CA1119671A

CA1119671A - Method of and apparatus for automatically detecting and treating ventricular fibrillation

Info

Publication number: CA1119671A
Application number: CA000336065A
Authority: CA
Inventors: Leslie A. Geddes; Joe D. Bourland; Reese S. Terry
Original assignee: Purdue Research Foundation
Current assignee: Purdue Research Foundation
Priority date: 1978-09-21
Filing date: 1979-09-20
Publication date: 1982-03-09
Also published as: EP0074126A3; US4291699A; EP0074126A2; JPS619862B2; EP0009255A1; JPS56109673A; EP0009255B1

Abstract

ABSTRACT OF THE DISCLOSURE
Method of and apparatus for automatic defibrillation of the cardiac ventricles of a heart wherein both the mechanical and electrical activities of the ventricles are sensed and used as operating inputs to the controls. Electrical activity is detected and measured with a pair of electrodes, and the waves of an electro-cardiogram (ECG) are analyzed. When such electrical analysis indicates that ventricular fibrillation is present and persists, an electrical circuit is actuated for detecting mechanical pumping activity of the heart. Mechanical pumping activity is measured by the change in impedance between the pair of electrodes in one of the ventricles. The change of ventricular impedance is caused by the varying volume of blood contained within the ventricle and depends upon whether the ventricle is in a contracted or a relaxed state. The defibrillator is actuated only when both the mechanical and electrical activity of the ventricle indicates a need for defibrillation. Because some conditions may be encountered which closely resemble ventricular fibrillation, the defibrillator quantitatively proprograms and weighs the relative importance of the electrical and mechanical signals from the heart.

Description

1 BACKGROUND OF THE INvENrr~()N
Ventricular ~ibrillatiorl is a liEe-threatenin~ cardiac arrhythmia resulting in the immediate loss of ~lood pressure.
Fibrillation must be treatedwithin minutes of its onset, or the patient may die. The o~ly ef-Eective treatment of ventricular fibrillation is the delivery of an adequately strong electic shock to the ventricles of the heart. At: present, th~re exist~ an iden-tifiable population of patients ~ho survive an episode oE ventri cular fibrillation, because of prompt therapy. Although these patients may survive their first episode of ventricular ~i~rill-ation, due to the efforts of emergency resuscitation -teams, their long-term prognosis is very poor. For these patients, who are becoming more identiEiable, an alternative treatment is implant ation of an automatic defibrillator. A major obstacle to be over-come in the creation of such a device is development of the low p~r demand device and a relia~le detection circuit to identify accurately v~ntricular fibrillation. It would, therefore, be desirable to provide an automatic implantable defibrillator incorp~
orating a reliable detection circuit that quantitatively prepro-:` :
grams and weighs multiple ~ignals received from the heart beforea defibrillatory shock is delivered to the cardiac ventricles.
When functioning normally~ the muscle fiber~ of the heart are stimulated hy a ~ave-like electrical excitation that originates in the sino-atrial node in the right atrium, The excitation proceeds ~ia the atrium of the heart to the ventricles.
The wave-like excitation txiggers the ventricular muscle fibers by causing a sequential depolarization of adjacent cells~ thu~
creatin~ an efficient contraction and pumping action, i.e., proper mechanical aativity. Under certain conditions, e g., partial deprivat1on~of~the oxygen supply~to parts of the heart, this organized wave-liXe pattern is interrupted and ~ibrillation, a :

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disorganiæed, random contraction and relaxation of the fibers of the ventricular muscle can result; this is fibrillation. Duriny ventricular fibrillation, the muscle fibers are electricall~
depolarizin~ and repolarizing in random fashion, resulting in a chaotic twitching of the ventricular musclé, with the resul-t that no effective pumping of blood is accomplished. By applying a suitable discharge of electrical current to the ventricular muscle fibers, it is possible to depolarize enough of the fibers at once to re-establish synchrony, th-us enabling the ventricles to resume the normal rhythmic pumping.
Defibrillation as it is used today :in emergency situa-tions generally employs two electrodes placed on the chest of a patient. An electrical current is discharged through the electrodes and defibrillation of the heart is acco~plished. It ~ is well known that within minutes of the onset of ventricular -~ fibrillation, irreversible changes start to occur in the brain and other vital organs; hence it is desirable to effect defibril-lation as promptly as possible. Therefore, a reliable automatic defibrillator is desirable because of the need to terminate fibrillation promptly. It is not reasonable to expect that a trained hospital attendant will be present to aid a patient experiencing ventricular fibrillation.
Automatic çardiac defibrillator devices, which sense and analyze the electrical activity of the heart, are known in the art such as shown by U.S. Patent No. 3,8~7,398. The electrical activity of the heart has typically been detected by a pair of electrodes placed in or around the heart. Such a ,:
method enables detection of an electrocardiogram (ECG) showing a record of R and T wa~eforms or complex indicating stages of electrical depolarization and repolarization of the ventricles of the heart. However/ those devices which sense electrical activity alone have not been proven reliable, since many types of ~; arrhythmia, i.e~, a rapid beating of the heart, may mimic

