Cardiac Arrhythmias (Part - Circulationcirc.ahajournals.org/content/47/6/1356.full.pdf · SYMPOSIUM Cardiac Arrhythmias (Part 6 ) Present Status of Electroversion in the Management

SYMPOSIUM

Cardiac Arrhythmias(Part 6 )

Present Status of Electroversion in the Managementof Cardiac Dysrhythmias

By LEON RESNEKOV

SUMMARYThe theoretical and practical considerations of electrical reversion of cardiac dysrhythmias are

reviewed and a comparison made between AC and DC defibrillation, indicating the superi-ority of DC under all circumstances. The indications for, immediate and late results of DCshock for atrial and ventricular dysrhythmias are presented, the complication of such treatmentreviewed, and the need for anticoagulant cover, anesthesia, and drug therapy preceding andfollowing the electrical treatment discussed. Each patient requires individual assessment, par-

ticularly those with chronic rhythm disturbances, especially atrial fibrillation, in whom electricalenergy settings in excess of 300 joules are rarely indicated for the risk of complications becomesprogressively higher as the energy setting is increased and the length of time sinus rhythm per-

sists in this group of patients may be short. Patients with acute rhythm disturbances, however,with potentially serious hemodynamic consequences should be treated with maximum electricenergies if needed. Caution is also advised in patients with coronary heart disease, atrial fibrilla-tion, and a slow ventricular rate, even in the absence of digoxin, patients with rapidly changingrhythm disturbances, those who cannot maintain sinus rhythm for a significant period of timedespite drug therapy, patients with the "sick sinus syndrome," those with atrial fibrillation ofmore than 5 years standing with a cardiothoracic ratio exceeding 55%, and patients in lone atrialfibrillation. Heavily digitalized patients in general should have their electroversion postponed ifpossible, but if not, they should be protected against serious ventricular rhythm disturbances im-mediately after the shock by an intravenous dose of lidocaine, phenylhydantoin, or procaineamide immediately before and the initial energy setting should be reduced to 5 joules. Quinidineor some other antidysrhythmic drug may be needed in an attempt to maintain sinus rhythm aftersuccessful electroversion, but even when controlled with adequate blood levels, results are poor.

Additional Indexing Words:AC defibrillationAntidysrhythmic drugs

DC defibrillationDigitalis

Sick sinus syndromeAnticoagulants

DRUG therapy, often successful in treatingcardiac dysrhythmias, has many limitations

which cause serious disadvantages in its routine use.There is, for example, no universal agreement

From the Department of Medicine, Section of Cardiology,University of Chicago Pritzker School of Medicine, Chicago,Illinois.

Supported in part by U. S. Public Health Service ContractPH 68-13-34 (Myocardial Infaretion Research Unit),National Heart and Lung Training Grants HL-05793, HL-05673, and the Chicago Heart Association.

regarding the choice of drug nor any standardizeddosage scheme applicable to all patients. Further-more, the patient has to be kept under closeobservation over several days while the dose givenand effect caused are titrated. Only a small marginseparates the therapeutic from toxic effects, andmany of the antidysrhythmic drugs also haveimportant negative inotropic and dromotropiceffects. Should toxic manifestations emerge, theymay be more serious than the original rhythmdisturbance for which the drug was given, and

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ELECTROVERSION AND DYSRHYTHMIAS

paradoxically drug overdosage may well depress thenormal sinus mechanism, thereby inhibiting rever-sion to sinus rhythm.

In contrast, an electric shock across the chest andmyocardium causes momentary depolarization ofthe majority of heart fibers, terminates the ectopicrhythm, and allows the sinus node to be reestab-lished as the normal pacemaker.

