Electrical Dose for Ventricular Defibrillation ofLarge and Small Animals Using PrecordialElectrodes

L. A. Geddes, … , A. G. Moore, P. S. Cabler

J Clin Invest. 1974;53(1):310-319. https://doi.org/10.1172/JCI107552.

Electrical ventricular defibrillation of heavy subjects (over 100 kg body weight) is uncommonfor the human or any animal species. This paper reports trans-chest ventricular defibrillationof subjects ranging in weight from 2.3 to 340 kg using conventional defibrillation current(heavily damped sine wave) of 0.3-30 ms duration. It was found that a body weight-to-electrical-shock strength relationship exists and can be expressed in terms of eitherelectrical energy or peak current. For the duration of current pulse used clinically (3-10 ms),the relationship between energy requirement and body weight is expressed by the equationU = 0.73 W1.52, where U is the energy in W·s and W is the body weight in kilograms. Thecurrent relationship is I = 1.87 W0.88 where I is the peak current in amperes and W is thebody weight in kilograms. The energy dose is somewhat more species and weightdependent and ranges from 0.5 to 10 W·s/kg (0.23-4.5 W·s/lb). The data obtained indicatethat the peak current dose is virtually species and weight independent and is therefore abetter indicator than energy for electrical defibrillation with precordial electrodes. In theduration range of 3-10 ms, the electrical dose is very nearly 1 A/kg of body weight (0.45A/lb).

Research Article

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Electrical Dose for Ventricular Defibrillation of Large

'and Small Animals Using Precordial Electrodes

L. A. GEDDES, NV. A. TACKER, J. P. ROSBOROUCi,A. G. MOORE4,andP. S. CABLER

From the Department of Physiology, Baylor College of Medicine,Houston, Texas 77025

A B S T R A C T Electrical ventricular defibrillation ofheavy subjects (over 100 kg body weight) is uncom-mon for the human or any animal species. This paperreports trans-chest ventricular defibrillation of subjectsranging in weight from 2.3 to 340 kg using conventionaldefibrillation current (heavily damped sine wave) of0.3-30 ms duration. It was found that a body weight-to-electrical-shock strength relationship exists and can beexpressed in terms of either electrical energy or peakcurrent. For the duration of current pulse used clinically(3-10 ms), the relationship between energy require-ment and body weight is expressed by the equation U =0.73 W"52, where U is the energy in Ws and Wis thebody weight in kilograms. The current relationship isI = 1.87 W0M where I is the peak current in amperes andWis the body weight in kilograms. The energy doseis somewhat more species and weight dependent andranges from 0.5 to 10 Ws/kg (0.23-4.5 Ws/lb). Thedata obtained indicate that the peak current dose is vir-tually species and weight independent and is therefore abetter indicator than energy for electrical defibrillationwith precordial electrodes. In the duration range of 3-10ms, the electrical dose is very nearly 1 A/kg of bodyweight (0.45 A/lb).

INTRODUCTIONUntil 1970 no reports of successful transthoracic ven-tricular defibrillation of a human subject weighing over100 kg were found in a review of the published literature(1) ; this survey presents the energy vs. body-weightdata appearing in all of the published literature datingfrom 1899 to 1970. Since that review we have located areport (2) which describes the successful defibrillation

Received for publication 6 April 1973 and in revisedform 13 July 1973.

of one female subject weighing over 237 lb using 300Ws. Weknow of one successful defibrillation of a 200lb human male subject who required multiple 400-W scountershocks. Defibrillation of heavy subjects may be socommonplace that they are not reported; however, cor-respondence with numerous cardiologists has revealedthat defibrillation of such subjects has been achievedinfrequently. Their experience, plus the lack of pub-lished data indicate that success must be rare in heavysubjects. A possible explanation for failure to defibrillatesuch subjects is that existing commercially available de-fibrillators (400 W* s) do not provide an adequateelectrical output. There have been four recent reports(3-6) which have documented that virtually all com-mercially available defibrillators deliver substantially lessenergy than is indicated by their dial settings. There-fore published values of energy used for defibrillationare higher than those that are actually delivered to thesubject. However, it may be unfair to criticize low de-fibrillator output too strongly because there have beenno studies which quantify the electrical "dose" (i.e.,energy) needed to defibrillate subjects of widely differ-ing body weights. Wehave been unable to ascertain whythe 400 Ws figure was chosen as the maximum energyfor commercially available defibrillators. The study re-ported herein presents data on the threshold values fordelivered energy and peak current necessary to defibril-late mammalian subjects weighing 2.3-340 kg and, infact, shows that 400 Ws is an inadequate energy for thedefibrillation of heavy subjects using precordial elec-trodes. However it will be shown that many of thepresently available 400-W s defibrillators, which deliverless than this output, can defibrillate heavy subjects if theelectrode-subject impedance is reasonably low, indicatingthat energy may not be the best descriptor for the elec-trical dose required for defibrillation.

