Comparison of alternating current with direct current electroshock across the closed chest

Experimental

Studies

Comparison

of Alternating

Direct

Current

Electroshock Closed

BERNARD LOWN,

Current Across

with the

Chest*

M.D., F.A.c.c., JOSE NEUMAN, M.D., RAGHAVAN AMARASINGHAM,M.B., B.S. and

BAROUH V. BERKOVITS, E.E.ING. Boston,

I

Massachusetts

current (DC) countershocks were compared in 85 mongrel dogs. The AC defibrillator used was the widely employed unit developed by Zo11.5 This instrument provides 60 cycle alternating current for a duration of 150 msec. (0.15 set). The voltages were selected from the scale setting provided on the unit (150 to 750 volts in 100 volt steps). For voltages below

T IS BECOMING increasingly

recognized that ventricular fibrillation is an important cause of sudden death. The treatment of this arrhythmia is by electrical countershock delivered to the heart either directly or indirectly through the intact chest wall. From the onset of ventricular fibrillation only a few minutes are available for restoring an integrated cardiac mechanism. Until recently the successful use of countershock has been largely limited to the operating room where this brief time could be prolonged by the prompt institution of direct cardiac massage. The demonstration by Kouwenhoven and co-workers1 that in the arrested heart pressure on the lower sternum maintains blood flow to vital organs has greatly extended the time available for effective use of electrical defibrillation. Recently it has been shown2-4 that electrical countershock across the closed chest will abolish cardiac arrhythmias other than ventricular fibrillation. It is therefore pertinent to determine whether alternating current, widely accepted for inducing countershock, is indeed the best available method. The present study compared the action on the heart of alternating current and three types of direct current both during ventricular fibrillation and during normal sinus rhythm.

150 a variable step-down transformer was added. The three DC defibrillators tested utilized in common a single pulse discharge from a storage capacitor. The units differed only in the wave form and duration of the countershock. A simplified schematic diagram is presented in Figure 1. The capacitor C is charged to a DC voltage which is dependent upon the wiper position on the variable transformer T. This charge is built up during a standby time of approximately 15 seconds. The capacitor discharges through the inductor L and the body resistance R when the relay S is switched to the discharge position. The total energy of the discharge W is equal to the initially stored energy in the capacitor. It is not dependent on the resistance of the patient as is the case with an alternating current discharge. Since it has been shown?7 that in closed chest defibrillation an important property of the shock is its energy, the DC apparatus was calibrated in energy units (watt seconds). This energy can be measured with a voltmeter connected in parallel with the capacitor. The energy is computed by the following equation: w = i/z v2 c where W = the total energy in watt seconds V = the initial DC voltage on the capacitor, C = the capacitor in farads

MATERIALS AND METHODS The effects of alternating current (AC) and direct

in volts

* From the Department of Nutrition, Harvard School of Public Health, and the Medical Clinic of the Peter Bent Brigham Hospital, with cooperation of the American Optical Company, Buffalo, New York. Supported in part by the John A. Hartford Memorial Fund, the Nutrition Foundation, Inc., the Fund for Research and Training, Department of Nutrition, Harvard School of Public Health, Boston, Massachusetts, The National lnstitutes of Health Grant H-4140, and the Leo Rosenthal Fund, Standard Drug Company, Richmond, Virginia. AUGUST 1962

223

224

Lown et al. TABLE II AC and DC Electrical Discharges Administered at Fixed Countershock Levels (EDss)* to 25 Animals in Normal Sinus Rhythm (Group 2) Shocks per Animal

Type

of Shock

1

1

FIG. 1. Simplified schematic discharge or DC defibrillator.

I

diagram of the capacitor For details consult text.

AC DC 1

TABLE I The Use of AC and Three Types of DC Defibrillators to Treat 750 Episodes of Ventricular Fibrillation in 30 Animals (Group 1) Type of Shock

NO. .4nimals

No. Episodes of V.F.

AC

10

200

DC 1

10

250

2

5

150

3

5 30

Total

V.F. = ventricular fibrillation; current; DC = direct current.

