Med. & biol. Engng. Vol. 7, pp. 1"/-29. Pergamon Press, 1969. Printed in Great Britain
A STUDY OF PARAMETERS INVOLVED IN
ALTERNATING-CURRENT DEFIBRILLATION*
C. D. FERRIS,t T. W. MOORE,~ A. H. KHAZEI and R. A. COWLEY
Department of Electrical Engineering, College Park and Division of Thoracic Surgery,
Department of Surgery, University of Maryland School of Medicine, Baltimore, Maryland, U.S.A.
Abstract--The findings from the research reported in this paper may be summarized as follows:
Cardiac defibrillation is an electric current oriented phenomenon. There is a preferred
cardiac axis for effective defibrillation. The cardiac preferred axis cannot be related easily to
body surface electrode placement. More effective methods of defibrillation involve the use of
endoesophageal or endotracheal electrodes rather than two body surface electrodes. Impedance
measurements of the thoracic region and the heart indicate that low frequency alternating
current is probably the most effective defibrillating stimulus. While direct current is effective,
there is a greater risk of electrolysis than with alternating current.
SEVERAL years ago, the Department of Surgery,
Division of Thoracic Surgery and the Department of Electrical Engineering at the University
of Maryland embarked upon a joint project
to define some of the parameters involved in
electrical defibrillation of a heart. Much prior
work had been done in various areas and is
summarized in several pertinent papers. (FERRIS
et aL, 1936; WmGERS, 1940; LOWN et al., 1962;
BALAGOT et aL, 1964; MACKAY and LEEDS,
1953; KOUWENHOVEN and MILNOR, 1954).
The purpose of our study was directed toward
clarifying certain areas in the hope that a more
efficient means for effecting ventricular defibrillation might be developed. Both theoretical and
experimental studies were conducted. Dogs were
selected as the experimental animals primarily
for convenience and because a supply of these
animals was readily available. The animals used
in the experiments were healthy mongrels with
a weight range from 6 to 30 kg. General anesthesia was employed on the basis of 30 mg/kg
I.V. nembutal. Repeated injections were required
to maintain an approximately constant level
of anesthesia as the electric shocks counteracted
the effect of the nembutal. Respiration was maintained by means of a mechanical respirator.
In the cases, reported in a later section of this
paper, where it was necessary to expose the heart,
access was achieved by entering the left chest
through the fifth intercostal space. F o r the
external defibrillation experiments, the skin of
the animals was prepared by close shaving and
cleansing with germicidal soap.
In the several cases when electrodes were
implanted directly upon the heart, or within the
body, the animals were allowed to heal for a
period from 2 to 6 weeks depending u p o n the
number and location of the implanted electrodes.
The leads f r o m the electrodes were buried subcutaneously on the backs of the animals where
they could be retrieved quickly by nicking the
skin. The animals, however, could not gain
access to the leads by biting or scratching.
Three goals were outlined: (1) Definition for
the electrical mechanism for defibrillation. (2)
* Received2 July 1968.
t Present address: Department of Electrical Engineering and Bioengineering, University of Wyoming, Laramie,
Wyoming.
:~Present address: Drexel Institute of Technology, Philadelphia, Pennsylvania.
Supported by U.S. Public Health Grant No. HE-04595.
17
18
C . D . FERRIS, T. W. MOORE, A. H. KHAZEI and R. A. COWLEY
Determination of the existence of a preferred
axis at the heart for placement of the defibrillating electrodes. (3) Translation of the preferred
axis, if any, to placement of external chest electrodes, or other electrode systems.
-
i
Rp/2
Cp'2
ELECTRODE STUDIES
Because their use is critical to any physiological experiment involving electrical stimulation,
a careful study of metallic electrodes was undertaken. Three primary factors must be considered
in the use of stimulating electrodes. These are
electrode material, stimulating waveform, and
the electrical intensity of the stimulating signal.
An electrode material must be selected for its
electrical properties and its tolerance by body
tissues. This limits electrode material generally
to the noble metals and to stainless steel. Although stainless steel electrodes exhibit some
undesirable electrical properties, they are generally tolerated by the body. In addition, they
are easily fabricated and are inexpensive. For
these reasons, we selected stainless steel as our
electrode material, although platinum would
have been preferable from an electrical standpoint.
The frequency range over which the electrodes
would be used extended from 30 to 400 Hz. The
range was determined by the power generating
capabilities of the equipment available to us for
these studies. This frequency span proved to be
more than necessary. Over this range of frequency, certain electrode phenomena must be
considered. Whenever a metallic electrode is in
contact with an electrolyte, and any body
material may be considered electrically to be an
electrolyte, an electrical interface impedance is
developed at the contact surface. SCHWAN
(1951, 1957) has shown that over a limited frequency range, a body electrolyte can be represented by the equivalent circuit shown in Fig. l(a).
