CA1086383A - Demand anti-arrhythmia pacemaker - Google Patents
Demand anti-arrhythmia pacemakerInfo
- Publication number
- CA1086383A CA1086383A CA280,748A CA280748A CA1086383A CA 1086383 A CA1086383 A CA 1086383A CA 280748 A CA280748 A CA 280748A CA 1086383 A CA1086383 A CA 1086383A
- Authority
- CA
- Canada
- Prior art keywords
- stimulation
- heart
- depolarization
- sensing
- output
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
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Classifications
-
- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61N—ELECTROTHERAPY; MAGNETOTHERAPY; RADIATION THERAPY; ULTRASOUND THERAPY
- A61N1/00—Electrotherapy; Circuits therefor
- A61N1/18—Applying electric currents by contact electrodes
- A61N1/32—Applying electric currents by contact electrodes alternating or intermittent currents
- A61N1/36—Applying electric currents by contact electrodes alternating or intermittent currents for stimulation
- A61N1/362—Heart stimulators
- A61N1/3621—Heart stimulators for treating or preventing abnormally high heart rate
Abstract
DEMAND ANTI-ARRHYTHMIA PACEMAKER
ABSTRACT OF THE DISCLOSURE
A demand anti-arrhythmia pacemaker having a plurality of electrodes adapted for connection to a heart for sensing depolarizations. A first responsive circuit provides stimulation signals to at least one area of the heart if a depolarization corresponding to a natural heartbeat fails to occur within a first pre-determined time period. A second responsive circuit provides stimulation signals to the heart in a plural-ity of areas in response to sensed depolarizations which occur within a second predetermined time period.
ABSTRACT OF THE DISCLOSURE
A demand anti-arrhythmia pacemaker having a plurality of electrodes adapted for connection to a heart for sensing depolarizations. A first responsive circuit provides stimulation signals to at least one area of the heart if a depolarization corresponding to a natural heartbeat fails to occur within a first pre-determined time period. A second responsive circuit provides stimulation signals to the heart in a plural-ity of areas in response to sensed depolarizations which occur within a second predetermined time period.
Description
BACKGROUND OF THE INVENTION
, ' !
The prevention of cardiac arrhythmias such as fibrillation has long been of interest in the art.
Certain cardiac stimulation circuits have been developed to produce cardiac stimulation signals to prevent or stop fibrillation. One such device is disclosed in U.S. Patent No. 3,937,226, issued to Dr. Herman D. Funke.
In the Funke device, a plurality of eIectrodes are connected to a heart in spaced reIation to each other for sensing depolarizations that occur at a plurality of areas of the heart. Output circuitry responsive to any sensed depolarization applies stimulation signals simultaneously to a plurality of areas of the heart rapidly after sensing a depolarization. The circuitry disclosed in the Funke patent includes a free running or astable multivibrator which generates a stimulation pulse to be applied to the plurality of areas of the heart if no depolarization signal is sensed within a predetermined time period. Thus, the Funke device acts to prevent premature ventricular contractions leading to ventricular fibrillation and has the capability to operate in a demand mode in the event ~
of bradycardia or "skipped" beats, for example. ~ -The circuitry of the Funke patent applies a stimulation signal to a plurality of areas on the heart each time the heart beats, even when the heart is beating at a normal rate. Consequently, a considerable amount of electrical power is used by the Funke device to stimulate the heart. Since the life of an implanted cardiac stimulation device is often dependent on the ~ ~',, '~
~086383 life of the power supply, it is considered highly desirable to reduce the drain on the power supply whenever possible.
SUMMARY OF THE INVENTION
The present invention comprises circuitry for sensing cardiac arrhythmias and applying appro-priate stimulation signals to a heart which utilizes considerably less power than the prior art. :
The reduction in power consumption is ;.
achieved by applying cardioversion signals to a plurality of areas on the heart when depolarization signals are sensed within a time period corresponding ~:
to an unacceptably high beat rate, by pacing the heart at fewer areas when the natural heart rate i falls below a predetermined minimum, and by not applying ~;
I stimulation signals to the heart when the heart is i beating naturally within a certain rate range. Thus, -~
the apparatus of the present invention employs the multiple output stimulation system of Funke to cardiovert -:
tachyarrhythmias and has the capability to operate in a demand mode in the event of bradycardia or "skipped"
~1 .
beats, at a considerable reduction in power requirements.
. In a preferred embodiment, the present inven- :
tion is formed of circuitry including a first path which :
applies a stimulation signal to one area of the heart - :~
i if a depolarization corresponding to a naturally occur-ring heart beat fails to occur within a predetermined time period and a second path which applies a cardiac stimulation signal to a plurality of locations on the ~01!36383 heart if depolarizations occur within a second predetermined time period. The first path is a demand pacing path which pro-vides pacing signals in the event of "skipped" beats or brady-cardia and the second path is a synchronous pacing path which provides cardio-version signals to stimulate a plurality of areas of the heart when a tachycardia exists. The present invention therefore operates as a demand pacer at a first rate, applies no stimulation to the heart up to a second higher rate, and above the second rate operates as a multiple electrode synchronous pacer for the prevention or correction of undesir-able tachyarrhythmias.
Thus, in accordance with one aspect of the invention there is provided cardiac electrical stimulation apparatus com-prising: means for sensing depo~larization at a plurality of areas on a heart; first means connected to the sensing means for applying a stimulation signal to a heart at a single area on the occurrence of a bradycardia, and second means oonnected to the sensing means for applying a stimulation signal to a plurality of areas on a heart on the occurrence of a tachycardia.
