US3805795A - Automatic cardioverting circuit - Google Patents

Abstract

Pulse generating apparatus which provides electrical heartstimulating pulses only in the absence of normal heart activity. If the patient''s heart has developed a life threatening arrhythmic condition the inventive apparatus automatically applies an electrical shock to the heart having sufficient magnitude to restore normal heart activity. The inventive apparatus features a redundant heartbeat sensing system which monitors two dynamic characteristics of heart function, for example, heart contraction and EKG. An electrical heart stimulating pulse is delivered to the patient''s heart following the elapse of a specified period of time since the sensing of a dynamic characteristic indicative of a normal functional heart. Sensing control is automatically regained following successful heart stimulation, thereby inhibiting the application of further electrical pulses. In the event that the patient''s heart fails to resume normal heartbeat action, the inventive apparatus will continue delivering intermittant shocks-a lower energy pulse is applied first followed by higher energy pulses.

Description

United StatesPatent 11 1 Denniston et al.

[ AUTOMATIC CARDIOVERTING CIRCUIT [75] Inventors: Rollin H. Denniston, Minneapolis;

Thomas E. Davis, Forest Lake, both Primary Examiner-William E. Kamm Attorney, Agent, or Firm--Lew Schwartz; Wayne Sivertson of Minn. T

57 ABS RACE" [73] Assignee: Medtronic, Inc., Minneapolis, Minn. 1

- Pulse generating apparatus which provides electncal Filed: 1972 heart-stimulating pulses only in the absence of normal heart activity. If the patients heart has developed a 1.N 2 756 [211 App life threatening arrhythmlc condltion the inventive apparatus automatically applies an electrical shock to U.S- Cl. D, R the heart having ufficient magnitude to restore [51] Int.Cl A6ln 1/36 h t a ti it The inventive apparatus features a Field Of Search R, A1206 redundant heartbeat sensing system which monitors l23/419 419 P, 206 205 205 two dynamic characteristics of heart function, for ex- 338/5 ample, heart contraction and EKG. An electrical heart stimulating pulse is delivered to the patients heart fol- [56] 1 Re erences C tfi lowing the elapse of a specified period of time since UNITED STATES PATENTS the sensing of a dynamic characteristic indicative of a 3,716,059 2/1973 Welborn et al. 128/419 D normalfuPctional Sensing Control 2 3339704 6/1968 Buchowski et a] 128/419 D cally regamed followmg successful heart stlmulation, 2,976,865 3/1961 Shipley 128/205 D th reby inhlbiting the application of further electrical 3,323,367 6/1967 Searle 338/5 pulses. 1n the event that the patients heart fails to re- ,6 ,95 10/1971 Mirowski 6t 128/419 D sume normal heartbeat action, the inventive apparatus Haber P ontinue delivering intermitmant h0cks a lower 3,638,656 2/1972 Grfamlban 128/419 P energy pulse is applied first followed by higher energy 3,680,544 8/1972 Shmnlck et a1 128/419 P ulses 3,608,545 9/1971 Novack et al. 128/206F p 1 13 Claims, 8 Drawing Figures 24 l EKG 23 [26 l SENSOR OR ?5WAVE 1 2| GATE CONFORMER l CONTRACTION SENSOR 1l 13 L L m J J H l4 IO SYSTEMDISABLE LL 30 l l CONTROLLER I ALERT 3 l l SYSTEM /32 1 00-00 I F CONVERTER 34 3e 1 l QTORAGE P5 RE GULAT OR I [I6 I CAPA C lTOR I INTRAVASCULAR L wELECTRICAL LEAD 1? PATENTEDAPR 2 3 I974SHEET 2 UF 5 m OE PATENTEDAFR 2a 1974 SHEET 3 [IF 5 E 3950 2596 w 2- omm PATENTEBAPWIQM SHEET 4 BF 5 oom h. 3 @0258. VllilllllJ 52m AUTOMATIC CARDIOVERTING CIRCUIT BACKGROUND OF THE INVENTION During the past several decades, coronary heart discase has come to occupy the first position among the causes of death in the developed areas of the world. In the United States, for example, this disease is responsible for over one-half million deaths yearly. And of this number, more than half occur suddenly, outside the hospital, and therefore before the patient is able to obtain the necessary medical assistance. Although the precise cause of sudden death in coronary heart disease has not yet been entirely clarified, the available evidence permits the medical field to ascribe death in the majority of these cases to grave disturbances in cardiac electrical activity culminating in ventricular fibrillation.

Another frustrating but related problem is the present inability to deal effectively with lethal and nonlethal arrhythmias outside of a hospital setting. Within the hospital environment, however, recent experience has clearly demonstrated that ventricular fibrillation and its frequent precursor, ventricular tachycardia, are reversible phenomena when prompt cardioversion of the heart is instituted. Under such circumstances, cardiac function can frequently be restored to normal without the patient suffering from residual disability. Unfortunately, however, the present state of the art makes cardioversion very dependent upon a highly specialized medical environment, thus limiting such treat- ,ment to fully equipped, modern hospitals.

There is no question that a great need exists for a defibrillator which would be carried by those who are prone to having one of the many life-threatening arrhythmias generally discussed above. Thus, in some pa tients having coronary heart disease,-a fatal outcome from ventricular tachycardia or ventricular fibrillation could be avoided, even in the absence of immediate medical assistance. The first step, of course, is the detection of those prone to suffering from cardiac malfunctions leading to ventricular tachycardia or ventricular fibrillation.

While it is not possible to predict with unerring exactness which patients suffering from coronary heart disease will die from ventricular fibrillation or ventricular tachycardia, several high risk groups of patients can be recognized. For example patients who have experienced myocardial infarction, even though they may be surviving in good'health, runa substantial risk of dying suddenly, a risk several times greater than that asso ciated with the general population. Further, if patients with myocardial infarction have a history of serious ventricular arrhythmias and/or of cardiac arrest, or if evidence of persistent myocardial irritability is present, it may be logically assumed that the risk of sudden death is increased substantially. A patient like those described above would greatly benefit from an automatic defibrillator.

Also, such an automatic defibrillator would be an asset to those patients who have suffered myocardial infarction in the coronary care unit and remain hospitalized in the coronary care unit or some other area of the hospital. Under such circumstances, the defibrillator could be used temporarily for the remainder of the expected hospital stay; or the automatic defibrillator could be permanently implanted for use both in the hospital and after discharge. And another recognizable class of patients particularly in need of an automatic defibrillator is the class composed of those who have not shown prior histories of myocardial infarction but who show severe symptoms of coronary heart disease, such as ventricular arrhythmias resistant to medical treatment or angina pectoris.

From the brief discussion above, there should be little doubt that the possible applications for an automatic defibrillator are numerous. Such an automatic defibrillator has been developed by Medtronic, Inc. and is described in US. Pat. application Ser. No. 124,326, filed Mar. 15, 1971, now abandoned by Mieczyslaw Mirowski, et al. and entitled CARDIOVER- TER HAVING SINGLE INTRAVASCULAR CATHE- TER ELECTRODE SYSTEM.

The automatic standby defibrillator described in the above-identified patent application employs a pressure sensing element attached to a body implantable electrical lead such that it can be positioned within the right ventricle of the heart. Since the pressure in the heart drops severely when the heart goes into the fibrillation state, ventricular fibrillation can be easily detected by monitoring heart pressure. However, several difficulties with measuring heart pressure are encountered. One disadvantage with using pressure as an indicator of the fibrillation state is that the small pressure sensing elements which are suitable for use with body implantable electrical leads are quite expensive. A second disadvantage with using these pressure sensing elements is that they must either be located alongside, on the outer surface, or at the tip of the body implantable electrical ened by the surrounding heart muscle.

The apparatus of this invention uses a single ,intravascular electrode'of the type described in US. Pat. application Ser. No. 202,238, filed Nov. 26, 1971, by Rollin H. Denniston, lll, entitled MUSCLE CONTRAC- TION DETECTION APPARATUS, to perform three functions; namely; (1) detecting heart contractions;

(2) detecting heart electrical activity in the form of R waves; and (3) applying electrical impulses to the heart for cardioverting it.