Early HistoryIn papers dealing with the effects of electric

current on the myocardium, Prevost and Battellil 2noted almost as an afterthought that direct currentshock across the heart would end ventricularfibrillation in dogs. This important fact continuedgenerally unrecognized or seemed largely forgottenuntil Kouwenhoven, Hooker, and Langworthy3 4and Ferris, King, Spence, and Williams5 undertookdetailed studies on the effects of electricity on theheart and reported the following important conclu-sions: (1) current rather than voltage is a propercriterion for shock intensity, (2) the passage ofelectrical current across the heart may precipitateventricular fibrillation even in the absence of anyrecognizable myocardial damage, and (3) deathwill follow unless this is successfully treated byanother shock within a few minutes.

Subsequently, pioneer work into the use ofcapacitor discharge (direct current) for clinicalapplication was undertaken in the Soviet Unionbetween 1935 and 1950;6 these studies can beregarded as an important inspiration to laterinvestigators, including Peleska of Czechoslovakia,Tsukerman of the Soviet Union, and Lown and hisgroup7 in this country.

Alternating or Direct CurrentWhether alternating or direct current is used,

electrical defibrillation requires a high-energy im-pulse of short duration to be passed across themyocardium, either between two concave paddlesclosely applied to the heart (internal defibrillation)or through the chest wall using two flat paddles(external defibrillation). The total electrical energydelivered to the heart muscle depends not only onthe electrical current, but also on the resistance ofthe heart, bony cage, and skin to its passage.Much of the confusion in the earlier literature

comparing alternating with direct current defibrilla-tion relates to the infinite wave forms obtainableusing direct current discharge. In contrast, thealternating current wave form is constant anddetermined at the power station as a sinusoidal-Circulation, Volume XLVII, June 1973

shaped impulse with a frequency of 60Hz but at avariable voltage level. A minimal current of 1 ampis needed to bring all the heart muscles instanta-neously to the same refractory point. The requiredvoltage for internal defibrillation is 100 v and thepower 100 w. Electric energy (power X time) is notsynonymous with electrical current, and for internaldefibrillation the energy needed would be about 20joules (wsec). In contrast, for external defibrillationa sixfold current increase is used producing anenergy of 360 joules.With direct current defibrillators, the duration of

the impulse is short (1.5-4 msec). The wave form isshaped by adding varying amounts of inductance tothe circuit, thereby insuring minimal biologic dam-age to its passage across the tissues of the body,particularly the heart. The important differencebetween alternating and direct current defibrillationis that DC develops many times the power of AC.Direct current discharge, however, is much shorterthan alternating current (3 msec vs 200 msec).The first successful human defibrillation was

reported by Beck, Pritchard, and Feil in 1947,8 andthereafter the convenience of AC defibrillationdetermined it as the standard method. Alternatingcurrent, however, was subsequently found to fail onmany occasions when ventricular fibrillation wasdue to myocardial infarction, and also the need forelectrically converting rhythm disturbances otherthan ventricular fibrillation. These two factorsstimulated further work in the use of direct current.

Despite the fact that Lown and his colleaguesreported the first AC termination of an organizedrhythm disturbance," the experience of Zoll andLinenthal'0 gave clear warning of the real risk ofprecipitating ventricular fibrillation and even deathwhen alternating current was used in this way.Furthermore, severe deterioration of ventricularfunction follows transmyocardial AC shocks.'1 12 By1966 Nachlas et al.13 were able to show conclusivelythat DC was superior to AC in terminatingexperimental ventricular fibrillation.From all this evidence, therefore, it can be

concluded that alternating current is feasible fortreating ventricular fibrillation, but that directcurrent is more effective; alternating current,however, cannot be recommended for electivelytreating atrial rhythm disturbances or ventriculartachycardia.

SynchronizationFor many years a vulnerable period of ventricular

excitability had been postulated in a wide variety of

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animals and Wiggers and Wegria"4 were able toshow this to be 27 msec before end of systole in thedog; a similar period of atrial vulnerability has alsobeen demonstrated.'5 Nonuniform recovery fromthe refractory state occurs during the vulnerableperiod of the ventricle, and reentry of thedepolarization wave and self-sustained activity arethereby favored. The risk of ventricular fibrillationfollowing the shock should be reduced, therefore,by synchronizing with the R or S wave, therebyavoiding the apex of the T wave. It will beappreciated that it is almost impossible to avoid thisphase when AC shocks are used because of theirlong duration. The chance occurrence of ventricularfibrillation following random unsynchronized DCshocks is about 2% and Kreus, Salokannel, andWaris'6 deliberately use no synchronization inclinical practice without dire consequence. Theimportant point when no synchronizer is used,however, is to insure that sufficient energy isdelivered so that a current of at least 1.5-2 ampspasses across the heart; smaller energies may wellbe dangerous. Of course, when ventricular fibrilla-tion is to be treated, the synchronizer must beswitched out of the circuit.