The Journal of Clinical Investigation Volume 53 January 1974- 310-319310

METHODS rounded pulse approximating a half-sinusoid in which theThe current waveform employed for ventricular defibrilla- duration in each particular case depends upon the designtion is that which is presently used in clinical medicine of the defibrillator and upon the electrode-subject impe-(1, 3-5, 7) namely a heavily damped sine wave, i.e., a dance (7). To investigate the importance of the duration

CAPACITOR- INDUCTOR CURRENT

400 W. s_ _ _ _ ___ _. .

.I -

U = 0.891 W1.48

50

20

10

5

2

0.5

/ '/

X .0/

* 0

,. 0

*/0

*0

a

1p00

BODY WEIGHT, kg

FIGURE 1 Threshold (delivered) energy required to defibrillate subjects of various bodyweights for all durations (0.3-30 ms). The dashed line represents the energy dose (1 W-s/lb) used by some pediatric cardiologists.

Ventricular Defibrillation 311

5_00

2P00

2p00

500

200

100

Co

0

zLU

0uJ

LU

-iLUa

a

0

11

0

0.

TABLE IDefibrillation Data

Animal Bodyspecies weight

Delivered Peak Pulseenergy current duration

kg W-s

Rabbit 2.3 1.33

2.5 0.83

2.8 3.802.981.942.693.513.746.857.90

19.9

2.9 2.35.1

- 8.516.9

3.2 4.96

3.2 10.410.510.6

3.5 4.24.8

10.910.5

- 18.723.2

3.4 1.141.443.61.81

Dog 3.5 7.810.2

5.399.27

10.35.376.557.48

10.520.9

7.89

4.0 15.624.115.515.9

5.0 5.145.824.83

A

0.8

3.0

4.06.54.54.64.754.45.04.87.0

4.85.25.56.8

4.5

9.257.57.0

8.256.57.257.57.07.0

4.03.44.02.1

5.511.0

7.49.88.85.67.06.07.48.44.4

17.010.013.8

7.8

9.06.55.2

ms

12.0

4.0

0.30.81.753.03.55.0

10.017.020.0

2.58.0

12.025.0

10.0

3.08.0

12.0

0.752.08.0

13.020.030.0

0.73.08.0

13.0

0.41.01.52.753.55.06.07.0

10.022.023.0

0.51.53.56.0

1.03.08.0

Heartweight

g

5.0

5.75

6.0

6.5

8.0

7.6

8.1

7.5

34

48

42

Animal BodySpecies weight

Delivered Peak Pulseenergy current duration

kg Ws

7.0310.212.6

6.5 2.88.7

17.016.023.417.0

7.5 5.87.75.06.9

14.018.617.1

11 18.518.331.534.445.755.166.9

14.5 15.026.735.553.564.963.170.156.1

15 20.613.427.618.846.665.8

17 33.2

20 2230311934225968

41 136224380522

A Ms

5.2 12.05.2 15.05.0 30.0

8.0 1.511.0 3.010.5 10.0

8.5 15.010.5 25.0

6.5 35.0

7.0 2.57.0 8.04.5 12.04.5 16.06.0 25.06.8 30.06.0 35.0

16.0 2.012.5 5.015.0 8.015.5 11.015.5 16.015.0 20.015.5 24.0

14.5 2.516.5 4.017.0 8.019.5 10.019.0 12.018.0 16.018.0 19.014.5 24.0

16.0 2.511.5 4.013 8.011.0 10.012.5 12.012.5 15

16.5 7.0

18.0 2.516.0 5.515.0 7.512.0 8.513.0 10.511.0 17.014.0 20.012.5 25.0

50.0 2.058.0 3.557.0 8.056.0 15.0

312 L. A. Geddes, W. A. Tacker, J. P. Rosborough, A. G. Moore, and P. S. Cabler

Heartweight

g

55

60

95

120

110

150

185

360

TABLE I-(Continued)

