VOL 60
AUGUST
ir
cAn Official
NO 2
1979
Journalof the cAmerican Heart c.Association, Ic.
EDITORIALS
Editorial Note
In the previous issue of Circulation, Gold et al. (Circulation 60: 187, 1979) presented data compatible with
the thesis that the defibrillation threshold in calves depends on body weight. The extrapolation of this observation to man is extremely controversial. In this issue, two original articles present data in man which are at
some variance with the observation in calves. In view of the importance of the required energy levels for human
defibrillation, we are including two editorials on this subject. We hope that these viewpoints will stimulate the
design of more definitive studies in man to settle this crucial issue.
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Ventricular Defibrillation: Appropriate Energy Levels
A. A. JENNIFER ADGEY, M.D., F.R.C.P., J. NORMAN PATTON, M.B., M.R.C.P.,
NORMAN P. S. CAMPBELL, M.D., M.R.C.P., AND SAMUEL W. WEBB, M.D., M.R.C.P.
When ventricular fibrillation in the adult is corrected transthoracically, the majority of studies advocate the maximum stored energy of the defibrillator, i.e., 400 watt-sec.'-3 From this stored energy,
many commercially available defibrillators deliver
270-330 watt-sec through a resistance of 50 Q. It has
been suggested that a trial at a lower energy level than
a stored energy of 400 watt-sec offers no advantage.4
Originally, depolarization of every cell in the ventricles was considered necessary to terminate ventricular fibrillation. However, it has been shown that
successful defibrillation occurs when a critical mass of
myocardium is depolarized.5 Other workers have
shown that lower energies than 400 watt-sec stored
can successfully effect transthoracic ventricular
defibrillation in the adult.6 7
In 1974, Tacker et al.8 9 indicated that the maximal
energy delivered from commercially available defibrillators might be insufficient to achieve defibrillation
in heavy persons. These workers claimed that "300
watt-seconds maximum energy" delivered from commercial defibrillators was insufficient to defibrillate
35% or more of subjects weighing over 50 kg, and that
it was ineffective in 60% of patients weighing 90-100
kg,8 These claims were based on retrospective clinical
data and on experimental studies in which they
observed that rabbits weighing 2.3 kg required much
less energy than horses of 340 kg to effect successful
defibrillation, although there was a wide variation
within each species of the energy required for
defibrillation.'0 In this animal study, Lown et al.1"
pointed out that the heart weights varied by a factor of
nearly 500, while in the adult human heart, the weight
range rarely varies by a factor of more than 3.
In 1975, the Belfast group'2 made preliminary
observations on the correction of ventricular fibrilla-
ENERGY REQUIREMENTS for the successful correction of ventricular fibrillation in adults is a controversial topic. The majority of clinicians advocate
the use of the maximum stored energy of the
defibrillator, i.e. 400 watt-sec. Some workers believe
that this energy level is inadequate to defibrillate 35%
or more of subjects weighing more than 50 kg, and
have proposed an energy dose-weight concept and
recommended that defibrillators should be capable of
delivering 500-1000 watt-sec. Apart from the increased risk of myocardial damage, these devices
would be larger, less portable, and less readily
available. Other workers have been unable to relate
the success of defibrillation to body or heart weight in
patients weighing up to 225 kg. A success rate of 95%
has been recorded from the use of 200 watt-sec
(stored) in adult patients whose weights ranged up to
102 kg. Thus, for most patients, the use of 400 wattsec (stored) energy may be excessive. Defibrillation
with the least energy will minimize the risk of myocardial damage. The percentage of long-term survivors of
resuscitation from ventricular fibrillation outside
hospital would be increased if defibrillators were more
readily accessible. Therefore, the use of small
(preferably pocket-sized), inexpensive, lightweight
defibrillators with a stored energy that need not be
greater than 400 watt-sec is essential.
From the Department of Cardiology, Royal Victoria Hospital,
Belfast, Northern Ireland.
Address for reprints: Dr. A.A.J. Adgey, Department of Cardiology, Royal Victoria Hospital, Belfast, BT12 6BA, Northern
Ireland.
Received November 1, 1978; revision accepted February 26,
1979.
Circulation 60, No. 2, 1979.
