OR' WITH
00018 * THE CRITERIA QF BIT~ 0,1,3 0001~ * BIT 3 -- NEED THE LO~ICAL 'AN~' OF ONSET AND RATE
00020 * STABILITY FQR TACHYCAR~IA ~ETECTION. tFO~ THE
00021 * LOGICAL 'OR' OF THE TWO CRITERIA, SET BOTH
00022 * BIT O AN~ BIT 1 HIGH.
00023 * BI-r 4 = TRIGGERE~ MODE (AAT~
00024 * BIT 5 = NOT SENSE (AOOi 0002S * BIT 6 - NOT PACE ~OAO~
00026 * BIT 7 = NOT USED
00027 *
C0028 ~ TEMP_CONTROL 1 IS LOA~ED BY AN EXTE~NAL PROGRA~ER WHEN IT
00029 ~ WANTS TO CHANGE THE BRADYCARI~A MO~E OR THE CO~POSIT
00030 * TACHYCARDIA ~ETECTION CRITERIA. O~CE EACH CARDIAC CYCLE
00031 * lHE INTERTACH WILL CHECK BIT 7 OF TEMP CONTROL_l. IF
00032 * THE INTERTACH FIN~S THI5 BIT SET, IT WILL TRANSFER
00033 * TEMP_CONTROL_l TO CONTROL_l, THEN CLEAR BIT 7.
~0034 *
0003S * RATEl HOL~S THE PRO~RA~ME~ ERA~YCAROIA PACIN~ RATE.
000~ *
00037 * VPW HOL~S THE PROGRAMMED PUL5E WI~TH.

, ~ ~ ` .

0003~ ~ COhlrRQL_4 IS A BIT PACKED VARIA~LE THAT CONTROLS SO~E OF THE
00040 * AMTITACHYCARIA ACTIVITY AND DEFINES THE INTERTACHS RESPONSE
00041 ~ TO A CLU5ED REED SWITCH. ITS eITS ARE DEFINED AS:
00042 *
00043 * IF BITS 0,1 ARE BOTH ONES THEN 'NOT IN ANTITACHY ~O~E'.
00044 * OTHERWISE
OOa45 * BIT O = ~0 NOT RESTARl- ANTITACHY THERAPY
00046 * BIT 1 = NEED RATE STABILITY TO RESTART ANTITACHY THERAPY
00047 * BIT 2 = t~lEED PERSISTANT HIGH RATE TO RESTART ANrIrACHY THERAPY
00048 * BIT 3 = DO MOT TRY TO USE SECONDARY THERAPY FIRST
0004~ * BIT 4 = REED SWITCH ~OES NOT ACTIVATE HIGH RATE QVERRIDE
00050 * BIT 5 = MAGNET TELE~ETRY MODE: AOO (HIGH~, hAT (L~W) 00051 * BIT 6 = REED SWITCH CAUSES ANTITAGHY PACING
00052 * BIT 7 = HI~H RATE AND REE~ SWITCH CAUSE ANTITACHY PACIM~
00053 *

00055 l~
000~6 * FLh~ IS A BrT PACKED VARIABLE THAT IS VSED TO ~EEP TRACK OF
00057 * THE PRIMArIVE DETECTION CRITEREON A~ THE CURRENT STATE OF
00058 * AN ANTITACHYCARIA THERAPY.
00059 ~
00060 * BIT O = SU~DEt~_OMSET_DETECTED
00061 * BIT 1 = STABLE_RATE_DErECTE~
00062 * BIT 2 = PER5ISTAMT_HR_~ETECTED
00063 * BIT 3 = HIGH_RATE_~ETEC~ED
00064 * BIT 4 = TACH ~ETECTE~
00065 * BIT 5 = THERAPY_IN_PRO~RE5S
00066 * BIT 6 = PRIt~ARY THERAPY
00067 * BIT 7 = NOT USE~
~0~6~ *
0006~ * FLAG2 IS A BIT PAC~ED VARIABLE THAr IS USE~ TO KEEP TRACK OF
00070 * A VARIETY OF FL~S. ITS BITS ARE ~EFI~ES A5:
~0071 *
00072 * BIT O = JUST PACED
00073 * BIT 1 = FOURTH_MOST_RECENT_IMTERVAL_WAS_TACH
00074 * BIT 2 = BQTH THERAr'YS_FAILE~
00075 * BIT 3 = CVRRENr THERAPY IS NOT AUTO BECREMEM-rAL.
00076 ~ BIT 4 = FIRST BURST IN A THERAPY.
00077 * BIT 5 - DOIt`lG_SECONDARY_FIRST
;0007S * BIT 6 = ALREADY CALCULATED 5X. INCRE~EMT
00079 * BIT 7 = SCANNING FRO~ REME~BERED VALUES

~3 .

PAGE 3 INrERTACH PSUEDO CODE
OG0~1 * FLA~3 IS A BIT PAC'~E~ VARIAELE THAT IS USE~ TO KEEP TRACK OF
OOG~2 * A VARIETY OF FL.AGS. ITS BITS ARE ~EFINES AS:
000~3 OOOB4 * BIT O - TACHY FLA~
00085 ~ BIT 'l = NULL tPROGRA,M~E~ BIT~
OOOS6 * BIT Z - EOS
00087 * BIT 3 = PW CORRECTION LSB (PROÇRAMME~ BIT~
000~8 * BIT 4 = IGhlORE EOS ~PROGRAMME~ BIT~
OOG~ * BIT 9 = REE~ SWITCH CLOSE~
00090 * BIT 6 = ~0 REE~ SWITCH ANTITACHY
000~1 * BIT 7 = DO REE~ SWITCH ANTITACHY IF HIGH RATE
0009Z *
00093 ~ STAeLE_RATE_MI~_POINT CONTAINS THE IhlTERVhL AGAINST WHICH
OC0~4 * TACHYCARI~IA INTERVALS ARE COMPARE~ TO 5EE IF THEY FALL
OOOqS * WIT,HIN THE STABILITY CRITEREON.
000~6 *
OOOq7 * REOEUIRED STABLE CQUNT CONTAINS THE NU~BER OF CONSECUTrVE BEATS
OG05~B * REOUIRED TO ~ETERMI'NE RATE STABILITY.
000~ ~
C0100 * ~AX IINSTA~ILITY CONTAINS THE ,~AXIMUM THAT A SEQUENCE ~F
00101 * Il\lTERVALS ~AY VARY FRO~ 5TABLE RATE I~ID_PDINT AND 5TILL BE
00102 * CONSIDERE~ STABLE.
00 1 0~ *
00104 * RE~UIRE~ HIG.H_RhTE_COUNT CQNTAINS THE NU~BER OF CONSEC'UTIVE
00105 * BEATS WHUSE INl'ERVALS ARE SHQRTER THhN TACH_LI~IT REQUIREE
~0106 * TO ~ETER~INE THE HIGH RATE COhl~ITION.
001~7 *
00108 * TACH_LIi1IT HOL~S THE VALUE OF THE LONGEST INTERVAL THAT WILL
0010~ * ~E CONSI~ERE.'O A TACHYCARDIA INTERVAL. THAT IS. IT SETS THE
00110 * BREA,~POINT BETWEEN HIGH-RATE TACH INrERVALS AND SLUWER
00111 * NON-TACH I,NTERVALS.
OU~12 *
~0011~ * ONSET CONTAINS THE A~OUNT TWO INTsERVALS HAVE TO INCREASE FOR
00114 * T~tE SU~EN ONSET TO rE DETECTE~.

~12~`

00116 * STABILITY COUNT CONTAINS THE NUMBER OF CONSECUTIVE STABLE
00117 * INTERVALS THAT HAVE BEEN ~ETECTEU.
00~ 1~ *
0011q * AUrO_~ECREMEhlT CONTAINS THE AMOUNT THE BURST CYCLE LENGTH
00120 * IS TO BE ~ECREMENTE~ WHEN ~ELIVERIN~ AN AUTO-~ECRE~ENT
00121 * TYPE BURSr.
00122 ~
00123 * MIN_BUR5T DELAY HOLDS A LOWER BOUhlD FOR THE LENGHT OF INTEQVAL
00124 * THAT MAY BE USED IN ADAPTIVE SCANNIN~ AND AUTO-DECRE~ENTAL ~UR
0012~ ~
00126 * Mosr - RECENT INTERV~L CUNTAINS THE LENGTH OF THE INTERVAL l-HAT
00127 * JUST OBSERVE~.
00128 *
0012~ * SECOND MOST RECENT_INTERVAL CONTAINS THE LENGTH OF THE INTERVA
00130 * THAT WAS OBSERVED JUST BEFORE THE PlQST_RECENT I~TERVAL.
00131 *
00132 ~t THIRD MOST RECENT INTERVAL CONTArNS THE LENGTH OF THE INTERVAL
00133 ~t THAT WAS OBSERVED JUST BEFORE THE SECON~_MOST RECE~T_INTERVAL.
00134 *
00135 * ATTEMPT COUNT HOL~S THE NUMBER OF TIMES EITHER THE
00136 * PRIMARY OR SECONDARY THERAPY HAS BEEN USED TO TRY
00137 * TO BREAK THE TACHYCARIDA CURRENTLY IN PRO~RESS.
0~13~ *
0013~ * HI~H RATE COUNT HOLDS THE NUMBER OF CONSECUTIVE INTERVALS
00140 * THAT HAVE BEEN ~ETECTED ABOVE THE TACHYCARDIA RATE.
001~1 *