In accordance with another aspect of the invention there is provided cardiac electrical stimulation apparatus com-prising: means for sensing depolarizations at at least two areas on a heart; first means having output means responsive to the sensing means for providing cardiac stimulation signals to an area on the heart in response to depolarizations occurring below a first predetermined rate; second means having output means and responsive to the sensing means for providing cardiac stimulation signals to a plurality of areas on the heart in response to depolarizations occurring above a second predeter-mined rate.
In accordance with another aspect of the invention there is provided cardiac electrical stimulation apparatus ~ -3-~0l~63~33 comprising: a plurality of electrode means adapted for connection in spaced relation on a heart; first means for res-ponding to depolarization signals from the plurality of electrode means occurring below a first predetermined rate to provide stimulation signals to less than all of the plurality of electrode means; and second means for responding to depolar-ization signals from the plurality of electrode means occurring above a second predetermined rate to provide stimulation signals to all of the plurality of electrode means.
According to a further aspect of the invention there is provided cardiac electrical stimulation apparatus comprising:
a plurality of sensing electrode means adapted to be connected in spaced relation on a heart; at least two stimulation output means adapted to be connected in spaced relation on a heart;
first means for responding to depolarization signals from the plurality of sensing electrode means occurring below a first predetermined rate to provide stimulation signals to one of the stimulation electrode means; and second means for responding to depolarization signals from the plurality of sensing electrode means occurring above a second predetermined rate to provide stimulation signals to a plurality of stimulation output means.
BRIEF DESCRIPTION OF THE DRAWINGS
The single Figure shows a block diagram of a pre-ferred embodiment of the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring to the single Figure, a circuit for demand pacing and cardioversion of tachyarrhythmias is shown. A
plurality of electrodes 10 are adapted for connection in a spaced relation on a heart. Each electrode 10 is adapted for sensing depolarizations occurring in the area of the heart adjacent the electrode. Such electrodes for sensing cardiac depolarization signals are well known in the art and may be -3a-, ,, ' ' ~0~36383 as described in the Funke patent referenced above. Electrodes ;
10 are each connected to a sense amplifier 12 which may be any one of the amplifiers known in the art to be utilized with cardiac electrodes for amplifying , , ' ~, -3b-,~ .
sensed depolarizations. While five electrode-sense amplifier combinations are'shown in the Figure, it is considered within the scope of the invention that a different number may be 'used for sensing depolariza-tions on a heart at a plurality of locations.
The'output of each sense amplifier 12 is connected to one input of OR gate 14, which is a con-ventional gate for deIivering at its output any signals applied to any one of its inputs in the order in which r they are applied. The output of OR gate 14 is con- ' nected through'a refractory determining circuit 16, which is described more'fully below, to a junction 17.
The junction 17 is common to a demand pacing circuit 18 and a synchronous anti-fibrillation circuit 20.
Demand pacing circuit 18 includes a resettable ' astable multivibrator or pulse generator 22 which is connected to junction 17 to be reset by sensed depolari-zation signals appearing at junction 17. Generator 22 -' has a timing period corresponding to a first heart beat ; ' rate, for example, a time period of 1,000 ms corres- ' ponding to a rate of 60 bpm. So long as generator 22 is reset by sensed depolarization signals at junction 17 which occur within 1,000 ms of one another, i.e., occurring at an effective rate of 60 or more bpm, the Q output of generator 22 is held low and not allowed to go high. The Q output of generator 22 is connected to pulse former 24 which may be a retriggerable one shot having a short duration pulse, such as 1 ms, triggered by a positive going pulse edge. The Q output of pulse --former 24 is applied to an OR gate 26, the output of ~0~q6383 :~
which is supplied to an output amplifier 28. Amplifier 28 may comprise any known form of output pulse amplifier suitable for use in cardiac pacemaker application. The output of amplifier 28 is connected to a terminal 23 which is adapted for connection to an electrode, not shown, for applying stimulation signals to the heart `;~
at a single'location.
Synchronous anti-fibrillation path or circuit ~' 20 includes a delay circuit 34 connected to receive sensed depolarization signals appearing at terminal 17 at its input, or trigger terminal. The delay circuit 34 may be a retriggerable one shot having a short pulse duration of, for example, 10 ms. The output of delay circuit 34 is connected to one input of an OR gate 36, the'output of which is connected to a retriggerable ~`
monostable multivibrator or one shot 38. The one shot 38 has a time period in its astable state corresponding ' to a second heart beat rate, as for example, a 500 ms time period corresponding to a rate of 120 bpm. The Q ~
output of one shot 38 is connected to one input of AND ~' gate 40 and the other input of AND gate 40 is connected ' directly back to junction 17. The output of AND gate ~' 40 is connected to a short duration one shot pulse former ' 42, which may be identical to the pulse former 24 in the demand path'l8. The output of pulse former 42 is connected to one input of OR gate 26 and is also connected directly to a plurality of output amplifiers 29 to 32. The output of each'of the output amplifiers 28 and 32 is con-nected to a different terminal 25, the terminals 23 and 25 being adapted for connection to electrodes, not shown, positioned in spaced relation to each other for applying ~0~3~33 stimulation signals to the heart at a plurality of loca-tions. Alternatively, terminals 23 and 25 may each be connected to a different one of the eIectrodes 10 which would then perform the function of both sensing depolari-zation signals and applying stimulation signals, in a known manner.