Thus the apparatus of this invention overcomes many difficulties existent in the prior art devices while providing a compact and practical automatic cardioverting system. i

SUMMARY OF THE INVENTION The present invention relates to a cardioverter, an electronic system which, after detecting one of the above-noted lethal or non-lethal arrhythmias, automatically cardioverts the heart of the user. Cardioverting or cardioversion" as used herein is intended to mean a method of correcting a number of arrhythmic heart conditions including atrial tachycardia, atrial fibrillation, junctional rhythms, ventricular tachycardia, ventricular flutter, and ventricular fibrillation, and any other non-pacing related arrhythmic condition which may be corrected by applying electrical shocks to the heart. Obviously then, defibrillation is included in the term cardioversion as a method of applying electrical shocks to the heart to defibrillate a fibrillating atrium or a fibrillating ventricle. The system of the present invention may be installed in patients particularly prone to develop ventricular tachycardia and/or ventricular fibrillation, or other types of tachyarrhythmias which may be corrected by cardioverting, either on a temporary or a permanent basis. And, because of extremely small and compact size, the system including both electrodes may be totally and completely implanted under the skin of the patient, or alternatively, may be carried externally, save for the sensing probe carrying the two electrodes.

More particularly, the present invention relates to an automatic cardioverting circuit for monitoring cardiac contraction and sensing when the heart has developed an arrhythmic heart condition, and which then automatically applies a cardioverting shock to the heart of sufficient magnitude to restore effective heart rhythm. The device is adapted to continue delivering intermittent shocks to the heart in the event that the heart fails to return to its normal behavioral pattern, and has the ability of automatically regaining sensing control over a functional heart, thereby insuring that further shocks are inhibited after successful cardioversion has taken place.

The automatic cardioverting circuit comprises two basic subsystems;a sensing system, which continuously monitors heart activity; and a stimulation system which upon receiving a signal from the sensing system applies a cardioverting shock to the heart myocardium through an intravascular electrical lead.

The sensing system of the present invention monitors two dynamic characteristics of the heart and provides an electrical signal corresponding to each heart contraction. The absence of both these characteristics for a predetermined period of time is required before the stimulation system will be activated to transmit a cardioverting shock to the heart. One of the characteristics monitored is the EKG. The EKG is obtained from the electrodes located on the intravascular lead. The second characteristic monitored is muscle contraction. The muscle contraction signal is obtained from a contraction sensing device positioned in the intravascular lead and consisting of a conductive elastomer body having carbon particles imbedded therein. The contraction signal is generated whenever the contraction sensing device is flexed by a heart contraction.

The EKG and the heart contraction signals are fed to a gating device. The gating device will allow a cardioverting shock to be delivered to the heart only if both signals are absent for a predetermined period. of time. Thus a heart contraction detected by either the EKG monitoring system or the heart contraction monitoring system is sufficient to prevent a cardioverting pulse from being delivered to the heart. Consequently, each of the monitoring devices provides a back-up signal for the other.

The stimulation portion of the present invention ap' plies energy to the heart in the form of electrical pulses delivered through the electrodes located on the intravascular lead. The application of these electrical pulses to the patients heart is delayed for a preset period of time (on the order of -20 seconds) following the sensing of abnormal heart activity. If normal cardiac action resumes during this period, the application of the cardioverting pulses is automatically inhibited. This delay gives the heart the opportunity to convert spontaneously to normal cardiac rhythm if it is able to do so, and also insures that the cardioverting pulses are applied only when they are needed.

The present invention comprising the sensing system and the stimulation system provides an automatic cardioverting device capable of cardioverting a malfunctioning heart at relatively low energy levels. This device senses when the heart is malfunctioning and then automatically delivers a cardioverting shock to the heart. The device lies dormant during normal heart activity and applies a shock to the heart only when the heart functions become abnormal. This device is extremely compact and features an electrode system, in the form of an intravascular lead, which is totally and completely implantable in the body of a patient. This single intravascular lead is used for sensing the difference between a normally functioning heart and one which is functioning abnormally, and also for transmitting cardioverting shocks to the heart through the electrodes positioned on the same lead. The intravascular lead is also capable of being used for sensing heart conditions requiring heart pacing and for transmitting pacing pulses to the heart.

The invention features a redundant heart contraction sensing system. Two dynamic heart characteristics of the heart function-EKG and heart contractionare monitored by the invention. A cardioverting shock is transmitted to the heart only following the elapse of a specified period of time since the sensing of a dynamic characteristic indicative of a normally functioning heart. This aids in assuring that cardioverting shocks will be delivered to the heart only when they are needed, and thus largely eliminates the concern over possible heart damage being caused by the delivery of cardioverting shocks to a properly functioning heart.

A disabling feature of the invention further guards against unnecessary cardioverting shocks being applied to the heart. A fracture in the contraction sensor will be automatically detected by a disabling means which will then disable the portion of the circuit which generates and transmits cardioverting shocks to the heart. Therefore, a fracture in the contraction sensor will not result in an unnecessary cardioverting shock being applied to the heart. Further, using an endocardial implantable electrical lead, the invention provides a reliable way of cardioverting a malfunctioning heart with-,

out causing serious damage to the heart by the application of high energy densities directly to the heart endocardium. The truncated capacitive discharge waveform used in the circuit of the invention to apply energy to the heart helps minimize the peak and total energy required to cardiovert the heart. Another way the invention minimizes the energy densities applied to the heart is by applying a lower energy pulse first, and then, if that pulse does not restore normal heart functioning, applying cardioverting pulses having higher energy content. The invention also features a counting means which automatically disables the cardioverting circuit after a predetermined number of pulses have been delivered to the heart; thereby preventing cardioverting shocks from being applied when they have little chance of restoring the heart to normal functioning, and could damage the heart.

The invention additionally provides a means for delaying application of the first cardioverting pulse for a period of time, for example, to seconds, following the sensing of abnormal heart functioning. This delay gives the heart the opportunity to convert spontaneously to a normal cardiac rhythm, and also insures that cardioverting pulses are not applied if the heart condition is not critical. There is, of course, no need for the long built-in delay period with the succeeding cardioverting shocks as there is no longer any doubt but that the heart condition is now critical. Accordingly, the succeeding shocks are separated by significantly shorter time intervals.

Other features and advantages of the present invention will beset forth in, or become apparent from, the following description and claims and illustrated in the accompanying drawings, which disclose by way of example and not by way oflimitation, the principle of the invention and the structural implementation of the inventive concept.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram illustrating basic components of the apparatus provided by this invention;

FIG. 2 is a graph indicating the shape of electrical waves produced by the heart during normal heartbeat action;

FIG. 3 shows electrical circuitry of the heartbeat sensing means embodied in the apparatus of this invention;

FIG. 4 is a schematic diagram illustrating the power supply and the low battery indicator incorporated in the apparatus of this invention;

FIG. 5 is a schematic diagram illustrating the control means incorporated in the apparatus of this invention;

FIG. 6 is a schematic diagram illustrating the system disabling means incorporated in the apparatus of this invention;

FIG. 7 is a schematic diagram illustrating the regulating means incorporated in the apparatus of this invention;

FIG. 8 is a voltage v. time diagram illustrating the voltage on the energy storage means embodied in the inventive apparatus and the states of the reed switch and the SCR embodied in the inventive apparatus, and how these voltages and component states effect the wave form and voltage magnitude of the cardioverting pulses applied to the patients heart by the apparatus of this invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring generally to FIG. 1, the cardioverting apparatus of this invention includes: sensing means shown inblock 10 adapted to sense each contraction of the patients heart; stimulation means shown inblock 12 adapted to automatically provide electrical impulses which can be used to cardiovert the patients heart; an intravascular electrical lead represented inblock 16 adapted to detect heart R waves and contractions and to apply electrical impulses to the patients heart; disabling means shown inblock 14 adapted to disable stimulation means [2 wheneverelectrical lead 16 is rendered inoperative; and a power supply for the system shown in FIG. 4. Sensing means 10 monitors heart activity and provides an electrical signal to stimulation means 12 which corresponds with each heart contraction. When no electrical signal is received from sensing means 10 for a predetermined period of time, stimulation means 12 is automatically activated to transmit a cardioverting electrical impulse to the heart throughlead 16.

It will be understood that the normal beating of the human heart produces electrical signals or waves which are representative of the various stages in the occurrenceof each heartbeat. Thus a heart beating in sinus rhythm produces electrical waves conventionally identified as P, Q, R, S and T waves, as shown in FIG. 2. The R wave, for example, is representative of a hearts ventricular contraction and can be detected by the electrodes of a conventional electrical intravascular lead of the type commonly used in heart pacing.

An intravascular electrical lead is diagrammatically shown asblock 16 in FIG. 1. This block represents an intravascular electrical lead which is adapted to detect the EKG and contractions of the heart and to apply cardioverting electrical pulses to the patients heart. In a preferred embodiment of this lead the EKG is detected using electrically conductive electrodes; the heart contractions are detected by an elastomer body which changes impedance whenever it is flexed, as for example, by heart contraction; and the cardioverting electrical impulses are applied to the heart via the same electrodes as used to detect the EKG. However, it will be understood that the above-described embodiment is only one of the many different intravascular lead embodiments which can be advantageously used with the apparatus of this invention.