,:,, , ~`, ;.~ , ~I S

00143 * VBATA HOL~S THE OUTPUT PULSE AMPLITU~E AN~ THE AMPLIFIER
00144 * SENSITIVITY.
00145 * AND A~PLIFIER SENSITIVITY.
0~14~ *
00147 t~ RF~CTl HOLDS THE REFRACTORY PERIOD.
0014~ *
0014~ * REOUIRED PERSISTANT_COUNT CONTAINS THE NUMBER OF CONSECUTIVE
OOlSO * BEATS RE~UIRE~ TO DETERMINE PERSISTANT HIGH RATE.
00151 t~
00152 * BURSTL HOLDS THE NU~BER OF PULSES IN A PRI~ARY BURST.
00153 *
OOlS4 ~ SERNO HOLD5 THE SERIAL NUMBER OF EACH UNIT.
00155 *
00156 ~ REVLEV HQLDS THE REVISION LEVEL OF EACH UNIT.
001~7 *
00158 * 5AlP HOL~S THE PRIM~RY Sl DELAY.
0015q t~
00160 * PSSAl HOL~S THE LAST 5UCCES5FUL PRI~ARY Sl DELAY.
aol6l *
00162 * SA2P HOLDS THE PRIMARY BURST CYCLE LE~GTH.
00163 *
00164 * PSSA2 HOLDS THE LAST SUCCES5FUL PRI~ARY 52 ~ELAY.
00165 *
0016~ * LAST_PRIMARY TACH HOLDS THE LAST ThCHYCARDIA INTER~AL SEEN
00167 * WHILE USIN~ THE PRIMARY THERAPY.
001~3 *
0016~ * PRI~ARY ATTE~PT_LIMIT HOL~S THE MAXI~W~ NUMBER ~F TI~ES THE
00170 * PRI~ARY THERAPY SHOULD BE A~MINISTERED BEFORE TR~IMG THE
OQ171 * SECONOARY THERAPY.
0017~ *
00173 * 5CANTl IS A 3IT PACKE~ VARIA3LE THAT CONTROLS SCANNING
00174 * BEHAVIOR OF THE PRI~ARY BURST.
00175 ~
00176 * LOW NIBBLE = SCANNIN~ INCRE~ENT
00177 * BIT 4 = SCANNING ~ECREMENT IS ONE HAI_F OF SCANNING INCRE~ENT
00175 * 3I r 5 = NOT IN MEMORY ~ODE
0017~ * BIT 6 = 5CAN SA2 ~1~. SAI ~0 OOlSO ~ BIT 7 , ~ 2~ .3 PA~E 6 INTERTACH PSUEDQ CODE
00182 * CNTP~L2 IS ~ BIT ~PPE~ VARIABLE TH~T CONTROLS
001~3 * PRIt~ARY ANTI TACHY BEHA~IOR.
00184 *
C01~5 * IF BIT 0,1 ARE ONES THE~ SUCCESSIVELY APROXI~ATE SAl 00186 * OTHERWISE
00157 * BIT O = DECREMENT SAl ~SCANNING THERAPY) 00188 * BIT 1 = INCRE~ENT C.Al (SCANNING THERAPY~
0018~ * BIT 2 = SAl IS ADAPTIVE
OOlqO * BIT 3 = DO NOT MEED RATE SI~ILARITY TO USE ~EMORY OPTIQN
00191 ~
001~2 ~ IF 3IT 4,5 ARE ZERO THE~N THE THERAPY IS AUTO~ECRE~ENTAL
0019~ ~ IF BIT 4,5 hRE OMES THEN SUCCESSIVELY hPROXI~ATE SA2 001~4 * OTHERWISE
001~5 * BIT 4 = ~ECRE~IENT SA2 (SCANNING THERAPY~
OOlq6 * BIT S = INCREMENT SAZ (SCANNING THER~PY~
00197 * ~IT 6 = SA2 rs A~APTIVE
OOl~S * BIT 7 = ~OESN'T ~IATTER IE A BURST CHANGES THE TACHY RATE, 0019~ * CONTINUE SCANNING.

, L~ ~

~2~)8~

PA~E 7 IhlTERTACH PSUE~O CODE
00201 * ~ATE HOIDS THE ~ATE OF IMPLANT OF THE I~TERTACH.
00202 *
00203 * N8CNT HOLDS THE NUMBER OF ALLOWE~ TRh~SITION5 DURI~G NOISE
00204 * SEN&E TIME BEFORE THE TRANSITIONS ARE TER~ED NOISE.
0020S *
OOZ06 * DIAGSN HOL~S THE SECONDARY ATTEMPT THERAPY COUNTER.
00207 *
0020S * BRSTL2 HOLD5 THE MU~BER OF PULSES IN A SECONDARY BURST.
OOZO~ *
00210 * OTINT HOl_~S THE QUIET TI~1E ~URATION.
OOZl1 *
00212 * PWF~G IS ~ ~IT MAPPED VARIABLE HOL~ING THE FOLLOWING FLAGS:
00213 *
00214 * RIT 4 =
0021~ ~ BIT ~ - NOISE REVERSION ~ODE : AOO ~1~, 000 (O) 00216 * RIT 6 ~ DO_ELECTO PHYSIOLOG~
OOZ17 * BIT 7 = DISABLE DIAGNOSrIC COU~lTERS
OOZ18 *
0021~ * SA3P HOLDS THE &ECONDARY 51 ~ELAY.
00220 *
00221 * SSSA1 HOLDS THE LA5T &UCCESSFUL SECONDARY S1 ~ELAY.
002~2 *
G0223 * SA4P HOL~S THE SECON~AQY BURST CYCLE LEN~TH.
00224 *
00225 * SSSA2 HOL~5 THE LA&T SU~CESSFUl SECON~ARY S1 DEL~Y.

4~

PA~E 8 INrERTACH PSUE~O CODE
OOZ27 * LAST_ZNDARY_TACH ttOL~S THE LA5T TACHYCARDIA INTERVAL SEEN
Q0228 * WHILE U5ING THE 5ECONDARY ~ODE OF THERAPY.
00;~2q *
00230 LAST_2NDARY TACH R~
OGZ31 *
OOZ3Z #
OOZ33 * SECONDARY ATTE~PT_LIMIT llOL~S THE ~AXIMU~ NUMBER OF TIMES THE
00234 ~ SECONDARY THERAPY SHOULD BE A~MINISTERE~.
002~5 *
OOZ36 *
00237 ~ SC~NT2 IS A BIT PACKED VARIABLE THAT CONTROLS THE SCANNING
00238 * BEHAVIOR OF THE SECaN~ARY BURST.
0023~ *
00240 * LOW NIBBLE - SCANNING; INCREMENT
00241 ~ RIT 4 = 5CANNIN~ DECREMENT IS ONE HALF SCANNING INCREMENT
00242 * BIT 5 = NOT IN MEMORY ~ODE
00243 * ~IT 6 = SCAN 5AZ ~ SAl (0 00244 * BIT 7 -00245 *
00246 * CNTRL3 BIT ~APPEU VARIABLE THAT CONTROL5 SECONDARY
00247 * ANTI-TACHY BEHAVIOR.

.

4q ~ ~29q)~

PA~E 7 I~ITERTACH P8UEDO CODE
0024~ *~***~**~***~********************~*~**********~******~*****
00250 *
00251 * KEERING TRACK QF ST~TE FLAGS
OOZ52 *
00253 ***~*******#~******~********************************~**********
002S4 *
0025~ * SUDDE~T_ONET ~ETECTED ~ 'FLAG', Bit O ) OOZ~56 * Onse~ Dnlg determined when a tach ~irst devel~pes. At that 00257 * time, the ON5ET flag i5 set or reset ('ThCHYl'). This 00258 * flag is also reset upon termination of a tach 0025~ * t'CHEC~_FGR_TACH'~.

00261 ~ 5TABLE_RATE ~ETECTED ( 'FLA0'. Bit 1 ~
00262 * This ~lag is set when rate stability has been determin~d.
00263 * It is reset when the primarg ancl secondary m~des OOZ64 * have failed ~'A~TI_ThCH_THER~PY'~, when T.he tach 00265 * terminates ('CHECI~_FOR_TACH'), 00266 * and after a burst ~'~ELIVER_B~RST'~.
00~67 *
OOZ68 * PERSISTAhlT_HR DETECTED l'FLAG' Bit 2) 0026~ * This flag ~3 get ,I)hen persistant high rate has been establish 00270 * either in detectir)g a tach or after t:he primar~J and second3ry OOZ71 * modes have failed ~PERSIS from 'TAt,HY2'~.
00272 * This flag is reset after a burst ~'DELIVER_BURST') or i~ the 0;:)27~ terminates (~C~ECK FOR_TACH') or if the primary and 00274 * gerondarg modes fail ('ANTI TACH_THERAPY').
OOZ75 ~
00276 * I~ H_RATE DETECTEI~ t 'FLAtY'. Eit 3~
00Z77 il This flag ig set after there hav~ been en~ugh high rate 00278 * intervals ~o ~e~ect (or redete~t af~er a burst) a taeh 0027q * ('TRIG1'). I~ is reset after a burs~ ('DELIVER_BURST')~
00280 * and if the tach terminates ~'CHECI~_FOR_TACH' ).
0028 ~ *
00282 * TACH r~ETECTED ('FLAG', Bit ~
C)0283 * When all the necessary tachy criteria have been met, this 00284 * flag i5 set (S~T_TACH_DETECTE~_FLA~, in 'TACHY,2'). Between 00285 * bursts this flag is set as soon as She HIÇH_RATE_DETECTEO
OOZ86 ~ ~lag is set ('TRIGl'). This Plag is reset aPter each burst 00287 * ('DELIVER BURST') and when the primary and se~ondar~ modes 00288 * ~ail ('ANTI TACH THERAPY'), an~ when the tachycardia OOZ8~ * termin~tes ('CHECK_FOR TACH').
0~290 ~
002q1 * T~tERAPY IN PROG,RESS ('FLAG', Bit 5) 002q2 ~ The THERAPY IN PRQGRESS Plag is set beFore ~he First burst 00293 * and reset when the primary and ~econdarg modes ~ail and when 002~4 ~ the tc~ch terminate~.

~.2~

PAGE 10 I~ITERTACH PSUEDO COUE
002~6 * PRIIYARY_THERAPY ~'FLA~'. Bit 6) 002~7 * Maintair1ed in 'ANTI_TACH_THERAPY' and cleared in 002~8 * 'CHECK_FOR TACH' when the ta~h terminates.
002~ *
00~00 * JUST PACED t'~LA~2', Bit O) 00301 * Set in 'PACE' and reset in 'SENSE' (5ense Interv~13..
00302 *
00~03 1~ FOURTH_~05T RECENT_INTERVAL _WAS_TACH ~'FLAG2'/ Bit l) 00304 * Updated by 'SHIFT_INT~RVALS' and reset after ~ burst 00305 * ('DELIVER_BURST').
00306 *
00307 * BOTH_THERAPYS_FAILED t'FLAG2', Bit 2) 00308 * Maintained in ~ANTI TACH_THERAPY' and reset when the tach 00304 * terminates ~'CHECK,_FOR TACH'), 00310 ~ _ 00311 * CURR~NT THERAPY IS Nor AUTO DECREI~IENTAL ('FLAG2', BIT 3) 00312 * ~aintained in 'ANlI,,TACH_THERAPY'.
003~3 *
00314 * FIRST BURST IN A THERAPY ~'FLAG2', Bit 4) 00315 ~ Set in 'A~TI_T~CH_THERAPY', reset in 'DELIVER_BURST'.
0031~ *
003l7 * DOING SECON~ARY_FIRST ~'FLAGZ', Bit 5) 00318 * ~his flag i~ set ~rue when the software has de~i~ed to try 003l9 ~ the se~Gndar~ treatment first, 003ZO * ~aintained in 'ANTI_rAC11_THERAPY' ~d reset when the taeh 00321 * termin~tes ~'CHECK_FOR_TACH'~.

"'""~

PAGE 11 INTERTACH PSUED0 caDE
00323 * 'CRA~H' i~ the l~op ~hat the pacer execu~ea in the even~
003Z4 ~ ~f a failure. It rann~t be exited excep~ un~er pr~grammer 003Z5 ~ con~rol.