Clinical Use of Direct Current CapacitorDischarge for the Management

of Cardiac DysrhythmiasThe overall success rate for the DC termination

of atrial and ventricular rhythm disturbancesapproaches 90%.17-20 Even when determined effortsat conversian with drugs fail, direct current mayoften succeed.21 The correct choice of patient,meticulous attention to detail, correction of electro-lyte imbalance, postponement of treatmentin the presence of overdigitalization, propersynchronization, and choice of antidysrhythmicagent immediately prior to and following treatmentinsure both immediate success and an absence of ahigh incidence of complications. The importance ofineticulous attention to detail, however, cannot beoveremphasized. Monthly checks of the apparatusshould be made for overall electrical safety,including inspection of the wave form and measure-ment of the actual electrical energy followingdischarge across a 50-ohm load in the laboratory.Most apparatus provides a moving coil metercalibrated in joules (wsec). Models, however, arestill in use, in which the desired energies areobtained by depressing a labeled switch, a highlyundesirable feature. During actual patient treat-ment, the assisting personnel should not touch the

patient, his bed, or any of the apparatus, for thelarge electrical field created at the moment ofdischarge may result in shocking any person incontact. The synchronizer should always be testedjust before undertaking patient treatment bycarefully examining the superimposed artifact on theECG signal, or if this welcome refinement is notavailable, by discharging the capacitor away fromthe patient with the two paddles in close contactand their leads in apposition to the patient'selectrocardiogram leads. In this way an artifact issuperimposed on the electrocardiogram tracing andcan be examined for correct timing.Paddles used should always be of adequate size,

for if they are too small the electric current densityis extremely high and the possibility of myocardialdamage very real.22 It has been reported that theanterior and posterior paddle position for externaldefibrillation significantly lowers the electric energyneeded for electroversion;23 others, however, couldnot confirm this.20 Indeed, experimental work13 hasshown that anterior positioning of both paddles inthe longitudinal plane delivers more current to theheart. The failure to note more striking clinicaldifferences with changes in paddle positioning isprobably due to the excess electrical energies whichare consistently used to achieve electroversion. Theadded safety of a flat posterior paddle supportedonly by the weight of the patient and untouched bythe operator is advantageous, however, and theanteroposterior position is therefore recommended.

Digoxin or other digitalis preparations should bewithheld for 24-28 hours before treatment if at allpossible. If the treatment cannot be postponed buthas to be undertaken in the presence of heavydigitalization, the initial energy setting should bemarkedly reduced to 5 joules for an adult, and anintravenous injection of 50 mg lidocaine, 50-100 mgphenylhydantoin, or 50-100 mg of procaine amideshould always precede the shock. Many usequinidine or some other antidysrhythmic agentroutinely before administering the shock, but theirefficacy in reducing energy requirements or inhelping to maintain sinus rhythm thereafter isquestionable.20 General anesthesia is not manda-tory, and amnesia produced by diazepam 5-10 mgi.v., can now be recommended.24Treatment should be undertaken in an area fully

equipped for cardiac monitoring and resuscitation,including emergency pacemaking. The heart rateshould be displayed on a tachometer, and theelectrocardiogram constantly on an oscilloscope,and preferably recorded as a direct tracing as well.