219
220
CIRCULATION
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tion using 200 watt-sec stored energy, i.e., 150-165
watt-sec delivered through a resistance of 50 P. It was
shown that 89% of episodes were corrected by a single
shock and 98% were corrected by two low-energy
shocks. In 1977 and 1978, they reported the effect of
similar energies in 233 episodes of ventricular fibrillation among 120 patients.'3 14 Two hundred twenty-two
episodes (95%) were successfully converted by up to
three 200-watt-sec shocks; in 199 episodes (85%), a
single shock was successful. In patients weighing more
than 60 kg, 95% of the episodes were successfully converted and in patients weighing more than 80 kg, ventricular fibrillation was stopped in 90% of the
episodes. There was no statistically significant
difference between the percentage success in each of
the weight groups examined, and the weights ranged
up to 102 kg. In the same study, when the effect of
shocks of 100 watt-sec stored energy was observed,
successful defibrillation occurred in 81% of the episodes with up to three 100-watt-sec shocks; the initial
shock was successful in 67% of the episodes.
Among the few patients in the study who were not
defibrillated by 100- or 200-watt-sec (stored) shocks,
there was no failure to correct ventricular fibrillation
using 400 watt-sec (stored); the maximal energy
delivered by the defibrillators was 330 watt-sec.
The difference between these results and those of
Tacker et al.8 requires explanation. The Belfast study
was prospective: 90% of the patients had ischemic
heart disease and 74% had had an acute myocardial
infarction. Sixty-five percent of the cases in the Belfast
study had primary ventricular fibrillation. Ventricular fibrillation was present for 2 minutes or less in
74% of the episodes.
The study of Tacker et al. was retrospective. The
proportion of patients with ischemic heart disease or
the number with secondary ventricular fibrillation,
i.e., fibrillation complicating cardiogenic shock or
pump failure, was not indicated. Since it appears that
many of the patients developed ventricular fibrillation
in surgical wards, it may have occurred in association
with electrolyte disturbance, digoxin toxicity,
pulmonary embolism, or other surgical complications. Lown et al."5 showed that ventricular fibrillation induced by digoxin in animals was unaffected
even when multiple high-energy shocks were applied
to the chest wall. If this is also true in man, then
failure to remove ventricular fibrillation may not be
related to the energy delivered to the myocardium, but
to a direct effect of digoxin on myocardial cells. Forty
percent of the hospitalized patients of Tacker et al.8
developed ventricular fibrillation after cardiac surgery, which suggests that the majority did not have
ischemic heart disease.16 None of the patients in the
Belfast study had ventricular fibrillation after cardiac
surgery. The number with primary ventricular fibrillation, the duration of ventricular fibrillation before
defibrillation, the defibrillation technique, and the personnel involved in defibrillation, have not been
documented in the study of Tacker et al.
It has become clear that the position of the
paddles,", " their application,19 electrode paste, and
VOL 60, No 2, AUGUST 1979
paddle size20 influence the amount of stored energy
required for successful defibrillation. In the Belfast
study, the personnel were medically qualified and all
had experience of coronary care and had received intensive training in resuscitation techniques. The
paddles used were 8.5 cm in diameter. One was placed
to the right of the sternum below the clavicle, and the
other in the fifth left intercostal space in the anterior
axillary line. The electrode paste was chosen to give
maximum reduction in transthoracic impedance. In
the study of Tacker et al., the patients were in ventricular fibrillation for "5 minutes or less before discovery.' If resuscitative attempts are not commenced
early after collapse, the success of defibrillation may
be limited.
Energy Dose-Weight Concept
Tacker et al.8 proposed an energy dose-weight concept for the correction of ventricular fibrillation. They
suggested that the initial shock for patients weighing
less than 50 kg should be between 3.5-6 watt-sec/kg
body weight (delivered energy), and for patients
weighing more than 50 kg, the full output of defibrillators (400 watt-sec stored) should be used. These
guidelines have been recommended by the American
Heart Association.2' The energy dose-weight concept
was derived by comparing the weights of 10 patients
(seven adults and three children) in whom failure to
defibrillate at one energy setting was followed by
success at a higher energy level.8 In the same year,
they advocated that adult subjects who weigh more
than 40 kg without known cardiac disease should
receive a delivered energy of 5-10 watt-sec/kg body
weight.'0 In 1976, they advocated 6.6 J/kg or more for
patients weighing 45 kg or more.22 In 1977, the dosage
recommended was "'4-6 joules per kg body weight"
delivered energy.23 In the Belfast study,'3 1using 200watt-sec (stored energy), no relation was found
between energy required for defibrillation and the
patient's weight. Kerber and Sarnat24 -studied 52 cases
of ventricular fibrillation. Body weight and heart
weight made no difference to success of defibrillation.