AC

Total No. Shocks

20 40

5 5

100 200

40

6

240

20 40

4 5

80 200

25

820

2 3

The wave shape and duration of the discharge are dependent on the values of capacitance and inductance used in the circuit. Unit number 1 (DCr) used a capacitor of 8 microfarads and gave an underdamped Unit numimpulse of 1.25 milliseconds’ duration. ber 2 (DCJ used a capacitor of 16 microfarads and gave an overdamped (aperiodic) impulse of 2.5 milliseconds. The third unit (DCd also had a 16 microfarad capacitor and gave a 2.5 millisecond underdamped impulse. Dogs were anesthetized with intravenous sodium pentobarbital in a dose of 30 mg./kg. and ventilated with a Harvard respiratory pump through an endotracheal tube. Ventricular fibrillation was induced by means of a 60 cycle sine wave delivered directly to the heart through a flexible teflon coated 00 Surgaloy multistranded wire. The wire was introduced percutaneously into the heart and anchored to the free wall of the left ventricle. This was accomplished by placing the wire within a cardiac needle with the proximal end of the wire bent back for a length of 3 mm. upon the shaft of the needle. After entering the left ventricular cavity, the needle was withdrawn, leaving the wire in the heart. A gentle tug “fishhooked” the wire into the ventricular myocardium. In all animals the two defibrillator electrode paddles were applied with pressure on either side of the

No. .4nimals

Total

* The minimum countershock level for reverting per cent of episodes of ventricular fibrillation.

shaved chest wall at about the level of the apex This position gave the most consistent rethrust. sults and required the lowest countershock levels for restoring sinus rhythm. The 85 dozs were divided into 3 proufis: In the jirst group, consisting of 30 animals, multiple episodes of ventricular fibrillation were induced (Table I). Reversion with countershock was attempted immediately following the development of ventricular fibrillation. In 10 animals (200 episodes of ventricular fibrillation) AC countershock was employed. In 20 animals (550 episodes of ventricular fibrillation) DC countershock was employed. The average interval between episodes of ventricular fibrillation was 2.5 minutes. The objective was to determine the minimal countershock level effective for reverting two-thirds (about 65 per cent) of the episodes of ventricular fibrillation (abbreviated as the ED66). If the first countershock did not restore normal sinus rhythm, another shock was immediately administered at the next higher-volt or watt-second setting. If, however, the first countershock proved effective, the level for treating subseTABLE III AC and DC Electrical Discharges Administered to 30 Dogs in Normal Sinus Rhythm at Varying Countershock Intensities

Type of Shock

No. Animals

No. Shocks 158

.4C

10

150

DC 1

10

158

750

2

5

150

3

5 30

150

= alternating

65

Total

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Electroshock

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Control

TABLE IV Changes Observed in 10 Animals After Reversion of 200 Episodes of Ventricular Fibrillation with AC Countershock Total no. of shocks

385

EDG&

350 volt.5

Arrhythmias

following defibrillation

Ventricular

750 v. AC without effect

tachycardia

26%

Atrial fibrillation

87%

S-T segment change*

51.5%

T wave inversion

51 .OY”

Death

1

* 35 % were S-T segment elevations and 16% depressions.

quent bouts of ventricular fibrillation was reduced. In nearly all instances fewer than four shocks were required to restore a normal mechanism. These animals were observed for a period of 24 hours after the experiment. In 25 normal dogs in sinus rhythm constituting Groub 2, a series of shocks were administered with both AC and DC at the previously determined EDc5 levels (Table II). A total of 820 such fixed shocks was given. Sixteen animals received 40 shocks each while the remaining 9 dogs received 20 shocks. Each animal received the shocks over a period of 45 minutes. Thereafter these animals were followed with daily electrocardiograms for a period of one week. In the third groufi consisting of 30 dogs, the immediate effects of differing levels of countershock Here studied. These levels ranged from 25 volts and 7 watt seconds for the AC and DC units, respectively, to the highest intensities required for defibrillating animals resistant to countershock. A total of 616 countershocks was administered (Table III). AC was employed 158 times in 10 dogs while DC was employed 458 times in 20 dogs. RESULTS VENTRICULAR

Alternating shocks sodes AC

DEFIBRILLATION

Current:

were

required

of

ventricular

failed

to restore

A total to

FIG. 2. Numerous AC shocks up to 750 volts were ineffective in defibrillating the heart. A single DC discharge at 190 watt seconds then restored normal sinus rhythm.

electrocardiographic changes of hyperkalemia and died shortly thereafter in cardiac arrest. The voltages required to defibrillate the heart varied widely among the animals. By contrast, the minimal defibrillating levels for any one animal remained relatively stable even

% REVERSIONS

m

% Defibrillation8

17

Cummulotive

at specific

100

1)

of 385 AC counter-

fibrillation

the

200

(Table

mechanism

60

epiIV).

in one

10 animals. In this dog the first episode of ventricular fibrillation did not respond to 7 closely repeated shocks even though the level was increased progressively from 150 to 750 volts (Fig. 2). Defibrillation and restoration of sinus rhythm was then accomplished with a single DC discharge of 190 watt seconds. This animal, however, exhibited the progressive of the

AUGUST 1962

150

250

350

450

DEFlBRlLLATlNG

FIG. 3. episodes minimal episodes

Distribution of of ventricular level effective (EDe,) was 350

voltoges

% of defibrillotions

80 (GROUP

control

a normal

190 ws. DC

were

550

650

? 750

VOLTAGES

AC voltages for reversion of 200 fibrillation in 10 dogs. The in reverting 65 per cent of the volts.