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A short strip of V, before administering the shock isadvantageous for subsequent comparison, as imme-diately after the shock P waves can be difficult todetect in the standard limb leads, even when sinusrhythm is present. The skin should be prepared by aliberal application of ECG paste rubbed well in toreduce electrical resistance, and thereby preventpainful skin burns. Great care must be taken toinsure that no part of the patient's skin is in directcontact with the metal of the trolley or the metal ofthe bed on which he is lying.With either two anterior, or preferably an

anterior and a posterior paddle, small energiesshould be administered first, and if unavailing,shocks are repeated at increased energy levelsettings. For an adult, an initial setting of 25-50joules is satisfactory, increasing in 25-50-joule stepsas needed. If heavy digitalization is present, an in-itial shock of 5 joules is appropriate. Should ectopicbeats follow the first shock, 50 mg lidocaine shouldbe given intravenously and as a routine before anypatient known to be heavily digitalized.The initial setting for a child is 5-10 joules

delivered across appropriately sized pediatric pad-dles and increasing by 5-10-joule increments.There should be great reluctance to exceed an

energy setting level of 300 joules in an adult beingtreated for a chronic rhythm disturbance, althoughthe situation is quite different when an acuterhythm disturbance producing serious hemodynam-ic effects is present; maximal energies (400 joules)should now be used if needed.The initial setting for treating ventricular fibrilla-

tion (no synchronizer in circuit) in an adult is 200joules, increasing by 100-joule steps to a maximumof 400 joules.

Appropriate settings for internal defibrillation(special paddles) are 20-100 joules in 20-jouleincrements for an adult, and 5-50 joules in 5-jouleincrements for a child.Immediately after the shock with the develop-

ment of sinus rhythm or failure to achieve sinusrhythm after optimal energy, the amnesic drug isdiscontinued and a 12-lead electrocardiogram re-corded. The electrocardiogram should be monitoredfor the next 24 hours or longer if need be, andrecords of blood pressure should be taken everyhalf hour if hypotension occurs.

Individual Rhythm DisturbancesAtrial Fibrillation

Atrial fibrillation is the most common rhythmdisturbance to be treated, but lone atrial fibrillationCirculation, Volume XLVII, June 1973

deserves special mention, for the success rate of itselectroversion is low, the incidence of complicationshigh, and the length of time during which sinusrhythm persists is often disappointingly short.25Initial success rates for atrial fibrillation are ingeneral around 90%, irrespective of the underlyingcause; for lone atrial fibrillation it is only 79%.Successful electroversion is not related to age or sex,type of heart disease (lone atrial fibrillationaccepted), overall body size, nor to the size of the fwaves in lead V1 of the electrocardiogram,18 butdoes depend on the duration of the rhythmdisturbance, being less than 50% when atrialfibrillation has been present for 5 years or longer.Similarly, a cardiothoracic ratio of 50% or more andselective enlargement of the left atrium lessen thechance of success.'7' 20Every patient, therefore, with chronic atrial

fibrillation requires individual assessment to deter-mine whether treatment is worthwhile. Neverthe-leiss, hemodynamic benefit maybe achieved in sinusrhythm,26 27 especially when patients are studied atprogressive exercise loads.28 Certain groups ofpatients, particularly those with severe mitralregurgitation, may only be maintained free ofcardiac failure by repeated electric terminations ofepisodes of atrial fibrillation.

Unless sinus rhythm is needed to maintain thecirculation or the mechanical efficiency of prostheticheart valves, electroversion should be postponeduntil patients are convalescing following open- orclosed-heart surgery.29 Reversion to atrial fibrilla-tion in the immediate postoperative phase is almostuniversal if open-chest electroversion is undertakenat the time of surgery, and atrial fibrillation with aventricular rate controlled by digoxin is often to bepreferred to rapidly changing rhythms in thepostoperative phase.The following groups of patients are not suitable

for the electroversion of atrial fibrillation, whichshould be attempted only under unusual circum-stances: (1) Coronary heart disease with atrialfibrillation in which the basic ventricular rate isslow, even in the absence of digoxin; (2) patientsnot able to maintain sinus rhythm for more than abrief period, even when maintained on an adequatedose of an antidysrhythmic drug; (3) patientspresenting with variable atrial rhythm disturbancesin rapid succession; (4) patients with the "sicksinus syndrome".30 If electroversion is done duringthe rapid atrial phase of the syndrome, a transve-nous pacemaker should first be positioned in the