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ventricular fibrillation and may deceive a detector monitoring only -the electrical activity o~ the ven-tricles and cause it -to deliver an unnecessar~ defibrillatory shock. With the relatively high current levels required to defibrillate the cardiac ~ ventricles, it is imperative that no defibrillatory shock be ; delivered unless necessary. If the cletecting system should make a false positive decision, i.e., diagnose the presence of ventricular fibrillation when it is, in fact, not present, the patient will unnecessarily experience an uncomfor-table, perhaps painful and possibly harmful electric shock. If the detector should arrive at a false ne~ative decision, i.e., fail to recognize the presence of ventricular fibrillation, the patient will probably die.
Automatic cardiac defibrillator devices which sense not only the electrical activity but also the mechanical activity oE
the heart are also well known in the art. Such devices have typically utilized an ECG in con~unction with one of the many methods known in the art for measurement of ventricular mechani-cal activity. Developmen-t of devices for measuring stroke volume are briefly discussed in an article by Geddes et al. titled "Continuous Measurement of ~entricular Stroke Volume by Electrical Impedance," (pages 118-131) appearing in the April-June 1966, Cardiovascular Research Center Bulletin published by Baylor University College of Medicine.

The electrical impedance method of measuring ventri-cular stroke volume has been recognized for a numher of years as an efEective method of instantaneously detecting mechanical pumpi~ng activity of the heart. It is well ~nown that the resistance of a conductor depends upon the resistivity of its component material, and var es with~ the length, and inversely with the cross-sectional area. If the length is kept constant and the amount of ¢onducting mAterial between a paix of electrodes is varied, the resis-tance varies accordingly. Since the apex-base ~0 (AMADA
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length o~ the hear-t ~emains substan-tially cons-tant cluring systole, -the resistance measurecl between a pair of electrodes inserted in-to the base ~nd apex of a ventricle varies inversely with cross-sectional area. ~urther, s:Lnce the conductivity of the conductive material (blood) is more than five times that of cardiac muscle, -the majority o~ the current between the pair of electxodes is con~ined to the bloc)d within the ventricle. Thus a decrease in diameter during systole decreases the cross-sectional area of the blood between the electrodes and increases the resistance measured between the eleckrodes inserted into the cavity at the apex and base oE the heart. The blood in the ventricle constitutes, therefore, a condwctor of irregular and changing shape, establishing a definite relationship between the changes in impedance and in volume during a cardiac cycle. A
further understanding o~ the continuous measurement of ventricular stroke volume by electrical impedance is contained in the above article, which is hereby incorporated herein by reference.
Workers in the field have utilized and combined the teachings described in the article ~ith the circuitry of an ECG
for automatically detecting fibrillation. Heilman et al., U.S.
Patent No. 4,030,50~, issuing June 21, 1977, also describe the placing of base and apex electrodes around portions of the heart for discharging energy. The use of an electrode covering the apex of the heart in combination with a superior vena cava ; catheter elec-trode is also described in the literature. All of the devices for measuring ventricular stroke volume by electrical impedance have required either a thoracotomy or a laparotomy.
In either procedure the heart itself must be surgically exposed.
Pressure transducers attached to a catheter introduced into the heart via the superior vena cava have been employed for measuring cardiac mechanical activity, but such transducers have proven susceptible to mechanical failure and to premature disintegration during the high-current levels delivered for ; .
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defibrillation. It woul~, ~hereEore, be deslrable to employ a single catheter imp:Lantable in the right ventricle of a heart by insertion through a superficial vein, or the superior vena cava, in the right atrium thereby decreasing surgical risk and trauma to the patient and having a pluralit~ of electrodes for detect-ing and measuring ECG signals, for detectlng and measuring ventricular stroke volume by electrical impedance, and for discharging a defibrillatory shoc]c to the heart.

SUMMA Y OF THE INVEN_ION
The present invention rela-tes generally to cardiac defibrillators and, more particularly, to an automatic defibril-lator of the type wherein both the mechanical and electrical activity of a heart are sensed and used to control the delivery of a defibrillating shock to the heart and to a method o automatically defibrillating the cardiac ventricles.
Briefly, the present invention relates to a method of and apparatus for automatic cardiac defibrillation wherein both electrical and mechanical activity of the ventricles of the heart are measured with the mechanical activity or absence thereof being sensed only at such time when the electrical activity sensor indicates possible presence of a fibrillatory condition in the ventricular myocardium. A catheter having a pair of electrodes on the distal portion thereof is insertable into the right ventricle of a heart. A third electrode located on the .:
catheter lies in the superior vena cava. Leads from the pair of electrodes on the catheter communicate with either an implantable defibrillator control unit or an extracorporeal unit containing electriGal circuits for sensing electrical R-wave activity, i.e., the electrical signal (ECG) of the ventricles and, upon command, ,: ~: :
; for sensing the existing impedance between the pair of electrodes in the right ventricle thereby sensing mechanical pumping activity. The EC~ and impedance circuits generate output voltages :

1 which are Eed into a log;c control circuit: that commands the defibrillator to generate a defibrillatory shock when both mechanical ancl electrical activity sensors indi~ate the presence of a fibrillatory condition. Part of the logic control circuit includes a missing-pulse detector whieh delays actuation of the meehanical activity sensor until the electrical siynals indicate eritieal fibrillatory activity of a predeterminecl character and extent, thus reducing the power requirement for the device.