Sensing means 10 comprisingEKG sensor 20,contraction sensor 22, orgate 24, andwave conformer 26 is shown in FIG. 3. Sensing means 10, using intravascularelectrical lead 16, is adapted to sense R waves and heart contractions and to provide an electrical signal corresponding with each sensed normal heartbeat.

With reference to FIG. 3,contraction sensor 22 comprises fixed resistor ll4,capacitor 112, andoperational amplifier 110. One side of fixedresistor 114 is connected to the 4 volt power supply. The other side ofresistor 114 is connected to the junction betweenelectrical line 11 and to capacitor 1112 for convenience denoted asjunction 113.Capacitor 112 is used to AC .couple junction 113 to the input side ofcontraction amplifier 110. The output of amplifier is transmit ted online 21.

Contraction sensor 22 is connected toelectrical lead 16 byelectrical line 11 and to orgate 24 byelectrical line 21 and is adaptedto provide a usable electrical signal corresponding with each heart contraction.

In a preferred embodiment,electrical line 11 is connected to a conductive elastomer body withinelectrical lead 16 which changes impedance when flexed by a heart contraction. This change in impedance is easily detectable as it will cause a change in the current flowing from the 4 voltpower source'through resistor 114,junction 113,electrical line 11, and the elastomer body. 7

The resulting change in voltage atjunction 113 is AC coupled bycapacitor 112 tooperational amplifier 110 where an electrical output signal in the form of an electrical pulse, is generated in response to the voltage and transmitted to the orgate 24 onelectrical line 21.

EKG sensor is adapted to amplify each R wave signal detected by theelectrical lead 16 corresponding to a normal heartbeat. More specifically,EKG sensor 20 amplifies R waves produced by a human heartbeat, discriminating against the electrical heart waves produced by a heart in fibrillation or otherwise abnormally functioning, as well as the pacer pulses applied usinglead 16.

EKG sensor 20 is electrically connected toelectrical lead 16 viaelectrical line 13 andline 17 from stimulation means 12 and to orgate 24 byelectrical line 23.EKG sensor 20 comprisesR wave amplifier 120, compensatedmonostable multivibrators 122 and 130,capacitor 124,resistor 126, and andgate 140. The input side ofR wave amplifier 120 andmultivibrator 130 are connected toelectrical line 13 atjunction 119. The output ofmultivibrator 130 is directly connected to the input side of andgate 140, whereas the output side ofamplifier 120 is connected to the input side of andgate 140 through the series combination ofmultivibrator 122 andcapacitor 124. One side ofresistor 126 is connected to the junction betweencapacitor 124 and andgate 140 and the other side is connected to the system ground. The output of andgate 140 is transmitted onelectrical line 23.

R wave amplifier 120 is an amplifier which operates in the same manner as those commonly used in demand pacer. It is adapted to select and amplify the R waves produced by heartbeats while discriminating against electrical heart waves produced by an abnormally functioning heart. The selection of the R waves is commonly performed by amplitude and frequency filtering.

Monostable multivibrators 122 and 130 are of a conventional design. In a preferred embodiment, the multivibrators used are conventional RCA Monostable Oscillators using COS/MOS Digital Integrated Circuits. The exact multivibrator circuitry used in this preferred embodiment is described and shown schematically in FIG. 9 of RCA Application Note 'lCAN-6267.

The preferred embodiment multivibrators have two states, a high'state and a low state. They are normally in the high state, and are switched into the low state, for a predetermined period of time (T,,), upon receipt of an electrical pulse of sufficient magnitude. The period of time (T,,) the multivibrator is in the low state and the threshold voltage (V of the pulse required to trigger the multivibrator into the low state can, of course, be varied by varying the component values of the circuitry associated with the multivibrators. Accordingly, the output from the multivibrators. upon receipt ofa pulse of sufficient magnitude (V,), will be an electrical pulse ofa predetermined pulse width (T Capacitor 124 andresistor 126 are electrically connectedv tomultivibrator 122 in such a way that they differentiate the output frommultivibrator 122. Thus ifmultivibrator 122 remains in the high state, there will be no input frommultivibrator 122 through the differentiating circuit ofcapacitor 124 andresistor 126 to and"gate 140. However, this differentiating circuit will provide and"gate 140 with a negative spike pulse followed by a positive spike pulse at a time (T,,) later when a negative electrical pulse is generated bymultivibrator 122.

Gate 140 is a conventional and" gate. It is adapted so that it will transmit an electrical pulse, if at the time it receives the positive pulse from the differentiating circuit ofcapacitor 124 andresistor 126, the electrical signal received frommultivibrator 130 is in a high state. If at the time the positive spike pulse is received from the differentiating circuit the electrical signal received frommultivibrator 130 is in the low state, thengate 140 will not transmit an electrical pulse.

Selectingmultivibrators 122 and 130 having the proper threshold voltages (V,) and the proper pulse widths (T will allowEKG sensor 20 to differentiate between pacer pulses and R waves. In a preferred embodiment,multivibrator 122 will have a threshold V of 10 m-v and a pulse width of T,, of 1 m-sec andmultivibrator 130 will have a threshold V of 0.5 v and a pulse width of 5 m-sec. R waves from a human heart beating in normal sinus rhythm commonly have a magnitude in the 20 m-volt range when sensed through the intracardiac lead system; whereas pacer pulses are commonly in the 1.0 to 2.0 volt range. Accordingly, a normally produced R wave will be insufficient to triggermultivibrator 130 into its low state but the R wave amplified by amplifier will be sufficient to triggermultivibrator 122 into its low state and thus will cause the differentiating circuitry to supply a positive spike pulse togate 140 whenmultivibrator 122 returns to its high state 1 m-sec. later. This positive spike pulse will causegate 140 to transmit an electrical pulse online 23 as multivibrator will be in the high state. Conversely, pacer pulses will trigger bothmultivibrator 122 andmultivibrator 130. Since the output ofmonostable multivibrator 122 is effectively delayed l m-sec. bydifferentiation elements 124 and 126,monostable multivibrator 130 will be in the low state when gate receives the positive pulse frommultivibrator 122. Thusgate 140 will not transmit a pulse online 23.

Gate 24 comprises transistors and 160. The base 151 oftransistor 150 is electrically connected tocontraction sensor 22 viaelectrical line 21; theemitter 155 is connected directly to the system ground; and thecollector 153 is electrically connected to waveconformer 26 viaelectrical line 25. The base 161 of transistor is electrically connected toEKG sensor 20 viaelectrical lead 23; the emitter is connected directly to the system ground; and the collector 163 is electrically connected to theelectrical line 25 and thecollector 153 oftransistor 150.

Gate 24 functions as a conventional or gate.Transistors 150 and 160 are normally in the non-conductive state; however, if an electrical pulse fromcontraction sensor 22 is received at the base 151 oftransistor 150, it will rendertransistor 150 conductive, thus providing a low resistance electrical path fromelectrical line 25 to ground. Likewise, an electrical pulse fromEKG sensor 20 will rendertransistor 150 conductive; thus providing a low resistance electrical path fromelectrical line 25 to ground. Consequently, whenever an electrical pulse is received fromcontraction sensor 22 orEKG sensor 20 or from both,gate 24 will provide a low resistance path fromelectrical line 25 to ground.

Wave conformer 26 is electrically connected togate 24 viaelectrical line 25 and to stimulation means 12 viaelectrical line 15, and is adapted to conform the electrical signals received fromgate 24 into pulses having substantially the same pulse width and amplitude. The conformed electrical pulses received fromwave conformer 26 have a predetermined pulse amplitude and width which is sufficient to effect the functioning of stimulation means 12.

Wave conformer 26 comprises aprogramable unijunction transistor 180 electrically connected in a monostable multivibrator arrangement.Programable unijunction transistor 180 has a gate input 178, an anode input 179, and acathode 177. This type of transistor is commonly referred to as a PUT in the engineering literature. It is rendered conductive, thereby providing a low impedance from both the PUT anode and gate to its cathode, when the anode voltage exceeds the gate voltage by a specified amount, for example, 0.7 volts.

PUT 180 is connected with its gate 178 electrically connected tojunction 181, its anode 179 electrically connected tojunction 183, and itscathode 177 electrically connected toelectrical line 15.Resistor 194 is electrically connected between electrical line and the system ground. Junction 181the junction between resistors 182 and 184-is electrically connected to gate means 24 viaelectrical line 25.Resistors 182 and 184 are connected in series between the 4 volt power supply and ground, thereby forming a voltage divider which establishes the voltage atjunction 181 at a predetermined value.Junction 183 is the junction betweenresistor 186 anddiode 188.Resistor 186,diode 188 and the parallel combination ofresistors 192 andcapacitor 190 are connected between the 4 volt power supply and the system ground. The component values ofresistor 186 and 192 andcapacitor 190 are chosen such that the voltage atjunction 183 is kept at a predetermined value which normally forcesPUT 180 into a non-conducting state.

