CA1281081C - Cardiac signal real time monitor and method of analysis - Google Patents

Abstract

ABSTRACT
An apparatus for monitoring EKG information includes a programmable apparatus carried by an ambula-tory patient for performing continuous, real-time ana-lyses of EKG information derived from the patient. The apparatus facilitates the determination of the existence of various conditions based on these analyses which portend cardiac complications including myocardial is-chemia, and arrhythemia activity and further instructs the patient on the manner of treatment required for the detected condition.

Description

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CARDIAC SIG~AL REAL TIME MONITOR AND METHOD OF ANALYSIS
_ Field of the Invention The present invention relates to apparatus employed to monitor EKG information, and more particu-larly relates to a programmable apparatus carried by an amhulatory patient for performing continuous, real-time nalyc~e~ of EKG information derived from the patient, ro~ determining the existence of various conditions ba~sed on these analyses which portend cardiac compllca-tions including myocardial ischemia, and arrhythemia activity and for instructin~ the patient on the manner of treatment required for the detected condition.
Background of the _ vention ~he 1eading cause of death in adults in the J.,~',.h. i'; coronary artery di3ease, yet the disease re-mains silent or dormant in the majority of patients until the fourth or fifth decade of life. Then, coro-nary artery di3ease typically moves from the "silentn pha~e to a symptomatic phase, at which time the patient may experience as the firYt symtoms, angina pectoris, myocardial infarction, and/or sudden death.
The prevalence of coronary artery disease in the tTnited States has been estimated at over 4,000,000 ~er~on~. O~er 1,000,000 are expected to have myocardial infarction~ each year and of these, approximately 500,000 per~ons are expected to survive through the first few hours and the subsequent hospitalization. Put another way, a U.S. male has a 1 in 5 chance of having a myocardial infarction or suffering sudden death before the age of 60. Further, once coronary artery disease is ~ymptomatic - regardless of whether the symptom is an-gina or myocardial infarction - the mortality rate is increased ~o 4% per year overall and 8% per year in those with an abnormal electrocardiogram or hyperten-sion. Thi~ increased mortality i3 due to sudden death or the complications of repeated myocardial infarction.
Nearly all symptomatic coronary artery di~ease i~ due t:o coronary atherosclerosi~, a pathologic proce~s which result~ in the narrowing of the coronary arterieq (the arteries which supply the heart it~elf with blood) due to the presence of exces.s cellular and connective tissue materials and an abnormal accumu:Lation of choles-terol. The presence of these narrowings in addition to spasm o~ the arteries in the area of the narrowings results in an inadequate blood supply to the myocardium or mu~cle of the heart. Thi~ inadequate blood supply is ; called i.schemia and is expre3sed by a spectrum of condi-tions including angina, myocardial infarction and sudden death. However, and most ~ignificantly, myocardial ischemia ~ay be entirely "silentn, i.e. the patient rnay be totally unaware of a sudden and potentially dangerous decreaqe in the blood supply to hi~ heart.
Regardless of the initial expres~ion of the coronary artery disease, patients with symptoms are at a~n increased risk for myocardial infarction and/or sud-den d*ath. The current approach to the therapy of this condition has been to make a definitive dia~nosis by historical criteria, stre~s testing, radionuclide ~tu-dies, and coronary arteriography and then to treat the patient with medication and/or coronary artery bypass surgery. Despite major advances in surgical technique, 3~ and the availability of long acting nitrate~, beta-adrerlergic b]ocker~, and calciu~ antagonists, the death rate rrom cardiovascular disease haq declined only ~lightly. Thi~ suggests the need for new therpeutic approache~.
Traditionally, physicians have recognized the :
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presence o~ acute myocardial ischemia by noting the ~ccurrence of angina in the patient. Indeed, succe3s of ~herapY i~ often gauged by ho~ well the symptom of an-gina is controlled, i.e. how effective medication or surgery has been at decreasing the frequency and se-verity of anginal attacks. This is because when angina occurs, it indicates that i~chemia is present, and when ischemia is present the chance of myocardial infarction or ~udden death is increased. In theory, decrease in lC ~ttacks of anqina ~hould translate into a decrease in 3ll~0ca~dial ioIdrction and sudden death: in point of ~act, ~he decrease has been small.
The development of apparatus to perform ana-lyse~ on electrocardiographic (EKG) signals ha~ facili-tated recognition of myocardial ischemia in a patient.
Through the~e analyses it has become widely accepted that a depres~ion of the portion of the SKG ~ignal known a~ the ST segment, relative to the isoelectric segment of the signal, correlates with partial lack of blood s~pply, ~hile elevation of the ST segment relative to the isoelectric segment of the ~ignal correlates with a complete lack of blood supply.
Once the ST segment was identified as an indi-cator of myocardial ischemia, i~ was then verifie~ that durnq anginal attacks the ST segment wa~ altered; a deviation of the ST segment could actually precede the experience of angina by several minute~, or even be ~ntirely silent. Silent episode~ are no le~s danqerous then anginal episodes, and occur in patients with equal-ly as extensive coronary disea~e as tho~e with anginal episodes, and are frequently accompanied by ventricular rhythm di3turbances.
An individual patient may express ischemia silently at all times, may have angina during many is-3~ chemic episodes, or h~ve both silent and ~ymptomatic . . .
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episode~. Recently it has been sugge~te~ that these silent epi~odes may be a predictor of myocardial infarc-tion and death.
The patient'~ failure to ~ense the myocardial ischemia by experiencing discomfort has been called the result of a defective anginal warning system as it were, and such a defect may be one of the reasons for the high incidence of myocardial infarction and sudden death.
Concern for patients with coronary artery ease and rhythm disturbances has led to the develop-ment of various devices for the monitoring of EKG sig-nals. These devices typically are classified into three grol~ps:

(1) devices which rec~rd EKG signals continu- -lS ously for predetermined periods of time on maqnetic tape for subseq~ent p~inting and analysis by specially trained techni-- cians an~/or computers (see U.S. Patent No. 3,267,934 to Thornton);

(2) devices which analyze the EKG signal as it is generated by the patient and which store selected data for subsequent analy-sis (~ee U.S.Patent ~os. 4,073,001 and 4,006,737 to Cherry et al); and -~3) patient activated devices which record, store and or transmit EKG signals to a remote location for analysis when the patient notices ~omething abnormal, or on a pre~elected ba~is (see U.S. Patent No.

3,724,454 to Unger).
`7'he ~irst two group~ of device~ require ~o phi8ticated and costly off-line analy~i~ of large - . ... : -'' ' ~ ' .