Lown

226 ‘rABLE

‘l-ABLE

”

Changes Observed in 20 Animals After Reversion of 550 Episodes of Ventricular Fibrillation with DC: Countershock

DC*

ED66

70 watt sec.

Arrhythmias following defibrillation Ventricular tachycardia

30.0:; 0.97,

S-T segment changes

32 .oc,:;

T-wave inversion

0

Death

0

(70 watt seconds)

No. of dogs

:\trial fibrillation

No.

1

=I* REVERSIONS

1

I

8o

0

% Defibrillotions watt

second

Cumulative defibrillotion

at specific

level “/. of n

n

60

20I I 20 30 40 5o 60 WATT

IBr 70

80 90 100 m

+

SECONDS

4. Distribution of DC energy levels for reversion of 550 episodes of ventricular fibrillation in 20 animals. The minimal level effective in reverting 65 per cent of the episodes (EDas) was 70 watt seconds. FIG.

of countershocks

Arrhythmias Ventricular

after man>- episodes of ventricular fibrillation. The distribution of AC voltages for successful reversion of the 200 episodes is illustrated in Figure 3. It shows that 65 per cent of reversions were accomplished at or below 350 volts. AC defibrillation was followed by a number Transient changes. of electrocardiographic ventricular and atria1 arrhythmias were frequently observed immediately aftrr reversion. Ventricular tachycardia and atria1 fibrillation occurred after 26 per cent and 87 per cent of the The countershocks respectively (Table IV). incidence of these arrhythmias was unrelated to the number of episodes of ventricular fibrillation the animal had already experienced. Changes in S-T segment and T wave occurred Currents of injur) in about half the animals. In one animal the were frequently observed. sequential changes of a lateral wall infarct was noted; it consisted of a current of in.jur)

i

“I

Comparison of Effects of Repeated Countershocks with Eithrr AC or DC at Their Respective Defibrillating I,evels ( EDG)

784

Total no. of shocks

100

et al.

fibrillation

Vrntricular dias

tachycar-

Ventricular beats

premature

15

520

50 (17Yc)

10 (1.9%)

50 (17(,‘{)

153 (29%)

37 (120,C.)

:\trial fibrillation hlyocardial

10 300

199 (66<2,)

infarction

Dead

46 (9%)-t 0

7

5

5

0

* Represents 6 dogs treated with DC1 and 9 with DG. t Observed nearly exclusively following use of the DC, unit.

followed by characteristic T wave inversion and emergence of significant Q waves. Direct Current: A total of 784 DC countershocks were employed to control 550 episodes of ventricular fibrillation in 20 dogs. The three DC units are considered together since only minor differences were noted in their performance as defibrillators (Table v). DC countershock was consistently effective in restoring a normal mechanism. There were no deaths. The mean minimal energy level required for controlling ventricular fibrillation was nearly identical for the three DC units (DC, = 85 + 25 watt sec.; DC2 = 82 + 26 watt sec.; DC& = 86 + 27 watt sec.). Approximately 65 per cent of the episodes of ventricular fibrillation was reverted with 70 watt seconds or less (Fig. 4). As was the case with AC, there was considerable variation in the countershock intensities required for defibrillating However, in any one animal different animals. succassivc defibrillations were accomplished at approximately the same levels. Immediately following defibrillation, differences were noted between animals receiving AC and DC countershock. While with the use of AC atria1 fibrillation accompanied 174 of the 200 reversions (87 per cent), following DC shock the incidence was only 0.9 per cent or 5 episodes of 550 reversions. S-T segment shifts occurred after THE

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Electroshock

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AC Countershock

FIG. 6. Development of atria1 fibrillation after single AC discharge at defibrillating voltage setting (EDss).

FIG. 5. Sequential electrocardiographic changes over three successive days following 20 AC shocks at EDGE. Upper strip is control; middle strip is taken 24 hours later, while lower strip is taken after another 24 hours.