Because there is a finite conduction velocity even in the normal heart the plurality of sense electrodes 10, placed in a spaced reIation on the heart, will sense depolarizations occurring during a single heart beat at slightly differing times. For example, normal conduction veIocity in a normal heart is known to be approximately 80 ms. Therefore, the time between -sensing the first depolarization and last depolariza-tion reIating to a single heart beat may be as much as ;;
80 ms. A refractory circuit is necessary in order to aid the apparatus of the figure to differentiate between depolarizations that occur during a single heart beat and !, depolarizations thatmay occur as the result of a tachy-; 20 cardia. A refractory circuit 16 is therefore connected between OR gate 14 and terminal 17.
Refractory circuit 16 includes an OR gate 44 -having two inputs one input being connected by way of line 52 to the output of OR gate 26. The second input is connected by way of line 54 to junction 17. The output of OR gate 44 is connected to the input trigger of deIay circuit 46 which may comprise a retriggerable one shot having a short duration time period of approximately 2 ms. The Q-NOT output of delay circuit 46 is connected to the trigger input of refractory timer ~01~6383 48 which may comprise a retriggerable one shot having `~
an astable state with a time period corresponding to the desired refractory period of, for example, 100 ms.
Refractory periods of other durations may be considered ~-more appropriate for other applications. The Q-NOT
output of timer48, which is norma~y high, is connected to one input of AND gate 50. AND gate 50 is connected between the output of OR gate 14 and terminal 17 for gating the sensed depolarization signals to circuits 18 and 20. Other refractory circuit arrangement could be used. For example, a plurality of refractory cir- `
cuits similar to circuit 16 could be inserted between sense amplifiers 12 and the inputs of OR gate 14, or sense amplifiers 12 could be constructed with a built-in refractory circuit.
The operation of the preferred embodiment is as follows. Electrodes 10 are connected in spaced relation on a heart for detecting depolarizations that occur in each area of the heart adjacent each electrode.
In one example, one eIectrode is connected to the intra-ventricular septum and the other electrodes are connected in spaced relation on the heart ventricles. Depolari-zations occurring adjacent an electrode 10 are sensed and amplified by sense amplifiers 12 and applied through OR gate 14 to one input terminal of AND gate 50.
Refractory timer 48 is normally high, at its Q-NOT output, so that AND gate 50 is enabled to allow a pulse occur-ring at the output of OR gate 14 to be applied to terminal 17.
When the first sensed depolarization pulse is applied to terminal 17, at the output of AND gate 50, -~086383 the pulse is also applied through OR gate 44 to deIay circuit 46 which deIays for a period of 2 ms before triggering refractory timer 48. The deIay is necessary to assure'that the'depolarization pulse gets through'before the''refractoryperiod is initiated.
When refractory timer 48 is-triggered, its Q-NOT
output goes low, thereby causing AND gate 50 to be blocked for a period determined by the timer 48. This is the refractory period. Any sensed depolarizations amplified by amplifiers 12'and applied to AND gate 50 by OR gate'14 will be blocked from application to terminal 17'during the refractory period.
The sensed depolarization that does appear at terminal 17 is applied to set resettable astable `
multivibrator 22. So long as sensed depolarizations '.'J' are applied to terminal 17, and thereby to the set input of multivibrator 22, within 1,000 ms of one `~
another, astable multivibrator 22 will be continuously ' reset and no output pulse will occur. If, however, no depolarization pulse'appears within 1,000 ms the Q output of multivibrator 22 will go high at the end of the l,000'ms time period. This will cause pulse shaper 24 to be triggered and generate a 1 ms pulse at its Q output to be applied through OR gate 26 and output amplifier 28 to terminal 23 and thereby to an electrode ' connected to the heart. Circuit 18 therefore senses ~' the failure of the heart to be beat within a first pre-determined time period, and applies a stimulation ;~
pulse to the heart through'output amplifier 28 to stimulate the heart to beat. Circuit 18 therefore' ~01~6383 operates as a demand pacer for pacing the heart in the ;~
event of a "skipped" beat or bradycardia.
The first pulse'applied at terminal 17 also triggers the'delay circuit 34, the'Q-NOT output of which goes low for the'duration of its astable state.
At the end of the 10 ms del'ay period when the Q-NOT out- .
put goes high,' this positive'going edge is applied through'OR gate'36 to the trigger input of one shot 38.
The output of one shbt 38 then goes high'and is applied :- ' to one input of AND gate'40. Because the duration... of a sensed depolarization pulse'is less than 10 ms, the first depolarization pulse which'triggers deIay circuit 34 does not pass through'AND gate 40. However, should .'-a second depolarization pulse be'applied to terminal ' 17 during the'500 ms period that the Q output of one ~'~
shot 38 is high, the 'second depolarization pulse will pass through AND gate 40'and be applied to the trigger ':' .
input of pulse'shaper 42. A second depolarization pulse will also restart the 500 ms time period of one shot 1 20 38. When pulse'shaper 42 is triggered, a pulse is ;. applied at its Q output and through OR gate 26 and output amplifier 28 to terminal 23 and simultaneously to output amplifiers 29 to 32 and terminals 25. A
I stimulation pulse is thereby applied to a plurality of areas on a heart by a plurality of electrodes .
connected to terminals 23 and 25, in response to a sensed tachyarrhythmia. Circuit 20 operates as a synchronous multiple electrode pacer.
. .