PAÇE 12 INTERTACH PSUEI:~O CODE
00327 *
003~ *
0032`? * LA13EL PROÇRAI~I STARTII~IG_PC)INT
()0330 *
00331 ~ CALL CLEARl 00332 *
003~3 * GOTO 5TART_UP ~ IN SENSE_TIME SECTIOhl l:lF ~ODE }

", !`

PA~E 13 START QUIET_TIME
00336 * 'START aUIET TIME' (START QUIET TIME~
00337 * THIS SECTIOM OF THE PROGR~M IMPLIMENTS THE NOISE DISCRIM-00333 * INATION FOR THE PACEM~KER. A 50 MSEC QUIET TIME I5 BEGUN
0033Y * AM~ IS RESET (10 TIMES MAX.) IF MOISE IS SENSED. A RATE
00340 * TIMEOUT ~URIr`lG ~T ALSO CAU.5E5 NOISE REVERSIQN. IN EITHER
00341 * CASE. ASYNCHRONOUS P~CING ~AOO) ENSUES. IF NO NOISE I5 00342 * SENSED. THE NOR~AL SENSE INTERYAL BE~INS.
0034~ *
00344 *
00345 * L~BEL START_~WIET,_TIME
00346 *
00347 * NUMBER_OF~EXTETIONS - O
00348 *
0034~ * ~n 00350 ~ IF NWME3ER_OF_EXTENTIONS == 10 00351 ~ THEM
00352 * CAL.L CLEAR1 00353 * ~OTO AS`~NCHROMOUS_BEHA~IOR
00354 * ENDIF
0035S *
003S6 * START TIMER 5 FOR ~UIET TIMER
00357 ~i 0035~ * 5LEEP UNTIL THE QUIET TIME EXPIRES, 00~5~ ~ THE BR~DY INTERV~L TIMER EXPIRES.
00360 * OR h SEMSE EVENT OGCWRES.
0~61 *
00362 ~ IF W~KLUP CAUSED BY RATE TIMER
on363 * THEN
00364 * CALL CLEAR1 003~S * ~OTO OUTPWT
00366 * ENDIF
Q0367 *
00~6S * IF ~UIET TI~lER CAWSED WAKEUP
0036~ * THEN
00370 * IF SENSE INPUT I~ LOW
'~00371 * THEN ~OTO SEMSE_TIME
' 00372 * EM~IF
",~i,00373 *
`` 00374 * NUMBER"_OF_EXTENTIOMS = NWt1BER_OF_EXTENTIONS~l ,~,'1,00379 * REPEAT
00:376 *

, PA~E 14 SEP.ISE_TI~IE
00379 * ~SENSE_TI~E' t5ENSE INTERVAL~
00380 *IF THE SENSE TI~E ENDS WITH A RATE WA~EUP, THEN THE PROGRA~I
00381 *JUMPS TO 'OUTPUTE IF A SENSE E~ENT O~CURS, ALL THE NECESSARY
00382 *UP~ATING OF INTERVAL STOR~GE AND RATE TI~ING ETC. IS PER-00383 *FORMED IF THE PACER IS IN TRIÇ~ERE~ ~O~E, THEN A PACE EVENT
00384 *IS PRODUCE~. THIS SECTIUN OF THE PROGRAM EXITS TO THE TACHY-00385 *CARDIA OETECTION SECTION: 'CHECK_FOR_TACH'.
0~386 ~
00387 * LA~LE SENSE_TI~E
00388 *
0~38~ ~ ENABLE RATE AN~ 5ENSE WAKEUPS.
003~0 *
003ql * IF DO_ELECTRO_PHYSIOLOGY
00392 * THEN ~OTO ELECTRO_PHYSIOLOGY_5TUDY

003~4 ~ SLEEP UNTIL RATE TIME OUT OR SENSE E~ENT
00395 ~
003q6 K IF RATE TI~E OUT CAUSE~ THE WA~EUP
00397 * THEN
00398 * IF NOT 'DO REED SWITCH ANTITACHY REG~RDLESS OF RATE' 003~q * THEN CALL CLEAR2 00400 *
00401 * ~GTO OUTPUT
00402 * EN~IF

PA~E 15 SE~SE_TI~IE
00~04 * LABEL STAPT_UP
00~05 *
00406 * 5TOP INTERVAL TIMER
00407 ~ CALL SHIFT_INTE~ALS
00408 ~ CLEAR PACE FLA~
0040~ * START REFRACTORY TIMER
00410 *
00411 * IF NOT AAT MODE
00412 * THEN GOTW CHECK_FOR_T~CH
00~13 *
00414 * IF THE REE~ SWITCH IS CL05ED
00415 * THEN
00416 * IF PRO~RAMME~ SG A5 TO LIMIT RATE
00417 ~ THEN
00418 * IF THE lZ5 PPM LI~IT NOT EXCEEDED
0041q ~ THEN CALL PACER
00420 * GOTO CHEC~_FOR_TACH
00~21 ~ ELSE
00422 * CALL PACER
004Z3 * ~OTO UP~ATE
004Z4 ~ EN~IF
00425 * EN~IF
00426 *
00427 * ~ NOrE: TO ~ET HERE, REE~ 5WITCH MU5T ~E OPE~ }
C0428 * IF THE 125 PPM LIMIT NOT EXCEE~E~
004Z~ ~ THEN CALL PACER
0043g ~
00431 * GOTO CHECK_FOR_TA~H

~2~

PA~E 16 OUTPUT
00434 ~'OUTPUT' IS THE RETURN POINT AMY TI~E THERE IS A PACER RATE
00435 *TIME OUT. UNLES5 THE MQDE I5 OAO, IT PRO~UCES A PACE PUL5E
0043~ ~AM~ EXITS TO 'UP~ATE'.
00437 *
0043S * LABEL OUTPUT
0043~ ~
00440 * CALL 5HIFT_INTERVAL~.
00441 ~
00442 ~ IF NOT OAO MODE
00443 ~ THEN CALL PACER
00444 ~
0044~ ~ LABEL MGBRST
0044~ *
00447 * IF REED SWITCH ANTITACHY PACING REGAR~LESS OF RATE
00448 * THE~ GOTO R~TCH
0044~ ~
00450 ~ ~ FALL ~ INTO UPDATE }

. ", 1,, ,j,l PA~E 17 UPDATE
00453 * 'UP~ATE' I5 RETURNED TO AfTER SENSE EYENTS AN~ A~TITACHY
00454 ~ PACING. IT UP~ATES THE LINEAR I.C. STATE AND PACEMAKER
004S5 * MODALITY. IN THE EVENT OF PROGRAMMING
00456 * ALL THE STArUS FLAGS ARE CLEARED.
00457 * THE REED SWITCH IS CHEC~ED, AN~. IF APPROPRIATEJ THE 'REED
00458 * 5WITCH ANTIrACHY MO~E' FLAG IS SET.
0045~ *
00460 * LA~EL UP~ATE
00461 * CALL UPDATE_LINEAR_IC
00462 * IF NEWLY PROGRAMME~ ~ALUES ARE AVAILABLE FROM
00463 * AN EXTERNAL PROGRA~ER
00464 * THEN
00465 * UPDATE MODE
00466 * CLEAR EVERYTHING
00467 ~ EN~IF
0046~ *
0046Y * LABEL READER
00470 ~ IF REED 5WITCH I5 OPEN
00471 * THEN
00472 * IF 'REED SWITCH ANTITACHY MODE' FLAG5 ARE SET
00473 ~ THEN CALL CLEAR2 00474 * GOTO CHECK_MODE
00475 * ENDIF
00476 *
00477 * ~ NOTE: TO GET HERE, THE REED SWITCH MUST BE CLOSED 3 00478 * IF REED 5WITCH DOES NOT CAUSE ANTITACHY PACING
00479 * THEN GOTO TELEM
00480 *
00481 * IF HI~H RATE NEEDED ALSO
0048Z * THEN IF HIGH_RATE_DETECTED
00483 * THEN
00484 * SET 'DO REED SWITCH ANTITACHY IF HIGH RATE' 00485 * ELSE
00486 * CLEAR ~no REED SWITCH ANTITACHY IF HIGH RATE' 00487 * IF THERAPY_IN_PRO.GRESS = FALSE
00488 * THEN GOTO TELE~I
~ 9 * ENDIF
004SO * ELSE
. 004~1 * SET '~0 REED SWITCH ANTITACHY REGARDLESS OF RATE' Q04~Z * EN~IF
~:~004~3 *
~,,004~4 * GOTO CHECK_MnDE

3~1.3 PA$E 18 CHECK_MODE
00~7 * 'CHECK MO~E' (CHEC~ ~ODE~ ~IVERTS THE PRO~RA~ FLOW TO
004qB * A~YNCHROMOUS PACIN~ tASYNCt-lRONOUS_BEH~VIOR~ IF
004~ * APPRCPRIATE. OTHERWISE THE NOISE SENSE TI~E tNSTM~
00500 * IS SET UP.
0~0 1 *
00502 * LABEL CHEC~_MaDE
00503 *
00504 * IF AOO ~ODE
00505 * THEN GOTO ASYNCHRONOUS~BEHA~IOR
~0506 *
00507 * IF JUST PACE~
0050S ~ THEN
~050~ * SLEEP FOR ALL OF NOISE SEhl5E TI~E
00510 * GOTO STAKT QUIET_TI~E
00511 ~ ENDIF
0051~ *
00513 ~t LOOP COUNTER
00514 *
00515 * DO
0051~ * LOOP COUrlTER = LOOP COUNT - 1 00917 * IF LOOP GOVNTER = O
00518 * THEN ~OTO ASYNCHRONOUS_BEHAVIOR
0051~ * CLEAR SENSE I~PUT LAlCHES
00520 * 5LEEP UNTIL 5EhlSE E~ENT OR NOI5E 5ENSE TIME EXPIRE
00521 *
00522 * IF hlOISE SE~SE TIME HAS EXPIRE~
00523 * THEN ~OTO 5TART_OUIET_TIME
0~5Z4 *
00525 * PEPE~T

,; , . .