The effect of the electrode interface impedance,
or alternating current electrode polarization
impedance as it is properly designated, is illustrated in Fig. l(b) for a single electrode-electrolyte interface. When two electrodes contact a
physiological electrolyte, Figs. l(c) and (d)
(b)
(o)
Rp/2
(d)
(c) -~
FIG. 1. Equivalent circuits for physiologicalelectrolyte
and a.c. electrodepolarization impedance.
represent the situation. The properties of the
a.c. electrode polarization impedance are well
documented. (ScI-IWAN, 1957; SCHWAN and
MACZUK, 1965; JARON et aL, 1967; FEgRIS and
MELLMAN, 1967). It manifests both linear and
non-linear behavior depending upon the electric
current density which is present at the interface.
At low current densities, linearity exists and
the electrode polarization impedance decreases
linearly with an increase in the frequency of the
applied signal (stimulus). Consequently, at high
frequencies the polarization impedance virtually
disappears. In the linear range, the magnitude
of the impedance, when frequency is held constant, remains a constant value as current density
changes. In the non-linear range, the polarization impedance decreases in magnitude as current
density increases, again with frequency maintained constant. Figure 2 illustrates the properties of the a.c. electrode polarization impedance.
The threshold current density which separates
the linear and non-linear ranges is strongly a
function of the electrode material and the
A STUDY OF PARAMETERS INVOLVED IN ALTERNATING-CURRENT DEFIBRILLATION
19
trodes may produce quite low current density
and linear behavior of the interface impedance.
It must be dearly understood that the foreC p(ufd)
going discussion has nothing to do with mechanical contact problems associated with electrodes. Poor contact between the electrodes and
Lineor
~on
-linear
tissue can also cause voltage drops at the interface. This factor can be easily eliminated by
proper positioning and contact pressure of the
electrodes. The a.e. electrode polarization impedance is an ever present factor.
I
JARON et al. (1967) have developed a matheII
matical formulation for the polarization resisThreshold
tance Rp, the polarization capacitance Cp, and
Current density
FIG.2. Behaviorof polarization capacitanceand resistance the interface voltage drop as a function of time
as a functionof current densityat the electrode-electro- v(t). While their expressions were developed for
lyte interface.
platinum-iridium electrodes, they feel confident
that they apply equally well to other materials.
electrolyte. (SCHWANand MACZUK,1965 ; JARON (JARON, private communication.)
et aL, 1967; FERRIS and MELLMAN, 1967;
Rp = (rl-~/C~)[sin(l -- ~)~/2]oJ-~
KOnLRAUSCFX,1897).
Cp = Co[1 + co*X-%os(1 -- a)zr/2]-1
The effect of the a.c. electrode polarization
v(t) = (Io/Co)[t q- r x-'t'/l"(1 q-a)]
impedance is to introduce a voltage drop at the
electrode-electrolyte interface. Hence, if one where:
applies 2 V across an electrode pair in contact
Co= base level capacitance determined
with body tissue less than 2 V is applied
empirically
at the tissue itself, because of the voltage drop
Io = magnitude of applied current
introduced by the interface impedance. For
~-= system time constant determined
relatively low-level stimulation, linear behavior
empirically
of the polarization impedance may be assumed;
a = system constant
for high-level stimulation, non-linear behavior
must be assumed. Thus, for a given set of elec/" = the gamma function
trodes in contact with a non-varying tissue, the
~o = radian frequency = 2rrf where f =
voltage drop at the interface varies according to
natural frequency.
the intensity of the applied stimulus. In the linear
range, the voltage drop will increase linearly with The polarization impedance Zp is given by the
increasing current density up to the threshold relation,
region. Above threshoId, in the non-linear
Z p = R v + ( j o ~ C v ) -1 where j 2 = _ I.
region, the voltage drop will tend to decrease as
current density increases. Electrode size is not an
The effect of the a.c. electrode polarization
important parameter. Since current density is impedance enters in two separate situations.
the controlling factor for a.c. electrode polariza- It is responsible for an electrode-electrolyte
tion impedance, applied current divided by (electrode-tissue) voltage drop with either
electrode area is the important parameter. There- stimulating or recording electrodes. The voltage
fore high current densities are possible with low- drop is frequency sensitive. When a complex
level stimulation using very small electrodes, waveform is being studied, distortion of the
while high current stimulation by large elec- waveform may be expected. Because Zp is larger
RplC 0
~
iJ
R
' ~(a)
20
C.D. FERRIS, T. W. MOORE, A. H. KHAZEI and R. A. COWLEY
at low frequencies than at high frequencies, the
voltage drop will be greater for the low frequency
components of the waveform than for the higher
frequency components of the waveform. With
signals which have a broad frequency spectrum,
low frequency distortion of the waveform is to
be expected.
When tissue impedance measurements are
conducted, the polarization impedance adds
in series with the true impedance of the tissue
sample under study as illustrated in Fig. l(c).
Impedance data must be corrected to eliminate
Rp and Cp from the measurements. Waveform
distortion is generally not a factor in impedance
measurements as such measurements are generally made at a single frequency using a pure
sinusoidal waveform. Various techniques have
been proposed for correcting experimental data
to account for the presence of Rp and Cp.
(ScHwAN, 1957; FERRIS, 1963; SCHWAN and
FERRIS, 1963).