Wave conformer 26 is adapted to provide a pulse having a predetermined amplitude and width in response to each electrical signal received fromgate 24. Whenever an electrical pulse is received bygate 24 fromcontraction sensor 22 or EKG sensor or from both,gate 24 becomes active, providing a low resistance path from electrical line to ground. Junction 18] is electrically connected toelectrical line 25 and thus becomes connected to ground via a low resistance path whenevergate 24 is active. Consequently, whenevergate 24 is active, the voltage atjunction 181 is decreased and falls to a voltage such thatPUT 180 is rendered conductive.

Transistor 180 will remain conductive for a predetermined period of time. This time period is determined by the discharge time ofcapacitor 190.

OncePUT 180 becomes conductive,capacitor 190 is prevented from discharging through it bydiode 188. Consequently,capacitor 190 must discharge throughresistor 192. Thecapacitor 190 andresistor 192 component values are selected such thatcapacitor 190 dis charges at a predetermined rate, thus keeping the voltage atjunction 183 sufficiently high to keepPUT 180 conductive for a predetermined period of time. Accordingly, this time period establishes the pulse width of the pulse generated bywave conformer 26. The amplitude of the generated pulse is established by the voltage at whichjunction 183 is maintained whilePUT 180 is conductive. The generated pulse having a predetermined amplitude and width is transmitted to stimulation means 12 onoutput line 15.

Referring to FIG. 4, the power supply. for the cardioverting system is shown schematically. With reference to FIG. 1, the system power supply (not shown) must provide the energy needed to chargestorage capacitor 34 as well as providing the energy needed to drive and bias the circuitry of sensing means 10, and the associated circuitry of stimulation means 12. This requires that it have a substantially constant output, as the sensing and stimulation circuitry do not function well when they are driven and biased by a supply that fluctuates significantly; that it be able to supply the relatively large amount of energy required to chargestorage capacitor 34; and that it be as compact as possible.

The above stringent requirements are met by the power supply embodiment shown in FIG. 4 which comprises a 6volt battery 210 which drives a 4volt supply 220. The 6volt battery 210, via a DC to DC converter 32 (FIG. 1), supplies the energy needed to charge capacitor 34 (FIG. 1), whereas the 4volt supply 220 supplies a constant driving and biasing voltage for the circuitry of sensing means 10 and the associated circuitry of stimulation means 12. This particular embodiment prevents fluctuations in the output of the 6volt battery 210, caused by the drain put on it when thestorage capacitor 34 is charged, from affecting the 4volt source 220 output, provided the output of the 6volt battery 210 remains above 4 volts.

Alow battery indicator 230 is also shown in FIG. 4. Theindicator 230 is set so that it is activated whenever thepower source 210 output falls below apredetermined voltage level, for example, 4.0 volts, and is used to drive a light emitting diode which indicates that the power source output is below this predetermined level.

Controller 30 is shown schematically in FIG. 5. It comprisesprogramable unijunction transistor 340,transistor 310,diode 328,capacitor 330 andresistors 326, 352, 354 and 346.Programable unijunction transistor 340 has agate input 341, ananode input 343, and acathode 345. This type of transistor is commonly referred to as a PUT in the engineering literature. It is rendered conductive, thereby providing a low impedance from both the PUT anode and gate to its cathode when the anode voltage exceeds the gate voltage by a specified amount, for example, 0.7 volts.Resistors 352 and 354 are electrically connected in series between the 4 volt power source and the system ground.Resistor 326,diode 328, andcapacitor 330 are likewise electrically connected in series between the 4 volt source and the system ground. The junction betweenresistors 352 and 354, designatedjunction 335, is electrically connected togate 341 of PUT 340-the junction betweenresistor 326 anddiode 328 designatedjunction 333, is electrically connected to anode 343 ofPUT 340. Thecathode 345 ofPUT 340 is electrically connected toelectrical line 31 and also to the system ground throughresistor 346.Transistor 310 has itscollector 313 electrically connected to the junction betweendiode 328 andcapacitor 330, designatedjunction 320; itsemitter 315 electrically connected to the system ground; and itsbase 311 electrically connected to sensing means 10 viaelectrical line 15.

Thejunction 335 voltage is maintained constant as it is the junction betweenresistors 352 and 354 which form a voltage divider; whereas thejunction 333 volta'ge varies depending upon the charge oncapacitor 330.Capacitor 330 is charged by the 4 volt energy source through the series connection ofresistor 326 anddiode 328. In a preferred embodiment the component values ofcapacitor 330,diode 328 andresistor 326 are chosen so that it takes approximately 5 seconds to chargecapacitor 330 to the predetermined level where it will render PUT 340 conductive.Diode 328 preventscapacitor 330 from discharging throughPUT 340. Sincetransistor 310 is connected acrosscapacitor 330 to the system ground, whenevertransistor 310 is renderedconductive capacitor 330 rapidly discharges to ground. However,transistor 310 is in the nonconductive state unless it receives an electrical signal from sensing means 10 onelectrical line 15. This signal comes fromwave conformer 26 and is of sufficient pulse amplitude and width to keeptransistor 310 on long enough forcapacitor 330 to totally discharge.

Consequently, whenever an electrical signal is received from sensing means 10,capacitor 330 will discharge,rendering PUT 340 non-conductive. PUT 340 will remain non-conductive for at least seconds; longer if another pulse is received from sensing means during that five second interval. However, whenPUT 340 becomes conductive, it will remain conductive until a pulse is received from sensing means 10. This is the case sincecapacitor 330 cannot discharge except throughtransistor 310, and thus will remain at substantially the same voltage untiltransistor 310 is rendered conductive by a pulse from sensing means 10.

System disable 14, shown schematically in FIG. 6, continuously monitors the contraction sensing circuitry ofintravascular lead 16. It is adapted and connected so that if an open circuit should occur in the contraction sensor, whether due to a break inlead 16 or in the sensor itself, a visual alarm is activated and thecontroller 30 is clamped so that it is non-conducting.

System disable 14 comprisesconventional Darlington amplifier 210,visual alarm 220 in the form of a light emitting diode, andresistors 230 and 240.Visual alarm 220 is electrically connected between the six volt power supply andinput 212 ofamplifier 210.Amplifier 210 is electrically connected to the contraction sensor ofintravascular lead 16 atinput 214 viaelectrical line 11. The twooutputs 216 and 218 fromamplifier 210 are electrically connected to the system ground throughresistors 230 and 240 respectively.Output 216 is additionally electrically connected tocontroller 30 viaelectrical line 15.

When an open circuit occurs in the contraction sensing circuit, system disable 14 will prevent stimulation means 12 from applying a cardioverting pulse to the patients heart. Specifically, when the contraction sensing circuit is broken, the increase in voltage atinput 214 will renderamplifier 210 conductive.Amplifier 210 will remain conductive until the break in the contraction sensing circuit is repaired. Whenamplifier 210 conducts,visual alarm 220 will be activated and an electrical signal will be transmitted tocontroller 30 onelectrical line 15. This electrical signal clampscontroller 30 in an off state thereby preventingcontroller 30 from activating DC-DC converter 32 and thus prohibiting a cardioverting pulse being applied to the patients heart.

Regulator 36 is shown schematically in FIG. 7. It controls the application of stimulating pulses to the heart. That is, it allows stimulating pulses to be transmitted fromcapacitor 34 to the heart only when they have an energy content which is sufficient so that they are likely to be able to stimulate heart activity, but not so great so that it is likely to cause permanent heart damage. The energy content of the applied pulses is determined byregulator 36. Specifically,regulator 36 is adapted to apply a relatively low energy cardioverting pulse first, and then if that does not restore normal heart function to apply a higher energy cardioverting pulse.

Referring generally to FIG. 7,regulator 36 will allow energy fromcapacitor 34 to be applied to the heart when silicon controlled rectifier (SCR) 410 is in the conductive state andreed relay 420 is in the position designated position B. IfSCR 410 is in the nonconductive state orreed switch 422 is in the position designated position A, then energy cannot be applied fromcapacitor 34 to the heart.SCR 410 and reed switch 422 (when it is in position B) are electrically connected in series betweenelectrical line 35 and electricalline l7electrical line 17 is electrically connected tointravascular lead 16 so that it is capable of transmitting a cardioverting pulse to the heart.Reed switch 420, when it is in position A, electrically connectsEKG sensor 20 to lead 16. Specifically,reed relay 420 electrically connectsEKG sensor 20 viaelectrical line 13 to lead 16 viaelectrical line 17. Accordingly,EKG sensor 20 is electrically disconnected fromlead 16, wheneverreed switch 422 is capable of transmitting energy fromcapacitor 34 to lead 16 (position B). Conversely,EKG sensor 20 is electrically connected to lead 16 wheneverreed switch 422 is incapable of transmitting energy fromcapacitor 34 to lead 16 (position A). This isolatesEKG sensor 20 from the cardioverting pulse being applied to the heart.