One of the impor-tant features of the present invention is to preelude eontinuous sensing by the mechanical activity sensor beeause of its relatively increased power requirements, substitutin~ instead a "power on" whieh seleetively eommenees and terminates heart surveillance by the meehanieal aetivity sensor, limiting sueh aetivities to intermittent surveillanee and thus obviating increased power demands whieh would otherwise be required. The deviee is readily usable ~or ambulatory surveillanee and for implantation. The defibrillating shoek is delivered hetween the third eleetrode in the superior vena eava and the pair of eleetrodes in the right ventricle t the pair of eleetrodes being electrieally eonneeted during defibrillation. The third eleetrode in the superior ~ena eava ean be replaeed by an eleetrode loeated elsewhere within the body. In faet, the metal ease of the automatie de~ibrillator ean eonstitute this electrode. ~n important ~eature of the present invention is the implantation of ECG and impedanee sensors wlthin the right ventricle in order to obtain more reliable information, whieh is relatively free from extraneous signals derived, ~or example, from respiration~ skeletal museular eontraetions, and other spurious signals whieh ean be sensed as inadvertent signal.

~ 6 -Accordingly, an ohject of the present invention is to provide an automatic cardiac defibrillator wherein both the mechanical and electrical activity of the heart are quantitati~ely measured and utilized to trigger defibrillation and a mekhod of defibrillating the cardiac ventricles.
Another object of the present invention is to provide a cardiac defibrillator having a more reliable detection circuit for detecting ventriculax mechanical activity than currently available and to a method of preprogramming an ECG signal with an impedance siynal representing mechanical activity.
Another object of the present invention is to provide a cardiac defibrlllator with a ventricular mechanical activity sensor having a pair of spaced electrodes suspended in a ven-tricle of the heart for measuring stroke volume.
Another object of the present invention is to provide a cardiac defibrillator having a combination ventricular elec-trical and mechanical activity sensor of simplified construction to facilitate impIantation thereof.
Another object of the present invention is to provide ~

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a cardiac defibrilla-tor wi-th a catheter extending into the super.ior vena cava and into the right ventricle of the heart and having a pair of electrodes in the ventricle and a third elec-trode in the vena cava and a method for sensing electrical (ECG) and mechanical (pumping) activities with the pair of electrodes and for connecting or shorting the pair of electrodes when criteria delivered to an accumulalor circuit i5 accepted and delivering a defibrillator~ shock to the heart through the pair of shorted electrodes and the third electrode.
Another object oE the present in~ention i6 to pro~ide a cardiac clefibrillator wherein the mechanical pumping activity of the heart is sensed by measuring chanyes in electrical impedance, between a pair of electrodes immersed in the blood contained in one of the ventricles of the heart.
Another object of the present invention is to provide a cardiac de~ibrillator having a control member in which the criteria for detecting ventricular fibrillation can be digitally preprogrammed.
Still another object of the present invention is to provide an automatic implantable cardiac defibrillator wherein the impedance sensor for mechanical activity is only actuated when the electrical (ECG) activity sensor ~uantitatively indicates the possible presence of a fibrillatory condition, thus resulting in lower power usage by the device and consequent longer battery life of an implantable defibrillator.
Further objects and advantages of the present invention `~ ~ will become apparent as the following description proceeds, and the features of novelty characterizing the invention will be pointed out with particulari-ty in the claims annexed to and ~0 forming a part of this specification.

BRI:EF DESCRIPTION OF THE DRAWINGS
For a better understanding of the present in~en-tion, ::

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1 reference may ~e had to the accompanying drawings wherein -the sam~ re~erence numer~ls have been applied -to ]ike par-ts arld wherein;
Figure 1 shows a block di.agram of an automatic defi-brillator elec-trically connected to a catheter having a pair of electrodes implanted in the heart and a third electrode located in the superior vena cava~ the catheter electrodes being opera-atively connected to the overall logic circuitry of the fiberll-ation detection system and defibrillatori Figure 2 shows in greater detail a ~lock diagram of the : ECG and impedance analog processors shown .in Fig. l;
Figures 3 and 3~ illustrate the mechanical pumping activity of the right ventricle during contraction and relaxation of the ventricle and the chanye in the cross-sectional area of the conducting material (.~lood) resulting in a change in impedance;
Figure 4 sho~s in yreatsr detail a block diagram of the accumulator and control logic unit with the missing-pulse det ctor included therein.
Figure S shows a recording of waveforms useful in de-scribing the functions of the components of this invention;
Figure 6 illustrates the output from the analog pro-cessor in a physiological condition known as pulsus alternans, in which only every other electrical depolarization (in the ECG~ is ;~ follo~ed by a mechanical contraction and performance of the detec-t~on system, preprogrammed ~or equal weighing of the electrical ~; and mechanical signals, is illustrated;
; Figure 7 shows a recording of a condition ~imilar to that illustrated ln Fig, 6; ho~ever, the detection system has ~een preprogrammed so that mechanical activity has twice the ~eight of :electr~ical activlty; and ~ !
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1 E~lgu:res 8~ and ~s sho~ a recording representing pe:r-forrnance oE -the detection system in an anima]. experimen-t in ~h.ich the detecting system falsely diagnosed a condition as bein~
fibrilla-tion when only -the ECG was analyzed, bu-t correctly : 10 ~ .
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1 distin~uished the c~nd:ition from fibrill~tion wher~ both the electrical and mech~nic~l s:ic3nals properly prograr~ned and weighed were av~ilab].e to the detection system.