Electrolytic tank studies, simulating the
chest region, were conducted to examine the
electrode behavior. It was discovered that while
electrode polarization impedance existed, it was
not a severe problem. The voltage drop across
the electrodes was of the order of a few volts
and is not significant when of the order of 250 V
and above is applied as the usual defibrillating
signal. This drop is significant in low level
stimulation directly at the heart. Many of our
experiments concerned measurements at the
heart itself. It was observed that at the current
levels necessary for effective defibrillation (in
excess of 3 A, see Figs. 7 and 8) electrolysis was
significant. For the normal chest electrode configurations used during defibrillation this results
in lowered impedance presented to the electrodes
and increased current levels. With rapid successive shocks to the patient it would be expected
that skin burning would not increase linearly,
but rather as a higher order function.
Several different types of electrodes were used
for the studies reported in this paper. Two types
of electrodes were used for the external chest
defibrillation experiments. Initially the usual
circular, slightly cupped, (45.6 cm z) stainless
steel electrodes were used. Some problems were
encountered with variable contact of electrodes
and a new set of electrodes was designed. These
were fabricated from a stainless steel mesh similar to chain mail. This flexible material was
backed with a 0.5 in. layer of foam rubber
which, in turn, was mounted on a solid matrix.
The electrode surface dimensions were the same
as the cupped electrodes. These new electrodes
were adaptable to the contour of the body surface and reduced many of the problems associated with variations in contact.
For the measurements which were conducted
at the heart, again, two different types of electrodes were employed. The stimulating electrodes, for inducing fibrillation and effecting
defibrillation, were fabricated from 2 cm dia.
stainless steel discs. The discs were mounted at
right angles to insulated handles. Electrical connection to the electrodes was accomplished by
insulated wires passed through holes drilled
through the handles and concentric with the
handle longitudinal axis. Certain other studies
involved the use of chronically implanted electrodes. These were also made from stainless
steel. Two-centimeter-diameter electrodes were
crocheted from stranded stainless steel wire.
(Ethi-PackR size 00, B and S 28 gauge multifilament surgical sutures). A long tail of wire was
left attached to the crocheted electrode to form
the contacting lead. This wire was insulated by
fitting it through a fine plastic catheter. The
electrodes were attached to the heart muscle or
other tissue by placing silk sutures through the
holes in the electrode mesh.
In studies reported in later sections of this
paper, other indwelling electrodes were used.
An endoesophageal electrode was fabricated
from a No. 26 endotracheal tube. A 3-in.
braided copper wire mesh bulb was attached to
the tip. The electrode was inserted into the esophagus keeping the bulb extended in the longitudinal direction. A wire stylette was connected
to the tip of the bulb. After insertion of the
electrode, the stylette was pulled. This caused
the mesh to deform and make firm contact with
the inner wall of the esophagus. The wire stylette
A STUDY OF P A R A M E T E R S INVOLVED IN A L T E R N A T I N G - C U R R E N T D E F I B R I L L A T I O N
also formed the electrical connection to the
electrode.
An endotracheal electrode was fabricated
from a No. 36 (8.5 mm dia.), endotracheal tube.
The inflatable pressure cuff on the end of the
tube was coated inside and out with flexible
conducting silver paint. The paint was also
poured inside of the tube over its length. A wire
connection was made to this silver paint coating
to form the electrical connection to the electrode.
In use the pressure cuff was inflated so that positive contact was assured between the silver paint
electrode and the inner wall of the trachea.
Electrode contact problems were investigated.
Studies were carried out using saturated-salinewetted-electrodes applied to the skin directly,
saturated-saline-soaked gauze pads between the
electrodes and the skin surface and standard
electrode paste between the electrodes and the
skin. The quality of the contact was evaluated
by measuring, under constant electrode pressure,
the impedance presented to the electrodes by
the chest region of experimental animals.
It was found that the electrode paste gave
the most unreliable and variable results. The
smallest variation was found with the salinesoaked gauze pads. The saline-wetted electrodes
gave uniform results but a constant contact
potential drop was noted. Higher impedance
values were noted than with the electrode paste
and the saline-soaked pads. Recent studies have
indicated that an interface paste is not necessary.
(RICHARDSON, 1967).
Impedance measurements
Measurements were conducted to determine
the variation as a function of applied frequency
in the magnitude of the impedance (effective
resistance) presented to internal and external
electrodes. The behavior as a function of applied
frequency of the electrical impedance presented
by dogs to chest-surface-placed defibrillating
electrodes is presented in Fig. 3. Standard
(45.6 era 2) electrodes similar to those used with
human patients were used. Depending upon the
size of the animal, the effective resistance varied
from 50 to 100 f2 and decreased with increasing
~
9c
21
(best fit line)
- -
c
~o o
-m -t:)
8s
.~cz
~,.~ 7c
45'6 cmz electrodes with
OT saline-s0aked-pad interface
I
IO0
I
IO00
I
IO,O00
Frequency, Hz
F[o. 3. Chest impedance as a function of frequency.
frequency. The inverse variation with frequency
indicates that more defibrillatory current is
necessary at high frequencies than at low frequencies. This was clearly borne out in the
experimental results presented in Figs. 7 and 8.
Gauze pads (two layers of surgical gauze)
soaked with concentrated saline (NaC1) solution
were placed under the electrodes to assure
good electrical contact between the electrodes
and the skin surface.