- ~ -~ 2~ .3 PA~E 1~ ASYNCHRONOUS_ BE~AYIOR
00~28 * 'ASYNCHRONOUS BEHAVIOR' WAITS FOR A RATE TI~EOUT AN~ THEM
0052~ * RETURNS TO 'OUTRUT' IF THE NOI5E REYERSION ~ODE IS AOO- IF
00530 * IT XS 000 THEN THE PROGRA~ RETURNS TO '~GBRST'.
00531 *
00532 * LABEL ASYNCHRONOUS_BEHAVIOR
00533 *
VV53~ * SLEER UNTIL THE RATE TI~ER EXPIRES
OOS35 *
00536 * IF NOISE REVERSIO~ MO~E IS ~00 00537 * THEN GOTO OUTPUT
00538 *
0053~ * CQLL SHIFT_INTERVALS
OV540 *
OOS41 * GOTO ~GBRST

C~) 8~
PAGE 20 ASYNCHRO~OU5 BEHAVIOR
00S45 * 'CHECI~_FOR TACH' ~ETER~I~ES IF THE LAST INTERVAL WA5 ABOVE THE
00546 * TACHYCARDIA RATE CRITERIA ~TACH_LIMIT~. IF NOT, THE PRUGRA~
00547 * RETURNS TO 'UP~ATE'. IF IT WAS, CHEC~ING OF OTHER
OO~S * TACHYCAR~IA CRITERIA STARTS IN 'TACHY1'.
0054~ * IF THE LAST INTERVAL WAS LONGER THAN 'TACH_LIMIT' BUT IT WAS
00550 * THE FIRST INTERVAL AFTER A BUR5T, 'HIGH_RATE COUNT' I5 00551 ~ INÇRE~ENTED AN~ MONE OF THE STATUS REGISTERS ARE CLEARED. THE
00552 * ASSU~PTION IS THAT A SEMSE EVENT ~AY HAVE FALLEN IN THE
00553 * REFRACTORY PERIOD OF THE LAST PULSE OF THE B~RST.
00~54 *
OOS55 * LA~EL CHECK FOR_TAGH
00~56 *
00557 * IF '~0 REE~ SWITCH ANTITACHY REGAR~LESS OF RATE' FLAG SET
00558 * THEN GOTO RDTCH
0055~ ~
00~60 * IF TACH_LI~TT~OST_RECENT_INTERVAL
00561 ~ THEN GOTO TACHY1 00563 * IF NOT THERAPY_IN_PRaGRESS OR TACH_DETECTE~
00564 * OR THIS IS NOT THE FIRST INTERVAL AFTER A BURST
00S65 * THEN
00566 * CALL CLEAR2 00567 * GOTO ~P~ATE
00568 * EN~IF
00569 *
00570 * HIGH_RATE COU~T - HIGH_RATE_COU~T ~1 00571 * G2TO UP~ATE

... .
, .3 PA~E 21 TACH1 00574 * 'TACHY1' IS ONLY ENTERED FRO~i 'CHECK_FOR_TACH' IF IT IS
00575 * DETER~IINED THAT THE LAST INTERVAL WAS SHORTER THAN
00576 * THE TACHY INTERVAL CRITERION ('TACH_Lr~IT').
00577 * IF IT IS APPR~PRIATE, T'IE RATE STABX~ITY IS CHECKED, 00578 * THE HI~H RATE COUNT I5 INCREPiENTED. AND THE RAPIDITY
00~7q * OF ONSET IS DETER~INE~.
005~0 *
00581 *
00582 * IF 'DO REED SWITCH ANTITACHY IF HI~H RATE' FLAG SET
00583 * THEN ~OTO TACHYZ
00584 *
00585 * IF NOISE WAS DETECTED ~THIR~_M05T_RECENT_INTER~AL == O) 00586 * THEN ~OTO UPDATE
0~587 *
00588 * IF TACH_DETECTED
OO50q * THEN ~OTO DELIVER_BURST

. , ~, ...

L~ ~

3~
PAGE Z2 TACHl 005~1 * CHECK THE RATE STABILITY OF THE TACHY AS A CRITERION
005q2 * FOR SINUS VS. RE-ENTRANT DISCRI~INATION. TO DO tHIS A
005q3 * VARIABLE (STAELE_RATE_MI~_POINT) ~UST BE GENERATED h~AINST
005~4 * WHICH THE TACHY RATE CAN BE COMPARED. IF THE MOST RECENT
005q5 * INTERVAL IS WITHIN A CERTAIN RANGE tMAX_~NSTABILITY) OF
005~6 * STA~LE RATE MID POINT THEN THE TACH IS CONSI~ERE~ STABLE FOR
005~7 * THAT INTERVAL AND STABILITY_COUNT IS INCRE~ENTED. WHEN A
005~S * SUFfICIANT NU~BER OF INTERVALS tREOUIRE~_STABLE_CDUNT~
005~ * HAVE BEEN STABLE, THE STABLE_RATE_DETECTE~ FEA~ IS SET.
00600 *
00601 * IF THE ~OST RECENT INTERVAL WAS NOT WITHIN ~hX_INSTABILITY OF
00602 * STABLF RATE MID_POINT THEN A NEW STABLE_RATE ~ID_POI~T IS
00603 * ~ENERATE~. THE NEW STABLE_RATE_MID_ROINT IS THE AVE~AGE OF
00604 * THE ~AX AND ~IN OF THE LhST THREE INTERVALS.
Ot)605 *
00606 * If NOT STABLE_RATE_DETECTED
00607 * THEN
00608 1~ IF ,STABLE_RATE_~I~ POINT-CURRENT INTERVAL~
0060~ * C ~AX_INSTABILITY
00610 * THEN
00611 * STABILITY_COUNT=STACILITY CQUNT+l 0061Z * IF RE~UIRE~ STABLE_COUNT-STA8ILITY_COUNT
00613 * THEN
00614 * SET STABEE RATE DETECTED = TRVE
00615 * INCREMENT DIAGNOSTIC COUNTER
aO616 * ENDIF
00617 * ELSE
0061S * ChLL FIN~_EXTREEMS
0061~ * EN~IF
006ZO * EN~IF
00621 *
00~22 *
00623 * IF HIGH_RATE_DETECTED
00624 * THEN GOTO TACHY2 00625 *
00626 * HIGH RATE COUNT = HIGH RATE COUNT ~1 0~6Z7 *

, . : `

:,: .. .~ - .

.3 PA~E 23 TACH1 0062~ * SEE I F THE SUDI:: EN ONSET CR I TER I ON I S MET .
C0630 * CCiMPARE IvlOST RECENT_IhlTERVAL
00631 * AGAINST SECOND M05T_RECENT_INTER~AL AND
00632 * THIRD M05T _ RECEhlT _ INTERVAL TO SEE IF THE RhTE OF CHAN~E OF THE
00633 * RATE WAS ABRUPT (AS DETERI~IINED BY THE ~IARIABLE 'ONSET ~.
00$3~ * NOTE: IF THIRD ~IOST _ RECENT INTERVAL AND THE FOURTH MCtST RECENT
00635 * INTERVAL WERE SHORTER THAN TACH LItYlIT ( THE VAR IABLE
00636 * DEFININt~ A HIÇH RATE~, TtlEN THE ONSET FLAG IS CLEARED. THIS
OG637 * AVOID5 DETERtVlINING THE O~SET AFTER A PVC AND 5UI~SE~UE:NT
0063~3 * C OMP ENS I TOR Y P AUSE .
00*3~ *
C~0640 * IF (NOT THERAPY_IN_PROGRE55~ t-lIGH RATE CC1UhlT == 1) 00641 * THEN
00642 * { x xL.5 ~
00643 *IF THIRD MOST_RECENT_,INTER~JAL WA5 00644 l~A TACHYCAR I l:)A TYPE I t~lTERVAL
00643 * THEN
00646 *~ x SL5 00647 * IF NOT FOURTH M05T RECENT INTR~AL_WAS_TAGH
00~$48 * THEN
00649 * ~ LSLS ~
OOf~50 * IF (SECOND_MOST _ RECENT INTERVAL
00651 * --t~105T_RECENT INTERVAL):~ONSET
00652 * Tt-lEtl 00653 * { LSLS ~nd meets onset criteri~ }
00654 ~ SUDDEhl OhlSET_DETECTED = TRVE
OC)655 * INCREt~lENr CORRESPONDIhl~ DAGNCISTIC
00656 * COUNTER
00657 * ELSE
00658 * SUDDEN_ON5ET_DETECTED = FALSE
00659 * ENDIF
00660 * ELSE
00661 * SUDDEN ONSET_DETEC TED = FALSE
001S62 * ENDIF
00663 * ELSE
0066~ * { x LLS }
00665 * IF (THIRD _ MOST _ RECENT 3:NTERVAL
00666 * --MOST_RECENT_INTERVAE ~ ~SUDDEN
00667 * THEN
006613 * { xLLS and meets the onset cri~eria 00669 * SUDDEN_OhlSET_DETECTE:D = TRUE
00670 * INCREI~lENT CORRESPONDING DIAÇ~NOSTIC COUNT
00671 * ELSE
00672 ~t SUODEI:I_OhlSET_l)ETEC TED = FALSE
0067~ * . EMID I F
OOb74 ~ EhlD I F

~ (~

PA~E ~4 rRIGl 00677 * 'TRIGl' CHECKS TQ SEE IF THERE HAVE BEEN ENOUGH FAST ~EATS
00678 * TO CONSIDER THE RHYTH~ A TACHYCAR~IA.
00~7q * THIS NU~IBER rs 'REOUIRED_HIGH_RATE_COUNT' IF
00680 * THERAPY_IN_PROGRESS IS FALSE A~D IS EITHER
00~81 ~ 'REOUIRED_HI~H_ r ~TE COUNT' OR FIFTEEN-00682 * WHICHEVER IS LEAST, IF THEPAPY_IM PROGRESS IS TRUE.
00683 * IF THERE HAVE EEEN ENOUGH INTERVALS, THE 'HIGH_RATE_DETECTED' 00684 * FLAG IS SET AN~ THE PROGRA~I CONTI~UE TO 'TACHY2'. IF NOT.
00685 * THE PRO~RAM RETURNS TO 'UP~ATE'.
00686 * IF IT IS BETWEEN BUPSTS (THERArJ~_IN_PROGRE55 IS TRUE~, 00687 * THE TACH_DETECTED FLAG I5 SET RIGHT AW~Y BY GOINÇ TO
00638 ~ 'SET_TACH DETECTED_FLA~' INSTEAD OF 'TACHYZ'.
00689 *
006qO *
006ql * LABEL TRIGl 006q2 *
00~3 * IF HIGH RATE_C OUN r = RE~UIRED_HIGH_RATE_COUNT
00694 * THEN
006~S * HIGH_RATE._DETECTED = TRUE
006~6 * INCREMENT CORRESPON~ING ~I~GNOTIC COUNTER
006q7 * GOTO TACHYZ
006~8 * ENDIF
006~q *
00700 *
00701 * IF THER~PY_IN_PROGRE5S AND HIGH_RATE_COUNT == 15 0070~ * THEN
0070~ * HI~H_RATE_DETECTED = TRUE
00704 * INCREMENT CQRRESPONDING ~IA5NOStIC COUNTER
00705 * GOTO SET_TACH_DETECTE~_FLAG
00706 * EN~IF
00707 *
00708 * GOTO UP~ATE
00709 *