~086383 Whether an output stimulation pulse is produced by pulse shaper 24 or pulse shaper 42, it is applied through OR gate 26 and output amplifier 28 to terminal 23 which, along with its associated electrode, is common to both the demand pacing circuit 18 and the synchronous anti-fibrillation circuit 20. In either event, the pulse signal occurring at the output of OR gate 26 is applied through OR gate 44 to delay circuit 46 and, 2 ms later, to refractory timer 48. A
refractory period is thereby initiated after each stimu-lation signal. -When a stimulation signal has been applied to the heart, it is desirable that demand circuit 18 and synchronous circuit 20 be conditioned to deal with arrhythmias t~at may later occur. Astable multivibrator 22 is reset by automatically returning to its reset position after applying a high going pulse edge to -pulse shaper 24. It is also reset by a pulse which appears at junction 17. Likewise, because delay cir-cuit 34 and one shot 38 are retriggerable they are reset and the 500 ms time period is restarted when a `
pulse is applied to junction 17. The possibility exists, however, that a tachycardia may occur after a stimulation pulse is generated by generator 22 in response to a bradycardia. Because the refractory period is immediately initiated by such a generated pulse the heart beat that occurs at th~ point and the associated ~;
depolarization signals will be blocked from application to synchronous circuit 20 by refractory circuit 16.
Line 58 is therefore necessary as a connection between ~0l36383 the output of pulse shaper 24 and OR gate 36 to immedi-ately trigger one shot 38 to start its timing period :~
when a pulse is generated by generator 22. Line 58 may be unnecessary when other refractory circuitry is used.
In the embodiment shown, with refractory connection line 54 connected between the output of AND gate 50 and an input to OR gate 44, a refractory period is immediately initiated upon the generation of a pulse appearing at the output of AND gate 50. ~:~
This refractory period has a duration in the example given of 100 ms. In the patient with normal heart conduction veIocity, all depolarizations associated with the same heart beat will have occurred before the end of the refractory period. However, in patients with slow conduction, such as those with a myocardial infarction, some depolarizations associated with the heart beat may not occur until after the end of the ..
refractory period, thereby giving a false indication to the of the circuitry that a tachycardia is taking ; place.... In those patients, it may be preferable to replace the connection 54 with connection 56 shown in phantom to the output of OR gate 14. With the input of OR gate 44 connected to the output of OR gate 14 by way of connection 56 those depolarizations which -occur during the refractory period will retrigger refractory timer 48 so as to extend the refractory :
period for a time necessary to prevent false indications of a tachycardia from being applied to terminal 17. In the alternative, the refractory period as determined ~086383 :
by timer 48 could be extended for a larger time by designing the timer to have a period of 160 ms, for example. However, in some patients with slow con-duction, it may be difficult to predict the interval over which the heart will complete a single beat.
In those cases, connection 56 would be preferable.
For a clearer understanding of what is con-sidered to be the scope of this invention reference is made to the appended claims.
, ' !
The prevention of cardiac arrhythmias such as fibrillation has long been of interest in the art.
Certain cardiac stimulation circuits have been developed to produce cardiac stimulation signals to prevent or stop fibrillation. One such device is disclosed in U.S. Patent No. 3,937,226, issued to Dr. Herman D. Funke.
In the Funke device, a plurality of eIectrodes are connected to a heart in spaced reIation to each other for sensing depolarizations that occur at a plurality of areas of the heart. Output circuitry responsive to any sensed depolarization applies stimulation signals simultaneously to a plurality of areas of the heart rapidly after sensing a depolarization. The circuitry disclosed in the Funke patent includes a free running or astable multivibrator which generates a stimulation pulse to be applied to the plurality of areas of the heart if no depolarization signal is sensed within a predetermined time period. Thus, the Funke device acts to prevent premature ventricular contractions leading to ventricular fibrillation and has the capability to operate in a demand mode in the event ~
of bradycardia or "skipped" beats, for example. ~ -The circuitry of the Funke patent applies a stimulation signal to a plurality of areas on the heart each time the heart beats, even when the heart is beating at a normal rate. Consequently, a considerable amount of electrical power is used by the Funke device to stimulate the heart. Since the life of an implanted cardiac stimulation device is often dependent on the ~ ~',, '~
~086383 life of the power supply, it is considered highly desirable to reduce the drain on the power supply whenever possible.
SUMMARY OF THE INVENTION
The present invention comprises circuitry for sensing cardiac arrhythmias and applying appro-priate stimulation signals to a heart which utilizes considerably less power than the prior art. :
The reduction in power consumption is ;.
achieved by applying cardioversion signals to a plurality of areas on the heart when depolarization signals are sensed within a time period corresponding ~:
to an unacceptably high beat rate, by pacing the heart at fewer areas when the natural heart rate i falls below a predetermined minimum, and by not applying ~;
I stimulation signals to the heart when the heart is i beating naturally within a certain rate range. Thus, -~
the apparatus of the present invention employs the multiple output stimulation system of Funke to cardiovert -:
tachyarrhythmias and has the capability to operate in a demand mode in the event of bradycardia or "skipped"
~1 .
beats, at a considerable reduction in power requirements.
. In a preferred embodiment, the present inven- :
tion is formed of circuitry including a first path which :
applies a stimulation signal to one area of the heart - :~
i if a depolarization corresponding to a naturally occur-ring heart beat fails to occur within a predetermined time period and a second path which applies a cardiac stimulation signal to a plurality of locations on the ~01!36383 heart if depolarizations occur within a second predetermined time period. The first path is a demand pacing path which pro-vides pacing signals in the event of "skipped" beats or brady-cardia and the second path is a synchronous pacing path which provides cardio-version signals to stimulate a plurality of areas of the heart when a tachycardia exists. The present invention therefore operates as a demand pacer at a first rate, applies no stimulation to the heart up to a second higher rate, and above the second rate operates as a multiple electrode synchronous pacer for the prevention or correction of undesir-able tachyarrhythmias.