Impedance studies were also conducted directly at the heart using the sutured crocheted disc
electrodes previously described. Again an inverse
relationship of impedance and frequency was
8
-~
~ooc
eoc
~,,r 6oo
~'~ 400
g
~
o~
i n vivo
I
I00
measurement with i-5cmz
crocheted electrodes
I
I000
)
IO.OOu
Frequency, Hz
FIo. 4. Cardiac impedance as a function of frequency.
observed as shown in Fig. 4. The cardiac impedance is approximately an order of magnitude
greater than the chest impedance. In order to
make the measurements, the disc electrodes
(1.5 cm 2) were sutured on opposing sides of
the myocardium. There is some variation of
22
C.D. FERRIS, T. W. MOORE, A. H. KHAZEI and R. A. COWLEY
range. These units were built for several special
purposes and are described in the literature.
(TIsCHLER et aL, 1961; COWLEY et aL, 1962;
ATTAR et aL, 1965). It was decided to restrict
Power level measurement
experimentation to one particular unit in order
Experiments were conducted to determine to avoid data which might be colored by the
how much of the defibrillating power applied type of defibrillator used.
Examination of the literature showed that
at the chest surface actually reached the heart.
Various sets of meshed disc electrodes (described researchers were in disagreement as to both the
previously) were located at strategic points mechanisms involved in defibrillation and the
within experimental animals, including on the type of defibrillator to use. Voltage, current,
heart, on the intercostal muscles, and subcu- power, and energy were all claimed to be the
taneously. Insulated connections to these elec- primary agent. Various claims were made controdes were brought out to the dorsal surface cerning a.c. and d.c. operated units. Through
of the animals.
our own examination and analysis, we deterThe power applied at the surface defibrillating mined that it really makes little difference
electrodes was measured directly. Power at whether a.c. or d.c. operated defibrillators are
internal points was determined by measuring used relative to certain boundary conditions.
the voltage drop generated between a given pair Successful defibrillation can be easily achieved
of electrodes during the application of the de- using a 0.1 sec pulse of alternating current.
fibrillatory signal. The impedance was then Direct current defibrillators depend upon a
measured between the same pair of electrodes capacitor discharge and the resultant pulse
using the same frequency as the defibrillatory waveshape depends upon the value of the capacisignal. The power was calculated from these tor and the effective resistance presented by the
subject being defibrillated. It is therefore more
two measurements.
At the power line frequency (60 Hz) usually difficult to control the electrical output from a
employed by a.c. defibrillators, less than I per d.c. defibrillator than an a.c. defibrillator. For
cent of the power applied at the chest surface these and additional reasons presented in the
appeared at the heart. This easily accounts for next section, we decided to construct a transthe fact that no serious damage is sustained by former-operated a.c. defibrillator with approthe heart during defibrillation in spite of the priate automatic timer which would operate
large electrical signals used. The remaining part from the 60 Hz power mains. The electrical
of the power applied is dissipated as heat in the circuit and waveform produced are shown in
Fig. 5.
body tissues which surround the heart.
Our results show very low internal power
Figure 6 illustrates the experimental situation.
levels. This results from the ventral placement of The current and voltage applied at the elecboth defibrillating electrodes. A recent paper trodes is monitored by a Tektronix type 564
(Rr~srI et aL 1967)reports substantially higher storage oscilloscope. The electrodes are activated
internal power levels using one dorsal surface by a footswitch which controls the automatic
and one ventral surface electrode. Such a result timer. Fibrillation and defibrillation are deteris to be expected. External electrode placement mined by examining the lead I trace on an EKG
is discussed at length in a later section of this recorder. The input to the recorder is disconpaper.
nected automatically during the applied shock
and for a period of several seconds following the
Instrumentation
shock. This is necessary to protect the recorder
The initial data were obtained by using several and to allow for the EMG signals which follow
defibrillators over a relatively wide frequency the shock to disappear.
impedance at a given frequency as a result of
the volume of blood within the heart chambers
at any given instant of time.
C , ~ , ~ c ~ 20A
IlOV
o. off
60'~ ~ J
+++++,+~+,~++
_ ......
+
-
, Vorioc, 2kvo
-t.____,~ [ i
pilot
_ j ||
pilot ~~_j
+
:
_
r
1~ ~
hi-voltage
control relay
~ __~,
house"EP"
2 kvo
E =electrode connection
V = voltmeter connection
Output waveform
C =ammeter connection
T = timer connection
Defibrillator
I10v
4
9 cam op.sw.
0
60".'
I/lOsec
M= gear-train motor
'scope trigger
c i
3
O.I sec.
cam dwell sequence
IIOv relays
Timer
o
timer output
- - o
FIG. 5. Circuit schematic for fibrillator/defibrillator a n d timer.
(facing p. 22)
A STUDY OF PARAMETERS INVOLVED IN ALTERNATING-CURRENT DEFIBRILLATION
Respirotor ~
23
~ \
Defibrilletor
_I
FIG. 6. Experimental set-up.
The a.c. fibrillator-defibrillator has the advantage of simplicity of operation and repeatability
of waveform.