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~ 5 --amounts of data which may be available only after the event(s) being monitored has occurred. The third group of devices has the limitations that only symptomatic events detected by the patient are availahle for analysis, or the preselected schedule established for monitoring signals may permit major EKG events to be missed entirely.

Summary of the Invention In summary, starting from this technology, one aspect of an embodiment of the present invention provides a portable heart monitoring device which in a real time on-going manner "looks at" each and every heart beat, which analyzes each heart beat for certain abnormalities, and upon detecting a problem or even a potential problem, alerts the user, at the discretion o his physician by programming to the fact, and does so virtually instantly no later than upon completion of that particular suspect heart beat or group~s) of heart beats or ST segment deviations. Because of the data storage and handling abilities and the speed of current computer technology, an aspect of one embodiment of the present invention device in effect provides the patient the benefit of a "cardiologist"
who is "diagnosing" each beat of his heart, and who will "prescribe" treatment or recommend other action instantly upon any one of a relatively large num~er of problems (stored in the computer's memory) arising.
The invention is thus a dramatic step forward in the healing arts, and it is expected that the invention will save a large number of lives.
According to one aspect of the present invention there is provided a method of evaluating a curve having a rapidly changing value by determining the positive or negative quality of the slope of the curve and by determining when the value of the curve is above or ~elow a predetermined threshold value, ' .' ' . , , ~

comprising the steps of: determining a frequency of sampling; determining the slope oE the curve between a Elrst sampling and a successive later sampling by subtracting the value of the curve at each first sampling from the value of the curve at -the la-ter sampling, providing four shift registers each having space for a plurality of bits and for a Flag Bit;
assigning a shift register to each of the curve values of positive slope, negative slope, above threshold and below threshold; feeding an appropriate bit value to each shift register at each sampling;determining a numerical value represented by the plurality of bits arrayed in each shift register; providing a table of values correlating the status of the Flag bit to each one of the numerical values possibly represented by the array of bits; finding the determined numerical value in the table changing~ as needed, the sta~us of said Flag Bit in accordance with the determined numerical value found in the table; and performing at each sampling the sequence of steps so that the status of the Flag bit may be changed as needed.

According to another aspect of the present invention there is provided a method for continuously monitoring every beat of the heart of a human patient subject to detect abnormal functioning of the heart and to alert the patient immediately upon the occurrence of any one of a plurality of detected abnormal heart functions, comprising the steps of:
providing electrode means, using the output signal of the electrode means to produce EKG signals, determining, by analyzing the signals, whether or not each heart beat includes an abnormal QRS portion, determining, by analyzing the signals, whether or not each heart beat is a VPB, and continuously repeating each of the determining steps without interruption ' .
~, ,- ' : : -whi.le actuating alarm means no later than upon conclusion of each beat if either of the determining steps indicates an abnormal QRS portion or a VPB, -.
which in turn indicates some abnormal heart function, and signalling to the patient instructions for treatment of each indicated abnormal heart function as it occurs.
According to another aspect of the present invention there is provided a portable computerized EKG monitor, comprising: real-time recognition means for recognizing abnormal cardiac events in an ambulatory patient, real-time diagnosis means for diagnosing each the recognized abnormal cardiac event, and signalling means for communicating to the ambulatory patient a treatment for the recognized and diagnosed abnormal cardiac event.
According to a further aspect of the present invention there is provided a portable cardiac monitor for an ambulatory patient comprising: computer means for performing continuous real-time analysis of EKG
information derived from the patient, including first means for recognizing abnormal cardiac events, and second means for diagnosing each of the abnormal cardiac event, and means for signalling~ to the patient, a treatment corresponding to each the recognized and diagnosed abnormal cardiac event at the onset of each of the abnormal cardiac events, whereby the patient may immediately begin selE-treatment of each recognized and diagnosed abnormal cardiac event without the need for intervention of a trained cardiac specialist.
: According to another aspect of ~he present inventior. there is provided portable apparatus for continuously monitoring EKG signals generated by the heart of an ambulatory patient, comprising: self-contained, computerized analyzing means, carried on " ' :. , ' ~ ' ' '' . " ' o~

- 7~ -the patient, for performing real-time analysis of the EKG signal~, the computerized analyzing means including means for diagnosing abnormal cardiac events and means for issuing instructions, to the patient, or treatment of the abnormal event.
According to yet another aspect of the present invention there is provided portable apparatus for continuous real-time monitoring of EKG signals from an ambulatory patient, comprising: means for detecting, amplifying and digitizing the signals, means for analy~ing the digitized signals to determine the existence of abnormal heart conditions; means for correlating information resulting from analysis of the signals, with apparatus condition, and patient treatment, instructions, and means for signalling, to the ambulatory patient, the instruments.
According to yet a further aspect of the present invention there is provided portable apparatus for continuous real-time monitoring of EI~G signals from an ambulatory patient, comprising: electrode means ~or detecting the EKG signals; means for amplifying and digitizing the EKG signals detected by the electrode means, means for analyzing the digitized slgnals and identiying abnormal events, and means for instantaneously instructing the patient to proceed in manner corresponaing to the abnormal event identified.
According to a still further aspect of the present invention there i5 provided a method for determining cardiac conditions of an ambulatory patient using apparatus carried in the patient including electrode sensing means located in the vicinity of the patent's heart and capable of picking up waveforms corresponding to heartbeats, signal processing means for identifying at least an EKG
signal pattern characteristically including an isoelectric baseline portion, a spike portion and a : ' ' ' ~ ' ~L~8~
- 7b -generally linear portion following the spike portion at approximately the same level as the isoelectric portion, a computer means, and a display alarm means actuated by the computer means, the method comprising the steps of: sampling a number of the waveforms picked up by the electrode means, detecting, in the waveforms, distortions from the EKG signal pattern indicative of abnormal cardiac conditions, distinguishing between a first distortion pattern characterized by a variation in the peak-to peak distance between each spike of the waveforms and indicative of a ventricular premature beat, and a second distortion pattern characteri~ed by a deviation of the linaar portion from the level of the isoelectric portion in at least one of the waveforms and indicative of a myocardial ischemia condition, and alerting the ambulatory patient o at least one o~ the distortion patterns.
According to a still further aspect of the present invention there is provided a mèthod ~or detecting the significance of slope conditions for a ~ :
series of complex waveforms in which a computer means and a plurality of shift registers are used for analyzing the waveforms, comprising the steps of:
calculating a current slope value as the difference between the amplitudes of two successive values in the waveorm; assigning to a first group o shift registers from the pluxality of shift registers a value corresponding to the sign value of the current slope value; comparing the quantitative value of the current slope value with a predetermined threshold value; assigning to a second group of shift registers from the plurality of shift registers a value corresponding to the quantitative comparison;
assigning a bit from each of the first group of shift registers for the sign value of each current slope ,, - ~, ': ' .
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12~B3L~81 - 7c -value; assigning a bit from each of the second group of shift registers for the output of the step of comparing; and updati~g one of the peripheral bits of each of the registers as a Flag Bit after each sampling period for indicating a trend, or the absence of a trend, in the registers.