DESCRIPTION OF THE PREFERRED EMBOl)IMENT
Referring now to the drawings and, more particularly to Figure 1, a catheter 1 is shown with the distal portion 2 con~ained within the r.ight ventricle 3 of the heart 4 and having a pair o~ sensing electrodes 5, 6 on the distal portion 2. A third electrode 7 i5 located on the catheter such that, when the distal portion 2 of the catheter 1 is inserted into the heart 4, the third electrode 7 will be located in the superior vena cava 8. In accord with the present invention, sensing both electrical and mechanical activities by locating the pair of electrodes 5, 6 on the catheter 1 in the right ventricle 3 does not require a thoracotomy and, when the pair of electrodes 5, 6 are shorted and employed in ~onjunction with the .
third electrode 7, defibrillation with a low intensity electri-cal shock is achieved. It constitutes an important feature o~
the present invention that the same electrodes which are dis-2~ posed by the catheter in the manner described, provide a muchmore liable signal of the condition of the heart than in pre-vious devices which xelied upon an el~ctrodes exterior of the heart and exterior o the v~ntricle cavity. Moreover, the device, disposed as it is within the heart, is efficient in deliverance of a defibrillation shock to the ventricles.
As shown in Figure 1, there is illustrated an automatic defibrillator 9 consisting of two major blocks of electronic circuitry: a detection system 10, 20 and 30 that utilizes both the electrical and mechanical activity of the cardiac ventricles .
to confirm the presence of ventricular fibrillation; and an _ g _ I

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1 energy-delivery system 40 for generating the voltage and current necessary to defibrillate the ventricles. The energy-delivery system can be any defibrillator that can be connected to the automatic detection system through an appropriate logic interface. During operation of the defibrillator 9 shown in Yigure 1, electrodes 5 and 6 first sense electrical activity of the ventricles, i.e., an ECG signal, which is relayed to an ~CG
analog processor 10 via a lead la. ~fter an output ~ECG signal has occurred continuously for a predetermined number of pulses, the missing pulse detector i.5 disabled. Thereafter when the net number of waves which satisfy criteria for fibrillation reaches a second predetermined number, a control logic unit 30 gives a command signal through a power on/off line to an impedance analog processor 20. An impedance circuit of ~he processor then begins to measure signals, i.e., an impedance change (~Z~
across the pair of electrodes 5, 6 thereby measuring the instantaneous stroke volume or mechanical pumping activity of the right ventricle 3. Fibrillation is indicated when there is little if any change in impedance in the heart because of the 2~ failure to effact a rythmic volumetric change in blood during successive phases of heart beats. Therefore, if there is no change or only little change of impedance because o~ low variation in blood volume within the ventricles, this is an ; accurate indicator of fibrillation. Electrical activity of t e heart 4 monitored by the ECG signal will accurately indicate a suspected fibrillatory state which can then be confirmed by the lack of change or rate of impedance sensed by the impedance analog processor 20.
According to the present invention and, as best shown in Figure 2, the ECG analog processor 10 contains a plurality ; . . . . .

1 of circuits for fil te~incJ signals that li.e outside the bandwkltl of the ECG signal, for establishiny minimum amplitude excursion criteria for the fibrillation waves, and for providing means for tracking amplitude variations in the ECG signal. The low-pass sec-tion lla of a band-pass filker 11 removes frequency components above that oE the fibrillation waves. In particular, the low-pass section lla attenuates the impedance signal produced by the impedance circuit. The high-pass section llb o~ the band pass filter 11 attenuates artifact signals, whose fre~uency lG components are below the spectrum of the fibrillation waves.
In particular, the high-pass section llb is effective in removing noise caused by respiration and electrode movement.
The ECG signal is then amplified by an amplifier llc. After amplification an envelope of the ECG signal is established by a pair of positive and negative peak detectors 12, 13.
Transitions in khe ECG signal greater than a ~ixed percentage, determined by a pair of attenuators 14, 15 of the peak-to-peak value of the siynal, axe detected by a pair of comparators 16, 17. A transition in the positive direction in the ECG signal greater than the value set by the positive attenuator 14 causes a histable multivibrator (flip-flop3 18 to be set. A similar transition in the negative direction causes the flip-flop 18 to be reset. Thus, according to the present invention, the waveform of the ECG signal must '~ ' : ~ .

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exhibit excursions that a~proach the peak-to-peak value of the si~naL, as determine~ by the recent his-tory of the signal, in order for -the output signal ~ECG 19 to change states. In a normally beating heart, -the ~ECG signal 19 contains one pulse per R-wave and false sensing of the T-wave of the ECG signal is avoided unless it hecomes almost as large, has the same polar:Lty and has nearly the same frequency spectrum as the R-wave. When fibrillation occurs, the ~ECG signal 19 contai.ns one pulse for almost every fibri.llation wave. The derived aECG signal lg is then fed into the control logic unit 30, as shown in Figure 1.
Referring now to the :impedance analog processor 20 o~
the present invention, the impedance between the pair of elec-trodes S, 6 is measured by passing a low amplitude, high fre~uency constant-current through the electrode circuit and measuring the resulting voltage drop across the pair of electrodes 5, 6.
According to Ohm's Law, V = IZ, V is voltage across the electrodes, I is the value of current from the constant-current ~ource and Z
is the impedance between ~he electrodes. Since I is constant, : the voltage between the pair of electrodes 5, 6 is directly proportional to the impedance between them.
Preferably in accord wi.th the present invention, and as shown in Figure 3, instantaneous impedance is measured across ; the pair of electrodes 5, 6 during the contraction and relaxation phases of the right ventricle 3. During the contraction phase, the diameter of the ventricle 3, represented schematically by line A, is smaller than the diameter during the relaxation phase, ~: represented as line B. Thus, in the relaxed state, more blood is present in the ventFicle 3, thereby providing a greater conductive volume for flow of the constant-current source through the pair of electrodes 5, 6 and, therefore, the impedance is lower than .
: during the contracted state. In the contracted state, a lesser olume of blood in the ventricle 3 results in a smaller conductive , volume between the electrodes and, therefore, a higher impedance.