DEFIBRILLATION USING EXTERNAL
ELECTRODES
CHEST
Over a year's period, 491 attempts at defibrillation using external chest-to-chest electrodes
were carried out. Data points were determined
from 36 dogs. Defibrillation was attempted over
the frequency range from 30 to 300 Hz. Frequency sources included motor-generator sets,
60 Hz power mains, and special electronic power
oscillator units. In the analysis of the data
points, attention was directed toward the applied
voltage and current. The applied power was
calculated from the product of applied voltage
and current. It may be assumed, for the given
frequency range, that the animal presents a
purely resistive load to the external electrodes.
Using the 0-1 second pulse duration specified,
the applied energy was also calculated.
Applied power = V • I watts
Applied energy = V • I • T joules
where
V = applied voltage (rms V)
I = applied current (rms A)
T = pulse duration (see).
It is the opinion of many researchers that
current is the determining factor in defibrillation. (FEgms et al., 1936; WI66ERS, 1940). Using
current as the primary measured variable in
defibrillation experiments avoids certain artifacts associated with electrode contact at the
chest. These problems will be discussed in the
concluding section of this paper. In the analysis
of the experimental data, close attention was
paid to the current required for effective defibrillation over a range of frequencies.
The data were analyzed by the following
technique: The experimental points (current
reading as a function of frequency and success
or failure of defibrillation) were separated into
five frequency ranges--below 80 Hz, 80-100 Hz,
100-200 Hz, 250-300 Hz. For each range, the
percentage of successful defibrillation attempts
at various current levels was calculated. Equal
numbers of readings were used in the calculation
of each point so that the curves plotted from the
data have equal reliability over their extents.
From these points, curves were then plotted
showing current as a function of frequency for
60 per cent and 80 per cent confidence of successful defibrillation. These curves (Figs. 7 and 8)
indicated that as frequency of the defibrillating
signal is increased, increased current is required.
MAC~:AY and LvEDS (1963) reported that the
24
C.D. FERRIS, T. W. MOORE, A. H. KHAZEI and R. A. COWLEY
6.0-5,5
5-0
.
4"5
4"0
3.5
3.0
iy
I
I
I
I00
200
Frequency, Hz
0
300
FI6. 7. Electrode current as a function of applied
frequency for 60 per cent confidence ]evel of successful
defibrillation.
6<--
<:t 5-C
9~
4"5
3
4.0
3.5 /
/t
/
factor. One reason is that each muscle fiber in
the heart must have a certain a m o u n t of charge
removed from it in order to initiate its depolarization. This depolarization process does not
take place instantaneously in all fibers. Various
relaxation times are inherent. KOUWENHOVEN
and MILNOR (1954) found a.c. defibrillation more
effective than a straight capacitor discharge.
They suggested, however, that by the use of discharge circuits which prolonged the time
duration of the defibrillating shock, improved
results could be obtained with capacitor discharges.
LOWN and his co-workers (t962) using various
capacitor discharge circuits, found that a 70
J discharge gave a 65 per cent reliability
of defibrillation. BALAGOT et aL (1964) reported
good results with a d.c. defibrillator which
supplied 80 J into a 100 s resistive load. The
results of our experiments, when extrapolated
to zero frequency, are in close agreement with
the literature. In fact, our results show slightly
lower energy levels are required with a.c. defibrillation for a higher confidence of success (80
per cent). Figure 9 indicates the energy required
/.o.
3.0
20C
0
100
200
Frequency,
o
]
e
30O
Hz
FIG. 8. Electrode current as a function of applied frequency for 80 per cent confidence level of successful
defibrillation.
energy in a d.c. defibrillating pulse was the
determining factor for successful defibrillation.
Others, experimenting with capacitor discharge
devices (LowN et aL, 1962; BALAGOT et al.,
1964) found similar results. F r o m our analysis
of the data obtained with a.c. defibrillators, and
from an examination of the literature pertaining
to d.c. defibrillators, we feel that total energy
p e r se is not the determining factor. The determining factor for successful defibrillation is
more probably a combination of current and
time. We feel, then, that energy as a function of
time, rather than energy alone is the determining
/./60
~sc
% confidence
///,"
~ ioc
uJ
--///
5(1
>-
I
IO0
I
200
Frequency,
I
300
Hz
FIG. 9. Energy required as a function of frequency for
successful defibrillation.
for successful defibrillation with a level of confidence of success with the first shock of 80 per
cent. The duration of the defibrillating shocks in
all cases is 0.1 sec and the magnitude of the
A STUDY OF PARAMETERS INVOLVED IN ALTERNATING-CURRENT DEFIBRILLATION
impedance presented to the electrodes varied
from 50 to 100 t2 depending upon the size of the
animal used.
The results of this work have been previously
reported. (FEgms et aL, 1966).
I00
25
- -
9
90 --
Longitudinol (L)
o Tronsverse (T)
tx Oblique (0)
80-70--
PREFERRED CARDIAC ELECTRIC AXIS
Two years ago, we conducted measurements
to determine if their exists a preferred axis in
the heart for electrical stimulation by external
means. A total of 962 measurements were made
in situ on healthy canine hearts. The left chest
was entered through the fifth intercostal space
and the pericardium was left intact. The two
stimulating electrodes were stainless steel discs
measuring two centimeters in diameter.