Brief Description of the Drawings Fig. 1 is a graphic representation of a typical, normal EKG waveform showing the conventional nomenclature for the various portions thereof;
Fig. 2 is a schematic illustration of apparatus embodying the invention;
Fig. 3 is a master flow chart of the system logic;
Fig. 4 is a flow chart of the logic of the Beat Detection Block shown in Fig. 3;
Fig. 5 is a flow chart of the logic oE the QRS
Verification Block shown in Fig. 3;
Fig. 6 is a flow chart of the logic of the VPB
Verification Block shown in Fig. 5;
Fig. 7 is a logic flow chart of the VPB
Verification Block shown in Fig. 3;
Figs. 8-10 illustrate the logic flow chart of the Housekeeping Block shown in Fig. 3;
Fig. 11 is a chart illustrating four slope shift registers;
Figs. 12 and 13 are flow charts of a slope for EKG samples calculated according to an equation; and Fig. 14 is a flow chart showing the procedure for updating slope quality shift register Flag Bits.

Detailed Description of the Invention -Referring now to the drawings in more detail, there is shown in Figure 1 a typical EKG waveform of a heart of a normal healthy person which exhibits a P

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- 7~ -wave of positive polarity, a QR~ complex consisting of a negative Q wave~ a positive R wave and a negative S
wave, and finally a T wave separated from the QRS
complex by an ST segment. J is a point in the ST
segment and defines the end of the S portion thereof.
Normally, in a healthy person the ERG signals -will occur regularly at a frequency of about 60-80 beats per minute. Unde~ abnormal conditions the pulse rate may be very erratic. The P wave is noemally a small positive wave in certain leads that corresponds to the initial impulse that triggers the commencement of the heartbeat and the resulting reflexive physiological expansions and contractions that are involved in the heart beat. Immediately following the P wave there is a quiescent portion of substantially uniform amplitude. Normally, this portion will have a time duration on the order of greater than 0.04 second and will have a con-~.

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stant or fixed amplitude that may be used as an isoelectric or base line signal AS a result, the amplitude of this portion may be employed as a reference against which the remaining portions of the EKG signal may be measured. Alternatively~ the segment just prior to the P wave, the TP segment, may be utilized ror deEinition of the isoelectric amplitude or base line At the conclusion of the isoelec-tric signal, normally after the P wave, the QRS complex occurs. The complex commences in certain ECG leads with a so-called Q wave which is a small negative pulse The Q wave is succeeded in certain ECG leads by the R wave, which is the most conspicuous portion of the EKG
signal. It comprises a positive pulse having an amplitude greater than any of the other waves present in the EKG signal.
1~ Normally, the R wave wilL have the appearance of a ~spike~ with a sharp rise, a sharp fall, and a relatively short duration More particularly, it is believed that the maximum time duration will normally be on the order oE 0.03 to 0.04 second. However, certain types of abnormalities, such as premature ven-tricular 2~ beats resulting from an ectopic focus ~or foci) oE depolari~ation in the ventricle, may result in an EKG signal characterized by a distortion of the R wave and particularly an increase in width thereof. In other forms of premature ventricular beats, the R
wave may even become inver-ted (i.e. of negative polarity).

Following the R wave the QRS complex terminates in an S
wave. The S wave may be similar to the Q wave in that it is usually a small negative pulse in certain ECG leads Following the QRS complex and the S wave, -there will normally be a T wave which is separated from -the S wave by the so-called ST segment. The ST segment normally originates a-t the ~ point which represents : - '' - . :
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- ~ -rhe te~mirlation of the S wave. l~he amplitude of this ST
~egment n(,l-nlally is approximately equal to the isoelec-tric portion between the termination of the P wave and the commencement of the 0 wave, i.e., the ST portion is usually at ba~e line level.
A waveform which is representative of myocar-dial ischemia may cause the amplitude or level of the ST
segment to appear substantially more negative or more ?03itive thar, the isoelectric portion. An ~ST seqment 1~ ~ep~es~ior i~ indicative of an inadequate supply of blood or oxygen to the heart, while an ST segment eleva-tion indicates that the entire heart wall thickness is without adequate blood or oxygen.
Referring now to Figure 2 there is shown a 15 generalized schematic view of the apparatu~ of the pre-sent invention in which leads 102, 103 and 104 represent ~ectrodes and wires attached to the patient P at pre~
determirled locations preferably in a conventional manner (the preférred embodiment envi~ions non-intrusive elec-20 trode-to-patient attachment). ~he electrodes are pre-ferably of the type disclosed in U.S. Patent Nos.
3,420,223, 3,490,440 and 3,665,064. Lead 104 functions to ground the apparatus, while leads 102 and 103 feed EKG signals, detected by the electrodes, to a pre-ampli-Pier and filtering component 106 to perform two func-tions: Elr~t, to amplify the ~ignalq detected by the electrodes, and second to eliminate unde~irable noi~e.
The amplifier, while of coRventional design must provide a uniform amount of ~ain over an adeq~ate bandwidth to 30 effectively amplify all of the components in the ERG
signal without producing any distortions 30 that the output ~ignal from the amplifier is a true and amplified reproduction of the EKG signal picked up by the elec-~rode~ a 3~j The output of the amplifier is fed to a con-verter 108 of the analog-to-digitel (A/D) type. The converter is connected, via a sy~tem b~1s 150, to a mi-croproce~sor 120 driven by a clock 122 through connec-tion 124, one or more random access memory (RAM) compo-5nents 130, one or more read only memory (ROM) components ?~, an a1pha-numeric display device 145, a keyboard 165 ~n~ ar, ~larm means 175. A lithium battery can be em-ployed as a back-~p for the memory components. A key-board interface co~ponent 160 couples keyboard 165 to he sy~tem bus 150 while an alarm interface 170 couples alarm mean~ 175 to the system bus. The speeds, capaci-ties, etc. of the hardware component~ needed to imple-ment the invention can be determined by persons skilled in these arts, based on the teaching~ herein.
li~`iqure 3, which is a ma~ter logic flow diagram uf the present invention, shows the ampliied, filtered and di~itized ~KG signal provided from A/D converter 108 in Fig. 2 pas~ing to heat detection bloc~ 200 (to be described in greater detail below). The logic of the 20beat detection block examines the EKG signal for a ~s-pected QRS complex and for suspected ventricular prema-ture beat ~VPB) occurrence~. If a pattern of signals ~hich sugge~ts the existence of a VP~ is detected, the logic of beat detection block 200 sends appropriate 25information via lead 111 to the VPB verification logic block 300 (al~o to be described in more detail below).
If a pattern of signals which suggests the existence of a Q~S complex is discerned, the loqic of beat detection block 200 sends appropriate information via lead 112 to 30the QRS verification block 400 (al~o to be de~cribed in ~n<)re ~tail below). I the logic o~ block 400 verifies QR~ ~ccurrence, the logic pas~es to block 500 by llne 117 to determine the posqible existence of a VPB. On the other hand, if prematurity is detected, the logic 35paqses to block 300 via line 115 to determine whether : `