Animal Body Delivered Peakspecies weight energy current

kg Ws

Goat 29 179.180.0

104.0126.4123.5325.0140.5260.7

33 220.3211.7179.1211.5242.8159.7211.4353.8302.7217.8231.4136.5

33 163

39 153258208384702

A

6440384439563740

726963556244556257654932

43

6065566875

Pulseduration

ms

1.52.54.05.05.57.09.0

11.0

1.01.52.04.04.55.05.56.07.08.09.0

11.0

7.0

3.55.57.5

10(.011.0

Heartweight

g

142

139

140

110

Animalspecies

Body Delivered Peakweight energy current

kg W-s

594

Pony 80 895

90 514

94 227607

2,043

104 1,046

105 1,528

123 8461,003

581

155 1,0822,2511,247

175 2,2502,232

181 1,474

193 3,687

Horse 277 3,463

340 4,535

A

56

100

70

8796

118

130

140

16013585

13014011)

120125

120

250

350

280

Pulse Heartduration weight

ms

16.5

7.5

8.0

4.08.0

17.0

5.5

8.0

3.58.0

11.5

4.07.0

10.0

8.08.0

7.0

6.5

7.0

6.8

g

550

450

730

524

795

1,135

750

1,630

1,475

1,i5O

2,460

3,150

of the current pulse, the range of durations used for thisstudy (0.3-30 ms) exceeds that presently employed inclinical medicine, which is 3-10 ms. The studies cited above(3-6) revealed that among 13 manufacturers, only twoprovided defibrillators with durations slightly outside thisduration range.

The defibrillator employed was especially constructed forthis study (7) and has a maximum energy-storage capacityof 5,000 W- s The capacitance bank in it allows selectionof values ranging from 0.5 to 100 OF which can be chargedfrom 0 to 10,000 V and the inductance values which canbe selected are 0, 11, 29, and 63 mH. The total internalresistance of the defibrillator depends on the inductor used,and is 4.46, 3.81, and 3.31 (1 respectively for the three in-ductance values available. Both current and voltage-mea-suring circuits are contained in the defibrillator and thecomplete operating characteristics are known so that theenergy actually delivered1 to the subject could be calcu-lated. All energy values presented in this report are de-livered energy rather than indicated energy.

Rabbits, puppies, dogs, goats, ponies, and horses werestudied. The small animals were anesthetized with sodium

1In any defibrillator, the delivered energy is always lessthan the stored energy because energy is consumed bythe internal resistance of the defibrillator. In a well-de-signed defibrillator, the internal resistance is low and thedelivered energy is very nearly the stored energy.

pentobarbital (30 mg/kg i.v.) and the large animals wereanesthetized with a mixture of halothane, nitrous oxide,and oxygen, after anesthesia had first been induced withintravenous glycerol guaiaiacolate. Arterial blood pressure,lead II electrocardiogram (ECG) and the impedance pneu-mogram were recorded continuously. In the large animals,the electroencephalogram (EEG) was also recorded as anaid in controlling the depth of anesthesia and evaluating re-covery; pH was monitored intermittently to evaluate theacid-base status of the animals and sodium bicarbonate wasgiven as needed to maintain an arterial pH above 7.30.Before each ventricular fibrillation-defibrillation trial, theanimals were well ventilated to minimize the effect of hy-poxia on defibrillation threshold.

In some of the small animals, ventricular fibrillation wasinduced by applying 60 Hz current to limb electrodes (8);the remaining small animals and all the large animals werefibrillated by applying 2-ms pulses of 25 V intensity with afrequency of 50 Hz to a catheter passed into the rightventricle via the right jugular vein. Fibrillation was con-firmed by a loss of blood pressure and replacement of theQRS-T complex of the ECG by fibrillation waves.

Defibrillation was achieved by applying capacitor-inductorcurrent to soft lead-plate electrodes implanted subcutane-ously; this technique was employed to guarantee a stablelow-impedance contact. One electrode was located just to theright of the manubrium, the other was over the area of

Ventricular Defibrillation 313

I

500

CAPACITOR- INDUCTORCURRENT

200

100 a

50

1 =1.79W0.88

Z 10 a. .