Cs 00712 * 'TACHY2' IS ENTERE~ AFTER THE HIGH_RATF_~ETECTED FLAG
00713 * HAS BEEN SET IN 'TRIG1'.
00714 * IT CHEC~S THE PROGRAMMED REQUIRE~ENTS FOR ~E~UCING
~0715 * A RE-ENTRAMT TACHYCAR~IA AGAINST THE REQUIRE~ENTS THE
00716 ~ TACHYCARDIA HAS ~ET. IF THEY ARE THE SA~E THE T~CH ~ETECTE~
00717 * IS SET (SET_TACH_~ETECTE~_FLAG~. OTHERWISE THE
00718 * S~STAINE~ HI~H RATE CRITERI~N IS CHECKE~.
0071~ ~ AFrER THE TACH_DETECTED IS SET. THE PROGRA~l EXITS TO
00720 * 'ANTI_TACH_THERAPY' TO 5ET UP THERAPY FLAGS FOR
007Z1 * 'BURST_DELAY_CALCULATIONS' AND 'DELIVER_BUR5T'.
00722 ~
007~3 *
00724 *
00725 * LABEL TACHY2 0072~ ~
007Z7 * IF PERISTANT HIGH RATE FLAG CLEAR
00728 ~ TtlEN
0072q * HIGH_RAlE_COUNT = HIGH_RATE_COUNT + 1 00730 ~ IF HIGH_RATE_C`OUNT == REQUIRED_PERSISTANT_COUNT
00731 * THEN
00732 * PERSISTANT HR_DETECTE~ = TRUE
00733 * INCRE~ENT ~IA~NOSTIC COUNTER
00734 * EN~IF
00735 * ENDIF

~G

00737 * LABEL RDTCH
0073~ *
007~ * IF TACH_DETECTED
00740 * THEN GOTO ~ELIVER_BURST
00741 *
00742 * IF B~TH_THERAPYS_FAILED
00743 * THEN
00744 * IF CAN RESTART ANTITACHY PACING IF CRITERIA
00745 ~ ARE ~ET
00746 * THEN
00747 * IF RESTART CRITERIA ARE ~ET
00748 * THEN ~OTO SET_TACH_~ETECTED FLAG
0074~ * EN~IF
00750 ~ GOTO UPDAtE
00751 * EN~IF
007~2 *
00753 * IF REED SWITCH ANrITACH~ ~IODE
00754 * THEN
007~5 * TACH_~ETECTE~ - TRUE
007~6 * GOTO ANTI_TA~H_THERAP~
00757 * ENDIF
0075~ *
C075Y * IF OTHER CRITERIA ~ESI~ES H~GH_RATE_~ETECTED ARE NEE~E~
00760 * TO ~I~GNOSE A RE-ENTRANT TACH
00761 * THEN
00762 * IF NEE~ 'AN~' CRITERIA AND HAVE 'AND' CRITERIA
00763 * THEN GOTO SET_TACH_~ETECTE~_FLAG
00764 * IF CAN USE '~R' CRITERIA AN~ HAVE IT
00765 * THEN GOTO SET TACH_~ETECTE~_FLAG
00766 * IF CAN USE PERSISTANT HIGH RATE AND HAVE IT
00767 * THEN GOTO SET_ThCH DETECTE~_FLAG
00768 * ~OT~ UPDATE
0076~ * ENDIF
.

l~

~.X~ 3~
PA~E 27 ThCHY2 00771 * L~BEL SET_ThGH ETEGTE~_FLA~
0~772 *
00773 * IF IN MONITUR ~ODE
00774 * THEN
0077~ ~ UP~ATE LAST_PRI~ARY_T~CH
00776 ~ BOTH_THERAPYS_FAILE~ = TRUE
00777 * ~OTO UP~ATE
00778 * EN~IF
00779 *
00780 * TACH_~ETECTED = TRUE
~0781 *
0073Z * ~ FALL I~TO A~TI_TACH_THER~PY
00783 *

~X~B~
PA~E Z~ ANTI_TACH THERAPY
0078~ * 'ANTI_TACH THERAPY' IS ENTERED AFTER A TACHYCARDIA IS DIA~N05E
00787 * (OR RE-DIAGNOSED IN THE CASE OF AN INEFFECTI~E BURST) AS
007~8 * BEING RE-ENTRANT. BETWEEN IT AND 'BUR5T_DELAY_CALCULATIONS' 0078q * THE PACEMAKER
007qO * IS PREPARED FOR PRODUCING THE CORRECT BURST WHICH IS TO
007ql * BE SYNCHROMIZED OFF OF THE NEXT SENSE EVENT.
007q2 *
007q~ * 'ANTI TACH_THERAPY' KEEPS VARIOUS FLAt,S ~BUR5T. PRIMARY THERAP
OO7q4 * BOTH THERAPYS FAILED~ VP TO DATE. IT ALSO CLEARS OTHE~ FLAGS
00795 * (RATE STABILITY AND PERSISTANT HIGH RATE~ IF REOUIRED AS WELL
007q6 * AS LOADING 'ATTEMPT t,OU~T' WITH EITHER 'PRI~ARY_ATTEMPT_LI~IT' 007q7 * OR 'SECON~ARY_ATTEMPT LIMIT tAND SET5 'FIRST BURST' FLAG~. IT
C!07q8 * ~ECREMENTS AND CHECKS 'ATTEMPT_COUNT' TO DETERMINE THERAPY
OO7qq * CHANGES. SECONDARY THERAPY MAY CE DONE FIRST IF THIS OPTION I8 00800 * ENA~LED. THE REt~UIREMENT IS THAT THE CURRENT TACHY RATE
OOSOl * BE SIMILAR TO LAST ZNDARY TACH ~ AND EIT~ER NOT BE SIMILAR TO
OOB02 ~ LAST PRI~ARY TACH, OR
OOSO~ * IF IT IS SI~ILAR~ THE PRI~ARY THERAPY ~UST HAVE LAST FAILED ~.
q "'~
P~E 2~ ANTI TACH THERAPY
0~805 * LABEL ANTI_TACH_THERAPY
00~06 *
00807 * IF NOT THERAPY_IN_PRO~RESS
00808 * THEN
0080~ * THERAPY_IN_PRO~RE55 - TRUE
00810 *
00811 * IF 0~ TO USE SECON~ARY THERAPY FIRST
00812 * *
00813 * THE SECON~ARY THERAPY HAS PROVEN
00814 * ITSELF EFFECTIVE
0~815 *
00816 * THE CURRENT TACH IS SI~:[LAR TO
00817 * LAST_2~DARY_TACH
00818 * THEN
00819 * IF CURRENT TACH IS No-r SI~ILAR
00820 * TO l_A5T_FRIMARY_TAGH
008Zl * OR
OOa22 * (CURRENT TACH IS SIMILAR
00823 * TD LAST_PRIMARY_TACH
008Z4 * ~
0082~ * PRI~ARY THERAPY HAS NOT PROVEN
00826 * ITSELF EFFECTIVE) 00827 * THEN
ooa28 * WING_SECON~ARY_FIRST - TRUE
00829 * ELSE
00830 * DOING SECON~ARY FISRT = F~L.SE
00881 * ENDIF
OOa32 * ELSE
00833 * DOING_SEC~N~ARY_FIRST = FLASE
00834 ~ ENDIF
~0~35 *
U08~ ~ IF ~GING_SECONUARY_FIR.ST
00837 * THEN
: 00~38 * PRI~ARY THERAPY -- FALSE
0083~ * ATTEMPT_COUNT = SECONDARY_ATTEMPT LIMIT
00840 * ELSE
00841 * PRIMARY_THERAPY - TRUE
00842 * ATTEMPT_COUNT - PRIMARY_ATTEMPT_LIMIT
0084~ * EN~IF
00844 ~
00845 * FIRST BUR~T - TRUE
~00846 * ENDIF
., .
. . .

7 o PA~E 30 ANTI_TACH_THERAPY
ove4s * ~o 0084~ * IF ATTE~PT_GOUNT != O
00850 * THEN
00851 * ATTE~PT_COUNT = ATTEMPT_CDUNT - 1 00852 * GOTO BURST_DEL~Y CALCUL~TIONS
00853 * ENDIF
OO~S4 *
00855 ~ IF MOT IN ~NTITACHY ~ODE
00~56 * P~.
00857 * NOT DOING A ~UR5T REOUESTE~ BY THE RFED
0085e ~ SWITCH
0085~ * THEN
00860 * GOTO UP~ATE
00861 * EN~IF
~0862 *
00863 * IF PRIMARY_THERAPY
00864 * THEN
0086~ ~ PRI~ARY_THERAPY = FALSE
008~ PRIMARY THERAPY FAILE~ = TRUE
00867 * IF DOING_5ECON~ARY FIRST
00868 * THEN
0086q * BOTH_THERAPYS FAILE~ = TRUE
00870 * ELSE
00871 * ATTE~PT_COUNT = SECONDARY_ATTE~PT_LI~IT
00872 * FIRST_BURST = TRUE
00873 * ENDIF
00874 * ELSE
00~75 * PRI~ARY_THE~APY = TRUE
00876 * SECONDARY THERAPY_FAILED - TRUE
00877 * IF DOIN~_SECONDARY_FIRST
0087B * THEN
00879 * ATTE~Pl COUNT = PRI~hRY_ATTE~PT_LIMIT
00880 * FIRST_BURST = TRUE
00881 ~ EL~E
00882 * BOTH T~ERAPYS_FAILE~-TRUE
00883 * ENDIF
00884 ~ ENDIF
00~85 *
00886 * IF BOTH_THERAPYS_FAILE~
00887 ~ THEN
00888 ~ ~OING_SECO~DARY FIRST = FALSE
. , r ooa~q *
008~0 * IF OTHER CRITERIA ARE RE~UIRED FOR RESTART
~ ao8~ 1 * THEN
008~2 * TACH_~ETECTED - FALSE
008~8 ~ THERAPY_IN_PRO~RES8 = FALSE
008~4 ~ GOTO TAGHY2 008q5 ~ EN~rF
008q6 ~t EN~IF
008q7 ~ REPEAT

7( . .. . . .