Reed relay 420 is of conventional design. It comprises acoil 430 which is adapted to mechanically moveswitch 422 from one terminal to another.Coil 430 is electrically connected at one end to 6 volt power supply and at the other to aconventional Darlington amplifier 435. Whenamplifier 435 isactive, current flows from the 6 volt source throughcoil 430. This causesreed switch 422 to mechanically move from terminal A to terminal B.

SCR 410 is connected with itsinput 411 electrically connected toelectrical line 35; itsoutput 413 electrically connected to terminal B ofreed switch 422; and itsbase 415 electrically connected to a Photo-Darlington relay 440. In apreferred embodiment relay 440 is a Monsanto MCA2 solid state relay. This relay is particularly adapted to isolateSCR 410 from the other circuit components ofregulator 36. It is capable of renderingSCR 410 conductive whenever it becomes active.SCR 410 will remain conductive as long as the current path through it is not interrupted. Specifically,SCR 410 will remain conductive, once it is rendered conductive, as long asreed switch 422 is at position B or until the potential online 35 is essentially zero.

The two voltage level detectors shown generally at 460 and 480control SCR 410 andreed relay 420. More particularly, voltage level detector 460 must be active to renderSCR 410 conductive andvoltage level detector 480 must be active to movereed switch 422 to position B. Accordingly, sinceSCR 410 must be conductive and switch 422 must be at position B for energy to be transferred to the heart in the form of cardioverting pulses,detectors 460 and 480 effectively control the application of the cardioverting pulses.

The elemental unit denotedlevel detector 480 comprises programable unijunction transistor 490,zener diode 484 andresistors 482, 486, 488 and 492. Programable unijunction transistor (PUT) 490 has a gate input 491, ananode input 493, and a cathode 495. PUT 490, likePUT 320 ofcontroller 30 and PUT ofwave conformer 26, is rendered conductive thereby providing a low impedance from both the PUT anode and gate to its cathode when the anode voltage exceeds the gate voltage by a specified amount, for example, 0.7 volts.Resistor 482 andzener diode 484 are electrically connected in series betweenelectrical line 35 and the system ground.Resistors 486 and 488 are likewise electrically connected in series betweenelectrical line 35 and the system ground. The junction betweenresistor 482 anddiode 484, designatedjunction 483, is electrically connected to the gate 491 of transistor 490-the junction betweenresistor 486 and 488, designatedjunction 487, is electrically connected to theanode 493 of transistor 490. The cathode 495 of transistor 490 is electrically connected toDarlington amplifier 435 and also to the system ground throughresistor 492.

Level control 480 is voltage sensitive. It will be rendered active when the voltage onelectrical line 35 is above some predetermined level, for example, 550 volts and will remain active as long as the voltage ofline 35 remains above 550 volts.Junction 483 is held at some predetermined voltage, for example, 6.0 volts byzener diode 484 over a broad range ofelectrical line 35 voltages, for example, 6.0 to 1,500 volts.Resistors 486 and 488 form a voltage divider, thus determining the voltage at junction 487-thejunction 487 voltage bears the same relation to theelectrical line 35 voltage as the resistive value of,resistors 486 and 488. By a proper selection of the resistive values ofresistors 486 and 488 the voltage onelectrical line 35 which is required to establish a voltage atjunction 487 sufficient to render transistor 490 conductive can be easily set at 550 volts.

Level detector 480 is electrically connected in controlling relation toreed relay 420. More particularly, the cathode 495 of transistor 490 is electrically connected to thecoil 430 ofreed relay 420 throughDarlington amplifier 435. The electrical signal produced at cathode 495 of transistor 490 when transistor 490 be comes conductive is transmitted to, and sufficient for activatingDarlington amplifier 435. This will cause current to flow throughcoil 430 ofreed relay 420, thus switchingreed switch 422 from terminal A to terminal B.

The element denoted level detector 460, is elementally and functionally quite similar to that oflevel detector 480. Level detector 460 comprises programable unijunction transistor (PUT) 470,zener diode 464,

transistor 478, andresistors 462, 466, 468, 472 and 474. PUT 470 is similar to the PUT 490 oflevel detector 480.Resistor 462 andzener diode 464 are electrically connected in series betweenelectrical line 35 and the system ground.Resistors 466 and 468, and the par-' allel combination ofresistor 474 and transistor 478 are likewise connected in series betweenelectrical line 35 and the system ground. Transistor 478 is connected with itscollector 481 connected to the junction betweenresistors 468 and 474 and itsemitter 477 connected directly to the system ground. The junction betweenresistor 462 andzener diode 464 for convenience denotedjunction 463 is electrically connected to thegate 471 of PUT 470-the junction betweenresistors 466 and 468 for convenience denotedjunction 467 is electrically connected to the anode 473 ofPUT 470. The cathode475 is electrically connected toDarlington amplifier 445 and to the system ground throughresistor 472. 3

Level control 460 is voltage sensitive. It will be rendered active when the voltage onelectrical line 35 is above some predetermined level, for example 900 volts. Thejunction 463 voltage is held at some predetermined value, for example, 6.0 volts byzener diode 464. A voltage of a predetermined amount, for example, 0.7 volts above the junction 4'63 voltage is required to renderPUT 470 conductive. Thejunction 467 voltage bears the same relation to theelectrical line 35 voltage as the resistive value of the series combination ofresistor 468 and the parallel combination ofresistor 474 and transistor 478 bears to the resistive value of the series combination ofresistors 466, 468, and the parallel combination ofresistor 474 and transistor 47 8. The resistive value of the parallel combination ofresistor 474 and transistor 478 will, of course, be greater when transistor 478 is in the non-conductive state than when it is in the conductive state. Thus, the resistance of the series combination ofresistor 468 and the parallel combination ofresistor 474 and transistor 478 will be larger in relation to the resistance of the series combination ofresistors 466 and 468 and the parallel combination ofresistor 474 and transistor 478 when transistor 478 is non-conducting, than when it is conducting. Accordingly, for any givenelectrical line 35 voltage, the voltage atjunction 467 will be greater when transistor 478 is non-conductive than when transistor 478 is conductive. The resistive values oftransistors 466, 468 and 474 may be selected, so that theelectrical line 35 voltage required to renderPUT 470 conductive is 700 volts when transistor 478 is nonconductive, and 900 volts when transistor 478 is conductive. The normal state of transistor 478 is the nonconductive state.

Level control 460 is electrically connected in controlling relation toSCR 410. Specifically,cathode 475 ofPUT 470 of level control 460 is connected throughDarlington amplifier 445 and Photo-Darlington amplifier 440 to thegate 415 ofSCR 410. The electrical signal produced atcathode 475 ofPUT 470 whenPUT 470 is rendered conductive is amplified and processed byDarlington amplifiers 445 and 440. The amplified and processed signal is transmitted toSCR gate 415 and is capable of causingSCR 410 to conduct. Accordingly,SCR 410 conducts when level detector 460 is active and level detector 460 is active when the voltage onelectrical line 35reaches 700 volts if transistor 478 is non-conductive, but does not become active until theelectrical line 35 voltage reaches 900 volts if transistor 478 is conductive. Sincereed switch 422 will normally be in position B when the voltage onelectrical line 35 is above 550 volts, wheneverSCR 410 conducts, a cardioverting pulse will be applied to the patients heart.

cathode 475 ofPUT 470 is transmitted to input 591 ofcounter 590.Output terminal 595 is electrically connected tojunction 335 ofcontroller 30 viaelectrical line 19. When four electrical signals have been received at input terminal 591 ofcounter 590, an electrical signal will be provided atterminal 595 ofcounter 590. This electrical signal keepsjunction 335 at a voltage sufficiently high so thatcontroller 30 is disabled.Controller 30 cannot now activate DC-DC converter 32.Terminal 596 ofcounter 590 is connected to areset circuit 500. When a positive electrical pulse is received atterminal 596, counter 590 will be reset to the zero state (the state in which there is no output signal from counter 590).

In the preferred embodiment thecounter 590 is electrically connected viaoutput terminals 592, 593 and 594 to thebase 479 of transistor 478 in such a manner that the signal fromcounter 590 corresponding to each and every electrical input signal at input terminal 591 will render transistor 478 conductive.