They showed that higher energy shocks per kilogram
were not more effective for defibrillation, and
suggested that higher energies may have been
deleterious. Lown et al." cited Crampton's results for
253 episodes of ventricular fibrillation in which
delivered energy of 196 ± 11 watt-sec was consistently
effective in 95% of the episodes. Body weight was not
related to the success of defibrillation.
Tacker2" suggested that using a defibrillator with a
damped sinusoidal wave form, the first attempt to
defibrillate an adult patient should be made using
300 or 400 watt-sec of delivered energy. He also
suggested that if this energy level failed, one should
progressively increase the energy by 100-200-watt-sec
increments. It has been reported that if a shock fails to
remove ventricular fibrillation, a further identical
shock may be successful.26 That an identical shock
may be successful in removing ventricular fibrillation
when the initial shock has failed may be related to the
DEFIBRILLATION ENERGY LEVELS/Adgey et al.
decreased transthoracic impedance with successive
shocks.27, 28 However, the Belfast group found that if
two low-energy shocks were unsuccessful, a third identical shock seldom -succeeded.13' 14
It has been estimated that if a damped sine wave
defibrillator is used to defibrillate human subjects who
weigh more than 100 kg, then a delivered output
passed across the chest in excess of 500 watt-sec will
be necessary.29 The Belfast data'3 14 showed that in
three episodes of ventricular fibrillation which occurred in two patients, each weighing 102 kg, either
200- or 400-watt-sec (stored) shocks corrected the ventricular fibrillation. Curry and Quintana30 removed
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ventricular fibrillation after an acute myocardial infarction in a 108-kg pregnant female, using one DC
shock of 300 watt-sec. Tacker et al.3' reported the
removal of ventricular fibrillation during coronary
arteriography in a patient weighing 102.5 kg using
three 300-watt-sec DC shocks (delivered energy). Lappin32 corrected ventricular fibrillation in a 145-kg man
with one 400-watt-sec (stored energy) shock. DeSilva
and Lown33 reported the successful resuscitation of a
man weighing 190.1 kg with a single 400-watt-sec
(stored) shock. The patient had been in ventricular
fibrillation for over 10 minutes. Lown et al." cited
Crampton's results where a delivered energy of
196 ± 11 watt-sec successfully defibrillated 45 (98%)
of 46 episodes of ventricular fibrillation in 12 patients
weighing 107 ± 11 kg. The heaviest patient weighed
225 kg.
Anderson and Suelzer34 found that using a
defibrillator which delivered a trapezoidal waveform
with a maximum of 250 watt-sec in 10 patients
weighing in excess of 100 kg, eight (80%) were
successfully defibrillated. All four who weighed
110-140 kg were successfully defibrillated.
The more recent data from Tacker et al.35 failed to
show a relationship between the energy required to
remove ventricular fibrillation during open heart surgery and the weight of the heart, estimated either by
the surgeon or at autopsy. Geddes et al.'0 proposed
that peak current and, in particular, peak current/kg
of body weight was a better measure of the requirements for clinical ventricular defibrillation than
delivered energy.36 It has been thought that peak
current for successful defibrillation may have a linear
relationship to body weight.'0 In adults it has been
suggested that 1 amp/kg is required for defibrillation.10 However, the Belfast group found that the
mean peak current/kg required for the removal of
ventricular fibrillation in adult patients was
0.35 ± 0.05 amp/kg (unpublished data). No correlation was found between body weight and the mean
peak current.