Thus, in accordance with one aspect of the invention there is provided cardiac electrical stimulation apparatus com-prising: means for sensing depo~larization at a plurality of areas on a heart; first means connected to the sensing means for applying a stimulation signal to a heart at a single area on the occurrence of a bradycardia, and second means oonnected to the sensing means for applying a stimulation signal to a plurality of areas on a heart on the occurrence of a tachycardia.
In accordance with another aspect of the invention there is provided cardiac electrical stimulation apparatus com-prising: means for sensing depolarizations at at least two areas on a heart; first means having output means responsive to the sensing means for providing cardiac stimulation signals to an area on the heart in response to depolarizations occurring below a first predetermined rate; second means having output means and responsive to the sensing means for providing cardiac stimulation signals to a plurality of areas on the heart in response to depolarizations occurring above a second predeter-mined rate.
In accordance with another aspect of the invention there is provided cardiac electrical stimulation apparatus ~ -3-~0l~63~33 comprising: a plurality of electrode means adapted for connection in spaced relation on a heart; first means for res-ponding to depolarization signals from the plurality of electrode means occurring below a first predetermined rate to provide stimulation signals to less than all of the plurality of electrode means; and second means for responding to depolar-ization signals from the plurality of electrode means occurring above a second predetermined rate to provide stimulation signals to all of the plurality of electrode means.
According to a further aspect of the invention there is provided cardiac electrical stimulation apparatus comprising:
a plurality of sensing electrode means adapted to be connected in spaced relation on a heart; at least two stimulation output means adapted to be connected in spaced relation on a heart;
first means for responding to depolarization signals from the plurality of sensing electrode means occurring below a first predetermined rate to provide stimulation signals to one of the stimulation electrode means; and second means for responding to depolarization signals from the plurality of sensing electrode means occurring above a second predetermined rate to provide stimulation signals to a plurality of stimulation output means.
BRIEF DESCRIPTION OF THE DRAWINGS
The single Figure shows a block diagram of a pre-ferred embodiment of the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring to the single Figure, a circuit for demand pacing and cardioversion of tachyarrhythmias is shown. A
plurality of electrodes 10 are adapted for connection in a spaced relation on a heart. Each electrode 10 is adapted for sensing depolarizations occurring in the area of the heart adjacent the electrode. Such electrodes for sensing cardiac depolarization signals are well known in the art and may be -3a-, ,, ' ' ~0~36383 as described in the Funke patent referenced above. Electrodes ;
10 are each connected to a sense amplifier 12 which may be any one of the amplifiers known in the art to be utilized with cardiac electrodes for amplifying , , ' ~, -3b-,~ .
sensed depolarizations. While five electrode-sense amplifier combinations are'shown in the Figure, it is considered within the scope of the invention that a different number may be 'used for sensing depolariza-tions on a heart at a plurality of locations.
The'output of each sense amplifier 12 is connected to one input of OR gate 14, which is a con-ventional gate for deIivering at its output any signals applied to any one of its inputs in the order in which r they are applied. The output of OR gate 14 is con- ' nected through'a refractory determining circuit 16, which is described more'fully below, to a junction 17.
The junction 17 is common to a demand pacing circuit 18 and a synchronous anti-fibrillation circuit 20.
Demand pacing circuit 18 includes a resettable ' astable multivibrator or pulse generator 22 which is connected to junction 17 to be reset by sensed depolari-zation signals appearing at junction 17. Generator 22 -' has a timing period corresponding to a first heart beat ; ' rate, for example, a time period of 1,000 ms corres- ' ponding to a rate of 60 bpm. So long as generator 22 is reset by sensed depolarization signals at junction 17 which occur within 1,000 ms of one another, i.e., occurring at an effective rate of 60 or more bpm, the Q output of generator 22 is held low and not allowed to go high. The Q output of generator 22 is connected to pulse former 24 which may be a retriggerable one shot having a short duration pulse, such as 1 ms, triggered by a positive going pulse edge. The Q output of pulse --former 24 is applied to an OR gate 26, the output of ~0~q6383 :~
which is supplied to an output amplifier 28. Amplifier 28 may comprise any known form of output pulse amplifier suitable for use in cardiac pacemaker application. The output of amplifier 28 is connected to a terminal 23 which is adapted for connection to an electrode, not shown, for applying stimulation signals to the heart `;~
at a single'location.
Synchronous anti-fibrillation path or circuit ~' 20 includes a delay circuit 34 connected to receive sensed depolarization signals appearing at terminal 17 at its input, or trigger terminal. The delay circuit 34 may be a retriggerable one shot having a short pulse duration of, for example, 10 ms. The output of delay circuit 34 is connected to one input of an OR gate 36, the'output of which is connected to a retriggerable ~`
monostable multivibrator or one shot 38. The one shot 38 has a time period in its astable state corresponding ' to a second heart beat rate, as for example, a 500 ms time period corresponding to a rate of 120 bpm. The Q ~
output of one shot 38 is connected to one input of AND ~' gate 40 and the other input of AND gate 40 is connected ' directly back to junction 17. The output of AND gate ~' 40 is connected to a short duration one shot pulse former ' 42, which may be identical to the pulse former 24 in the demand path'l8. The output of pulse former 42 is connected to one input of OR gate 26 and is also connected directly to a plurality of output amplifiers 29 to 32. The output of each'of the output amplifiers 28 and 32 is con-nected to a different terminal 25, the terminals 23 and 25 being adapted for connection to electrodes, not shown, positioned in spaced relation to each other for applying ~0~3~33 stimulation signals to the heart at a plurality of loca-tions. Alternatively, terminals 23 and 25 may each be connected to a different one of the eIectrodes 10 which would then perform the function of both sensing depolari-zation signals and applying stimulation signals, in a known manner.