32 per cent of DC and 50 per cent of AC reversions. The S-T segment changes following DC countershock were predominantly transient elevations above the isoelectric baseline and were not associated with T wave inversions. This was in contrast to the longer lasting S-T segment shifts with fixed symmetrical T wave inversions which were observed after AC defibrillation. It is of interest that DC, countershock was associated with the least degree of S-T segment and T wave changes. FIXED

COUNTERSHOCK

LEVELS

(GROUP

2)

The 25 animals in this group were subjected to repeated countershocks at the previously determined levels effective in reverting 65 per cent of the episodes of ventricular fibrillation. The 10 dogs in the AC subgroup received 300 countershocks of 350 volts each. Half of these animals received 40 shocks, and the remaining 5 received 20 shocks each over a period of 45 minutes. The 15 animals in the DC subgroups received 520 shocks at a fixed level of 70 watt seconds. A DC1 unit was used in 6 and a DC, unit in 9 of the animals. Eleven of 15 dogs received 40 shocks each over a period of 45 minutes. The remaining 4 received 20 shocks each with the DC& unit. Alternating Current: All 5 dogs receiving 40 shocks each developed electrocardiographic changes consistent with myocardial infarction and 3 died. Of the 5 animals receiving 20 shocks each, 4 showed evidence of myocardial infarction and 2 died. In 7 of the dogs exhibiting electrocardiographic changes, the Q waves developed in leads I and aVL. The sequential changes in one animal are illustrated AUGUST

1962

in Figure 5. In 2 dogs such changes were limited to leads II, III and aVF. Of the 5 animals that died, death occurred in 1 on the second day, in 3 on the fourth day and in 1 on the sixth day. Following AC countershock there was a high incidence of diverse cardiac arrhythmias. As was already noted after defibrillation with AC, atria1 fibrillation was the most common rhythm disorder occurring after 66 per cent of the countershocks (Fig. 6 and Table VI). This arrhythmia was generally transient, lasting but 3 to 15 seconds. However, a number of paroxysms continued through successive countershocks. In one animal atria1 fibrillation, provoked by the last countershock of a series, persisted for 2 hours and 5 minutes. The most serious rhythm disorder following AC was ventricular fibrillation, which was observed 50 times, an incidence of 17 per cent. Frequent paroxysms of ventricular tachycardia and numerous ventricular ectopic beats either uni- or multiform, were also noted. The occurrence of atria1 or ventricular fibrillation was unrelated to the number of shocks the animal had already received. These arrhythmias were as likely to follow the first as t.he last countershock of a series. Direct Current: None of the 15 animals receiving repeated DC countershocks died during the week of observation. Sequential electrocardiographic changes consistent with myocardial infarction were observed, however, in 5 animals. Two of these had received DC1 and three, DC3 countershocks. The changes suggestive of myocardial infarction were restricted to the limb leads and were characterized by the appearance of Q waves in leads I and aVL in combination with elevated S-T segments, which were then followed by symmetrical inversion of the T waves. In 3 dogs, changes occurred in the S-T segment and T waves. No electrocardiographic changes whatsoever

228

Before

FIG. 7. Complctc abscncc of clrctrocardiographic changes immediately followat the drfibrillating energy level of 70 watt ing 40 capacitor discharges seconds (EDs5). VI, is a left prrcordial unipolar lead.

were detected in the remaining 7 animals (Fig. 7). Except for ventricular tachycardia, Only 10 epiarrhythmias were infrequent. sodes of ventricular fibrillation occurred after the 520 DC discharges. Atria1 fibrillation A comparison of the was never observed. effects of DC and AC countershock in Group 2 animals is illustrated in (Table VI). The greater safety of DC discharge as contrasted to AC is indicated by the absence of mortality, the lesser incidence of myocardial infarction, the reduced frequency of ventricular fibrillation and the complete absence of atria1 fibrillation. While DC1 and DC3 countershocks each resulted in the same incidence of myocardial infarction, striking differences were noted in other effects of the two units. DC1 countershock was associated with a high incidence of arrhythmias. Of the 153 episodes of ventricular tachycardia 151 were due to DC,. Thus 63 per cent of DC, and only 1 per cent of DC:$ countershocks were followed by ventricular tachycardia. Similarly, ventricular ectopic beats occurred after 38 of DC1 countershocks Electroand after only 8 of DC, countershocks. cardiographic currents of injury immediately following countershock were noted frequently in 4 of the 6 animals treated with DC, and in only 1 of the 9 subjected to frequent DC:! discharges. VARIABLE

COUNTERSHOCK

LEVELS

(GROUP

3)

To determine whether shock intensity was a factor in the production of arrhythmias, 30

additional dogs were subjected to 616 discharges at varving countershock levels. In 10 animals receiving 158 AC shocks, the discharge was systematically varied from 25 to 750 volts. In the other 20 dogs receiving 458 DC shocks, the energy level was varied from 7 to 200 watt seconds (Table VII). .dltrrnating Current: The most serious arrhythmia following AC was ventricular fibrilThis occurred after 34 (21.5 per cent) lation. of the shocks. Ventricular fibrillation was directly responsible for death of 2 of the 10 Both dogs developed this arrhythmia animals. at the very beginning of the experiment after shocks of 100 volts each. Numerous transthoracic AC countershocks were unavailing even though the discharge level was progressively increased to 750 volts. While normal mechanisms were restored thereafter with a single DC shock of 100 watt seconds, increasing intraventricular block ensued, and both dogs died in cardiac standstill. Ventricular fibrillation was encountered at all countershock voltages employed (Fig. 8). Its incidence was, however, inversely related to the voltage of the ,4C discharge. Thus the incidence of ventricular fibrillation was 45 per cent after shocks of 50 volts but only 13 per cent when the discharge level was increased to 750 volts. The most frequent arrhythmia encountered after .4C countershock was atria1 fibrillation. This occurred after nearly 80 per cent of the shocks and was directly related to voltage. At a level of 75 volts, 4 of the 10 shocks resulted THE