Energy Levels and the Early Minutes
of Myocardial Infarction
It has been shown in dogs that there is a marked increase in the energy required for ventricular defibrillation in the early minutes after myocardial infarction.9
It has, therefore, been suggested that patients with
221
acute myocardial infarction, particularly those seen
shortly after the onset of symptoms, may require
higher energies to defibrillate the heart.9 37 However,
in the Belfast study"3 14 of the patients with primary
ventricular fibrillation which occurred within 1 hour of
the onset of acute myocardial infarction, 40 (98%) of
the 41 episodes were converted by 200 watt-sec
(stored).
Cardiac Damage and Energy Levels
The higher the energy setting of a defibrillator, the
greater the likelihood of cellular damage. In animals,
it has been shown that the higher the energy level, the
greater the amount of myocardial damage.38 Also in
animals, as the energy increases, an increase in the incidence of arrhythmias has been reported.39 4' In
isolated cultured myocardial cells, the severity of
arrhythmias increases as the shock levels increase.42' 4
These arrhythmias may be associated with prolonged
depolarization of the cell membrane, which increases
with the intensity of the applied stimulus.44 The
depolarization has been attributed to a transient electromechanical deformation of the cell membrane during the shock." In man, after synchronized defibrillation, it has been reported that the frequency of
arrhythmias and the amount of ST-segment displacement are directly related to the energy levels used.45 46
The present practice of many units in defibrillating
patients in ventricular fibrillation is to place the
energy setting at the maximum that the defibrillator
can deliver. If DC defibrillators capable of producing
a delivered energy of 500-1,000 watt-sec are used,37
even if there is an interlock mechanism which has to
be opened before these energies can be obtained, not
only may patients receive unnecessarily high energy
shocks, but the risk of irreversible myocardial damage
also will be high. It has been argued that when the initial shock is low energy, it may have to be repeated,
and that two low-energy shocks cause more damage
than a single shock of identical total energy. Animal
experiments carried out in Belfast do not support the
latter proposition. When a given amount of energy is
delivered by high-energy shocks, the resultant
myocardial damage is greater than when the same
total energy is delivered by twice the number of lowenergy shocks (unpublished data).
Current Clinical Practice
From current clinical experience, 400 watt-sec
(stored) is in excess of what is required for defibrillation in the majority of adult patients. Tacker and coworkers have suggested that heavier human patients
are more difficult to defibrillate.8 4 Despite several
publications indicating that patients over 100 kg are
successfully defibrillated using commercially available
defibrillators with a stored energy of not more than
400 watt-sec, 1-4, 30-33 widespread dissemination of information to physicians and paramedical personnel
advocating the use of higher energy defibrillators, i.e.,
those delivering 500-1000 watt-sec has been taking
CIRCULATION
222
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place.4849If similar high-energy levels are used in
animals, major arrhythmias can be invoked, some of
which may be irreversible.50 Until those advocating
the use of these high-energy defibrillators can show
that ventricular fibrillation cannot be corrected using
a DC defibrillator storing 400 watt-sec despite the
proper application of defibrillation techniques and
resuscitative measures and that, using a delivered
energy of 500-1000 watt-sec, the ventricular fibrillation is corrected and the patient survives to leave
hospital, there is no indication for using such highenergy machines.
Ischemic heart disease is the most common cause of
ventricular fibrillation in the adult. The average adult
patient who requires ventricular defibrillation weighs
70-100 kg; in the Belfast series of 214 patients, only
two (1%) weighed more than 100 kg.'314 Only 3% of
the patients encountered in Cobb's out-of-hospital
emergency medical service in Seattle weighed over 100
kg (personal communication). Increased oxygen consumption is associated with the asynchronous and very
rapid rate of contraction of the fibers of the fibrillating heart51 52 and even the shortest intervals of interrupted coronary flow may be expected to increase
the degree of ischemia and enlarge the area of injury.
Furthermore, damage to the myocardium may occur
with prolonged external cardiac massage. The longer
the patient remains in ventricular fibrillation,
although defibrillation is successful, the less likely is
the heart to contract effectively. Thus, the time the
patient is in ventricular fibrillation must be kept at a
minimum. Since defibrillation with the least energy
will minimize the risk of myocardial damage, the
lowest possible energy levels which will effectively
defibrillate should be used. To achieve these goals, the
development of small (preferably pocket-sized), inexpensive, lightweight defibrillators whose stored energy
need not be greater than 400 watt-seconds is essential.