the suspected signal has Eurther VPB charac-teristics. The outputs of blocks 300 and 500 are Eed via line 114 or line 118, respectively to the housekeeping block 600 (described in more detail below) for further processing. Lead lines 119 (from block 200), 113 tErom block 300) and 116 (from block 400) facilitate the transmission oE inEormation which is indicative of a discerned error to a system management or ~housekeeping" block 600 where, upon its receipt, an alarm may be set of depending on the nature of the event which generates the so-called "error~
signal Examples of such ~errors~ which could trigger activation of an alarm are disconnection of an electrode, insufficient battery power, battery Eailure, ~loss oE siqnal~ r excessive noise, and others.

Beat Detection Block_200 Figure 4 shows the logic in beat detection block 20~.
Beat detection block 200 determines the existence of, and discriminates between, two basic signal patterns received from A/D converter 108 These signal patterns are indicative of events which signal the onset of the cardiac complications with which this invention is concerned; one pa-ttern represents the onset and inflection points of QRS complexes, followed by an ST
segment, while the other pattern is indicative of ven-tricular premature beats (VPB'S).

Taking a closer look at the beat detection block 200 in Fig. 4, the sequence of ampliEied, filtered and digitized signal samples are examined at block 210 for a period of time up to, but not exceeding, 2 minutes In this time frame, the logic of block 210 calculates the slope of the signal values and then compares the slope with a predetermined threshold value. If the slope exceeds the threshold value within the 2 minute period, the logic of block 210 determines that a waveform indicative of a QRS
complex has begun, and the logic proceeds, via line 214, to block 220 If within the two minute nterval, the slope does not ~, o~
exceed the threshold valve, the logic of block 210 generates an - error signal which passes via l.ines 212 and then 119 to the system management or housekeeping block 600 to sound an alarm After block 210 determines the onset of a slope indicative oE an ~RS complex, calculations are made at block 2Z0 for the purpose of determining, and therefore confirming, whether a following beat actually occurs (the suspected QRS waveform is actually a VPs). The signal sequence is examined at block 220 Q ~uring the time in which the slope amplitude and direction (sign) remain within specified predetermined tolerances for a maximum of 2 seconds. If the sequence comple-tes in less than 125 milliseconds the logic oE block 220 indicates the existence of a suspected ~RS waveform, and the process moves to block 400 via line 112. If the change occurs in a time equal to or greater than 125 milliseconds, (and not greater than 2 seconds) the logic : of block 220 determines that the sequence of values exhibit characteristics of a VP~, and the logic moves to block 300 for confirmation oE the VPB via line 115. If no change occurs within 2 seconds, khe logic of block 220 issues an ~error~ signal which is sent to the system management or housekeeping block 600 via lines 216 and 119 While waiting for -the change in slope direction, the following calculations are made at block 220.
, (1) The area beneath the suspected QRS waveform This ------------ ___________ ____ __ value is stored for comparison with the area calculated Eor the next suspected QRS ~aveform (in the system management or housekeeping block 600).

(2) The__umber_of turns_(l.e lnflection points) in the waveform ThiS number is compared to predetermined values recognized as being indicative of a normal QRS waveEorm. Normally, if the number of turns :'-~ .
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counted falls be ~ ~ or ~xceeds 5, the waveform is not a QRS waveform and this informa~ion is passed to the system management or housekeeping block 600 via lines 116 and 119, More than 5 -turns may lndicate excessive noise in the system, : (3) The time from one suspected QRS waveform peak to the next suspected QRS waveform peak along the trace. This number is stored for use in identifying ~confirming) premature beats, (e,g.
Vps's)~ That is, in a normal sequence of beats, this peak-to-peak distance will be substantially constantO ~ariation from that constant value usually indicates a VPB.-- QRS verification Block 400 . . _ _ _ _ . ReEerring now to ~ig. 5, the logic flow diaqram of the QRS verification block 400 is shown in which the information from block 220 of Fig. 4 is checked to confirm the existence of a QRS
waveform, ~lock 410 counts the turns in the waveform and determines whether the number oE turns falls within a range indicative of a normal QRS waveform, If the number of turns counted is less than 3 or greater than 5, the suspected waveform is not a QRS waveform, and ~his information is passed to housekeeping block 600 via lines 412 and then 119. If the number of turns counted falls within.the range of 3, 4 or 5, the logic moves via ~yes'~ line 414 to block 420 where the amplitude of the suspected waveform peak is compared to an empirical value to make sure tha't the waveform detected by block 200 is a proper QRS
curve and not a P wave or a noise pulse or anything else not a QRS, I~ the peak amplitude does not fall within acceptable limits, an error slgnal is transmitted via lines 422 and 119 to housekeeping block 600. If it is determined that the peak amplitude falls within acceptable limits, the logic moves to block 430 via line 42,4 where a determination is made as to : . .
, ` ' `' ' whether the waveform generated by the heartbeat is premature.
This is accomplished by computing and maintaining a running, updated average of time duration between a series o~ successive QRS waveform peaks and then comparing the running average time to the time between the current QRS peak and the last QRS peak. In this manner, hear-t EKG information resulting from both a patient who is e~ercising and from a patient who is at rest is accommodated. If the lo~ic of block 430 determines that the beat is not premature, a QRS waveform is confirmed and that lo information is sent to block 500 via line 432. If the logic of block 430 determines that the time between the current and last Q~S peak is shorter than the running upda-ted average time, the beat is considered premature ta possible) vPs~ and this information passes to block 440 via line 434.