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Electroshock

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TABLEVI

The Immediate Effect of Varying Levels of AC and DC Countershock in 30 Animals

(25ZO No. of dogs No. of shocks

v)

DC* (7-200 ws)

10

20

158

458

Ventricular

fibrillation

34 (21.5%)

VentricuIar

tachycardia

32 (20%)

100 (21.9%)1

Ventricular beats

premature 10 (6.5%)

17 (3.7%)

Atrial fibrillation

126 (79.8%) 2

Dead

6 (1.3%)

0

in atria1 fibrillation; at a setting of 450 volts or higher all 42 shocks were followed by atria1 fibrillation. These were transient bouts lasting for 5 to 15 seconds; a number, however, Another arpersisted for many minutes. It ocrhythmia was ventricular tachycardia. curred after 32 per cent of AC shocks and, like atria1 fibrillation, was directly related to the level of discharge. Thus ventricular tachycardia was rarely observed when the voltage was less than 250. The incidence of ventricular tachycardia was 29 per cent at 350 volts and 60 per cent when the setting was at 450 volts or higher. Direct Current: None of the 20 dogs died during the 24-hour period of observation. Only six episodes of ventricular fibrillation followed the 458 DC shocks, an incidence of 1.3 per cent. Two of the episodes of ventricular fibrillation followed shocks of 25 watt Each seconds and two after 50 watt seconds. of the three DC units accounted for two of the The most episodes of ventricular fibrillation. frequent rhythm disorder was ventricular tachyThis occurred after 22 per cent of the cardia. DC shocks. Of interest is the fact that ventricular tachycardia followed the use of DC, and DC, but not DC, type of countershock. The occurrence of ventricular tachycardia was directly related to the energy level of the discharge. Thus at a shock level of 40 watt seconds, the incidence was 4 per cent while at 100 watt seconds the occurrence of ventricular tachycardia was 100 per cent with both DC, 1962

25-150

0

* Represents 10 animals treated with DCI, 5 with DC2 and 5 with DCS. t Limited primarily to animals receiving DC> and DC2 countershock.

AUGUST

Y0 Incidence of 80 Arrhythmios 60

250-350

Voltoge FIG. 8. cardiac shocks.

450-750

All

Voltages

Levels of AC Shocks

Relation of level of voltage to the production of arrhythmias in 10 dogs after 158 AC counter-

and DC2 units. observed.

Atria1 fibrillation

was never

DISCUSSION

Around the turn of the century Prevost and Battellis observed that the passage of a relatively small amount of electrical current directly through the heart provoked ventricular fibrillation and that the flow of a very strong current over a short interval stopped fibrillation. It is of interest that these experiments, accomplished in 1899, already employed both AC and capacitor discharge for defibrillating the heart. Scant attention was paid to these findings. More than 30 years elapsed before the subject of electrical defibrillation was reinvestigated. Kouwenhoven, Hooker and Langworthy,g JO in experiments conducted in the early 1930’s, established the foundation for the present use of electrical countershock. Their apparatus employed 60 cycle AC of 1.5 to 2.0 amperes at 120 to 130 volts; the electrode paddles were applied directly to the heart. The extensive investigations of Wiggers and co-workers” confirmed the consistent effectiveness of AC in defibrillating the exposed heart. A culmination to these studies occurred in 1947 when Beck successfully defibrillated a human heart with complete recovery of the patient.12 Since then, the lives of many have been saved by the prompt application of AC countershock to the fibrillating heart. The need for thoracotomy and direct application of the electrodes to the heart limited the clinical use of this method. In 1936 Ferris et a1.13 succeeded in defibrillating sheep by sending an AC of 25 amperes through the