As discussed above, the conduction or nonconduction of transistor 478 determines whether the cardioverting pulse applied to the heart is of a 700 or a 900 voltage magnitude. Transistor 478 is nonconductive whencounter 590 is in the zero state and conductive whencounter 590 is in any other state. Accordingly, the first cardioverting pulse applied to the patients heart will have a 700 volt' magnitude, and if that does not restore normal heart activity each succeeding pulse will have a 900 volt magnitude.

Reset circuit 500 comprisesinverters 510, 530 and 550,diode 512,resistors 514 and 526,capacitor 516,transistor 520 andnand gate 540. The inverters and the nand" gate are of conventional design. The input ofinverter 510 is electrically connected to thecathode 475 ofPUT 470 and the output is electrically connected to one side ofdiode 512. The other side ofdiode 512 is electrically connected to input terminal 542 of nand"gate 540. It is also electrically connected throughresistor 514 to the 4 volt power supply and throughcapacitor 516 to the system ground.Transistor 520 is connected having itsbase 521 electrically connected toelectrical line 15, itsemitter 525 electrically connected to the system ground, and itscollector 523 electrically connected throughresistor 526 to the 4 volt power source. Theemitter 523 oftransistor 520 and one side ofresistor 526 are electrically connected to the input side ofinverter 530. The output side ofinverter 530 is connected to input terminal 544 ofnand gate 540. Theoutput terminal 546 of nand"gate 540 is electrically connected throughinverter 550 to inputterminal 5960f counter 590.

Reset circuit 500 will reset counter 590 to the zero state whenever an electrical pulse corresponding to a normal heartbeat is received from sensingcircuit 10 onelectrical line 15.Circuit 500 is capable of differentiating between the heart activity associated with a normal heartbeat and the activity-induced by a cardioverting pulse being applied to the heart.Circuit 500 is nonresponsive to the induced heart activity, but responsive to the normal heart activity and capableof resetting counter 590 to the zero state in response thereto.

Each electrical pulse corresponding to a normal heartbeat produced by sensingcircuit 10 is transmitted to thebase 521 oftransistor 520. This pulse causestransistor 520 to conduct which allows current to flow throughresistor 526 andtransistor 520 to the system ground as long astransistor 520 is conductive, and thus lowers the voltage at theinput 531 ofinverter 530 for this time period. This negative pulse is inverted into a positive pulse byinverter 530 and transmitted to input 544 ofnand gate 540.Nand gate 540 will invert this pulse and transmit the inverted pulse toinverter 550, provided the voltage atinput 542 is not decreased. The voltage atinput 542 is decreased only when a pulse is received from an active level detector 460 which occurs only when a cardioverting pulse is applied to the patients heart. Specifically, when level detector 460 is active a positive pulse of short durationis transmitted toinverter 510 where it is inverted and transmitted on throughdiode 512. This negative pulse being transmitted throughdiode 512 allowscapacitor 516 to discharge thus decreasing the voltage input atterminal 542 of andgate 540 for a period of time equal to the time required to rechargecapacitor 516 from the 4 volt power source throughresistor 514. This period of time typically is of a long enough duration so that it keeps the voltage atterminal 542 depressed during the time in which the heart activity induced by the cardioverting pulse is exhibited.

Inverter 550 inverts the negative pulse received fromgate 540 into a positive pulse which is transmitted to theinput 596 ofcounter 590. This pulse is sufficient to reset counter 590 to the zero state. In this manner, resetcircuit 500 differentiates between a normal heart activity and the activity induced by a cardioverting pulse and resets counter 590 to the zero state when the heart activity is normal.

The apparatus of this invention comprises a sensing means 10 for monitoring heart activity and a stimulation means 12 for applying a shock to the patients heart of sufficient magnitude to restore normal heart activity. The sensing means 10 controls the stimulation means 12 allowing the stimulation means 12 to apply a cardioverting shock to the heart only after normal heart activity has ceased. Upon monitoring life threat ening arrhythmias, the apparatus of this invention automatically cardioverts the patients heart.

As shown in FIG. 1, sensing means 10 includesEKG sensor 20,contraction sensor 22, orgate 24, andwave conformer 26. TheEKG sensor 20 amplifies the R wave signal detected byelectrical lead 16 corresponding to normal sinus rhythm of the human heart and filters out all other heart electrical activity. Thecontraction sensor 22 is responsive to the heart contractions detected byelectrical lead 16 and is adapted to provide an electrical signal corresponding to each heart contraction.Gate 24 is constructed so that it provides an electrical output signal whenever it receives an electrical signal from either thecontraction sensor 22 or theEKG sensor 20, or both. Consequently, if either thecontraction sensor 22, relying on detected heart contraction, or theEKG sensor 20, relying on detected R waves or both provide an electrical signal togate 24 corresponding to a normal heartbeat,gate 24 will provide an electrical signal in the form of a pulse corresponding to the heartbeat.Wave conformer 26 is adapted to transform these electrical pulses received fromgate 24 which have varying amplitudes and widths into pulses having substantially the same pulse width and amplitude. Accordingly, sensing means 10 is responsive to each normal sinus heartbeatdetected by intravascularelectrical lead 16 in the form of an R wave or as a heart contractionand is adapted to provide an electrical pulse having a predetermined pulse amplitude and pulse width corresponding with each detected heartbeat.

Stimulation means 12 is adapted to apply electrical pulses to the heart viaintravascular lead 16 for cardioverting a malfunctioning heart. These cardioverting pulses are not applied immediately upon the sensing of abnormal heart functioning, but their application is delayed for a period of time. This delay gives the heart the opportunity to convert to normal heart functioning, if it is able to do so. Stimulation means 12 applies a cardioverting pulse having a low energy content first, and then, if that pulse does not restore normal heart functioning, cardioverting pulses having higher energy content will be applied until the heart resumes normal functioning or the cardioverter is automatically disabled.

As shown in FIG. 1, stimulation means 12 includescontroller 30, DC-DC converter 32,capacitor 34,regulator 36, andalert system 40. Stimulation means 12 is electrically connected to sensing means 10 by an electrical connection betweenwave conformer 26 of sensing means 10 andcontroller 30 of stimulation means 12 and tointravascular lead 16 viaelectrical line 17.

Controller 30 functions much like a timing device. Specifically, it provides an electrical signal if a predetermined period of time, for example, seconds has elapsed without an electrical signal being received fromwave conformer 26.Controller 30 continues to supply an electrical signal until it receives an electrical signal fromwave conformer 26 corresponding to normal heart functioning. This electrical signal activatesalert system 40 comprising both a visual and an audio alarm and activates DC--DC converter 32.Converter 32 is electrically connected tocapacitor 34 and capable of chargingcapacitor 34 to a 1,000 volt level.

Converter 32 is a DC-DC converter of conventional design which is capable of increasing the power supply 33 voltage from 6 volts to 1,000 volts. Voltages in the 700-1,000 volt range are necessary to charge capacitor storage means 34 to a sufficient level so that it is capable of providing cardioverting pulses of the necessary magnitude. It takes a predetermined period of time, for example -15 seconds, to charge capacitor means 34 to the necessary level. However, any normal heartbeat during this interval will deactivate controller which will then disableconverter 32 and thus stop the charging cycle of energy storage means 34.

Accordingly,capacitor 34 is charged to the level required for cardioverting within l5-20 seconds (five second delay incontroller 30 plus the 10-15 seconds needed to charge capacitor 34) following the last sensed normal heartbeat. 7

Regulator 36--electrically connected betweencapacitor 34 and intravascular lead l6controls the application of energy fromcapacitor 34 to the patients heart. It determines the energy content of the applied pulses, allowing only pulses to be applied when they have an energy content which is likely to be sufficient to stimulate heart activity.

The functional operation of stimulation means 12 can be best described with reference to the voltage diagram of FIG. 8-a chronological description of the operation is possible using this diagram in explaining the differences between the first pulse generated and suceeding pulses. All times and waveforms are merely illustrative- -the actual times and waveforms depend upon the particular components and component values used. FIG. 8 shows the voltage waveforms representing the voltage oncapacitor 34, the state ofreed switch 422, the state ofSCR 410, and the voltage applied to the patients heart. Specifically, waveform (a) shows the voltage oncapacitor 34 as represented by theelectrical line 35 voltage; waveform (b) shows the times when a voltage is applied acrosscoil 430 ofreed relay 420 as represented by the voltage at cathode 495 of control PUT 490 inregulator 36; waveform (c) shows the times when a voltage signal is applied togate 415 ofSCR 410 as represented by the voltage atcathode 475 ofPUT 470 inregulator 36; and waveform (d) shows the voltage waveform of the pulse applied to the patients heart as represented by the voltage atelectrical line 17.