Three electrode configurations were investigated:
(1) Longitudinal: One electrode was placed at
the base of the heart near the root of the
aorta with the other electrode over the apex.
(2) Oblique: One electrode was placed over the
left atrium and the other over the apex.
(3) Transverse: Opposing electrodes on the
right and left ventricles.
It was found that the longitudinal configuration was more sensitive to external stimulation
by a factor of approximately 30 per cent than
the other two configurations. Checks were made
at the heart directly with the pericardium
removed and no significant difference was noted.
The pericardium was left intact initially to take
into account the partial electrical short-circuiting
effect of the pericardial fluid. This was a necessary precaution since it was desired to relate a
possible preferred electrical axis to the placement
of external body surface electrodes. The experimental results are presented in Fig. 10. The
oblique and transverse axis data show considerable scatter, while the longitudinal axis data is
smooth.
The experimental results are not surprising
when one examines the normal electrical conduction path in the heart, which is along the
interventricular septum. The electrode placement
in the longitudinal case produces a current path
,~
6o
50
0
03 40
3o. /
I
2O
I0
I
o
50
ioo
15o
200
250
rnA/kg
Fio. 10. Percentagesuccess of defibrillationas a function
of axis and applied current.
in the heart which is parallel to the normal
conduction path. (MooRE et at., 1968). This
information concerning the preferred axis will
be related to position of external body surface
electrodes in a later section of this paper.
The results of the electrical axis experiments
led us to examine the possibility of using defibrillating electrode configurations other than surface
electrodes. We first attempted chest positions
of the electrodes to try to simulate the three axis
positions defined at the heart. The results were
not significantly different in the effectiveness of
defibrillation from the usual chest-to-chest
electrode configuration, The fact that the chest is
a layered medium composed of widely different
strata, electrically speaking, tends to change the
directions of the current lines. We did not attempt
ventral-dorsal placement of the electrodes because of possible neural damage to the spinal
column or other neural structures. In one experiment, the phrenic nerve structure in a dog was
completely and irreversably paralyzed. Apparently in this case, one defibrillating electrode
was close to the diaphragm. We submit the
observation that ventral-dorsal placement of
defibrillating electrodes should be very carefully
26
C.D. FERRIS, T. W. MOORE, A. H. KHAZEI and R. A. COWLEY
conducted so that the spinal column is not
located on the major current path axis.
The possibility of one internal electrode
utilizing a natural body cavity was examined.
This led us to develop both endotracheal and
endoesophageal electrodes which could be used
in conjunction with a single external chest
electrode.
DEFIBRILLATION USING AN INTERNAL
ELECTRODE
Studies were conducted using an endoesophageal electrode and a single chest electrode.
The electrode was fabricated as described in
the section on electrode studies. It was felt that
less power would be required in this configuration since one of the electrodes would be much
closer to the heart. On thirteen dogs 273 defibrillation attempts were made. The results are
less power would be required for successful
defibrillation than with two chest electrodes
because one of the electrodes would be positioned much closer to the heart. On ten dogs 125
defibrillation attempts were made. The experimental results are presented in Fig. 12. As before,
the data are normalized to the weights of the
animals. Again it was apparent that considerably
less current was required in this method than is
required using two conventional chest electrodes.
These two methods of defibrillating are compared with the conventional method in the coneluding section of this paper.
EVALUATION OF THE EXPERIMENTAL
RESULTS
If we examine the experimental results from
the various defibrillation attempts, it becomes
clear that current and not voltage is the primary
I00 -vector in effecting defibrillation. (FERRIS and
MOORE, 1966). Although scatter of data points
occurs, all the curves are monotonically increasing when defibrillation success is plotted against
normalized current. Although we did not present
6c-/
curves for applied voltage, we did record the
I
voltage applied across the pair of defibrillating
u)
4C-electrodes. As would be expected, the values of
the applied voltage fluctuated widely, resulting
from electrode contact and electrode polarization impedance problems. On the other hand,
current is an easily measured and controlled
I
I
I
I
I
factor.
IO
0 200
300
40o
50o
mA/kg
Experiments were conducted using four difFXG. l 1. Defibrillation success for endoesophageal elec- ferent methods of defibrillation which have been
trode.
described in previous sections of this paper.
presented in Fig. 11 where the data are normal- Defibrillation at the heart itself under open
ized to the weights of the dogs. It was apparent chest conditions was tried and this led to the
that considerably less current was required in determination of the preferred electrical axis
this method than is required using two conven- in the heart. This method, as would be expected,
tional chest electrodes, as reported in a prelimi- also provided reliable defibrillation with mininary study. (CowLvx et aL, 1964).
mum power requirements.
Studies were also conducted using an endoExperiments were then conducted to detertracheal electrode and a single chest electrode. mine if external body electrodes could be placed
This electrode was fabricated as described in the in a manner such that the preferred axis in the
section on electrode studies. As in the case of heart would be excited by the externally applied
the endoesophageal electrode, it was felt that defibrillating signal. The three external electrode
O/
;/
/.
/
.p
A STUDY OF PARAMETERS INVOLVED IN ALTERNATING-CURRENT DEFIBRILLATION
IOC
~c
.