Because there is a finite conduction velocity even in the normal heart the plurality of sense electrodes 10, placed in a spaced reIation on the heart, will sense depolarizations occurring during a single heart beat at slightly differing times. For example, normal conduction veIocity in a normal heart is known to be approximately 80 ms. Therefore, the time between -sensing the first depolarization and last depolariza-tion reIating to a single heart beat may be as much as ;;
80 ms. A refractory circuit is necessary in order to aid the apparatus of the figure to differentiate between depolarizations that occur during a single heart beat and !, depolarizations thatmay occur as the result of a tachy-; 20 cardia. A refractory circuit 16 is therefore connected between OR gate 14 and terminal 17.
Refractory circuit 16 includes an OR gate 44 -having two inputs one input being connected by way of line 52 to the output of OR gate 26. The second input is connected by way of line 54 to junction 17. The output of OR gate 44 is connected to the input trigger of deIay circuit 46 which may comprise a retriggerable one shot having a short duration time period of approximately 2 ms. The Q-NOT output of delay circuit 46 is connected to the trigger input of refractory timer ~01~6383 48 which may comprise a retriggerable one shot having `~
an astable state with a time period corresponding to the desired refractory period of, for example, 100 ms.
Refractory periods of other durations may be considered ~-more appropriate for other applications. The Q-NOT
output of timer48, which is norma~y high, is connected to one input of AND gate 50. AND gate 50 is connected between the output of OR gate 14 and terminal 17 for gating the sensed depolarization signals to circuits 18 and 20. Other refractory circuit arrangement could be used. For example, a plurality of refractory cir- `
cuits similar to circuit 16 could be inserted between sense amplifiers 12 and the inputs of OR gate 14, or sense amplifiers 12 could be constructed with a built-in refractory circuit.
The operation of the preferred embodiment is as follows. Electrodes 10 are connected in spaced relation on a heart for detecting depolarizations that occur in each area of the heart adjacent each electrode.
In one example, one eIectrode is connected to the intra-ventricular septum and the other electrodes are connected in spaced relation on the heart ventricles. Depolari-zations occurring adjacent an electrode 10 are sensed and amplified by sense amplifiers 12 and applied through OR gate 14 to one input terminal of AND gate 50.
Refractory timer 48 is normally high, at its Q-NOT output, so that AND gate 50 is enabled to allow a pulse occur-ring at the output of OR gate 14 to be applied to terminal 17.
When the first sensed depolarization pulse is applied to terminal 17, at the output of AND gate 50, -~086383 the pulse is also applied through OR gate 44 to deIay circuit 46 which deIays for a period of 2 ms before triggering refractory timer 48. The deIay is necessary to assure'that the'depolarization pulse gets through'before the''refractoryperiod is initiated.
When refractory timer 48 is-triggered, its Q-NOT
output goes low, thereby causing AND gate 50 to be blocked for a period determined by the timer 48. This is the refractory period. Any sensed depolarizations amplified by amplifiers 12'and applied to AND gate 50 by OR gate'14 will be blocked from application to terminal 17'during the refractory period.
The sensed depolarization that does appear at terminal 17 is applied to set resettable astable `
multivibrator 22. So long as sensed depolarizations '.'J' are applied to terminal 17, and thereby to the set input of multivibrator 22, within 1,000 ms of one `~
another, astable multivibrator 22 will be continuously ' reset and no output pulse will occur. If, however, no depolarization pulse'appears within 1,000 ms the Q output of multivibrator 22 will go high at the end of the l,000'ms time period. This will cause pulse shaper 24 to be triggered and generate a 1 ms pulse at its Q output to be applied through OR gate 26 and output amplifier 28 to terminal 23 and thereby to an electrode ' connected to the heart. Circuit 18 therefore senses ~' the failure of the heart to be beat within a first pre-determined time period, and applies a stimulation ;~
pulse to the heart through'output amplifier 28 to stimulate the heart to beat. Circuit 18 therefore' ~01~6383 operates as a demand pacer for pacing the heart in the ;~
event of a "skipped" beat or bradycardia.
The first pulse'applied at terminal 17 also triggers the'delay circuit 34, the'Q-NOT output of which goes low for the'duration of its astable state.
At the end of the 10 ms del'ay period when the Q-NOT out- .
put goes high,' this positive'going edge is applied through'OR gate'36 to the trigger input of one shot 38.
The output of one shbt 38 then goes high'and is applied :- ' to one input of AND gate'40. Because the duration... of a sensed depolarization pulse'is less than 10 ms, the first depolarization pulse which'triggers deIay circuit 34 does not pass through'AND gate 40. However, should .'-a second depolarization pulse be'applied to terminal ' 17 during the'500 ms period that the Q output of one ~'~
shot 38 is high, the 'second depolarization pulse will pass through AND gate 40'and be applied to the trigger ':' .
input of pulse'shaper 42. A second depolarization pulse will also restart the 500 ms time period of one shot 1 20 38. When pulse'shaper 42 is triggered, a pulse is ;. applied at its Q output and through OR gate 26 and output amplifier 28 to terminal 23 and simultaneously to output amplifiers 29 to 32 and terminals 25. A
I stimulation pulse is thereby applied to a plurality of areas on a heart by a plurality of electrodes .
connected to terminals 23 and 25, in response to a sensed tachyarrhythmia. Circuit 20 operates as a synchronous multiple electrode pacer.