The active operation of stimulation means 12 begins when a pulse representing normal heart activity has not been received from sensing means 10 for 5 seconds. When this occurscontroller 30 becomes active supplying an electrical signal toconverter 32.Converter 32 becomes active andcharges capacitor 34.Ittakes converter 32 approximately 9 seconds to chargecapacitor 34 to the 550 volt level. Whencapacitor 34 becomes charged to the 550 volt level (line 601 in FIG. 8) PUT 490 oflevel control 480 becomes active thus switchingreed relay 420 to position B. It takesconverter 32 an additional three seconds to chargecapacitor 34 to the 700 volt level. When this occurs (line 602 in FIG. 8) PUT 470 of level control 460 becomes active thus renderingSCR 410 conductive. Withreed switch 422 in position B andSCR 410 conductive,capacitor 34 has a discharge path through the patients heart.Capacitor 34 begins to discharge immediately uponSCR 410 being rendered conductive (line 602, FIG. 8) and discharges through the patients heart untilreed switch 422 is switched to position A (line 603, FIG. '8).Reed switch 422 is switched to position A when thecapacitor 34 voltage is reduced to the 500 volt level. Accord ingly, 17 seconds (5 sec. 9 sec. 3 sec.) following the I last sensed normal heart activity a cardioverting pulse is applied to the patients heart. This cardioverting pulse is in a truncated capacitive discharge waveform having a peak magnitude of 700 volts and being truncated at the 500 volt level.

If this first cardioverting pulse stimulates normal heart activity, sensing means 10 senses the resumed normal heart activity and disables stimulation means 12-but if this first pulse did not stimulate normal heart activity, a second cardioverting pulse is needed and is supplied by stimulation means 12. Assuming that normal heart activity has not been restored,controller 30 will become active again 5 seconds following the first cardioverting pulse. This occurs since the contraction sensing portion of sensing means 10 is responsive to the heart contraction caused by the cardioverting pulse. The pulse it generates which corresponds with the cardioverting pulse deactivatescontroller 30. It takes 5 seconds forcontroller 30 to be activated again.Capacitor 34 is still charged to nearly 500 volts 5. seconds after the first cardioverting pulse (line 604, FIG. 8). Thus it will take only 1 second to charge capacitor to the 550 ductive as a result of the first applied pulse. It takes approximately seconds to chargecapacitor 34 to the 900 volt level required to renderSCR 410 conductive (line 606, FIG. 8). Once the 900 volt level is reachedSCR 410 becomes conductive andcapacitor 34 discharges untilreed switch 422 is switched to position A. Accordingly, I 1 seconds (5 sec. 1 sec. 5 see.) after the first cardioverting pulse a second cardioverting pulse also having a truncated capacitive discharge waveform is applied to the heart.

The second applied pulse has a greater energy content than the first pulse. The energy content is greater as the peak voltage of the second pulse (900 volts) is greater than the peak voltage of the first pulse (700 volts) and both pulses truncate at 500 volts.

If thesecond cardioverting pulse stimulates normal heart activity, sensing means 10 will sense this and disable stimulation means 12. If not, a third cardioverting pulse which is similar to the second pulse will be applied in a manner similar to that of the second pulse. If the third pulse still does not restore normal heart functioning, stimulation means 12 will be disabled automatically.

Although the invention has been described with reference to a particular embodiment it will be understood that this embodiment is merely illustrative of the applications of the principles of this invention. It will be further understood that numerous modifications in the inventive embodiment may be made and other arrangements may be devised without departing from the spirit and scope of this invention.

By suitable modifications in the inventive circuitry many modifications in the functional operation of the invention can be achieved. For example, a P-wave amplifier could be used instead of the described R-wave amplifier inEKG sensor 20. A gating means which is nonresponsive to electrical signals having a repetitive rate greater than a predetermined amount could be used in place of or in addition to or gate 64 to discriminate against certain types of tachyarrhythmias and thus allow a cardioverting pulse to be applied when the heart is functioning in this manner. A dynamic heart characteristic such as heart pressure could be monitored instead of either EKG or heart contractions. Additionally, each cardioverting pulse could have an increased energy content; the time between cardioverting pulses could be decreased for additional applied cardioverting pulses; or the cardioverting pulse could be applied using an intravascular lead which is distinct from the intravascular lead which is used to sense heart activity. v

Many substitutions may, of course, be made in the circuit elements used in the inventive circuit without materially affecting the operation of the invention. For example, two independent power sources could be used instead of having a 6 volt battery drive or 4 volt constant voltage .source; various arrangements of SCRs and/or transformers as well as solid state switching devices could be used to control the transmission of the cardioverting pulse to the patients heart instead of the particular arrangement of an SCR and 'a reed relay actually used; and devices of various types could be used to perform the level detecting function performed bylevel detectors 460 and 480. Many more examples are possible-the above-listing is anything but exhaustive.

We claim:

1. Heart contraction sensing and stimulation circuit comprising:

a. first detecting means responsive to a change in a monitored electrical parameter produced by the normal beating action of the heart for providing a first identifiable electrical signal corresponding with each heart contraction;

b. second detecting means responsive to monitored heart electrical activity corresponding to heart contractions for providing a second identifiable signal corresponding with each heart contraction;

c. gating means electrically connected to receive electrical signals from said first and second detecting means, said gating means for providing an electrical output signal in response to either of said identifiable electrical signals produced by a single heart contraction;

(1. electrical energy storage means capable of storing sufficient energy to cardiovert a malfunctioning heart;

e. electrical energy source means;

f. control means connected in controlling relation to said energy storage means and said energy source means and operatively. connected to said gating means and responsive thereto, said control means for controlling the transmission of electrical energy from said source means to said storage means only in the absence of electrical signals from both the first and second detecting means for a predetermined period of time;

g. output means adapted for connection to the heart;

h. regulating means connected in controlling relation to said energy storage means, said regulating means for permitting energy to be transmitted from said storage means to said output means when the en-' ergy stored by said storage means becomes greater than a predetermined level.

2. Heart contraction sensing and stimulation apparatus comprising: 7

a. first heart monitoring means being in the form. of an elastomer body means having conductive particles imbedded therein and exhibiting a change in electrical impedance upon flexing, the body means including means adapted to be positioned adjacent heart muscle so that each heart contraction causes the body means to flex thereby changing its impedance;

b. first detecting means responsive to a change in impedance of said elastomer body means for providing a first identifiable electrical signal corresponding with each heart contraction;

c. second heart monitoring means in the form of conductive electrode means being adapted for insertion within the human vascular system and positioned adjacent the heart for monitoring heart electrical activity and transmitting electrical energy to the heart,

d. second detecting means responsive to the monitored heart electrical activity corresponding to heart contractions for providing a second identifiable signal corresponding with each heart contraction;

e. gating means electrically connected to receive electrical signals from said first and seconddetecting means, said gating means for providing an electrical output signal in response to either of said identifiable electrical signals produced by a single heart contraction;

f. electrical energy storage means capable of storing sufficient energy to cardiovert a malfunctioning heart;

g. electrical energy source means;

h. control means electrically connected in controlling relation to said energy storage means and said energy source means and operatively connected to said gating means and responsive thereto, said control means for controlling the transmission of electrical energy from said source means to said storage means only in the absence of both said first and second identifiable signals for a predetermined period of time;

i. regulating. means electrically connected to said electrode means and further connected in controlling relation to said energy storage means, said regulating means for permitting transmission of energy from said storage means to said electrode means when the energy stored by said storage means is greater than a predetermined level; and

j. disabling means electrically connected to said first monitoring means for sensing a break in the electrical circuitry of said first monitoring means, said disabling means for preventing electrical energy from being delivered to said electrodes when such a break occurs.

3. The apparatus ofclaim 2 further comprising flexible enclosure means substantially inert in living body fluids and tissue, the enclosure means being adapted for insertion within the vascular system of a living animal, the enclosure means further for enclosing, at least some of, the apparatus elements, thereby sealing them from living body fluids and tissues.

4. The apparatus ofclaim 2 wherein the second monitoring means includes two conductive electrode means, one of the electrode means being adapted to be positioned within the heart and the other electrode means being adapted to be positioned outside the heart to monitor heart electrical activity produced by the natural beating action of the heart.

5. The apparatus ofclaim 2 wherein the second detecting means includes discrimination means, said discrimination means for responding to the heart electrical activity produced by the natural beating action of the heart while discriminating against the heart electrical signals produced by an abnormally functioning heart and those artificially induced by a heart pacing device.

6. The apparatus ofclaim 2 wherein said gating means includes a conforming means, said conforming means for transforming the pulses having varying amplitudes and widths into pulses having substantially the same pulse amplitude and pulse width.