The Seattle group record a 25% long-term survival
rate among patients initially resuscitated from ventricular fibrillation outside hospital.53 This low percentage
might be improved to 50% or more if the same attention were directed toward the widespread availability
of defibrillators as is now directed to training of the
public in cardiopulmonary resuscitation.
7.
8.
9.
10.
11.
12.
13.
14.
15.
16.
17.
18.
19.
20.
21.
22.
23.
24.
25.
26.
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Crampton RS, Hunter FPJr: Low-energy ventricular
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Tacker WA Jr, Galioto FM Jr, Giuliani E, Geddes LA,
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Tacker WA Jr, Geddes LA, Cabler PS, Moore AG: Electrical
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Pantridge JF, Adgey AAJ, Webb SW, Anderson J: Electrical
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Connell PN, Ewy GA, Dahl CF, Ewy MD: Transthoracic impedance to defibrillator discharge. Effect of electrode size and
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Parker MR: Defibrillation and synchronized cardioversion. In
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Kerber RE, Sarnat W: Clinical studies on defibrillation dose:
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Geddes LA, Tacker WA Jr, Cabler PS, Chapman RJ, Rivera
RA, Kidder HR: Electrode-subject impedance with successive
defibrillations. Circulation 50 (suppl III): III-99, 1974
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defibrillation in man. J Thorac Cardiovasc Surg 75: 224, 1978
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40. Peleska B: Cardiac arrhythmias following condenser discharges
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Emergency Defibrillation Dose:
Recommendations and Rationale
W.A. TACKER, JR., M.D., PH.D.,
THE APPROPRIATE ELECTRICAL shock
strength (i.e., dose) for transchest defibrillation of
adult patients using damped sine wave defibrillators is
controversial." 2 Some recommend trying a weak
shock first, since an excessively strong shock may
cause cardiac damage, leading to a decreased chance
of survival or compromised cardiac function. Others
recommend trying a stronger shock first, because a
shock that is too weak will not defibrillate and, consequently, the increased time before defibrillation
decreases the patient's chances of survival.
As in most controversies, there are data to support
both positions, but there are not enough data to
resolve the issue. Studies to determine the best shock
strength are in progress, and may settle this issue
later. Meanwhile, practicing physicians need
guidelines for using defibrillators now. We briefly
review current knowledge about the effective electrical
From Purdue University, West Lafayette, Indiana, and the
University of Arizona, Tucson, Arizona.
Address for reprints: W.A. Tacker, Jr., M.D., Ph.D., A.A. Potter
Engineering Center, West Lafayette, Indiana 47907.
Received January 30, 1979; revision accepted February 26, 1979.
Circulation 60, No. 2, 1979.
AND
G.A. EWY, M.D.
dose and about cardiac damage from electric shocks,
and then suggest a strategy for selecting shock
strength that can be used until the appropriate electrical doses are better quantitated. This discussion
does not apply to children, who can be defibrillated
with low levels of energy, nor to trapezoidal wave
form defibrillators, for which effectiveness compared
with damped sine wave defibrillators is unknown.
Electrical Dose
There is overwhelming evidence that large experimental animals with no apparent heart disease
require stronger shocks for defibrillation than small
animals.3-6 Also, human pediatric patients can be
easily defibrillated with less energy than human adult
patients.6 Studies in hospitalized patients suggested
that outputs of greater than 300 J delivered energy
might be needed for human use, especially for large
patients.7 There is, however, considerable variation in
the shock strength required for individual human and
animal subjects,3 and it has been questioned whether
any useful electrical dose relationship can be
developed for human adult patients.' The variation in
shock strength required may be produced by variables
other than body weight - for example, disease state,
Ventricular defibrillation: appropriate energy levels.
A A Adgey, J N Patton, N P Campbell and S W Webb
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Circulation. 1979;60:219-223
doi: 10.1161/01.CIR.60.2.219
Circulation is published by the American Heart Association, 7272 Greenville Avenue, Dallas, TX 75231
Copyright © 1979 American Heart Association, Inc. All rights reserved.
Print ISSN: 0009-7322. Online ISSN: 1524-4539
The online version of this article, along with updated information and services, is located on
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