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right ventricle, for there is a serious risk of severebradyeardia or complete asystole following theshock; (5) patients with chronic valvar heartdisease and long-standing atrial fibrillation (morethan 5 years), considerable enlargement of theheart (cardiothoracic ratio more than 55%), and inwhom cardiac surgery is not contemplated; and(6) patients with lone atrial fibrillation.

Atrial Flutter

The success rate is more than 90%, and theaverage energy level setting required for electrover-sion is only 50 joules. Unlike lone atrial fibrillation,patients with idiopathic atrial flutter may still besuccessfully reverted by direct-current shock at lowenergy level settings, even when the rhythmdisturbance is known to have been present forseveral years; furthermore, sinus rhythm is fre-quently maintained for a significant period oftime.25

Paroxysmal Atrial Tachycardia

Simple vagal stimulation and drug therapyremain the initial treatment of choice and whenused for resistant PAT, electroversion succeeds inabout 80% of cases. It should only be used fordigitalis-induced supraventricular or junctionaltachycardias under the most exceptional circum-stances, for the risk of ventricular fibrillation beingprecipitated is high.3'

Ventricular TachycardiaThis is a particularly gratifying dysrhythmia to

treat; the initial success rate is 97% and electricenergies needed are low, the average setting being50 joules. There should therefore be no hesitation inrecommending electroversion for any ventriculartachycardia which fails to respond quickly toemergency drug therapy. Caution has to beadvised, however, when ventricular tachycardia isdigitalis-induced; electroversion can now only berecommended under the most exceptional circum-stances and drug therapy is the treatment ofchoice.

Ventricular FibrillationControlled clinical trials of direct current (unsyn-

chronized) vs alternating current for defibrillationare difficult to design, but there is good animalexperimental work to indicate the superiority ofDC,13 and in clinical practice successful resuscita-tion (patient leaving hospital) has been reported inmore than 50% of patients treated by DC shock andwell conducted principles of resuscitation.32 The ini-

tial energy setting should be 200 joules, increasingby 100-joule increments if needed.

ComplicationsComplications occur more frequently than initial-

ly predicted, and do not only relate to drugs givento maintain sinus rhythm. Indeed, an incidence of14.5% among 220 consecutive patients has beenreported;33 these did not include minor complica-tions such as superficial skin burns due to poorpreparation of the skin or transient rhythmdisturbances after the shock. Included, however,were the following.

Raised Levels of the Serum Enzymes LDH and CPK (10%)Their origin, however, is still uncertain

Mandecki et al.34 consider skeletal muscle damageas the cause, but as other signs of myocardialdamage frequently coexist when the serum enzymelevels are raised, the matter awaits definitivestudy.

Hypotension (3%)Hypotension is more common when higher elec-

tric energies are used, and may persist for severalhours, frequently requiring no particular interven-tion, but the patient should be carefully observed.

ECG Evidence of Myocardial Damage (3%)Patterns of myocardial infarction may follow the

shock and persist for many months; they are mostcommon following electroversion at high energysettings.

Pulmonary and Systemic Emboli (1.4%)The incidence is similar to that following quini-

dine conversion of rhythm disturbances but doesindicate the need for anticoagulant cover (seebelow).

Ventricular Rhythm DisturbancesVentricular premature beats and tachycardia are

common at low energy settings when the patient isheavily digitalized, and at high energy level set-tings even in the absence of any digitalis prepara-tion. Should a ventricular dysrhythmia follow thefirst shock, an intravenous antidysrhythmic drug, aspreviously recommended, should be given beforeincreasing to high energy settings.