Blocks 440 and 450 perform a secondary check on a suspected QRS waveform which also appears to occur prematurely, i.e. a VPB. For example, without the test provided by blocks 440 and 450 the invention device might otherwise incorrectly identify the end oE a waveform in a case where -there is an erratic signal portion before the actual termination of -the waveform. Block 440 Eirst determines whether the previous beat exhibited true QRS
waveform characteristics The double ended line 436 interconnecting block 440 to line 432 carries the "Q~S confirmed~
signal. If the previous beat was not a true QRS waveform, there is no proper QRS by which the comparison may be made and the logic returns to line 432. If true QRS waveform characteristics have been detected, and a comparison can be made, the V~s verification logic flows on -to block 450 where another check is accomplished by comparing the area under the present waveform to the area under the previous waveform. If the areas are similar, the logic confirms the existence of a proper, albeit premature, QRS waveform and returns to line 432. If the compared areas are not similar, the logic ~lows to block 300 tdescribed in detail below) where an analysis is performed to determine whether the ' ~28~L0~31 waveform is characteristic of a ventricular prem~ture Beat ~VPB).

VPB v_r1_1c_tlo__slock_300 Referring now to Figure 6, there is shown a detailea logic flow diagram for block 300 for the verification of suspected ventricular premature beat wavefo~ms detected at the beat detection block 200 shown in Fig. 4. The logic of block 310 determines whether the number of -turns of a curve associated with a heart beat counted at block ~20 (Fig. 4) falls within a range lo indicative of a VPg waveform, If there are at least 3 -turns, but no more than 7 turns, then the logic flows to block 320. whereas - 5 turns defined the upper limit for a QRS waveform, the larger number of 7 turns is permi-tted for VPs verification. If the number counted falls outside this rangel block 310 generates an appropriate ~error~ signal which is sent to housekeeping or system management ~y block 600.

The logic of block 320 compares the peak arnplitude of the suspected VPB waveform with empirical values inaicative of upper and lower acceptable limits in a manner similar to that comparison performed in block 420 ~see Fig. 5). If the peak amplitude of the waveform falls outside the range, an error signal is generated and sent -to housekeeping block 60~. If the peak amplitude falls within -the range oE acceptable limits, the logic flows to block 330 where the previous beat is examined to determine if it too was a VPB. If the previous beat was not a VPB r block 350 determines whether the current beat is premature.
If so, the inforrnation is sent to the system management or housekeeping block 600 via line 114. If not, an error signal is sent to the system management or housekeeping block 6V0. If the logic of block 330 determines that the previous beat was a VPB, it is not possible to check prernaturity of the current beat for obvious reasons. Instead block 340 compares the area under the waveform associated with the last beat with the area under the wave~orm associated with the current beat. ThiS comparison is ~' :. .

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made with the expectation that the areas will be similar. If the areas are not similar, the logic sends an ~'error" signal to system management or housekeeping block 600 via line 113. If the areas are similar, the logic returns to line 114 and then to system management or housekeeping block 600.

VPB veriflc-t--n-Block-5oo Referring now to Fig. 7, there is shown a detailed logic flow chart of the VPB vexification Block 500 which checks lo to see whether t,he waveform conEirmed by block 400 was preceded by a vPs. In a case where a QRS waveform follows a ventricular premature beat, the interval between the QRS waveform and the premature beat will be greater than the running updated average time interval c~mputed at block 430 (in Fig. 5).

Block 510 determines iE the previous beat was a suspected VPB. If not, control is transfer~ed to system m~nagement or housekeeping hlock 600 via line 118. If the pre~ious beat was a suspectèd VPB, the compensa-tory interval is calculated or the purpose o~ checking ~or the presence of a ; o~mpensatory pause which would indicate that the suspected VPB
-~ was a true VPs. The current average pulse interval is added to the time at which the QRS complex preceding the suspected VPB is known to have occurred. This result represents a point in time at which a normal beat following a VPB would fall if a compensatory pause were present. IE the current beat's time diverges from the calculated time by more than + 12.5~ of the current average pulse interval, a compensatory pause is not ; indicated, ~he foregoing procedure is repeated three (3) additional times with the average pulse interval being added to the previously calculated compensatory interval each time. This procedure allows for the veriEication of interpolated VPB'S as well as the possibility of veri~ication of VpB~s which are followed by ~undetected~ QRS complexes. If no verification can be made by the end of the fourth ~4th) attempt, control is ~: `

.
:
.
.

tran~ferred to line 118. If verification is possible, control is transEerred to block 530 where the suspected VPB is labelled a confirmed VPB.

System Management or Housekeeping Block 600 _ _ _ __ __ __ _ ____ _ _ _ _ _ __ _ _ .___ _ _ , The logic of the system management o~ housekeeping block 600, ill~strated in Fig.s 8-10, performs several functions:
a) certain even-ts (described in more detail below in connection with Fig. 8) which require the suspension of normal beak processing are monitored;

; (b1 specified parameters are updated or measured ~:~ (described in more detail below in connection with Fig.
9 ) ;

(c) certain events which trigger conditions are identified and appropriate alarm instructions are issued ~described in more detail below in connection with Fig. 10).

As shown in Fig. 8, the logic of block 810 tests whether the power supply is at an acceptable level, i e of sufficient vol-tage to maintain operation of the inventive device.
~: The test is performed by conventional means not shown If the level of power is not acceptabLe, the logic of block 810 moves to block 820 where an alarm flag is set for "LOW BATTERY~. This inEormation is passed via line 899 to the alarm block 1070 in Fig 10, while the logic flows to block 830. If the level of power is determined to be acceptable, the logic moves directly to block 830 where it is determined whether -there has been a loss of the signal. This condition results from the Eailure of the device to detect a heartbeat for a period of 2 minutes, and : generally is caused by system or patient failure. If~ within, the two minute interval, no signal has been detected, the logic moves to block 840 where an alarm flag is set for a "LOSS OF

;:

, .... .
, ~, . . .. ..
. ' ~ .

, SIGNAL" condition. This information is then passed via line 899 to the alarm block 1070 tshown in Fig. 10). If a beat has been detected within 2 minutes, the analysis proceeds to block 850 where the logic determines whether "5IGNAL CLIPPING" has occurred. If so, the analysis moves to block 860 where an alarm flag is set for a `'CLIPPING" condition, and the information is sent via line 899 to alarm block 1070 (shown in Fig. 10). If the logic fails to discern the existence oE "SIGNAL CLIPPING", the analysis moves to block 870 where a determination is made whether "NOISE", i.e. a conditlon exhibiting excessive changes in slope, has been detected. If so, the analysis moves to block 880 where an alarm flag is set for a "~OISE" condition and a signal corresponding to -this condition is sent to alarm block 1070 (shown in Fig. 10). If no noise has been detected, the analysis proceeds to block 910 (in Fig. 9) where the system determines whether a QRS waveform accompanied the previous beat. If not, the analysis proceeds directly to block 1010 in Fig. 10. If so, - however, the analysis moves successively to blocks 920, 930 and 940. At block 920 the pulse average is updated, at block 930 the ST segl~ent level is measured, and at ~lock 940 the ST segment average is updated. The analysis then moves to block 1010 in Fig. 10, where the logic looks at the results of the analysis performed for the current beat and the last two beats to determine whe-ther all 3 beats exhibits VPB characteristics If ` 2s they do, the analysis moves to block 1020 where an alarm flag is set for a condition indicative of ven-tricular Tachycardia and this information is sent to Alarm Block 1070 via line 1099. If the 3 beats examined at block 1010 do not exhibit VPB
characteristics, the analysis proceeds to block 1030 where the results of the analysis performed for only the current beat and the last beat are examined I~ the logic determines that for both beats VPB characteristics were exhibited, the analysis moves to block 1040 where an alarm flag is set for a condition known as "COUPLET" and an appropriate signal is passed to block 1070 via line 1099; otherwise the analysis moves to block 1050 where the ,~

.