PA~E ~1 ~URST_~ELAY_CALCULATIONS
00700 *'~URST_~ELAY_~ALCULATIONS' 00~0 1 * ~
00902 * ~CALCULATE SA1, THE FIRST COUPLING INTER~AL, AND SAZ, 00703 *THE BURST CYCLE LEN~TH.~
00~04 *THIS PORTION QF THE PROGRAM SETS UP SA1 AN~ SA2 FOR THE ANTI-00~05 *TAC~Y BURST THAT IS TO BE SY~CHRONI2EO OFF OF THE NEXT SENSE
ooqo6 ~EVENT.
00~07 *THE CODE IS ~ADE ~EMERAL ~ETWEEN PRI~ARY THERAPY AND 5ECOM~ARY
00~08 *THERAPY THROUGH THE ACTION OF THE 5WAP FLA~. IT IS SET IM
OO~Oq *SECONDARY THERAPY AND IS RESET OTHERWISE.
OOqlO *
OOq11 * LABEL BURST ~ELAY_CALCULATIONS
00~12 *
00913 * IF PRIMARY_THERAPY
OOq14 * THEN USE THE PRIMARY THERAPY TO CALCUL~TE THE DELAYS.
OOq15 * ELSE USE THE SECONDARY THERAPY TO CALCULATE THE DELAY5.
OOql6 *
OOY17 * IF FISRT_BURST
OOq18 ~ THEN
00~1q * IF ~EMORY OPTION SELECTE~ ~ LAST ATTE~PT SUCCEEDED
00~20 * THEN
40~Z1 * IF RATE SIMILARITY IS NEE~E~
OOS22 * ~ RATES ARE hlOT SIMILAR
00~2~ * TffEhl 00924 * CO~PUTE 51 AN~ SZ FROM EITHER FIXED
OOY25 * VALUES OR A~APTIVELY
OU~26 * EN~IF
00~27 * ELSE
00~28 * CO~PUTE 51 AN~ SZ ERUM EITHER FIXED VALUES
OO~S * OR ADAPTIVELY
00~30 * ENDIF
00931 * ELSE
00932 * IF THE NEW AN~ OL~ TACH RATES ARE SI~ILAR
~0933 * OR NOT ALLOWE~ TO RESET THERAPY ON RATE CHANGE
00~34 ~ THEN
00935 * CALCULATE NEW A~APTI~E OR SCANhlED P~RAMETERS
00~36 * ELSE
00937 * ATTEMPT_COUNTER = O
00~38 * CO~PUTE 51 AND S2 FROM EITHER FIXE~ VALUES
00~3q * OR ADAPTIVELY
OOMO ~ ~OTO UPDATE
OOq41 * EN~IF
00~42 * EN~IF

1 ~

P~GE 3Z BURST_~ELAY_CALCULATIONS
OOq44 * LhBEL PROG1 OOq45 * L~BEL SVAL1 -`
00946 *
00~47 *
00948 * ~OST_RE~ENT_INTERVAL = TCHRT
00~4~ * .
00~50 * INTL = VALUE COMPUTE~ FOR S1 00~51 * INTH = VALUE COMPUTE~ FOR S2 0~952 *
00~53 * IF THE CURRENT THER~PY IS NOT AUTO-~ECREMEhlT
00954 ~ THEN
00~55 * NOT AUTO~ECREMENT = TRUE
OOY56 * RETURN
00~57 * EN~IF
00~5~ *
OOq~q * NOT ~UTO~ECRE~ENT = FALSE
00~60 * AUTO ~ECRE~ENT = VALUE FRO~ THERAPY CESCRIPTION
OOq6 1 ~
0096Z * INTH = INTH-AUTO_DECREMENT
00963 * ~OTO UP~ATE

' '`

,. . ~

PAGE 33 ~URST ~ELAY_CALCULArIONS
OOqb5 *'ChLCl' SETS UP THE SC~NNlNG PARA~ETERS FOR ALL SCANNIN~
OOq66 * THERAPYS.
00~67 *
OOq68 * THIS 5ECTION OF CO~E IS MADE GENERAL BETWEEN PRI~ARY THERAPY
0096~ * AN~ SECONDARY THERAPY THROU~H THE ACTION OF THE SWAP FLA~ (SET
00~70 * IN BURST_DELAY CALCULATIONS~. FURTHER~ORE, THE ~AME CODF 5CAN
00~71 * SAl AN~ SA2 BY USING INDIRECT A~RES5ING ~SCAN12).
O~q72 *
OOq73 * IF THE THERAPY IS AUTODECREMENTAL
00~74 * THEN GOTO PROGl 0097~ *
00~76 * IF THE THERAPY IS AUTO~ECREMENTAL
00977 * THEN
OOq7~ * CALCULATE ~EW A~PTIVE OR SCANNED PARAMETE~S
OOq7~ * ~OTO PROGl 00980 * EN~IF
00~81 *
00~82 ~ USE FIXE~ OR A~APTIVE SA2 ~S REQUIRE~
ao~ *
00~54 * IF SE~RCH PATTERN SCANNING
00~05 * THEN
00786 *
00~87 * EABEL C~LCl_h OOq~8 *
00~8q * IF THERE HAVL BEEN AN EVEN NUMBER OF SCANS
00~0 * THEN
OOY~l * CALCULATE DECREMENT
OOq~2 * IF PSSAl+~ECREMENT ~OESN'T O~ERFLOW
00~3 * THEN
OO~S4 * IF ATTEMPT_COUNT==PRIMARY_ATTE~PT_LI~IT
OO~q5 * THEN ~OTO ANTI_TACH_THERAPY
OO~q6 ~ ATTEMPT COUNT - ATTE~PT CUUNT + l 00q~7 * ELSE
00~98 * PSSAl - P55Al + ~ECRE~ENT
00~ * GQTO SVALl 01000 * ENDIF
01001 * EN~IF
OlOO~
01003 * CLACULATE VALUE OF INCREMENT
01004 * IF PSSAl-IN~REME~T WESN'T UN~RFLOW
01005 * THE~
. ,01006 * IF ATTEMPT_COUNT = PRI~ARY_ATTEMPT_LIMIT
. 01007 * THEN GOTO ANTI_TACH_THER~PY
01008 * ATTEMPT_COUNT = ATTE~PT_COuN-r - l OlOOq * GUTO CALCl_A
01010 1~ ENUIF
0101 1 ~1~
0101;2 11 PSSAl - PSSAl - INCREIVlENT
01013 * GOTCI SVALl 01014 * ENI:~IF

? '( PAGE 34 BURST_DEL.AY_CALCULATI~N5 01016 * IF S~l SHOULD ~E INCREMENTE~
01017 * r~E~I
01018 * IF PSSAl-SCANl ~OES NOT UNDERFLOW
0101~ * THEN
01020 * P~SAl a PSSAl - SCANl 01021 * GOTCI SVAL 1 01022 * EN~IF
01023 ~ ATTE~PT COU~T a O
01024 * GOTO ANTI_TAGH_THERAPY
OlOZS * EN~IF
OlOZ6 *
01027 ~ ~ TO GET HERE, MU5T BE DECRE~ENTAL SCANNrN¢
01028 *
0102~ * IF P58A1~8CANl DOES NOT UNDERFLOW
01030 * THEN
01031 * PSSAl = PSSAl ~ SCANl 01032 * GOTO S~ALl 01033 ~ ENDIF
0~3~ ~
01035 * ~TTEMPT COUNT = O
01036 * GOTO ANTI_TACH_THERAPY

-i! S

-PAGE 35 ~ELIVER_BURST
0103~ *'~ELIVER BURST' PLRFOR~S THE ANTITACHY THERAPUTIC PACING.
~1~40 *
01041 * LABEL ~ELIVER_BURST
~1042 *
01043 * CALL ACTIVATE_HR_OVERRI~E
01044 *
01045 * IF ANTITACHY PACIN~ REGARDLESS OF RATE
01046 * ~x JUST PACE~
01047 * THEhl 01048 * 5LEEP FOR bOO MSEC
01049 * Ehl~IF
01050 *
01051 * START SA1 ~ELAY
01052 *
01053 * IF PRIMARY_THERAPY
01054 * THEN X RLG = BUR5TL
01055 ~f ELSE X-REG = BRSTL2 . ..~

PAGE 36 ~ELIVER_BURST
01057 * L~BEL ZEROP
01058 *
0105~ * IF X-REG != O
01060 * THEN
G1061 * DO
01062 * CALL SLEEP_THRU_B~SRT_~ELAY
01068 ~ IF AUTO~ECREMENTAL THERAPY
01064 * THEN
01065 * IF BURST INTER~AL ~ ~UTO_~ECRE~ENT DOES
01066 * NOT UN~ERFL9W
01067 * THEN
01068 * BURST INTERV~L
01069 * -- BURST INTERVAL-AUTO_DECRE~ENT
01070 # E~IF
01071 * ENDIF
~107Z ~
01073 ~ IF BURST INTERVAL ~: MIN~BUSRT_DFLAY
01074 ~ THEN BURST INTERVAL = MIN_BUSRT_DELAY
01075 *
01076 * START SA2 INTERVAL (BURST INTE~VAL) ~1077 ~
01078 * IF LAST PULSE OF BURST
0107q * THEM
01080 ~ CALL PACER
01081 * UNLQOP
01082 * EN~IF
010~3 *
01084 * CALL PACE
01085 * REPEAT
010~ *
01087 * RESET R ATE TIrlER
01088 * EN~IF
010~ *
OlOqO ~ IF ~O_ELECTRO~PHYSIOLOGY
01091 * THEN GOTO EP XTRA
010~2 *
01093 * C~LL CLEAR3 010~4 *
01095 * GOTO UP~ATE

.' ~
.. , P A~E B7 TELEM
OlOq8 * 'T:LEivl' is entered iP the reed switch is closed and ~ound 010~ ~ not to c~use antitach~ pacing. I P the ree~ switch daesn't 01100 * ~ctiv~te high r~te override, the progr~m con~inues to 'TLMTOP ' 01102 ~ LABEL TELE~
0~103 *
01104 ~ IF THE HIGH RATE OvERRIDE SHOUL~ BE ACTIVATE~
01105 * THEN
0110~ ~ CALL ACTIvATE HR_OvERRIDE
01107 * GOTO CHECK_MODE
OllOB ~ E~DIF

., ? ~

3~
PA~E 3S TELEM
01110 * per~orm all the telemetr~ ~un~tions. The mo~e is 01111 * programmable to either AOO or AAT. The re~d switch i5 cherke~
01112 * e~h ~y~le and i~ it is open, the program ~herks t~ see if 01113 * the telemetr~ is progra~d on. I~ it isn 't. the program 01114 * returns ~ UP~ATE.
01115 *
01116 * DO
01117 * IF THE REE~ SWITCH IS OPEN
01118 * THEN
0111~ * IF TELEMETY_COUNTER ~- O
01120 * THEN GOTO UPDATE
01121 * TELEMETRY_C WNTER = TELEMETRY_COUNTER - 1 01122 ~ ENDIF
011~3 *
01124 * SLEEP UNTIL 450 M5EC REFRACTORY PERIO~ EXPIRES
01125 *
OllZ6 ~ IF AOO TELEMETRY PIODE
01127 If THEN
01128 * SLEEP UNTIL THE INTER~AL TI~ER EXPIRES
OlIZ9 * ELSE
01130 * 5LEEP UNTIL THE INTERVAL TI~ER EXPIRES
01131 * OR A SE~SE EVENT 4CCURES.
0113Z * EN~IF
0113~ *
01134 * START 14~.5 MSEC DELAY
01135 * CALL PACER
011~6 * SET UP FIR5T ADDITIONAL NIBBLE
01137 * SLEEP UNTIL THE 143.5 ~SEC ~ELAY EXPIRE5 0113~ *
0113~ * TRANSFER THE FIRST AD~ITIONAL ~IBBLE TO THE LINEAR
01140 * IC SO THAT IT WILL BE SE~T WITH TELEMETRY.
01141 *
0114Z * START 39.27 MSEC ~ELAY ~3~.8 AÇTUAL~
01143 ~ SET UP SECOî~ ITIONAL NIBBLE
01144 * SLEEP UNTIL ~9.Z7 ~5EC ~ELAY EXPIREB
01145 *
01146 * TR~hl5FER THE SECON~ A~DITIONAL NIB8LE TO THE
01147 * LINEAR IC SO THAT IT WILL BE SENT WITH T~E
01148 * TELMETRY.
01I~ *
~011$0 * START 47.5 MSEC ~ELAY ~46.1 ACTUAL}
~1151 * SLEEP UNTIL THE 47.5 M5EC ~EL~Y EXPIRES.
; `. 01152 * I'IAKE TCl ON THE LINEAR IC CHIP HI~H
0~153 *
01154 ~ IDLE APPROXIMATELY 4 MSEC.
011~5 ~ CALL UPDATE_LINEAR_IC
01156 ~ REPEAT