Lown et al. intact chest wall. In extensive studies, Zoll and co-workers’” clearly demonstrated the effectiveness of ,4C discharge for transthoracic defibrillation of the human heart. The prodigious efforts of Kouwenl~oven,‘Z extending over three decades, clearly defined the electrical and other technical conditions for defibrillation and thus promoted the general acceptance of AC countershock as an experimental and clinical tool. There has been much less study of capacitor discharge defihrillators, though this subject has engaged the attention of a number of investigators.6’7’16”0 It has proved an intriguing problem, for by merely changing the parameters of the discharge circuit, capacitor discharge may be made to assume an infinite variety of wave forms. At the present time there is no physiologic basis for predicting the wave form which is optimal for defibrillation. The selection of a proper instrument has, therefore, been based on a trial-and-error approach in which the values of capacitance and inductance were randomly changed in relation to one another. To date, reported While Gurresults have been contradictory. vitch and Yunievr6J7 in the Soviet Union and PeleSkafi in Czechoslovakia found capacitor discharge highly effective in defibrillating the heart, Guyton and Satterfieldt8 as well as Kouwenhoven and Milnor20 noted only inKouwenhoven tested deconsistent results. fibrillators with capacitors ranging from 25 to 250 microfarads charged to voltages varying from 450 to 4,000 and with various values of resistance and inductance in the discharge The proportion of successful dcfibrilcircuit. lations was lower with all types of capacitor discharges tested than with a single application of AC. The difference in effectiveness was especially striking when fibrillation lasted over 30 seconds. Under these circumstances the heart could not be defibrillated with capacitor discharge ; however, with t\C, reversion was achieved even when fibrillation had persisted for as long as 14 minutes. The problem of finding the optimal form of countershock did not press for solution as long as defibrillation was infrequently attempted. This procedure was only reasonable when physician and apparatus were instantly available at the bedside at the very onset of the arrhythmia ; otherwise irreversible neural damage and death ensued even when the heart was defibrillated. In practice, attempts at de-

fibrillation were, therfore, limited to the environs of the operating room or to the patient with Adams-Stokes disease who developed ventricular fibrillation. The remarkable demonstration by Kouwenhoven and co-workers1 that blood flow to vital organs can be maintained in the arrested heart by merely compressing the lower portion of the sternum has revolutionized the concept of cardiac resuscitation. This maneuver provides critically important time to bring countershock technics effectively into play in most instances of witnessed sudden death. The demonstration by Lown and co-workers” that countershock can effectively terminate ventricular tachycardia refractory to the usual medical measures has further extended the use of this electrical method. It has, therfore, become important to determine which is the most effective and at the same time least hazardous form of electrical countershock. These considerations led to the present study. One objective of the investigation was to develop a capacitor discharging unit which would defibrillate the heart transthoracically. This was achieved. Moreover, the DC unit that was developed was more consistently effective than the conventional AC unit now in wide use. In 3 animals where AC failed even at the highest available voltages, DC proved promptly effective in defibrillating the heart. This result is especially impressive since several minutes elapsed before DC countershock was attempted; it is well known that defibrillation becomes more difficult with the passage of time.” A more striking demonstration of the superiority of DC as contrasted with AC was obtained in animals under hypothermia.22 Both types of countershock were compared in animals with ventricular fibrillation when the esophageal temperature was reduced to 20’~. by- an extracorporeal cooling system. The comparisons were made at analogous conditions of temperature, pH, POz, PC02 and serum electrolyte concentrations. AC defibrillation became increasingly difficult as the esophageal temperature was reduced below 30’~. Nearly one out of every five episodes of ventricular fibrillation could not be reverted even with three serial shocks of a 1,000 volts each. By contrast, only 1 of every 50 episodes of ventricular fibrillation could not be reversed with DC. Moreover, DC countershock restored normal sinus rhythm in every instance where AC failed. 4 second objective of the present investigation was THE

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to compare the relative safety of the two types of countershock. The advantage of DC over demonstrated. Thus of 30 AC was again animals receiving AC countershock 8 animals died, 3 immediately and the remaining 5 during an observation period of one week. By contrast none of the 55 animals similarly treated with DC shocks died. In two reported studiesz3J4 the pathologic effects resulting from the direct application of AC and DC to the heart were compared. In both studies DC was found to be associated with a lesser degree of myocardial injury. Tedeschi and White23 observed burns in all animals receiving AC countershock, while only 1 of 22 receiving DC showed such gross changes. Similarly Lape and Maisonz4 found myocardial burns after direct application of AC but not after defibrillation with single capacitor discharges. The greater safety of DC was also indicated by the lesser occurrence of ventricular as well as atria1 arrhythmias. When an animal with normal sinus rhythm receives AC countershock, there is 1 chance in 5 of inducing ventricular fibrillation. While the incidence of fibrillation varies inversely with the voltage employed, it has been observed after countershock at all voltage levels effective in defibrillation. Even discharges at 750 volts were associated with a 13 per cent incidence of ventricular fibrillation. While the majority of such episodes can be readily controlled, failure to restore a normal mechanism in two animals attests to the well recognized gravity of this rhythm disorder. By contrast, DC countershock was associated with only a 2 per cent incidence of ventricular fibrillation. A more striking difference between the two methods was observed in the occurrence of atria1 fibrillation. In the foregoing experiments this arrhythmia but rarely followed DC countershock. However, two thirds of AC shocks delivered at defibrillating voltage levels were followed by atria1 fibrillation. The incidence of atria1 fibrillation was 100 per cent when the discharge setting equaled or exceeded 450 volts. These episodes were transient but could be prolonged indefinitely by the administration of cholinergic drugs. These findings indicate that capacitor discharges are not only more effective than AC in defibrillating the heart but are also associated with less complication. DC affords additional advantages. The DC unit, by storing the countershock energy in a capacitor, even AUGUST