1 1.

1 2 5 10 20 50 100 200 500

BODY WEIGHT( W) ,kg9

FIGURE 2 Threshold peak current required to defibrillate subjects of various body weightsfor all durations (0.3-30 ins). The dashed line represents a current dose of 1 A/kg of bodyweight.

the apex beat of the heart. Defibrillation trials were con-ducted immediately after the confirmation of fibrillation.The method of defibrillation consisted of choosing a volt-age, which was judged to be appropriate for the animal'ssize, and discharging the capacitor-inductor circuit in thedefibrillator through the electrode-animal circuit. Whendefibrillation was achieved, the animal was allowed to re-cover before refibrillation and a second defibrillation trialwith 10% less voltage was attempted. Restoration of theEEG and blood pressure to near control levels were usedas signs of recovery. In most cases, arterial pH sampleswere monitored. Threshold testing was repeated until de-fibrillation could no longer be achieved. When this occurred,the voltage was increased to a level adequate to defibrillatethe ventricles. If the initial defibrillation trial failed, thevoltage was similarly increased in increments of 10% untildefibrillation occurred. For each duration of current pulse,the lowest voltage and current capable of achieving de-fibrillation were taken as threshold values. From the volt-age, current, duration, and the internal circuit constantsof the defibrillator (inductance, capacitance, and resist-ance), the electrode-subject impedance was calculated andthus, the essential information was available for calculationof the energy actually delivered to each animal (7).

With inductor-capacitor defibrillators the duration of thedefibrillating current pulse is a function of inductance andcapacitance and subject impedance (7). Various inductanceand capacitance combinations were used to obtain a widerrange of pulse duration (0.3-30 ms) than is employed in

human defibrillation in order that the full clinical rangecould be evaluated. Data from a previous study (9) usingdogs, had shown that a 3-8 ms duration range requiresminimum energy and current.

In all, 35 animals ranging in weight from 2.3 to 340 kg(5-750 lb) were employed. Over 750 fibrillation-defibrilla-tion trials were performed, resulting in the establishmentof 144 paired threshold values for delivered energy andcurrent.

RESULTS

Table I presents the threshold-delivered energies andpeak currents used to defibrillate all of the animals stud-ied. The values for threshold energy and body weightfor the entire duration range (0.3-30 ins) are plotted inFig. 1; the least-squares line for the data points wasfound to be U = 0.891 Wf8' with a correlation coeffi-cient of 0.945. In this expression, U is the deliveredenergy in watt-seconds and W is the body weight inkilograms. Similarly, the data points for peak currentfor the entire duration range (0.3-30 ms) were plottedvs. body weight, and are shown in Fig. 2; the least-squares line for these points is I = 1.79 W'", with acorrelation coefficient of 0.943. In this expression, I isthe peak current in amperes and Wis the body weight

314 L. A. Geddes, W. A. Tacker, J. P. Rosborough, A. G. Moore, and P. S. Cabler

ELECTRODES

a .

* 0

: 3

9 :

RABBITS PUPPIES DOGS GOATS PONIES

5 10 20 50 100 200 500

BODY WEIGHT (W),kg

FIGURE 3 Impedance appearing between the terminals of the subcutaneous defibrillating elec-trodes during passage of the defibrillating current through the animals of various bodyweights.

in kilograms. The data points shown in Figs. 1 and 2 rep-

resent values for all of the durations listed in Table I.

Fig. 3 presents the calculated values for the impedance(Z) appearing between the electrode terminals duringpassage of the defibrillating current for the various ani-mals. The data points were subjected to a least-squaresfit to obtain the following relationship Z = 1451W""',where Z is the impedance in ohms and Wis the bodyweight in kilograms. The correlation coefficient obtainedwas 0.865. The size of the electrodes used was dictatedby the body weight; the electrode dimensions are shownin Fig. 3 inset.