Pulmonary Edema and Increase in Heart SizeThese may occur in -3% of patients coming on

within 1-3 hours of treatment.35 Unlike other majorcomplications, they occur only in patients actuallyreverted to sinus rhythm. While Lown considers


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pulmonary emboli as a possible cause, othersbelieve that following electroversion there isconsiderable depression of the mechanical functionof the left atrium.36 Any additional obstruction toflow across the mitral valve, any lessening of leftventricular wall compliance or left ventriculardysfunction will aggravate the situation and mayresult in pulmonary edema.The incidence of complications relates to the

energy level setting, being 6% at 150 joules but ris-ing to exceed 30% at a setting of 400 joules. One canconclude, therefore, that there is rarely an indica-tion for exceeding a 300-joules setting in patientspresenting with long-standing rhythm disturbances,particularly atrial fibrillation of more than 5 years'duration.

Follow-up StudiesWhile the initial success rate is remarkably good,

direct current shock is disappointing in long-termfollow-up studies, particularly when atrial fibrilla-tion is treated.17, 20, 37 Reversion to atrial fibrillationis most likely by the end of the first month ofelectroversion, and not infrequently occurs withinthe first day. Those in whom atrial fibrillation haspersisted for more than 3 years, those withsignificant underlying heart disease, or with consid-erable overall enlargement of the heart areparticularly liable to revert to atrial fibrillation.Those with lone atrial fibrillation are exceptional;they do not remain in sinus rhythm even in theabsence of these unfavorable circumstances.25

Quinidine and Other Antidysrhythmic DrugsRossi and Lown38 reported that quinidine pre-

ceeding direct current shock improves the chancesof persistent sinus rhythm, diminishes the electricenergy needed for the conversion, and reduces theincidence of postconversion rhythm disturbances.Studies such as these are difficult to control, andother groups have been unable to confirm theirconclusion.37'39 Several groups, however, haveinvestigated the use of drugs alone or in combina-tion to maintain sinus rhythm.39' 40 After transmyo-cardial DC shock, acetylcholine and catecholaminesare liberated,4' and their combined effects mayprecipitate ectopic rhythms, permit their continu-ance, and either prevent the emergence of sinusrhythm or curtail its duration. Szekely42 reportedthat quinidine, procaine amide, and propranolol donot necessarily reduce the instance of DC shock-induced rhythm disturbances, except for thosedirectly related to digitalis. Furthermore, theirCirculation, Volume XLVII, June 1973

clinical and experimental observations suggest thatthe toxic cardiac effects of these drugs may even beenhanced by high energy electric current; theytherefore advise caution in their routine use. Morerecently, quinidine bisulfate as a long-actingpreparation has been extensively investigated in anattempt to maintain sinus rhythm following DCshock.43 Even when a long-acting preparation iscontrolled with adequate blood levels, sinus rhythmpersists only for a slightly longer period of time,and furthermore, the incidence of complicationswith quinidine may still be high.

It can be concluded, nevertheless, that quinidineor some other antidysrhythmic drug should beconsidered for any patient who has reverted to hisoriginal rhythm disturbance, and in whom sinusrhythm is important. The chances of sinus rhythmpersisting, however, are not good, even whenadequate blood levels are maintained.

Digitalis and ElectroversionLown, Kleiger, and Williams44 reported that in

experimental animals the DC threshold for theemergence of ventricular tachycardia fell to 0.2joules in the presence of heavy digitalization.

In man, the counterpart of these observations isdemonstrated by ventricular premature beats,tachycardia, or even fibrillation being precipi-tated by the DC shock in heavily digitalizedpatients.17' 20, 31 In the presence of a knowndigitalis-induced rhythm disturbance, electroversionshould therefore rarely be used, for despite the veryoccasional record of a successful outcome, fatalventricular fibrillation may follow the shock, evenwhen properly synchronized.45

Anticoagulants and ElectroversionThe need for and efficiency of anticoagulant

protection has been the subject of much debate, inthe absence of any well-controlled study. Such astudy has now been reported46 demonstrating astatistical benefit in a group of patients who hadelectroversion under anticoagulant control. Unless acontraindication to its use is present, all patientsgoing forward to electroversion should be protectedby anticoagulant therapy, particularly patients withrecent cardiac infarction, chronic coronary heartdisease, mitral valvar disease, cardiomyopathy, andprosthetic heart valves when a coumadin derivativeshould be given or heparin used if the indication forDC shock is urgent. As the risk of reversion to theoriginal rhythm disturbance is highest within thefirst month of treatment, it is wise to maintain oral

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anticoagulant therapy for at least 4 weeks aftersuccessful DC shock when it may be discontinuedunless the underlying heart disease requires itscontinuance.