~2~
logic determines i~ the ST segment average is within acceptable limits. These limits are empirical values determined for any beat as a function of the isoelectric portion of the PQ~ST
waveform associated with tha-t beat. If the measured ST segment value falls within the limits, the logic proceeds to block 1070.
If the measured ST segment value falls outside the limits, the logic moves to block 1060 where an alarm flag is set to reflect either a condition for "ST SEGMENT DEPRESSION" or "ST SEGMENT
ELEVATION", and a signal corresponding to the condition detected is sent to alarm block 107U via line 109g.

Block 1070, which receives information passed through block 1050 from line 1099 and from line 899, and then reads the alarm flags set and displays alarms corresponding to the various detected conditions of the device and the patient. In addition, block 1070 updates the stored counts for VPB couplets, ventricular tachycardia episodes and their total duration, as well as the total ST segment dura-tion The logic then returns to the beat detection block 200.

The IRethod of determining the significance of the slope signal at each sampling period carried out by the logic of block ~ 210 is explained below with reEerence to Figures 11-14. ThiS
-~ method of handling data and determining a slope is deemed to have general utility beyond the present invention ': ' ' This method is accomplishecl using four shift registers ;~ each having six bits length (see Figure 11). of course, this portion of the invention can also be carried out by using shift ~ 30 registers of longer or shorter length, or even with a different - number of shift registers The patterns in these shift registers reflect slope conditions. Each bit represents one of Eour conditions at each sampling period and thus each shift register contains a running record oE the most current six sampling periods The four conditions are:

. .

~ ' .

., - , ' 8~

positive slope (upwardly directed negative slope (downwardly directed active slope (greater -than threshold ;

: .
':

~"~: :
:

.~ .
. .

~ 20 ' ~ : .
~ ' 1 , ~ , :
, . . .
.

8~

quiescent slope (less than threshol~) Each shift register bit will have either (1) a value of 1 (bit set) which indicates that the approxi-ma~ ond1tioll is fulfilled, or (2) a value of 0 (bit reset) whlch indicates that the respective condition has not been fulfilled. Each shift register also includes a -~ "Flag Bit". This bit is updated af~er each sampling - period and reflects either a majority of bits set, (Flag Bit ~et) or a majority of bits not set (Flag Rit reset) in the corresponding shift register. A Flag Bit which is set thus represents a trend in slope ~irection or maanitllde~
Referring now to Figures 12-13, at Block A the ~ slope for the current EKG sample is calculated in ac~
- 1r~ cordance with the equation:

- CURRENT SLOPE = C~RRENT E~G AMPLITUDE MINUS

At Block B, the slope is examined to determine whether the value is positive or ne~ative.
2~ If the slope has a negative value, the logic first proceeds to Block C where the positive slope shift register is shifted to the left and the~right~ost bit is set to zero, and then proceeds to Block D where the negati~e slope shift register is shifted to the left and ; 25 tlle rightmost bit is set to 1.
If, however, the Rlope has a po~itive value, ~tle logic ~irst: proceeds to B]ock E where the positive ~lope shift register i3 shifted to the left and the rightmo~t bit is set to 1, and then proceeds to Block F
where the negative slope shift register i~ shifted to the left and the rightmost bit is set to zero.
After shifting the appropriate slope registers , , d setting the appropriate bits corresponding to a detected ~ositive or negative slope value, the logic proceeds to block G
where the quantitative aspect of the calculated slope value is compared to the value which represents the predetermined quiescent threshold. (The quiescent threshold is generally taken to be 0.02 millivolts change in each 256th of a second period).
Thls value differentiates waveforms which represent QRS complexes from other waveforms with which this method is not concerned.
:
l~ If the value of the slope is less than the quiescent threshold, the logic proceeds (c~ntinue to Fig. 13) first to Block H where the active slope shift register is shifted to the left and the right-rnost bit is set to zero, and then proceeds to Block I where the quiescent slope shift register is shifted to the left and the right-most bit i5 set to l.

on the one hand, if the value o the slope is greater than, or equal to, the quiescent threshold, the logic proceeds first to Block J where t.he active shift register is shifted to the left and the right-most bit is set to 1, and then proceeds to Block ~ where the quiescent slope shift register is shifted one bit to the left and the right-most bit position is set to zero After completing the operations at either Block I or Block K the Flag Bit for each register is updated to indicate a trend (Flag Bit set to l) or absence of -trend (Flag Bit set to O).

Next, referring to Figure 14, the procedure for updating slope quality shift register Flag BitS is descri~ed (this procedure is performed four times, once for each shift register)~
.
overall, this invention uses the fact that six or some other number of positions in a shift register also represent a number, and the fact that machines are .,.
.. .

, very quick at "lookinq up~ numbers in a table. Thus, with a possibility of 1 through 64 possible answer~ for six bit positions, corre~ponding to the numbers 0-63, the invention provides a table stored in the machine, certain numbers of which correspond to certain realities o~ the slope and of the threshold. Thus, the machine A.arl Ic~ok at the contents of each ~hit register every 25~th part of a second, look at the number, look it up in the table, and thereby quickly determine the quality of the slope as to positive or negative, the threshold - exceeded or not exceeded, and set the Flag Bits accord-ingly.
More specifically, to implement this concept - the bits are used as an index, i.e., a six bit binary ~ord will corre~pond to one of 64 addresses in a 64 byte r~b~e (Block R) For 5 or 7 bit shift regi~ters, the addresses and other parameters would be adjusted accord-ingly.
Thi~ table is stored in me~ory and contains 64 en~ries, each of which corre~ponds re~pectively to each of the 64 six bit binary words which may be used to address the table. Each entry represents whether a majority or minority of bits, in the corresponding six bit wo~d obtained from one of the shi~t registers, have been set, i.e. have a value of 1. The value of the High Order Bit of each entry is either set (i.e. assigned the value of 1) if a majority of bits in the six bit word have been set, or reset (assigned the value of O) if a majority of bits in the six bit word have not been set. Thus the High Order ~it will have a value = O for the irst six entries, but will have a value = 1 for the ei~hth entry~
Using the 9ix bit binary addre~s obtained from the respective ~hift register being updated, a value i~
retrieved from the table (Block S in Figure 14). This .
~ ' ,.
.