1962

Current

Electroshock

231

at the highest countershock intensities, requires only one ampere from the power line. This decreases the possibility of line overload, voltage drop and fuse burnout. The above problems are encountered with AC defibrillators that may draw up to 70 amperes from the power line. Furthermore, the calibration of countershock intensity with the DC unit is independent of line-voltage variation and, therefore, is more accurate and dependable. A further advantage of DC is that with this method the occurrence of ventricular fibrillation can be entirely eliminated when used in the nonfibrillating heart. Apparently the brief capacitor discharge of 2.5 milliseconds must fall within the vulnerable phase of the cardiac cycle before it can disorganize the cardiac rhythm.25 If this is indeed the explanation for the rare and random occurrence of ventricular fibrillation, it should be possible to eliminate this arrhythmia entirely by programing the discharge to occur outside the vulnerable period. When this was accomplished, ventricular fibrillation never occurred.26 Conversely, there was nearly a 100 per cent incidence of ventricular fibrillation when the shock discharged during the vulnerable phase. By using properly synchronized capacitor discharges triggered to occur within the nonvulnerable phase of the cardiac cycle, Lown and co-workers2 have shown that it is possible to control serious clinical disorders of heart rhythm and yet avoid the production of ventricular fibrillation entirely. A @al objective of the present investigation was to determine the optimum type of capacitor All discharge. Three units were tested. proved equally effective in achieving defibrillation at nearly identical energy levels. Another unit currently under study, employing a 32 microfarad capacitor, also is effective at the same level. The energy level for defibrillating 65 per cent of episodes of ventricular fibrillation was 70 watt seconds when capacitors of 8, 16 and 32 microfarads were employed. These represent approximately 4,000, 3,000 and 2,000 volts, respectively. This confirms the conclusion of Mackay and Leeds7 that joules rather than volts are critical for defibrillation. The three DC units were equally effective in defibrillating the ventricle; selection of the best instrument was therefore determined by the incidence of side effects following countershock. The most prominent of these was the occurrence of ventricular tachycardia which

Lown et al. was encountered most frequently after DC1 and DC, discharges but rarely after the use of DCJ. The very nature of capacitor discharge that permits great variation in the resulting wave form will no doubt encourage more extensive experimentation. The present study affords a background of comparison for assessing efficacy of various wave forms. It also suggests a method of experimental study. Srrsfhtmy

AND C~ONCLUSION

1.

The effects of alternating current (AC) and direct current (DC) countershock were compared in 85 dogs. In 30 of the animals the countershock was administered during ventricular fibrillation, in the remainder during sinus rhythm. 2. Repeated episodes of ventricular fibrillation were controlled by either AC or DC The one failure encountered countershock. was with AC. This animal was then defibrillated with DC. 3. Repeated countershock was administered to 55 animals in normal sinus rhythm. Of 20 receiving AC 7 died, and of 35 receiving DC none died. 4. Electrocardiographic changes consistent with the development of acute myocardial infarction were observed in 9 of 10 animals subjected to repeated AC countershocks at defibrillating levels. Such changes were noted in 5 of 15 animals similarly treated with DC countershock. 5. Atria1 as well as ventricular arrhythmias were frequently induced by AC countershock. The incidence of ventricular fibrillation was 10 times more frequent after AC as compared to DC countershock. 6. It is concluded that DC or capacitor discharge is the preferred method for achieving cardiac defibrillation. REFERENCES I. KOUWENHOVEN, W. B., JUDE, J. R. and KNICKERClosed chest cardiac massage. BOCKER, G. G. J.A.M.A., 173: 1064, 1960. 2. ALEXANDER, S., KLEIGER, R. and LOWN, B. Use of external electric countershock in the treatment of J.A.M.A., 177: 916, ventricular tachycardia. 1961. 3. ZOLL, P. M. and LINENTIIAL, A. J. Termination of refractory tachycardia by external countershock. Circulation, 25: 596, 1962. 4. PAUL, M. H. and MILLER, R. A. External electrical termination of supraventricular arrhythmias in Circulation, 25 : 604, congenital heart disease. 1962.