Electric defibrillation of the heart, particularlysynchronized DC shock, is an exciting advance butfurther effort is needed to uncover the basicmechanisms of rhythm disturbances, thereby en-couraging the development of more physiologicapproaches to their treatment and particularly tothe maintenance of sinus rhythm thereafter.

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electriques: Courants alternatifs 'a haute tension. jPhysiol Path G6n (Paris) 1: 427, 1899

2. PREVOST JL, BATTELLI F: Quelques effects desdecharges electriques sur le coeur des mammifreres. JPhysiol Path Gen (Paris) 2: 40, 1900

3. LANGWORTHY OR, KOUWENHOVEN WB: An experimentalstudy of abnormalities produced in the organism byelectricity. J Indust Hyg 12: 31, 1930

4. HOOKER DR, KOUWENHOVEN WB, LANGWORTHY OR:The effect of alternating electrical currents on theheart. Amer J Physiol 103: 444, 1933

5. FERRIS LP, KING BG, SPENCE PW, WILLIAMS HB:Effects of electrical shock on the heart. ElectricEngin 55: 498, 1936

6. GunvicH NL, YUNYEV CS: Restoration of heart rhythmduring fibrillation by a condenser discharge. AmerRev Soviet Med 4: 252, 1947

7. LOWN B, NEUMAN J, AMARASINGHAM R, BERKOVITSBV: Comparison of alternating current with directcurrent electroshock across the closed chest. Amer JCardiol 10: 223, 1962

8. BECK ES, PRITCHARD WH, FEIL HS: Ventricularfibrillation of long duration abolished by electricshock. JAMA 135: 985, 1947

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24. KAHLER RI, BURROW GN, FELIG P: Diazepam inducedamnesia for cardioversion. JAMA 200: 997, 1967

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35. RESNEKOV L, MCDONALD L: Pulmonary oedemafollowing treatment of arrhythmias by direct currentshock. Lancet 1: 506, 1965

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37. MCCARTHY C, VARGHESE PJ, BARRITT DW: Prognosisof atrial arrhythmias treated by electrical counter-shock therapy: A three year follow-up. Brit Heart J31: 496, 1969

38. Rossi M, LOWN B: The use of quinidine incardioversion. Amer J Cardiol 19: 234, 1966

39. SZEKELY P, SIDERIs DA, BATSON GA: Maintenance ofsinus rhythm after atrial fibrillation. Brit Heart J 32:741, 1970

40. WAGNER GS, MCINTOSH W: The use of drugs inachieving successful DC cardioversion. Progr Cardio-vasc Dis 11: 431, 1969

41. CHILDERS RW, ROTHBAUM D, ARNSDORF M: Theeffects of DC shock on the electrical properties of the

heart. (Abstr) Circulation 36 (suppl II): II-85,1967

42. SZEKELY P, WYNNE NA, PEATON DT, BATSON GA,SIDERIS DA: Direct current shock and antidysrhyth-mic drugs. Brit Heart J 32: 209, 1970

43. RESNEKOV L, GIBsON D, WAICH S, MUIR J,MCDONALD L: Sustained release quinidine (KinidinDurules) in maintaining sinus rhythm following theelectroversion of atrial dysrhythmias. Brit Heart J33: 220, 1971

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Cardiac Arrhythmias (Part - Circulationcirc.ahajournals.org/content/47/6/1356.full.pdf · SYMPOSIUM Cardiac Arrhythmias (Part 6 ) Present Status of Electroversion in the Management