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When normal rhythmic changes in impedance are recorded, proper contractlon-relaxation cycles of the heart exist. However, if changes in impedance decrease and approach zero, as is -the case during ventricular fibrillation, a cessation of the mechanical pumping activity oE the heart 4 is indicated and the presence of a fibrilla-tory state is confirmed.
Referring again to Figure 2 ancl the impe~ance analog processor 20, a 20 KHz scluare wave is generated by a constant-current source 21. The average value of the current from the current source 21 should be zero so that polarization o~ the pair of electrodes 5, 6 is avoided. The high-pass section 22a of the band-pass ~ilter 22 of the impedance analog processor 20 passes the impedance-related voltage but attenuates signals ~ith a spectrum below that of the constant-current source. In particular, the high-pass section 22a o~ the band-pass filter 22 attenuates the ECG signal so that the impedance analog processor 20 responds only to the mechanical activity of the ventricles of the heart 4.
Changes in impedance are measured by detecting changes in the amplitude of the signal measured between the pair of electrodes 5, 6, i.e., by passing the signal through an envelope detector 23 a~ter amplification. Bandwidth of the impedance analog processor 20 is restricted to that associated with the mechanical activity of the ventricles by a band-pass filter 24.
After amplification of the impedance signal corresponding to m~chanical activity by an amplifier 24a, any change in impedance greater than the level set by the reference signal is detected by a comparator 25. In a normally functioning heart, the output ; signal QZ 29 from the impedance analog processor contains one pulse per ventricular contraction. Thé derived signal ~Z 29 is then fed to the acc~mulator and control logic unit 30 shown in Figures l and 4.
The algorithms that confirm the presence of ~ibrillation : :

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on the basis o~ the ~ECG 19 signal from the ECG analog processorand the ~Z signal 29 Erom the impedance analog processor are embodied in the control logic unit 30. The control logic unit also contains the means used to control the energy delivery system of the defibrillatox which provides the electrical shock necessary to arrest ventricular ibrillation.
In the initial state and during normal activi-ty of the heart, the impedance analog processor is inoperative while the ECG signal is continuously interrogated for fibrillation waves.
The time interval between pulses in the signal aECG 19 from the ECG analog processor 10 must be within the criteria set by a pair of retriggerable monostable multivibrators, co~monly known as one-shots, OS-l and OS-2, shown in Figure 4, as 31 and 32, respectively. Of course, other means for setting the frequency criteria for fibrillation waves could be employed. An advantage of using the retriggerable one-shots 31, 32 to set the frequency criteria for fibrillation is that the bandwidth limits are sharply defined. Transitions occurring faster than the limits set by one-shot 31 or slower than the limits set by one-shot 32 are rejected. Each wave in the ECG signal satisfying the amplitude criteria for fibrillation set by the ECG analog pro-~1 cessor 10 and the frequency criteria set by the one-shots 31, 32 causas an accumulator 33 to increment via a central control logic , member 34. Each wave in the ECG slgnal ailing to satisfy either j :
the amplitude criteria or frequency criteria causes the accumu-1; lator 33 to decrement via the central control logic member 34.
; Thus, in the absence of pulses ~rom the impedance analog processor 20, the number in the accumulator 33 represents the net number of waves in the ECG signal that qualify as waves of ~fibrillation.

When the ventricles are beating normally, if the accumulator 33 contains a number greater than zero, it will be decremented by each heartbeat. In a normally bea-ting heart, ::