. .
~086383 Whether an output stimulation pulse is produced by pulse shaper 24 or pulse shaper 42, it is applied through OR gate 26 and output amplifier 28 to terminal 23 which, along with its associated electrode, is common to both the demand pacing circuit 18 and the synchronous anti-fibrillation circuit 20. In either event, the pulse signal occurring at the output of OR gate 26 is applied through OR gate 44 to delay circuit 46 and, 2 ms later, to refractory timer 48. A
refractory period is thereby initiated after each stimu-lation signal. -When a stimulation signal has been applied to the heart, it is desirable that demand circuit 18 and synchronous circuit 20 be conditioned to deal with arrhythmias t~at may later occur. Astable multivibrator 22 is reset by automatically returning to its reset position after applying a high going pulse edge to -pulse shaper 24. It is also reset by a pulse which appears at junction 17. Likewise, because delay cir-cuit 34 and one shot 38 are retriggerable they are reset and the 500 ms time period is restarted when a `
pulse is applied to junction 17. The possibility exists, however, that a tachycardia may occur after a stimulation pulse is generated by generator 22 in response to a bradycardia. Because the refractory period is immediately initiated by such a generated pulse the heart beat that occurs at th~ point and the associated ~;
depolarization signals will be blocked from application to synchronous circuit 20 by refractory circuit 16.
Line 58 is therefore necessary as a connection between ~0l36383 the output of pulse shaper 24 and OR gate 36 to immedi-ately trigger one shot 38 to start its timing period :~
when a pulse is generated by generator 22. Line 58 may be unnecessary when other refractory circuitry is used.
In the embodiment shown, with refractory connection line 54 connected between the output of AND gate 50 and an input to OR gate 44, a refractory period is immediately initiated upon the generation of a pulse appearing at the output of AND gate 50. ~:~
This refractory period has a duration in the example given of 100 ms. In the patient with normal heart conduction veIocity, all depolarizations associated with the same heart beat will have occurred before the end of the refractory period. However, in patients with slow conduction, such as those with a myocardial infarction, some depolarizations associated with the heart beat may not occur until after the end of the ..
refractory period, thereby giving a false indication to the of the circuitry that a tachycardia is taking ; place.... In those patients, it may be preferable to replace the connection 54 with connection 56 shown in phantom to the output of OR gate 14. With the input of OR gate 44 connected to the output of OR gate 14 by way of connection 56 those depolarizations which -occur during the refractory period will retrigger refractory timer 48 so as to extend the refractory :
period for a time necessary to prevent false indications of a tachycardia from being applied to terminal 17. In the alternative, the refractory period as determined ~086383 :
by timer 48 could be extended for a larger time by designing the timer to have a period of 160 ms, for example. However, in some patients with slow con-duction, it may be difficult to predict the interval over which the heart will complete a single beat.
In those cases, connection 56 would be preferable.
For a clearer understanding of what is con-sidered to be the scope of this invention reference is made to the appended claims.
Claims (19)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. Cardiac electrical stimulation apparatus comprising: means for sensing depolarization at a plurality of areas on a heart; first means con-nected to the sensing means for applying a stimulation signal to a heart at a single area on the occurrence of a bradycardia, and second means connected to the sensing means for applying a stimulation signal to a plurality of areas on a heart on the occurrence of a tachycardia.
2. Apparatus according to claim 1 wherein the first means comprises multivibrator means for generating a stimulation signal upon the failure to sense a depolarization within a first predetermined time period.
3. Apparatus according to claim 1 wherein the second means comprise means for generating a stimulation signal upon the occurrence of a second sensed depolarization within a second predetermined time period after the occurrence of a first sensed depolarization.
4. Apparatus according to claim 1 wherein the sensing means comprise refractory means for blocking sensed depolarizations from the first and second means for a predetermined refractory period after the occurrence of either a sensed depolarization or a stimulation signal.
5. Cardiac electrical stimulation apparatus comprising: means for sensing depolarizations at at least two areas on a heart; first means having output means responsive to the sensing means for providing cardiac stimulation signals to an area on the heart in response to depolarizations occurring be-low a first predetermined rate; second means having output means and respon-sive to the sensing means for providing cardiac stimulation signals to a plurality of areas on the heart in response to depolarizations occurring above a second predetermined rate.
6. Apparatus according to claim 5 wherein the sensing means comprise refractory means having a predetermined refractory period for responding either to sensed depolarizations or to stimulation signals to initiate the refractory period.
7. Apparatus according to claim 6 wherein the refractory means com-prises: timing means for determining the predetermined refractory period;
first means for initiating the timing means in response to said sensing means;
second means for initiating the timing means in response to said first and second means; and means connecting said sensing means to said first and second means for inhibiting the response of the first and second means to the sensing means during the refractory period determined by the refractory timing means.
first means for initiating the timing means in response to said sensing means;
second means for initiating the timing means in response to said first and second means; and means connecting said sensing means to said first and second means for inhibiting the response of the first and second means to the sensing means during the refractory period determined by the refractory timing means.