5.

ZOLI.> I'. hf.. PAUL, hf. H., LINENTHAL, A. J., NORMAN, L. 1~. and GILESON, W. Effect of ex-

ternal electric currents on the heart. Control of cardiac rhythm and induction and termination of cardiac arrhythmias. Circulation, 14: 745, 1956. 6. PEI.&KA, B. Transthoracic and direct defibrillation. Rozhledy V. Chirurgii, 26: 731, 1957. 7. MACKAY, R. S. and LEEDS, S. E. Physiological effects of condenser discharges. J. Appl. Physiol., 6: 67, 1953. 8. PRIXV~S~, J. I,. and BATTELLI, F. La mart par les cam-ants electriques-courants alternatifs a haute tension. J. physiol. et path gen.; 1 : 427, 1899. ‘9. KOUWENIIOVEN, W. B., HOOKER. D. R. and LANGWORTIIY, 0. R. The current flowing through the heart under conditions of electric shock. .4m. J. Physiol., 100: 344., 1932. 10. HOOKER, D. R., KOUWENHOVEN,W. B. and LANGWORTHY, 0. R. The effect of alternating electric currents on the heart. iim. J. Physiol., 103: 444, 1333. 11. WIGGERS, C. J. The physiologic basis for cardiac resuscitation from ventricular fibrillation-method of serial defibrillation. Am. Heart J., 20: 413, 1940. 12. BECK, C. S., PRITCHARD, W. H. and FEIL, S. H. Ventricular fibrillation of long duration abolished by electric shock. J.A.M.A., 135: 985, 1947. 13. FERRIS L., KING, B. G., SPENCER, P. W. and WILI.IAMS, H. B. Effect of electrical shock on the heart. Electrical Engineering. 55 : 498, 1936. 14. ZOLL, P. M., LINENTHAL, A. J., GIBSON, W., PAUL, M. H. and NORMAN, L. R. Termination of ventricular fibrillation in man by externally applied NPW England J. Mpd., 254: 727, countershock. 1956. 15. KOU~ENHOVEN, W. B., MILNOR, W. R.? KNICKERBOCKER, G. G. and CHESTNUT, W. B. Closed chest defibrillation of the heart. Surgery, 42 : 550, 1957. 16. GURVICH, N. L. and YUNIEV, G. S. Restoration of regular rhythm in the mammalian fibrillating heart. Am. Rev. Soviet Med., 3: 236, 1946. 17. GURVICII, N. I,. and YUNIEV, G. S. Restoration of heart rhythm during fibrillation by a condenser discharge. Am. Rev. Soviet Med., 4: 252, 1947. 18. GUYTON, A. C. and SATTERFIELD, J. Factors concerned in electrical defibrillation of the heart particularly through the unopened chest. Am. J. Physiol., 167: 81, 1951. 19. KOUWENHOVEN, W. B. Effects of capacitor discharges on the heart. 7-rans. AIEE Power _‘I@. orzd Sys., 75: 12, 1956. 20. KOUWENIIOVEN,W. B. and MILNOR, W. R. Treatment of ventricular fibrillation using a capacitor discharge. J. Applied Physiol., 7 : 253, 1954. 21. KOUWENHOVEN,W. B. and MILNOR, W. R. ElecTrans. AIEE Power A#. and tric defibrillation. Sys., 74: 561, 1955. 22. LEFEMINE, A. A., ANARASINGHAM, R., HARKEN, D. E., BERKOVITS, B. and LOWN, B. A comparison of direct current and alternating current delibrillation under conditions of hypothermia. (Abst.) 54th Annual Meeting, Sac. for Clin. Invest., April 30, 1962, p. 43. 23. TEDBSCIII, C. G. and WHITE, C. W., JR. A morphoTHE AMERICAN

JOURNAL

OF CARDlOLOCY

Alternating

vs. Direct

logic study of canine hearts subjected to fibrillation, electrical defibrillation and manual compression. Circulation, 9 : 916, 1954. 24. LAPE, H. E. and MAISON, G. L. Cardiac resuscitation and survival: influence of rate of manual compression and type of countershock and of epinephrine. Am. J. Physiol., 172: 417, 1953. 25. KING, B. G. The Effects of Electrical Shock on Heart Action with Special References to Varying

AUGUST 1962

Current

Electroshock

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Susceptibility in Different Parts of the Cardiac Cycle. Doctorate thesis. Aberdeen Press, N. Y., May, 1934. 26. LOWN, B., AMARASINGHAM,R., NECMAN, J. and BERKOVITS,B. The use of synchronized direct current countershock in the treatment of cardiac arrhythmias. Presented before the 54th Annual Meeting, American Sot. for Clin. Invest., April 30, 1962, Atlantic City, N. J.