7. The apparatus ofclaim 2 wherein said control means has a transmitting and a non-transmitting state and includes a timing means for maintaining said control means in the non-transmitting state for a predetermined time interval following each signal received from said gating means. i

8. The apparatus of claim 7 wherein the timing means includes capacitive means for switching said control means from the non-conductive state to the conductive state when said capacitive means becomes charged above a predetermined level, said capacitive means being operatively connected to said gating means so that a signal from said gating means causes the capacitive means to discharge rendering said control means non-conductive.

9. The apparatus ofclaim 2 further comprisinga counting means operatively connected to said energy storage means for disabling the transmission of electrical pulses from said energy storage means to said electrode means after a predetermined number of electrical pulses have been transmitted without an intervening heart contraction having been detected by said first or second detecting means.

10. The apparatus ofclaim 2 wherein the regulating means includes multiple level control means, said level control means being constructed and arranged such that energy will begin being transmitted from said energy storage means to said electrodes when the energy stored by said storage means is above a certain first predetermined level and will cease being transmitted when the stored energy becomes less than a second lesser predetermined level, thereby causing the energy stored by said storage means to be transmitted to said electrodes in a truncated capacitive: discharge electrical pulse waveform.

11. The apparatus ofclaim 2 wherein the regulating means. includes means for setting the time interval between the generation of the latest pulse from said gate means and the generation of the first electrical pulse transmitted to said electrode means so that said time interval is substantially greater than the time interval between each of the succeeding electrical pulses transmitted to said electrodes, during the time interval in which no pulses are provided by said gate means.

12. The apparatus ofclaim 2 wherein the regulating means includes means for increasing the energy content of all but the first electrical pulse of the series of pulses transmitted to said electrodes during the time interval in which there is an absence of normal heart contractions.

13. In an automatic cardioverting system comprising intravascular electrical lead means having electrodes adapted for transmitting electrical pulses to the heart of a living animal, sensing means including electrically conductive means within said lead means and flexible therewith for sensing the action of a heart contration upon said lead means, means electrically connected with and responsive to said sensing means for continuously monitoring heart activity and producing an identifiable electrical signal corresponding to each sensed heart contraction, and stimulation means responsive to the identifiable signal and operatively connected to said intravascular lead for providing cardioverting shocks to said electrodes, the improvement comprising:

conductive means or its electrical circuitry.

Claims (13)

1. Heart contraction sensing and stimulation circuit comprising: a. first detecting means responsive to a change in a monitored electrical parameter produced by the normal beating action of the heart for providing a first identifiable electrical signal corresponding with each heart contraction; b. second detecting means responsive to monitored heart electrical activity corresponding to heart contractions for providing a second identifiable signal corresponding with each heart contraction; c. gating means electrically connected to receive electrical signals from said first and second detecting means, said gating means for providing an electrical output signal in response to either of said identifiable electrical signals produced by a single heart contraction; d. electrical energy storage means capable of storing sufficient energy to cardiovert a malfunctioning heart; e. electrical energy source means; f. control means connected in controlling relation to said energy storage means and said energy source means and operatively connected to said gating means and responsive thereto, said control means for controlling the transmission of electrical energy from said source means to said storage means only in the absence of electrical signals from both the first and second detecting means for a predetermined period of time; g. output means adapted for connection to the heart; h. regulating means connected in controlling relation to said energy storage means, said regulating means for permitting energy to be transmitted from said storage means to said output means when the energy stored by said storage means becomes greater than a predetermined level.

2. Heart contraction sensing and stimulation apparatus comprising: a. first heart monitoring means being in the form of an elastomer body means having conductive particles imbedded therein and exhibiting a change in electrical impedance upon flexing, the body means including means adapted to be positioned adjacent heart muscle so that each heart contraction causes the body means to flex thereby changing its impedance; b. first detecting means responsive to a change in impedance of said elastomer body means for providing a first identifiable electrical signal corresponding with each heart contraction; c. second heart monitoring means in the form of conductive electrode means being adapted for insertion within the human vascular system and positioned adjacent the heart for monitoring heart electrical activity and transmitting electrical energy to the heart, d. second detecting means responsive to the monitored heart electrical activity corresponding to heart contractions for providing a second identifiable signal corresponding with each heart contraction; e. gating means electrically connected to receive electrical signals from said first and second detecting means, said gating means for providing an electrical output signal in response to either of said identifiable electrical signals produced by a singlE heart contraction; f. electrical energy storage means capable of storing sufficient energy to cardiovert a malfunctioning heart; g. electrical energy source means; h. control means electrically connected in controlling relation to said energy storage means and said energy source means and operatively connected to said gating means and responsive thereto, said control means for controlling the transmission of electrical energy from said source means to said storage means only in the absence of both said first and second identifiable signals for a predetermined period of time; i. regulating means electrically connected to said electrode means and further connected in controlling relation to said energy storage means, said regulating means for permitting transmission of energy from said storage means to said electrode means when the energy stored by said storage means is greater than a predetermined level; and j. disabling means electrically connected to said first monitoring means for sensing a break in the electrical circuitry of said first monitoring means, said disabling means for preventing electrical energy from being delivered to said electrodes when such a break occurs.

3. The apparatus of claim 2 further comprising flexible enclosure means substantially inert in living body fluids and tissue, the enclosure means being adapted for insertion within the vascular system of a living animal, the enclosure means further for enclosing, at least some of, the apparatus elements, thereby sealing them from living body fluids and tissues.

4. The apparatus of claim 2 wherein the second monitoring means includes two conductive electrode means, one of the electrode means being adapted to be positioned within the heart and the other electrode means being adapted to be positioned outside the heart to monitor heart electrical activity produced by the natural beating action of the heart.

5. The apparatus of claim 2 wherein the second detecting means includes discrimination means, said discrimination means for responding to the heart electrical activity produced by the natural beating action of the heart while discriminating against the heart electrical signals produced by an abnormally functioning heart and those artificially induced by a heart pacing device.

6. The apparatus of claim 2 wherein said gating means includes a conforming means, said conforming means for transforming the pulses having varying amplitudes and widths into pulses having substantially the same pulse amplitude and pulse width.

7. The apparatus of claim 2 wherein said control means has a transmitting and a non-transmitting state and includes a timing means for maintaining said control means in the non-transmitting state for a predetermined time interval following each signal received from said gating means.

8. The apparatus of claim 7 wherein the timing means includes capacitive means for switching said control means from the non-conductive state to the conductive state when said capacitive means becomes charged above a predetermined level, said capacitive means being operatively connected to said gating means so that a signal from said gating means causes the capacitive means to discharge rendering said control means non-conductive.

9. The apparatus of claim 2 further comprising a counting means operatively connected to said energy storage means for disabling the transmission of electrical pulses from said energy storage means to said electrode means after a predetermined number of electrical pulses have been transmitted without an intervening heart contraction having been detected by said first or second detecting means.

10. The apparatus of claim 2 wherein the regulating means includes multiple level control means, said level control means being constructed and arranged such that energy will begin being transmitted from said energy storage means to said electrodes when the energy stored by said storage means is above a certain first predetermined level and Will cease being transmitted when the stored energy becomes less than a second lesser predetermined level, thereby causing the energy stored by said storage means to be transmitted to said electrodes in a truncated capacitive discharge electrical pulse waveform.

11. The apparatus of claim 2 wherein the regulating means includes means for setting the time interval between the generation of the latest pulse from said gate means and the generation of the first electrical pulse transmitted to said electrode means so that said time interval is substantially greater than the time interval between each of the succeeding electrical pulses transmitted to said electrodes, during the time interval in which no pulses are provided by said gate means.

12. The apparatus of claim 2 wherein the regulating means includes means for increasing the energy content of all but the first electrical pulse of the series of pulses transmitted to said electrodes during the time interval in which there is an absence of normal heart contractions.

13. In an automatic cardioverting system comprising intravascular electrical lead means having electrodes adapted for transmitting electrical pulses to the heart of a living animal, sensing means including electrically conductive means within said lead means and flexible therewith for sensing the action of a heart contration upon said lead means, means electrically connected with and responsive to said sensing means for continuously monitoring heart activity and producing an identifiable electrical signal corresponding to each sensed heart contraction, and stimulation means responsive to the identifiable signal and operatively connected to said intravascular lead for providing cardioverting shocks to said electrodes, the improvement comprising: disabling means electrically connected to said sensing means for sensing a break in said electrically conductive means and its electrical connection with said monitoring means, said disabling means for preventing cardioverting shocks from being transmitted from said stimulating means to said electrode upon sensing a break in said electrically conductive means or its electrical circuitry.

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