)8~ -value is used a3 a replacem0nt for the ~lag sit of the shift regi~ter being updated ~slock T).
After the shift registers have been updated as ~e~c~ibed above, the values of the Flaq Bits are exa-mined to detect the following condition~:

~EAT ONSET - indicated when the active ~lope shift regi~ter Flag Bit changes from zero to one, and the ~egat}ve slope--~ 10 or position slope shift re-gister fIag signals 1;

. .
B~AT TURN indicated when the active slope shift reqister Flag Bit remains set (i.e.
lS equal to 1) but Flag Bits of positive and negative slope shift registers change. This indicates a change in slope direc-20 ! tion.

~ EAT END - indicated when the quies-i cent slope shift register Flaq Bit changes from zero to one.

NOISE - indicated when the active slope shift register Flag ~it is set, but neither ~- the positive ~lope shift register Flag Bit, nor the negative ~lope shift re-~ gister Flag Bit, i~ set.

':~
.

~ , a~

Upon the completion of operation.s in Block 210 of the Beat Detection Block in which the onset of a : ~alope indicative of a QRS complex i 9 identified, the :~ lo~ic proceeds to Block 220, as describecl above.
It is to be understood that the present inven-tion is not limited to the embodiments disclosed which are illustratj.vely offered and that modifications rnay be ~*de without departinq from the invention.

~"~ . ' ,.

, ~ :
,

Claims (40)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS
FOLLOWS:

1. A method of evaluating a curve having a rapidly changing value by determining the positive or negative quality of the slope of said curve and by determining when the value of said curve is above or below a predetermined threshold value, comprising the steps of:
determining a frequency of sampling;
determining the slope of the curve between a first sampling and a successive later sampling by subtracting the value of the curve at each first sampling from the value of the curve at said later sampling;
providing four shift registers each having space for a plurality of bits and for a Flag Bit;
assigning a shift register to each of the curve values of positive slope, negative slope, above threshold and below threshold;
feeding an appropriate bit value to each shift register at each sampling;
determining a numerical value represented by said plurality of bits arrayed in each shift register providing a table of values correlating the status of said Flag bit to each one of the numerical values possibly represented by said array of bits;
finding said determined numerical value in said table changing, as needed, the status of said Flag Bit in accordance with said determined numerical value found in said table; and performing at each sampling said sequence of steps so that the status of said Flag bit may be changed as needed.

2. The method for continuously monitoring every beat of the heart of a human patient subject to detect abnormal functioning of the heart and to alert the patient immediately upon the occurrence of any one of a plurality of detected abnormal heart functions, comprising the steps of:
providing electrode means, using the output signal of said electrode means to produce EKG signals, determining, by analyzing said signals, whether or not each heart beat includes an abnormal QRS
portion, determining, by analyzing said signals, whether or not each heart beat is a VPB, and continuously repeating each of said determining steps without interruption while actuating alarm means no later than upon conclusion of said each beat if either of said determining steps indicates an abnormal QRS portion or a VPB, which in turn indicates some abnormal heart function, and signalling to said patient instructions for treatment of each indicated abnormal heart function as it occurs.

3. A portable computerized EKG monitor, comprising:
real-time recognition means for recognizing abnormal cardiac events in an ambulatory patient, real-time diagnosis means for diagnosing each said recognized abnormal cardiac event, and signalling means for communicating to the ambulatory patient a treatment for said recognized and diagnosed abnormal cardiac event.

4. A portable cardiac monitor for an ambulatory patient comprising:
computer means for performing continuous real-time analysis of EKG information derived from said patient, including first means for recognizing abnormal cardiac events, and second means for diagnosing each of said abnormal cardiac events, and means for signalling, to the patient, a treatment corresponding to each said recognized and diagnosed abnormal cardiac event at the onset of each of said abnormal cardiac events, whereby the patient may immediately begin self-treatment of each said recognized and diagnosed abnormal cardiac event without the need for intervention of a trained cardiac specialist.

5. Portable apparatus for continuously monitoring EKG signals generated by the heart of an ambulatory patient, comprising:
self-contained, computerized analyzing means, carried on said patient, for performing real-time analysis of said EKG signals, said computerized analyzing means including means for diagnosing abnormal cardiac events and means for issuing instructions, to said patient, for treatment of said abnormal events.

6. Portable apparatus for continuous real-time monitoring of EKG signals from an ambulatory patient, comprising:
means for detecting, amplifying and digitizing said signals, means for analyzing said digitized signals to determine the existence of abnormal heart conditions;
means for correlating information resulting from analysis of said signals, with apparatus condition, and patient treatment, instructions, and means for signalling, to said ambulatory patient, said instruments.

7. The portable apparatus of claim 6, wherein said analyzing means comprises first means for recognizing sequences of signals indicative of waveforms associated with QRS complexes and ventricular premature beats (VPB'S) and second means for recognizing sequences of signals associated with apparatus malfunction.

8. The portable apparatus of claim 7, wherein said first recognizing means comprises means for identifying a suspected QRS, or VPB, waveform associated with each heart beat and means for confirming said suspected QRS, or VPB, waveform.

9. The portable apparatus of claim 8, wherein said identifying means comprises first means for determining updatable slope values for successive digitized signals, second means for determining whether each said slope value exceeds a predetermined threshold value, third means for determining whether the sign of the slope value changes within a first predetermined time, and means for comparing the time interval between the onset of said suspected waveform and the occurrence of said slope sign change, said means for comparing being operative only if said first predetermined time is not exceeded.

10. The portable apparatus of claim 9, wherein said identifying means further comprises fourth means for determining whether said time interval is less than a second predetermined time, and means in said correlating means comprises first means for assigning a value to that sequence of signals indicative of a suspected QRS waveform if said first predetermined time is not exceeded and said time interval is less than said second predetermined time.

11. The portable apparatus of claim 10, wherein said first predetermined time is 2 seconds and said second predetermined time is 125 milliseconds.

12. Portable apparatus for continuous real-time monitoring of EKG signals from an ambulatory patient, comprising:
electrode means for detecting said EKG signals;
means for amplifying and digitizing the EKG
signals detected by said electrode means, means for analyzing said digitized signals and identifying abnormal events, and means for instantaneously instructing said patient to proceed in a manner corresponding to the abnormal event identified.