DISCUSSION

Figs. 1 and 2 indicate that for the entire duration range

(0.3-30 ms), there is a direct relationship betweenthreshold energy and peak current vs. body weight,thereby indicating that two dose concepts are identifiable,energy per kilogram and peak current per kilogram.These data also show that it is possible to achieve de-fibrillation with pulse durations longer and shorter thanthose presently in clinical medicine (3-10 ms). Howeverbefore quantification of these.two dose concepts and com-

paring the animal data to man, it is necessary to recog-

nize that the duration of the pulse of defibrillating cur-

rent importantly affects the threshold energy and peakcurrent required for defibrillation (9). To elucidate thispoint and. to minimize the effect of body weight, theenergy and peak current values for each species werenormalized by division by body weight; these dosagevalues (energy per kilogram and peak current per kilo-gram) were then plotted vs. the duration of the currentpulse. Fig. 4 and 5 present these normalized data foreach animal species.

Inspection of Fig. 4, which shows the curves for thethreshold-delivered energy per kilogram for each speciesplotted vs. the duration of the pulse of current, revealsthat there is a slight tendency for the energy requiredto be a minimum in the region of 2-5 ms. The fact thatthe curves for the different animals do not lie on top ofeach other indicates that there is either a species differ-ence or that the energy dose (watt-seconds per kilo-gram) is larger for heavier animals. Without debatingthis issue, in the 2-5 ms duration range the energy dosefor the lightest animals (rabbits) is 0.5 Ws/kg and forthe heaviest animals, it is 10 Ws/kg.

Fig. 5, which illustrates the threshold peak currentper kilogram of body weight for each species vrs. currentpulse duration, shows that the threshold peak current per

kilogram body weight tends to have a minimum in the

Ventricular Defibrillation 315

100*

80 .

c:

a

640

20

O

RABBITS 6X 4 cmPUPPIESDOGS 8.5X 6cmGOATS 10X 12.5cmGOATS 11.3 X 15 cm

PONIES 11.3 X 15 cm

HORSES 11.3 X 1S cm

HORSES 15 X 17.5 cm

2

HORSES-- - --- - -- ---- . - I..- . . %0~b-Fv .a a I a I a --,%

a120

<A

10

5.

2

0.5

0.2

0.1

0.1 0.2 0.5 2 5 10

DURATION - ms

FIGURE 4 Threshold delivered energy per kilogram of body weight vs. duration of defibrillat-ing current for different animal subjects. Note that the curve for each species exhibits aslightly different strength-duration relationship, indicating that this dose concept is relativelyspecies and weight dependent.

range of 5-10 ms. With a pulse in this duration range,

the electrical dose required varies between 0.5 and 2.0A/kg of body weight for the largest and smallest ani-mals. However, more importantly, this illustration showsthat the dose criterion of peak current per kilogram ofbody weight is virtually species and body-weight inde-pendent since the curves for the differing species andweights are almost superimposed.

With these animal data in mind, it is useful to relatethem to human defibrillation which employs capacitor-inductor discharge current ranging from 3 to 10 ms induration. Using the enrgy and peak current data shownin Table I for this range of durations provides the re-

lationship U= 0.73 W1Mfor energy and I = 1.87 W0M' forcurrent; the correlation coefficients are 0.967 and 0.968,respectively. In these expressions U is the deliveredenergy in watt-seconds, I is the peak current in amperes,

and Wis the body weight in kilograms. Figs. 6A and 6Bpresent both relationships. It must be emphasized thatthese relationships are for delivered energy and currentand for the average subject without known cardiacdisease.

With the data in Fig. 6 in view, it is now feasible torelate these animal data to human defibrillation values.From the energy relationship (U = 0.74 W.'2) for the

clinical range of pulse durations, it is seen that 472 Wsof energy are required to defibrillate the average 70 kgsubject. In view of the fact that 70 kg subjects areroutinely defibrillated with existing 400-W-s defibrilla-tors, there is a seeming paradox, particularly in view ofthe fact that such defibrillators provide less than theirindicated energy (3-6). An explanation for the para-dox can be found by examining the current requirements( =1.87 W0'M). For example from this equation, a 70kg subject requires 78 A and a 100 kg subjects requires107 A. In other words, the current dose is very nearly1 A/kg of body weight for adults. Therefore examina-tion of defibrillator output current is in order at thispoint.