8. Apparatus according to claim 7 wherein the inhibiting means com-prises gate means having an output, the first initiating means being connected to the output of the gate means and the second initiating means being con-nected to said first and second means output means.
9. Apparatus according to claim 7 wherein the inhibiting means com-prises gate means having an input, the first initiating means connecting said sensing means to the input of the gate means and the second initiating means connecting said first and second means output means to the input of the gate means.
10. Cardiac electrical stimulation apparatus comprising: a plurality of electrode means adapted for connection in spaced relation on a heart;
first means for responding to depolarization signals from the plurality of electrode means occurring below a first predetermined rate to provide stimu-lation signals to less than all of the plurality of electrode means; and second means for responding to depolarization signals from the plurality of electrode means occurring above a second predetermined rate to provide stimu-lation signals to all of the plurality of electrode means.
first means for responding to depolarization signals from the plurality of electrode means occurring below a first predetermined rate to provide stimu-lation signals to less than all of the plurality of electrode means; and second means for responding to depolarization signals from the plurality of electrode means occurring above a second predetermined rate to provide stimu-lation signals to all of the plurality of electrode means.
11. Apparatus according to claim 10 wherein the first means comprises multivibrator means resettable by said depolarization signals for providing a stimulation signal at the end of a first time period corresponding to said first rate to at least one of the plurality of electrode means.
12. Apparatus according to claim 10 wherein the second means comprise:
multivibrator means responsive to a first depolarization signal for changing state for a second time period corresponding to the second rate; and gate means responsive to the multivibrator means for initiating a stimulation signal at all of the plurality of stimulation electrode means in response to a second depolarization signal occurring during the second time period.
multivibrator means responsive to a first depolarization signal for changing state for a second time period corresponding to the second rate; and gate means responsive to the multivibrator means for initiating a stimulation signal at all of the plurality of stimulation electrode means in response to a second depolarization signal occurring during the second time period.
13. Apparatus according to claim 12 wherein the first means comprises multivibrator means resettable by said depolarization signals for providing a stimulation signal at the end of a first time period corresponding to said first rate to at least one of the plurality of electrode means.
14. Cardiac electrical stimulation apparatus comprising: a plurality of sensing electrode means adapted to be connected in spaced relation on a heart;
at least two stimulation output means adapted to be connected in spaced re-lation on a heart; first means for responding to depolarization signals from the plurality of sensing electrode means occurring below a first predetermined rate to provide stimulation signals to one of the stimulation electrode means;
and second means for responding to depolarization signals from the plurality of sensing electrode means occurring above a second predetermined rate to provide stimulation signals to a plurality of stimulation output means.
at least two stimulation output means adapted to be connected in spaced re-lation on a heart; first means for responding to depolarization signals from the plurality of sensing electrode means occurring below a first predetermined rate to provide stimulation signals to one of the stimulation electrode means;
and second means for responding to depolarization signals from the plurality of sensing electrode means occurring above a second predetermined rate to provide stimulation signals to a plurality of stimulation output means.
15. Apparatus according to claim 14 wherein the first means comprises multivibrator means resettable by said depolarization signals for providing a stimulation signal at the end of a first time period corresponding to said first rate to said one stimulation output means.
16. Apparatus according to claim 14 wherein the second means comprise:
multivibrator means responsive to a first depolarization signal for changing state for a second time period corresponding to the second rate; gate means responsive to the multivibrator means for initiating a stimulation signal at said plurality of stimulation output means in response to a second depolari-zation signal occurring during the second time period.
multivibrator means responsive to a first depolarization signal for changing state for a second time period corresponding to the second rate; gate means responsive to the multivibrator means for initiating a stimulation signal at said plurality of stimulation output means in response to a second depolari-zation signal occurring during the second time period.
17. Apparatus according to claim 16 wherein the first means comprise multivibrator means resettable by said depolarization signals for providing a stimulation signal at the end of a first time period corresponding to said first rate to said one stimulation output means.
18. Apparatus according to claim 14 wherein said plurality of stimu-lation output means includes said one stimulation output means.
19. Apparatus according to claim 14 wherein each of said stimulation output means are adapted for connection to a different one of said sensing electrode means.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US05/697,470 US4088140A (en) | 1976-06-18 | 1976-06-18 | Demand anti-arrhythmia pacemaker |
| US697,470 | 1976-06-18 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1086383A true CA1086383A (en) | 1980-09-23 |
Family
ID=24801248
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA280,748A Expired CA1086383A (en) | 1976-06-18 | 1977-06-17 | Demand anti-arrhythmia pacemaker |
Country Status (6)
| Country | Link |
|---|---|
| US (1) | US4088140A (en) |
| CA (1) | CA1086383A (en) |
| DE (1) | DE2727141A1 (en) |
| FR (1) | FR2354758A1 (en) |
| GB (1) | GB1576391A (en) |
| NL (1) | NL7706684A (en) |
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- 1977-06-13 FR FR7718014A patent/FR2354758A1/en active Granted
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- 1977-06-17 NL NL7706684A patent/NL7706684A/en not_active Application Discontinuation
- 1977-06-17 GB GB25495/77A patent/GB1576391A/en not_active Expired
Also Published As
| Publication number | Publication date |
|---|---|
| US4088140A (en) | 1978-05-09 |
| GB1576391A (en) | 1980-10-08 |
| NL7706684A (en) | 1977-12-20 |
| FR2354758A1 (en) | 1978-01-13 |
| DE2727141A1 (en) | 1978-01-05 |
| FR2354758B1 (en) | 1983-04-15 |
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