1 the central control lo~Jîc member ~4 latche~ the accumulator 33 atzero ~y inhibiting a decrement when the accumulator 33 contains zero, A mlssing-pulse detector 35, illustrated in Figure 4, de-mands that a number Nl, oE success:ive waves in the ECG signal sati~f~ the fibrillation criteria. If a single wave fails to satisfy the criteria before Nl successive waves which satisfy the fibrillation criteria are accumula1ed~ the accumulatvr 33 is reset to zero by -the mis~ing-pulse detecl;or 35 via the central control logic member 3~. The missing-pulse detector 35 prevents the ECG
waveEorms which contain t~o or more waves that satisfy the fibril-lation criteria followed by one ~hich does not satisfy the criteria from causing a net accumulation in the accumulator. Thus~ the missing-pulse detector 35 prevents the control logic member 34 from interpreting some conditions of ventricular tachycardia as ventricular fibrill~tion, ~ithout having to activate the impedance analo~ pxocessor 20 to make that decision. When a count of a Nl is reached, the missing~pulse detector 35 is inhi~ited via a decoding logic member 36. The mis~ing pulse detector 25 acts as a threshold to the accumulator by screening out fi~rillation sign~ls until a difinite pattern has developed after which the de~
tector 35 can no longer operatively reset the accumulator.
When the accumulator ~ounts a su~ficient numher N2, of ~ave~ in the ECG signal which satisfy the fibrillation criteria, an impedance control logic me~ber 37 is activate,d. A change in impedance satisfying the criteria for mechanical pumping causes the next N3 waves in the ECG signal to decrement the accumulator 33~ Thus in accord with the present invention, the relative importance o~ electrical and mechanical act_vity :
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1 can be digitally preprogrammed by selecting the decrementiny factor, N3~ For example, if N3 a 1~ then electrical and mechanical events have equal importance~ When N4 waves, which satisfy the criteria for ventricular fibrillation have been accumulated charging of the energy-storage capacitor is initiated~ When N5 waves have been accumulated and the energy-storage capacitor is charged, the energy delivery system or the de~ibrillator 40 is commanded to deliver a shock. Thereafter, the accumulator is automatically ., .
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reset to ~ero, monitorinq of the ECG signal is resumed and the impedance control logic 37 is deactivated via the decoding logic member 36.
Operation oE the automatic deEibrillator 9 can be more clearly illustrated by Figure 5, which shows plots of an R-wave complex 50 of the ECG output, an intraventricular impedance 51, a blood pressure record 52, and an accumulator record 53 obtained in animal tests utilizing the present invention. Sec-tion 1 of Figure 5 shows the ECG signal 50, impedance signal 51, arterial pressure 52, and content record or pen excursion 53 of the accumulator for a normally functioning heart. (It should be noted that the impedance analog processor has been overridden in order to demonstrate the impedance signal obtained from a normally functioning heart.) The number contained in the accumulator unit has been displayed by connecting the accumu-lator unit to a no-t shown digital-to-analog converter. The lower limit of pen excursion 53 corresponds to zero in the converter; the upper limit of pen excursion corresponds to N5 in the accumulator.
In section 2 of Figure 5 ventricular fibrillation has occurred, as noted by the dramatic change in the ECG signal 50, the absence of pumping signals in the impedance record 51, and the rapid decrease in arterial pressure 52. When N~ is reached in the accumulator, charging of the defibrillator energy-storage capacitor is initlated. When N5 is in the accumulator and the energy-storage capacitor is fully charged, the defibrillating shock is automatically delivered, thereby arresting fibrillation.
In section 3 of Figure 5, restoration of pumping is achiéved~and the automatic defibrillator returns to the monitor-ing state.

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invention relates to the ability to modify performance of the system slmply by changing the mechanical-to-electrical weighting ~, ~ ... .

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Eactor, N3. The weighting factor, N3, can be preproyrammPd so that a des]red decision is reached in the presence of a varie-ty of tac~arrhythmias. For example, an inappropriate choice of the weighting factor, N3, has been selected for the tacyarrhy-thmias illustrated in Figure 6, and an incorrect decision is reached. However, a correct decisi.on is reached when the weighting factor, N3, is appropriately preprogrammed, illustrated in Figure 7.
Figure 6 shows simulated records of an output signal 55 of the ECG analog processor, aECG, an output sig~al 56 of the impedance analog processor QZ, and a signal 57 which represents the number contained in the accumulator. Each increasing step in the accumulator signal represents an increase of one count in the accumulator.
In section 1 of Figure 6, a cardiac condition known as pulsus alternans, in which only every other electrical depolarization is ~ollowed by a mechanical contraction, has been simulated, and the electrical and mechanical signals have been preprogrammed to have equal weighting, i.e., N3 = 1. As indi-cated in the accumulator record 57, the net accumulation inthis condition is zero.
In section 2 of Figure 6, at a time T, a change in the cardiac condition occurred and every third instead of every other electrical depolarization of the ventricles causes a mechanical contraction. With N3 = 1, a (false) decision that ventricular fibrillation exists will be reached.
Figure 7 illustrates per~ormance of the detection system under the conditions of ~igure 6; however, the mechanical signal in~accord with the present invention had been preprogrammed to have~twice the weight of the electrical signal, i.e., N3 = 2.

The correct decision, that ventricular fibrillation does not exist, will be reached b~ the accumulator record 57a even when only every other or third electrical depolarization is followed ~50 CAMAA

by a mechanical con-traction, as illustra-ted in sections l and 2 of Figure 7.
It should be noted that, in practice of the invention, other weighting factors and algorithms for combining the elec-trical and mechanical activities of the heart may be employed.
It is to be understood that the above examples are merely illu~
strative and not restrictive.
Figure 8A shows a record of a complex arrhythm:ia 60 created in an animal experiment, a related impedance signal 61 that is disconnected and a related femoral artery pressure signal 62. The detection s~stem is deprived of the information from the mechanical system, i.e., the impedance signal 61, and, as illustrated, the accumula-tor 63 has made the (incorrect) decision that ventricular fibrillation exists. As the accumulator increases, it activates the impedance analog processor 20, charges the capacitor of the defibrillator 40, shorts the pair of electrodes 5, 6 and automatically delivers the shock to the heart. In E'igure 8B, the mechanical activity represented by an impedance signal 61a is connected to the control logic unit 30 and the (correct) decision, that ventri~
cular fibrillation does not exist, is reached. No unnecessary shock is delivered to a patient in this situation.
In addition to the advantages previously discussed wi.th regard to the method of utilizing preprogramming and weighting the relationship between the .intraventricular impedance and the ECG signal ~or detecting the loss o~ mechanical pumping, such a method also allows~identification of a fault in the electrodes, since any electrode break will immediatel~ produce a dramatic ncrease~in aircuit~impedance. Additional circuitry can be 30~ incorporated~to detect such an impedance increase and indicate electrode~malfunction.
It should be appreciate~ that the defibrillator 9 :
described herein may be advantageously combined with a not shown 450 ~IANADA

pacemaker unit, e.g., where defibrillation is accomplished but cardiac pumping is no-t resumed. In such a case, pacing is necessary. Also the enti.re defibrillator or any portion -thereof can be located either in an implantable unit or in an extracor-poreal unit, as desired.
While there has been illustrated and described what is, at present, considered to be a preferred embodiment of the invention, it will be appreciated that numerous changes and modifications are likely to occur to those skilled in the art, and it is intended in the appended claims to cover all those changes and modifications which fall within the true spirit and scope of the present invention.