~ CZ

~,væ~
PA~E 39 ELECTRO PHYSIOLO~Y_STUDY
0115~ * 'ELECTQ_PHYsIOLOGY_STUDY' set~ up th~ Sl dela~ and c~cl~
01160 * len~th for the first part o~ ~he EY ~urst.
01161 *
0116Z * LABEL ELECTRO PHYSIOLOGY_STU~Y
01163 *
01164 * SLEEP
01165 *
01166 * CALL ACTI~ATE_HR_Q~ERRI~E
01167 *
01168 * START Sl DELAY IM TIMER 4 0116~ *
01170 * If THE W~EUP WAS NOT CAUSE~ BY A RATE TIME OUT
01171 * THEN
01172 ~ RESET THE RATE TIMER
01173 * CALL PACE
01174 * E~IDIF
01175 *
0117h * SET UP Sl CYCLE LENGTH
01177 ~ SET UP NU~BER OF Sl'S
0117~ *
01179 * GOTO ZEROP
01 1130 *
01181 * 'EPXTR~' ~dds the extra stimuli at the end of the Surst. As 01152 * soo~ as ~he lo~p hits a ze~o, it is exited. As many as four 01183 * extr~s can ~e used.
01184 *
01185 * LA8EL EPXTRA
01186 *
011~7 * POINTER = START OF EXTRA STI~ULI DELAY LIST
01188 ~ VO WHIL~ tDELAY ~ POINTER~ != O
01189 * 8TART TIMER 4 FCR ~ELA~ @ POINTER) 011qO * CALL SLEEP_THRU_BUSRT_DELAY.
011~1 * CALL PACER.
011~2 * POINTER = POINTER ~ 1 011~3 * EN~-WHILE
0119~ *
011~5 * ~O_ELECTRO_PHYSIOLOGY = FALSE
01196 *
011~7 * RESET RATE TIMER
011~ * CALL CLEAR3 'Oll~q * GOTO UP~ATE

~0 PA~E 40 PACE PACER
01202 * SU~ROUTINE PACE
01203 * SUBROUTINE PACER
01204 ~
01205 *'PACE' IS CALLED WHEN AN OUTPUT IS DE~IRED. THE PACE
G120b ~REFRACTORY TIME IS STARTED AN~ BLANKING aCCURS DURING
01207 *THE OUTPUT PULSE AN~ 30.72 ~SEC OPR. THE PACE FLAG IS
01208 *SET AND THE SUBROUTINE RETURNS.
0120~ *(THE ERI VOLTAGE COMPARITOR IS ALSO SA~PLED~
0121~ *
01211 *'PArER' IS THE ENTRY POINT FOR ~RADY PACING AND RESETS THE
0121Z *BURST CYCLE LENGTH COVNTER. THIS IS SUBSE~UENTLY CHECKED IN
01213 *THE AAT ~O~E AS A MEANS aF RATE LI~ITING.
01214 *'PACE' IS ONLY ENTERE~ FROM '~ELIVER BUR5T'. TH~S E~TRY ALLOWS
OlZ15 *THE BURST CYCLE LENGTH TI~ER TO END OPR; ACCO~ODATING ARB-OIZ16 *ITRARILY HIGH RATE BURSTS.

, ~1 ~.2~
F~AGE 41 CLEARl CLEAR~ CLEAR3 01219 * SU~ROUTINE CLE~R
OlZ20 *
01221 *'CLE~Rl' IS CALi_ED IN THE EVENT OF NOISE QR REPRO~RA~MIN~.
01222 *'CLEAR2' IS CALLED FROM 'CHECK_FOR TACH' WHEN THE RATE IS BELOW
01223 * THE TACHYCARDXA ~RITERION (TACH_LIMIT~. AN~ FRQ~
OlZ24 ~ 'SENSE INTERVAL' UPON A RATE WA~EUP.
0122$ *'CLEAR3' IS CALLED AT THE Ei~ OF AN ANTIThCHY 8URST
01226 * (~ELI~ER_BURST).
OlZ27 *
OlZ28 * LABEL CLEARl 0122~ *
01230 * SEC~N~_MOST RECENT_INTERVAL = O
~231 *
01232 * LA~EL CLEAR2 O~Z~3 *
01234 * SUDDEN_ONSET_DETECTED = FALSE
01235 * STABLE RATE_DETECTE~ = fAlSE
01236 * PERSISTAN_i-iR_DETECTED - FALSE
012~7 * HIGH RATE_DETECTED = FALSi-OlZ38 * TACH DETECTED = FALSE
012~q * THERAPY IN PR~RESS = FALSE
01240 * PR I ~AR Y THERAPY = FALSE
01~41 *
OlZ42 ~ B~TH_THERAPYS FAILED = FALSE
01243 * DOIN~_SECONDARY_FIRST = FALSE
OlZ44 * FIRST_BUR5T = FALSE
OIZ49 *
OlZ46 * IABEL CLEAR3 OlZ47 *
OlZ48 ~ ST~BILITY_CQUNT = O
01249 * i~ H RATE_CUUNT = O
OlZ~O *
01251 * STABLE_RATE_DETECTED = FALSE
01~52 * PERSISTAN_HR_DETECTE~ = FALSE
01253 * HI~H_RATE ~ETECTED = FALSE
Ol~S4 * TACH_DETECTE~ = FALSE
01255 * FIRST ~URST = FALSE
0~256 *
OlZ57 * RETURN

"

PA~E 42 SUBROUTINE FIN~EXTRE-E~
012~0 * S~JBRQUTINE FIND_EXTREEMS
01Z61 *
0126Z *'FIND EXTREE~S' ErNDS THE EXTRE~ES OF
01263 ~ THIRD MOST RECENT INTERVAL- SECOND_MnST RECENT INTERV~L
01264 * AN~ ~OST RECENT INTERVAL. THE SHORTEST INTERVAL IS T~RED
01265 * AT INTL AND THE HIGHE5T IS STORE~ AT INTH.
01266 *
01267 * IF MOST REGENT_INTERVAL ~ SECON~_~OST_RECENT_INTER~AL
012~8 * T~EN
01269 * INTL = SEC~ND_~OST_RECENT_XNTERVAL
01270 * INTH = MOST_REGEN-r_INTERVAL
01Z71 * ELSE
01272 * INTL - ~OST_RECENT_INTERVAL
01273 * INTH = SECOND_~OST_RECENT_INTERVAL
01Z74 * EN~IF
01275 *
01276 * IF THIRD MOST_RECENT_INTERVAL ~ INTH
01277 * T~1EN INTH - THIR~ OST_RECEhlT_INTERVAL
01~7~ ~
01279 * rF THIR~ MOST_RECENT_INTERVAL ': INTL
01280 * THEN INTL = THIR~_~OST_RECENT_INTERVAL
012~1 *
012SZ * STABLE RATE_~I~_POINT = (INTH-~INTL)~2 01283 *
012~ * RETURN
01Z~5 *

..
~, ~ 3 3~
PAGE 43 ACTIVATE HR_OVERRI~E
0128~ * SUBROUTINE ACTIVATE_HR_OVERRI~E
0128q *
012~0 ~ 'ACTIVATE HR OVERRIDE' activates ~he high rate override 012~1 * eapabilit~J ~f the linear I.C.
~12~2 *
O12q3 * WRITE TO IfO LINE THAT ACTIVATES THE HIGH RATE OVERRIDE
OlZ~4 * CAPABILITY OF THE LI~IEAR IC.
OlZq5 *
OlZq* ~ RETURN

~d,~" ~
~,J~

~ ~( 3~

~. I
PA~E 44 SU~RQUTINE UPDATE_LINEAR_IC
~)12S~9 *
01300 * SU13ROUTINE UPDATE_LINEAR_IC
01301 *
01302 * 'UPDATE LINE~R_IC ' restores or upda~e~ the 1 inear IC sta~e.
01~0~ * VDATA is ser~ to VCHIP ~I,'O address~.
01305 * WRITE CONTENTS OF Vl~ TA TO IfO A~ RESS VCllrP
01306 *
C) 1307 * R~TUR 1~1 ~S

PA~E 45 SUBROUTINE SHIFT_IMTERVALS
01310 * SUBROUTINE SHIFT_INTERVALS
01311 *
01312 *tSHIFT INTERVAL5' SHIFTS SECON~ MOST_RECENT_IN'TERVAL TO
01313 * THIRD_MOST_RECENT_INTERVAL QN~ SHIFTS MOST_RECE~T_INTERVAL
01314 * TO SECON~ MOST RECE~T INTERVAL. THE
01315 * CURRENT INTERVAL IS STORED AT MOST_RECENT_INTER~AE.
01316 * THE INTERVAL GOU~TER I5 RESET.
01317 *
01318 *
0131S * LABEL SHIFT_INTERVALS
013~0 *
01321 * IF THIR~ MOST RECENT INTER~AL C TACH LIMIT
01322 * THEN FDURTH,_MDST~RECENT_INTERVAL_WAS_TACH - TRUE
01323 * ELSE FOURTH_MOST_RECENT_INTERVAL_WAS_TACH = FALSE
01324 *
01325 * THIR~ MC)ST RECENT INTERVAL = SECDND_~OST_RECENT INTERVA
01326 * SECOND ~OST RECENT_INTERVAL = MOST_RECENT_INTERVAL

01323 * IF JUST HA~ A SENSE EVENT ~ RATHER THAN A RAl'E TIMEnUT~
013Zq * THEN
0133~ * M~ST~RECENT_INTERVAL = MEASURE~ INTERVAL
01331 * ELSE
~1332 * MOST RECENT_INTERVAL = PROGRAMMED I~TERVAL
01333 * EN~IF
01334 ~
01335 * RESTART RATE TIMER
01336 *
01337 * RETURN

PA~E 46 ~UBROUTINE SHIFT~INTERVALS
0133~ ~ SV8ROUTINE SLEEP THRV_~URST_~ELAY
0~340 *
01341 * LABLE SLEEP_THRU_BURST_~ELY
0134~ *
01343 * RESET THE RATE TIMER sn IT CAN'T CAUSE ~ WAUEUP.
01344 *
01345 * 8LEEP UNrIL THE BURST ~EL~Y WHICH H~S BEE~ STARTED
0134~ * IN TIMER 4 EXPIRES.
01347 *
01348 * RETURN
013~9 ~
0~390 END

Claims (39)

The embodiments of the invention in which an which an exclu-sive property or privilege is claimed are defined as follows:

1. An antitachycardia pacemaker, comprising:
means for detecting electrical events occurring in at least one chamber of the heart;
means for detecting said events which exceed a predefined tachycardia rate;
means for determining the relative rate stabil-ity of the events which exceed said tachycardia rate;
and means for detecting a pace-terminable tachycar-dia when at least a first preselected number of said events exceed said tachycardia rate and a second pre-selected number of said events have a defined rate stability.