6C
8
=o
to
4C
/
/
I.
I00
200
I
I
. 300
I
400
500
mA/kg
FI~. 12. Defibrillation success for endotrachael electrode.
positions were defined as follows: Longitudinal:
one electrode at the sternal notch and the other
at the center, top of the chest; Oblique: one
electrode placed on the left chest below the heart
and the other electrode placed on the upper
portion of the right chest; Transverse: electrodes
placed on the right and left chest in line with the
heart. These three electrode configurations were
selected so that the field lines produced in the
heart would correspond, as nearly as possible,
to the axes defined at the heart itself.
The experimental results are presented in Fig.
13. The external axis experiments do not show
any clearly defined preference as do the internal
axis experiments (Fig. 10). There is too much
scatter in the data to make any statement
other than that external chest electrode place-
/
I00
/
80
J
o~
J
OA
/ e O
6C
8
r
./
A/o
4c
/Io
2C--
9 Longitudinal
o Transverse
/~e6c~.~e~I9
A
iO0
l~o
200
~xOb!ique
L
I
300
400
rnA/kg
I
500
_1
600
13. External chest electrical axis measurements.
27
ment does not appear to be very critical. The
various body structures, which underlie the
chest surface most probably cause sufficient
distortion of the electric field lines produced
by the external chest electrodes such that the
lines do not align with the heart internal axes as
anticipated.
In an attempt to couple the applied energy
more closely with the heart, two additional
defibrillation methods were examined. These
involved the use of one semi-internal electrode
and one external chest electrode. These methods
of endoesophageal and endotracheal stimulation
have been described in previous sections of this
report. As can be seen from Fig. 14, there is
100
"
o
80
60--
8
o
r
40--
oS/,
"o
/
..~
~//.
io : olo ;o
E oe oh ogo
*
----
Endotracheal
External chest
;o
;o
mA/kg
Fio. I4. Comparison of measurements.
little difference between the percentage of success achieved by these two methods. They are
significantly better, however, than the external
chest method as shown also in Fig. 14.
To check on the effect to the body of the
various electrodes, several of the experimental
animals were sacrificed and autopsied.
We detected no serious physiological damage
as a consequence of any of the various defibrillation methods attempted. The external Chest
electrodes produced some surface burns and
local edema. These effects were minimized by
using contoured electrodes with saline soaked
pads placed between the electrodes and the
28
C . D . FERRIS, T. W. MOORE, A. H. KHAZEI and R. A. COWLEY
surface o f the body. Some m i n o r surface burns
were noted on the pericardial surface as a consequence o f the cardiac electrical axis experiments, and were caused by p o o r electrode
contact.
I n the cases o f the endoesophageaI a n d endotracheal techniques, no visible damage to either
the esophagus or trachea could be detected,
even after repeated defibrillation attempts. It
was decided that histological examination was
n o t warranted. I n dogs, one side effect o f the
endotracheal technique was the production o f
vomiting with each shock until the s t o m a c h
emptied. This did n o t occur with the endoesophageal technique, most p r o b a b l y because the
electrode blocked the esophageal passage.
The advantages o f using a single external
electrode placement in combination with an
already positioned internal electrode are n u m erous. D u r i n g the open heart surgery especially
in those techniques which require right thoracotomies, it is difficult to place two electrodes over
the ventricles for defibrillation. I f adhesions are
present, it is impossible to place these electrodes
in contact with the ventricles until the adhesions
are cut away. Several minutes can be c o n s u m e d
during such a maneuver. A n electrode already
placed at the time o f anesthesia, either esophageal or tracheal, would eliminate this problem
as the second electrode could be placed anywhere over the heart. The advantages o f p o w e r
savings to accomplish defibrillation using this
technique are obvious.
There are still m a n y unresolved factors regarding fibrillation and defibrillation. One is the
single cardiac muscle fiber electrical waveform
during fibrillation. There are conflicting reports
on this. Before o u r results related to indwelling
electrodes are extended to clinical use with
h u m a n patients, primate studies should be conducted.
Acknowledgement--This research was supported by U.S.
Public Health Service Grant HE-4595.
REFERENCES
ATTAR, S., COWLEY,R. A., BLAIR,E. and TISCHLER,M.
(1965) Square wave 250 cycle cardiac defibrillator
for cardiac surgery. Archs Surg. 90, 29-34.
BALAGOT,M. D., et al. (1964) A monopulse DC current
defibrillator for ventricular defibrillation. J. Thorac.
and Cardiovasc. Surg. 47, 487-504.
COWLEX', R. A., TAMRES,A. and TISCHLER,M. (1964)
Esophageal defibrillation of the canine heart. Bull.
M d Univ. Sch. Med. 49, 34-36.
COWLEY,R. A., TISCHLER,M., ATTAR,S. and TAMRES,A.
(1962) Cardiac defibrillation above sixty cycles with a
portable square-wave defibrillator. Surgery 51, 207209.
FERRIS,C. D. Rev. scient, lnstrum. 34, 109-111.
FERRIS,L. P., KING, B. G., SPENCE,P. W. and WILLIAMS,
H. B. (1936) Effect of electric shock on the heart.
Electl. Engng. 55, 498-515.