: : :

~ ~ -18-

Claims

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

1. An automatic cardiac ventricular defibrillator comprising:
means for sensing electrical and mechanical activity of a cardiac ventricle in the form of ECG analog signals and the impedance of the ventricle, an ECG analog processor for producing an ECG
analog processor signal of a fibrillatory condition, means for communicating the sensed electrical activity to said ECG analog processor, accumulator control logic means for counting fibrillatory signals, means for communicating an ECG analog processor signal of a fibrillatory condition from said ECG analog processor to said accumulator-control logic means, an impedance analog processor operatively connected to said sensing means and responsive to said accumulator-control-logic means and for developing a signal of a non-fibrillatory condition, means for communicating an activation switching action to said impedance analog processor responsively to a predetermined number of counted fibrillatory signals to selectively activate said impedance analog processor, means for communicating impedance measurement of the ventricle to said impedance analog processor, means for communicating an impedance analog processor derived signal of a non-fibrillatory condition to said accumulator-control-logic means while the impedance analog processor is activated, said accumulator-control-logic means being thereafter simultaneously responsive to both ECG analog processor and impedance analog processor signals, and an energy delivery system responsive to said accumulator-control-logic means to effect a defibrillating electrical shock to the heart appro-priate to the correction of a fibrillatory heart condition.

2. The automatic cardiac ventricular defibrillator in accordance with claim 1, wherein the means for sensing electrical and mechanical activity comprises spaced ventricular electrodes for providing a first signal in the form of an ECG analog signal and a second signal in the form of an impedance analog signal whereby both the electrical and the mechanical activities of the ventricle are monitored.

3. The automatic cardiac ventricular defibrillator in accordance with claim 1, wherein said impedance analog pro-cessor intermittently monitors the mechanical activity, and is effective when said accumulator-control-logic means receives a predetermined number of fibrillatory ECG signals in sufficient predetermined pattern and number.

4. The automatic cardiac ventricular defibrillator in accordance with claim 1, including a preprogrammed means having a quantitative weighing factor assigned to the signals of said ECG analog processor and impedance analog processor whereby the respective signals are made correspondent to said weighing factor before a combination thereof is effective for communicating the energy delivery system to the heart for delivery of the defibrillating electrical shock.

5. The automatic cardiac ventricular defibrillator in accordance with claim 1, in which said accumulator-control-logic means effects a preprogrammed pattern representative of ventricular fibrillation and forming a standard against which the processed signals of the ECG analog processor are compared to identify changes indicative of fibrillation and for addi-tionally detecting changes in impedance as a potential heart fibrillation condition, each of said processed signals to said accumulator-control-logic means providing information

Claim 5 continued...

potentially confirming a fibrillatory ventricular condition when in accordance with a preprogrammed weighed decision imposed on said signals.

6. The automatic cardiac ventricular defibrillator in accordance with claim 1, wherein the accumulator-control-logic means includes control means and accumulator means for imposing a weighing factor and incrementing or decrementing whereby said accumulator means is effective for operation of said energy delivery system.

7. The automatic cardiac ventricular defibrillator in accordance with claim 2, including a catheter supporting said electrodes and receivable within the ventricle.

8. The automatic cardiac ventricular defibrillator in accordance with claim 1, wherein the accumulator-control-logic means includes a control means responsive independently to said ECG analog and impedance analog processor signals, and accumulator means responsive to said control means to be effective upon counting cycles in accordance with fibrillatory activity for said control means and accumulator means to detect and respond to discrete patterns of signals read in predetermined sets.
9. The automatic cardiac ventricular defibrillator in accordance with claim 1, wherein the accumulator-control-logic means includes an accumulator means and means for effecting decrementing and incrementing of the signal values collected by said accumulator means in accordance with said impedance analog and ECG analog processed signals, and a decoding logic means for activating said impedance analog processor whereby the signals are

Claim 9 continued...

accumulated in a predetermined weighed relationship to each other and the effecting of said defibrillatory electrical shock is in accordance with the respective signals.

10. The automatic cardiac ventricular defibrillator in accordance with claim 1, further comprising a third electrode for electrical connection to said electrical and mechanical sensing means, and a catheter, said means for sensing electrical and mechanical activity comprising a pair of spaced ventricular electrodes, said catheter supporting said spaced ventricular electrodes whereby said defibrillatory electrical shock is effected between the pair of spaced electrodes and the third electrode.

11. The automatic cardiac ventricular defibrillator in accordance with claim 1, said accumulator-control-logic means including an accumulator, a control member, a logic unit, and a missing-pulse detector, said control member comprising means for incrementing and decrementing said accumulator, said missing-pulse detector monitoring said ECG analog processor signals to detect a non-fibrillatory condition and responsively acting through said control member to reset said accumulator.