2. The antitachycardia pacemaker of claim 1, further including means for applying at least one electrical signal to said at least one chamber to ter-minate the defined pace-terminable tachycardia.

3. The antitachycardia pacemaker of claim 2, wherein said means for applying includes:
means for generating a first set of elec-trical signals having characteristics defining a primary tachycardia treatment modality and a second set of elec-trical signals having characteristics defining a secondary tachycardia treatment modality; and means for applying the primary and secondary treatment modalities to interrupt a detected pace-terminable tachycardia in a preselected order of prefer-ence.

4. The antitachycardia pacemaker of claim 3, wherein said means for applying the primary and second-ary treatment modalities includes means for applying the primary modality before the secondary modality to interrupt a currently detected pace-terminable tachy-cardia, unless the secondary modality was the only modality which successfully treated a previous similar detected pace-terminable tachycardia, in which case the secondary modality is applied before the primary modality.

5. The antitachycardia pacemaker of claim 3, further including means for selectively retrying the primary treatment modality a first preselected number of times if it fails to terminate the tachycardia and for selectively retrying the secondary treatment modal-ity a second preselected number of times if it fails to terminate the tachycardia.

6. The antitachycardia pacemaker of claim 5, including means for restarting the primary and second-ary treatment modalities if a tachycardia is unsuccess-fully treated and predefined restart criteria are met by the continuing tachycardia.

7. The antitachycardia pacemaker of claim 5, including means for restarting treatment by the primary and secondary modalities if the rate of said continuing tachycardia exceeds said predefined tachycardia rate for said preselected high rate number of events.

B. The antitachycardia pacemaker of claim 6, including means for restarting treatment by the primary and secondary modalities if the rate of said continuing tachycardia exceeds said predefined tachycardia rate for said preselected high rate number of events and the events have said defined rate stability.

9. The antitachycardia pacemaker of claim 6, including means for restarting treatment by said primary and secondary modalities if the rate of said continuing tachycardia exceeds said predefined tachycar-dia rate for a preselected sustained high rate number of events which exceeds said preselected high rate number of events.

10. The antitachycardia pacemaker of claim 6, including means for restarting treatment by said primary and secondary modalities if the rate of said continuing tachycardia exceeds said predefined tachycar-dia rate for said preselected high rate number of events and the events have said defined rate stability or the rate of said continuing tachycardia exceeds said prede-fined tachycardia rate for a preselected sustained high rate number of events which exceeds said preselected high rate number of events.

11. The antitachycardia pacemaker of claim 2, wherein said means for applying includes means for selectively applying at least one burst of electrical signals to terminate a detected pace-terminable tachy-cardia, the burst starting a predefined start delay time following a detected synchronizing event and in-cluding a preselected number of electrical pulses, successive pulses being separated by a predefined burst cycle interval.

12. The antitachycardia pacemaker of claim 11, further including means for remembering the values of the start delay time, number of burst pulses and burst cycle interval for a successfully terminated tachy-cardia and for selectively applying these values to terminate a subsequent similar detected pace-terminable tachycardia.

13. The antitachycardia pacemaker of claim 12, further including means for defining said subsequent similar tachycardia as a tachycardia having a rate within a preselected range of the rate of the previously success-fully terminated tachycardia.

14. The antitachycardia pacemaker of claim 11, further including means for defining fixed values for said start delay time and burst cycle interval.

15. The antitachycardia pacemaker of claim 11, further including means for defining adaptive values for said start delay time and burst cycle interval, each adaptive value being defined as a preselected per-centage of the rate interval for the associated detected pace-terminable tachycardia.

16. The antitachycardia pacemaker of claim 15, further including means for selecting a minimum value for said burst cycle interval and for preventing burst pulses from being generated with cycle intervals less than said minimum value.

17. The antitachycardia pacemaker of claim 16, further including means for generating burst pulses having said minimum value burst cycle interval in re-sponse to the definition of adaptive values of burst cycle intervals less than said minimum value.

18. The antitachycardia pacemaker of claim 11, further including means for selectively incrementally scanning the initial values of said start delay time and burst cycle interval by predefined increments for a preselected number of steps from burst to burst.

91 .

19. The antitachycardia pacemaker of claim 11, further including means for selectively decrementally scanning the initial values of said start delay time and burst cycle interval by predefined decrements for a preselected number of steps from burst to burst.

20. The antitachycardia pacemaker of claim 11, further including means for selectively and alternately incrementing and decrementing the initial values of said start delay time and burst cycle interval by predefined increments and decrements for a predefined number of steps from burst to burst.

21. The antitachycardia pacemaker of claim 20, further including means for defining said predefined decrement as a fraction of said predefined increment.

22. The antitachycardia pacemaker of claim 20, further including means for defining said predefined decrement as one-half of said predefined increment.

23. The antitachycardia pacemaker of claim 11, further including means for selectively and automati-cally decrementing said initial value of said burst cycle interval within a burst by a predefined amount for providing decreasing interval burst pulses within the burst.

24. The antitachycardia pacemaker of claim 23, further including means for selecting a minimum value for said burst cycle interval and for preventing burst pulses from being generated with cycle intervals less than said minimum value.

25. The antitachycardia pacemaker of claim 23, further including means for generating burst pulses having said minimum value burst cycle interval in re-sponse to the definition of decremental values of burst cycle intervals less than said minimum value.

26. The antitachycardia pacemaker of claim 1, further including means for determining the relative suddenness of the onset of events which exceed said predefined tachycardia rate, and means for detecting a pace-terminable tachycardia when said first preselected number of said events exceed said tachycardia rate, said second preselected number of said events have said rate stability and said events have an onset which exceeds a predefined rate of onset.

27. The antitachycardia pacemaker of claim 1, further including means for determining the relative suddenness of onset of events which exceed said prede-fined tachycardia rate, and means for detecting a pace-terminable tachycardia when said first preselected number of said events exceed said tachycardia rate and said second preselected number of said events have said de-fined rate stability or said events have an onset which exceeds a predefined rate of onset.

28. The antitachycardia pacemaker of claims 1 or 26 or 27, further including means for detecting a pace-terminable tachycardia when a preselected sustained high rate number of said events exceed said tachycardia rate, said sustained high rate number being greater than said first preselected number.

29. An antitachycardia pacemaker, comprising:
means for detecting electrical events occurring in at least one chamber of the heart;

means for detecting said events which exceed a predefined tachycardia. rate;
means for determining the relative suddenness of the onset of events which exceed said predefined tachycardia rate; and means for detecting a pace-terminable tachycardia when a first preselected number of said events exceed said tachycardia rate and said events have an onset which exceeds a predefined rate of onset or a sustained high rate number of said events exceed said tachycardia rate, said sustained high rate number being greater than said first preselected number.

30. An antitachycardia pacemaker, comprising:
means for detecting electrical events occurring in at least one chamber of the heart;
means for detecting said events which exceed a predefined tachycardia rate;
means for detecting a pace-terminable tachycardia when at least a preselected number of said events exceed said tachycardia rate;
means for generating a first set o electrical signals having characteristics defining a primary tachycardia treatment modality and a second set of electrical signals having characteristics defining a secondary tachycardia treatment modality; and means for applying the primary and secondary treatment modalities to interrupt a detected pace-terminable tachycardia in a preselected order of preference.

31. The antitachycardia pacemaker of claim 30, wherein said means for applying the primary and second-ary treatment modalities includes means for applying the primary modality before the secondary modality to interrupt a currently detected pace-terminable tachy-cardia, unless the secondary modality was the only modality which successfully treated a previous similar detected pace-terminable tachycardia, in which case the secondary modality is applied before the primary modality.

32. The antitachycardia pacemaker of claim 30, further including means for selectively retrying the primary treatment modality a first preselected number of times if it fails to terminate the tachycardia and for selectively retrying the secondary treatment modal-ity a second preselected number of times if it fails to terminate the tachycardia.

33. The antitachycardia pacemaker of claim 32, including means for restarting the primary and second-ary treatment modalities if a tachycardia is unsuccess-fully treated and predefined restart criteria are met by the continuing tachycardia.

34. The antitachycardia pacemaker of claim 33.
including means for restarting treatment by the primary and secondary modalities if the rate of said continuing tachycardia exceeds said predefined tachycardia rate for said preselected high rate number of events.

35. The antitachycardia pacemaker of claim 33, including means for restarting treatment by the primary and secondary modalities if the rate of said continuing tachycardia exceeds said predefined tachycardia rate for said preselected high rate number of events and the events have said defined rate stability.

36. The antitachycardia pacemaker of claim 33, including means for restarting treatment by said primary and secondary modalities if the rate of said continuing tachycardia exceeds said predefined tachycardia rate for a preselected sustained high rate number of events which exceeds said preselected high rate number of events.

37. The antitachycardia pacemaker of claim 33, including means for restarting treatment by said primary and secondary modalities if the rate of said continuing tachycardia exceeds said predefined tachycardia rate for said preselected high rate number of events and the events have said defined rate stability or the rate of said continuing tachycardia exceeds said predefined tachycardia rate for a preselected sustained high rate number of events which exceeds said preselected high rate number of events.

38. An antitachycardia pacemaker, comprising:
means for detecting electrical events occur-ring in at least one chamber of the heart;
means for detecting said events which exceed a predefined tachycardia rate;
means for detecting a pace-terminable tachy-cardia when at least a preselected number of said events exceed said tachycardia rate;
means for selectively applying at least one burst of electrical signals to terminate a detected pace-terminable tachycardia, the burst starting a pre-defined start delay time following a detected synchroniz-ing event and including a preselected number of electrical pulses, successive pulses being separated by a predefined burst cycle interval; and means for remembering the values of the start delay time, number of burst pulses and burst cycle inter-val for a successfully terminated tachycardia and for selectively applying these values to terminate a subse-quent similar detected pace-terminable tachycardia.

39. The antitachycardia pacemaker of claim 38, further including means for defining said subsequent similar tachycardia as a tachycardia having a rate within a preselected range of the rate of the previously successfully terminated tachycardia.