13. The portable apparatus of claim 12, wherein said abnormal events include both cardiac events and events associated with operation of the monitor, and said analyzing means includes means for discriminating between said events,

14. The portable apparatus of claim 13, wherein said analyzing means further includes means for detecting the onset of QRS complex waveforms.

15. The portable apparatus of claim 14, wherein said detecting means comprises first means for calculating the slope of said digitized signals, first means for determining whether the calculated slope has exceeded a predetermined threshold valve, second means for determining whether the sign of the slope has changed within a first predetermined time, and third means for determining the interval of time occurring between the slope exceeding said predetermined threshold value and the sign of said slope changing, said third determining means being operative only if said first predetermined time is not exceeded.

16. The portable apparatus of claim 15, wherein said identifying means comprises means for comparing said time interval to a second predetermined time, and means for assigning a first value to a condition in which said time interval is less than said second predetermined time.

17. The portable apparatus of claim 16, wherein said identifying means comprises means for comparing said time interval to a second predetermined time, and means for assigning a second value to a condition in which said time interval is greater than, or equal to said second predetermined time.

18. The portable apparatus of claim 5, wherein said analyzing means comprises first means for recognizing sequences of signals indicative of waveforms associated with QRS complexes and ventricular premature beats (VPB'S) and second means for recognizing sequences of signals associated with apparatus malfunction.

19. The portable apparatus of claim 10, wherein said correlating means further comprises second means for assigning a value to that sequence of signals indicative of a suspected VPB wave form if the first predetermined time is not exceeded and said time interval is equal to or greater than said second predetermined time.

20. The apparatus of claim 19, wherein said first predetermined time is 2 seconds and said second predetermined time is 125 milliseconds.

21. A method for determining cardiac conditions of an ambulatory patient using apparatus carried on the patient including electrode sensing means located in the vicinity of the patent's heart and capable of picking up waveforms corresponding to heartbeats, signal processing means for identifying at least an EKG signal pattern characteristically including an isoelectric baseline portion, a spike portion and a generally linear portion following said spike portion at approximately the same level as said isoelectric portion, a computer means, and a display alarm means actuated by said computer means, the method comprising the steps of:
sampling a number of said waveforms picked up by said electrode means, detecting, in said waveforms, distortions from said EKG signal pattern indicative of abnormal cardiac conditions, distinguishing between a first distortion pattern characterized by a variation in the peak-to-peak distance between each spike of said waveforms and indicative of a ventricular premature beat, and a second distortion pattern characterized by a deviation of said linear portion from the level of said isoelectric portion in at least one of said waveforms and indicative of a myocardial ischemia condition, and alerting said ambulatory patient of at least one of said distortion patterns.

22. A method according to claim 21, wherein said detecting step includes analyzing at least one of the slope, amplitude, the area, inflection points and sequences of said waveforms for determining whether said waveforms approximate said EKG pattern.

23. The method according to claim 22, wherein said detecting step further includes the step of comparing the slope of said waveforms with a predetermined threshold value for a given period of time.

24. The method according to claim 22, wherein said inflection points are within the range of from 3 to 5 for approximating said EKG signal pattern.

25. The method according to claim 22, wherein said sequence of said waveforms is detected for a given time period of between 125 milliseconds and 2 seconds.

26. The method according to claim 22, wherein said inflection points are within the rage of from 3 to 7 for a ventricular premature beat waveform.

27. The method according to claim 21, wherein an average time for successive peaks in said waveforms is computed, and further comprising the step of comparing said average time with a time between a current waveform peak and an immediately preceding waveform peak.

28. The method according to claim 21, wherein a compensatory time interval is computed for the succession of a normal waveform beat and a ventricular premature waveform beat for establishing a reference compensatory pause, and further comprising the step of comparing the time interval between a current succession of waveforms with said reference compensatory pause for determining the presence of an actual compensatory pause, and hence the presence of said ventricular premature waveform beat.

29. The method according to claim 21, including the further step of storing and updating the duration of said linear portions in said waveforms sampled in said sampling step.

30. A method for detecting the significance of slope conditions for a series of complex waveforms in which a computer means and a plurality of shift registers are used for analyzing said waveforms, comprising the steps of:
calculating a current slope value as the difference between the amplitudes of two successive values in the waveform;
assigning to a first group of shift registers from said plurality of shift registers a value corresponding to the sign value of said current slope value;
comparing the quantitative value of said current slope value with a predetermined threshold value;
assigning to a second group of shift registers from said plurality of shift registers a value corresponding to said quantitative comparison;
assigning a bit from each of said first group of shift registers for said sign value of each said current slope value;
assigning a bit from each of said second group of shift registers for the output of said step of comparing; and updating one of the peripheral bits of each of said registers as a Flag Bit after each sampling period for indicating a trend, or the absence of a trend, in said registers.

31. The method of claim 30, wherein said predetermined slope values comprise a negative slope value, a positive slope value, an active slope value and a quiescent slope value.

32. The method of claim 30, wherein for said current slope value corresponding to a negative value, bits of one register of said first group of registers are shifted to the left and the rightmost bit therein is set to zero, and bits of another register of said first group of registers are shifted to the left and the rightmost bit therein is set to one.

33. The method of claim 30, wherein for said current slope value corresponding to a positive value, bits of one register of said first group of registers is shifted to the left and the rightmost bit therein is set to one, and bits of another register of said first groups of registers is shifted to the left and the rightmost bit therein is set to zero.

34. The method of claim 30, wherein for said quantitative value corresponding to a value less than said threshold value, bits of one register of said second group of registers is shifted to the left and the rightmost bit therein is set to zero, and bits of another register of said second group of registers is shifted to the left and the rightmost bit therein is set to one.

35. The method of claim 30, wherein for said quantitative value corresponding to a value equal to or greater than said threshold value, bits of one register of said second group of registers is shifted to the left and the rightmost bit therein is set to one, and bits of another register of said second group of registers is shifted to the left and the rightmost bit therein is set to zero.

36. The method of claim 30, wherein said predetermined threshold value corresponds to 0.02 millivolt change in each 256th part of a second during the sampling period.

37. The method of claim 32, wherein the status of said Flag Bit is determined as a function of the number of ones in each of said shift register bits arrayed in each shift register.

38. The method of claim 33, wherein the status of said Flag bit is determined as a function of the number of ones in each of said shift register bits arrayed in each shift register.

39. The method of claim 34, wherein the status of said Flag bit is determined as a function of the number of ones in each of said shift register bits arrayed in each shift register.

40. The method of claim 35, wherein the status of said Flag Bit is determined as a function of the number of ones in each of said shift register bits arrayed in each shift register.