12. The automatic cardiac ventricular defibrillator in accordance with claim 11, wherein said logic unit is responsive to said accumulator for inhibiting the operation of said missing-pulse detector after the accumulator increments to a predetermined level.

13. An apparatus for continuously monitoring heart activity and automatically effecting a defibrillatory shock under heart fibrillating conditions, comprising means for sensing electrical

Claim 13 continued....

and mechanical activity of the heart and of a predetermined ventricular fibrillation condition, means for measuring the electrical activity of the heart responsively to said sensing means, means for accumulating said measured electrical activity, means for monitoring the mechanical activity of the heart and operatively connected to said accumulating means, said accumulating means responsive to information representing a predetermined ventricular fibrillatory condition communicated from said measuring means and for activating the means for monitoring the mechanical activity, and a delivery means res-ponsive to said accumulator means for correcting ventricular fibrillation when said accumulating means receives mechanical and electrical activity information each independently but conjointly confirming a ventricular fibrillatory condition.

14. A method for monitoring cardiac ventricular activity for detecting ventricular fibrillation, comprising the steps of continuously sensing the electrical activity of the heart, processing the sensed electrical information by an electrical monitoring means for detection of a predetermined pattern of ventricular fibrillation, operatively activating a mechanical monitoring means upon attainment of the predetermined pattern of ventricular fibrillation, and processing independently and conjointly signals derived from said electrical and mechanical monitoring means whereby upon their conjoint signalling of ventricular fibrillation, defibrillatory corrective action is effected.

15. The method in accordance with claim 14, further com-prising the steps of weighing the signals respectively generated by the electrical and mechanical monitoring means whereby the weighed signals attain an accumulated value in

Claim 15 continued....

accordance with the proportions of the respectively weighed signals, and in accordance with said accumulated value there-after delivering a defibrillating ventricular shock.

16. The method of claim 14, including the step of analyzing the electrical activity of the heart through a missing pulse detector circuit and suppressing defibrillating operation when the missing-pulse detector circuit detects a non-fibrillating ventricular condition.

17. The method in accordance with claim 14, including the step of positioning ventricular electrode means and thereafter sensing the electrical and mechanical activity of the ventricle.

18. The method in accordance with claim 14, including the steps of incrementing or decrementing an accumulator storage count as derived from the electrical and mechanical monitoring means to detect a pattern of heart activity and to evaluate the predominate presence or predominate absence of ventricular fibrillation, and generating a signal to inhibit decrementing operation at a predetermined accumulated storage count.

19. A method of monitoring cardiac activity and applying a ventricular defibrillation action upon sensing and confirming the existence of a fibrillatory condition, comprising the steps of: continuously monitoring the electrical activity of the heart for the presence of a predetermined pattern of fibrillatory heart activity, independently activating a second monitoring means which is responsive to the mechanical activity of the heart and which monitors a second and independent set of criteria

Claim 19 continued....

received from the ventricle and related to the stroke volume of the ventricle, and thereafter independently and conjointly monitoring the heart and delivering a defibrillatory action upon concurrent and jointly verified fibrillatory activity of a predetermined pattern and extent.

20. A method for monotoring cardiac ventricular activity for detecting ventricular fibrillation, comprising the steps of: supplying simultaneously to a monitoring means signals of electrical and mechanical activity of the ventricle, and weighing the respective signals by which there is determined a fibrillatory condition and in accordance with a predetermined formula whereby the condition of fibrillation is conjointly verified by both such signals, and delivering a defibrillating action in response to the conjoint verification by such signals.

21. A method for monitoring cardiac ventricular activity for detecting ventricular fibrillation, comprising the steps of sensing the electrical and mechanical activity of the heart, processing the sensed electrical and mechanical activity for detection of a predetermined pattern of ventricular fibrillation, weighing the signals respectively generated from the electrical and mechanical activity whereby the weighed signals enhance the accuracy in determining the presence of ventricular fibrillation, and conjointly processing the weighed signals to determine the presence of ventricular fibrillation, and there-after delivering a defibrillatory action.

22. An automatic heart defibrillator comprising: sensor means for detecting cardiac electrical and mechanical activity information, means for communicating in the form of electrical signals the cardiac electrical and mechanical activity information

Claim 22 continued...

to said sensor means, an ECG processor for receiving the electrical cardiac activity information from said communicating means, an impedance analog processor for receiving the mechanical cardiac activity information from said communicating means, accumulator-control-logic means receiving the output of said ECG processor and for counting cardiac signals from said ECG processor and for triggering a defibrillatory action at predetermined quantitative threshold values thereof, means for connecting said impedance analog processor and said accumulator-control-logic means to furnish an input signal which decrements the counted value derived by said accumulator-control-logic means from the ECG analog processor, the total cardiac infor-mation accumulated being the combined independently derived information from said impedance and ECG processors respectively said accumulator-control-logic means including logic means for deactivating said impedance processor at non-critical heart conditions.

23. The defibrillator in accordance with claim 22, in which said impedance analog processor is normally deactivated, said logic means responsive to said accumulator-control-logic means at critical heart fibrillatory conditions transmitted by said ECG processor and effective to activate said impedance analog processor whereby the ECG processor and impedance processor thereafter perform conjointly and independently to monitor both electrical and mechanical heart activity information and each processor furnishing information to said accumulator-control-logic means which counts the fibrillatory heart activity derived from continuous monitoring by each of said processors.