FERRIS, C. D. and MELLMAN, S. (1967) Proc. 20th
ACEMB, p. 15.3, Boston.
FERR/S, C. D., MOORE,T. W. and COWLEY,R. A. (1966)
Frequency and power considerations in the use of
alternating current defibrillators. Bull. M d Univ. Sch.
Med. 51, 36--48.
FERmS, C. D. and MOORE,T. W. (1966) Factors involved
in ventricular defibrillation by electronic means.
Proc. 19th ACEMB, p. 24, San Francisco.
JARON, D. Private discussion with author.
JARON, D. et al. (1967) Proc. 20th ACEMB, p. 15"2,
Boston.
KOHLRAUSCH,F. (1897) Annln. Phys. Chem. 60, 315-328.
KOUWENHOVEN, W. B. and MILNOR, W. R. (1954)
Treatment of ventricular fibrillation using a capacitor
discharge, d. appl. Physiol. 7, 253.
LOWN, B,, NEUMAN,J., AMARASINGHAM,R. and BERKOvrrz, V. V. (1962) Comparison of alternating current
with direct current electroshock across the closed
chest. Am. d. Cardiol. 10, 223-233.
MACKAY, R. S. and LEEDS, S. E. (1953) Physiological
effects of condenser discharges, d. appL Physiol. 6,
67.
MOORE,T. W., FERRIS,C. D., KHAZEt, A. H. and COWLEY, R. A. (I968) Preferred cardiac axis for electrical
stimulation. Bull. M d Univ. Sch. Med. 52, 3-5.
RICHARDSON,P. C. (1967) Proc. 20th ACEMB, p. 15.7,
Boston.
RUSH, S. et al. (1967) Proc. 20th ACEMB, p. 14.3,
Boston.
SCHWAN, H. P. (1951) Elektrodenpolarisation und ihr
Einfiuss auf die Bestimmung dielektrischer Eigenschaften van Flussigkeiten und biologischem Material.
7.. Naturf. 6b 3, 121-129.
SCHWAN,H. P. (1957) Electrical Properties of Tissues and
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Academic Press, New York.
SCHWAN, H. P. and FERRIS~ C. D. (1963) Proc. 16th
ACEMB, p. 84, Baltimore.
SCHWAN, H. P. and MACZUK, J. G. (1965) Proc. 18th
ACEMB, p. 24, Philadelphia.
TISCHLER,M., ATTAR,S., TAMERS,A. and COWLEY,R. A.
(1961) A new portable defibrillator above sixty
cycles. Bull. Md Unie. Sch. Med. 46, 8-10.
WIGGERS,C. J. (1940) The physiological basis for cardiac
resuscitation from ventricular fibrillation--method of
serial defibrillation. Am. Heart J. 20, 413.
A STUDY OF PARAMETERS INVOLVED IN ALTERNATING-CURRENT DEFIBRILLATION
ETUDE
DES PARAM~TRES IMPLIQUI~S DANS LA MI~THODE DE
DEFIBRILLATION PAR COURANT ALTERNATIF
Sommaire---Les r~sultats de recherches prdsentds dans cet article peuvent 8tre rdsumds comme
suit:
La ddfibrillationcardiaque est un phdnom~ne lid ~ l'orientationdu courant dlectrique.Il existe
un axe cardiaque prdfdrenticlpour une ddfibrillationefficace.Cet axe prdfdrentieln'estpas lidde
fagon simple h la position d'une dlcctrodc de surface. Des mdthodes plus efficacesde ddfibrillation utilisentdes dlectrodes introduites dans roesophage ou darts la trachde de prdfdrence aux
dlcctrodes de surface. Les mcsures d'irnpddance de la rdgion thoracique et du coeur rnontrent
que l'usage d'un courant alternatifh basse frdquence est probablernent le stimulus ddfibriUateurle
plus efficace.Bien que le courant continu soit ellicace,il y a un plus grand risque d'dlcctrolyse
qu'avcc un courant alternatif.
UNTERSUCHUNG DER FAKTOREN, DIE BEI
WECHSELSTROMDEFIBRILLIERUNG
VON BEDEUTUNG SIND
Zusammenfasstmg--Die in dieser Arbeit mitgeteilten Forschungsergebnisse k/Snnen folgendermaBen zusamrnengefaBt werden:
Die Herzdefibrillierung ist ein elektrisches Ph~inomen. Es gibt eine Vorzugsachse for die
wirksame Defibrillierung des Herzens. Die Vorzugsachse des Herzens kann nicht leicht zu
der Elektrodenlage auf der KSrperoberfliiche in Beziehung gesetzt werden. Wirksamere
Defibrillierungsrnethoden nehmen endo~ophageale oder endotraeheale Elektroden zu Hilfe,
nicht zwei KSrperoberfl~ichenelektroden. Impedanzrnessungen des Thoraxbereiches und des
Herzens ergeben, dab rtiederfrequenter Wechselstrom wahrscheinlich der wirksamste Defibrillierungsreizist. Obwohl Gleiehstrorn auch wirksam ist, besteht dort mehr als mit Wechselstrom die Gefahr einer Elektrolyse.
M.B.E,
7/I--c
29