The relationship between energy and peak current isdependent on the design of the defibrillator and the elec-trode-subject impedance. The capability for current out-put of present-day defibrillators was measured by Ewy,Fletcher, and Ewy (6). Using the data from his investi-gation, Fig. 7 was composed to show the peak currentthat can be delivered to various resistive loads whendefibrillator output controls were set to a maximum (400Ws). Inspection of Fig. 7 reveals that the peak cur-rent required for a 70 kg subject can be attained easilyif the equivalent electrode-subject resistance is low

316 L. A. Geddes, W. A. Taikcr, J. P. Rosborough, A. G. Afoore, and P. S. Cabler

20

CP-!I

(I)

0

z

0mu

-JuLJ

20 50

* RABBITSx DOGS* GOATSO PONIES & HORSES

0.2 0.5 1 5 10 20 50

DURATION - ms

FIGURE 5 Threshold peak current per kilogram of body weight vs. duration of defibrillatingcurrent for different animal subjects. Note that the curves for all species measured are almostsuperimposed, indicating that this dose concept is almost totally species and weight independent.

enough. For the best defibrillator ' (no. 6) this currentcan be attained with a subject resistance as high as 67 fl.The resistance values for the next best defibrillators(nos. 3 and 7) are 37 and 21 Q, respectively. The fourth

defibrillator tested could not provide this required current.It is important to note that there are no hard data

on the equivalent resistances appearing between the elec-trode terminals during passage of the defibrillating cur-

rent. It was for this reason that Fig. 3 was composed toshow the practical order of magnitude using electrodesappropriate for the size of a subject. Quite apparent is

the fact that with subjects in the weight range of 70 kg,resistance values of 10-40 Q were obtained. Although,in this study the electrodes were implanted subcutane-ously, the values encountered with electrodes applied tothe surface of the skin with low-resistivity (10) elec-trode paste (ca 10 f-cm) were found to be only about10% higher (unpublished data).

It is of some interest to speculate on the relationshipof decreasing impedance with increasing animal weight.Two factors underlies this relationship. As heavier ani-mals are encountered, the thorax becomes larger andconsequently the electrodes become further apart, therebyincreasing the impedance. However, when larger animals

'The numbers correspond to the figure numbers in thepaper by Ewy et al.

are encountered, larger electrodes are employed whichwould result in a decrease in impedance in proportionto electrode area. Thus, on the basis of these two factors,it is not too surprising to encounter a decreasing im-pedance with increasing subject weight. Fortuitously,this is highly desirable because the same defibrillatorwhen set to full output will deliver more current to theheavier subjects who require higher current than therelatively lighter subjects.

Therefore it can be seen that even if existing defibril-lators do not deliver their rated energy values, ventricu-lar defibrillation is achievable if the electrode-subjectimpedance is low enough, indicating that peak currentis a better criterion than energy for defining the elec-trical dose required for ventricular defibrillation. Ifenergy is used to express the dose required, then it canbe seen from Figs. 1 and 6A that for children in thepediatric dose of 2.2 Ws/kg. (1 Ws/lb) is consistentwith the animal data reported herein. Note that for adultsubjects, the energy dose increases to 5-10 Ws/kg ofbody weight (2.3-4.6 Ws/lb), as shown in Fig. 6A.

If peak current is used to specify the electrical dosefor ventricular defibrillation, Fig. 6B presents the cur-rent required for different body weights. Note that thecurrent dose is approximately 1 A/kg of body weight.Light subjects require slightly more current and heavysubjects require a current dose which is slightly smaller.

Ventricular Defibrillation 317

10

2

cy

w~

0.5 -

0.2 -

0.1 dI0.1 2

A

//

//

// / /

,/

/

/

/

U = 0.73(DURAT

3- 1

2 5 10 20

BODYWEIGHT(W), kg

plain if successful defibrillation requires that the same/ / current density be achieved within the ventricular myo-

/ cardium. Delivered energy is proportional to the subject// voltage, current and duration of the current pulse. How-

// / ever for the same threshold data point, focusing on cur-,/ / rent alone disregards the voltage that was needed to ob-

/ tain the current. Therefore to obtain the same mvo-/ cardial current density, there appears to he a dispropor-

-' / tionate need for voltage with increasing body wveight./ It is of some interest to speculate on the effect of

/ animal and heart weight on the requirements for de-/ fibrillation as identified in Figs. 4 and 5 which present

the energy per kilogram and peak current per kilogramdata. Fig. 4 shows that the rabbits required the leastenergy per gram and Table I shows that for all species,the rabbits had the smallest heart to body weight ratio(about 0.22%). The ponies and horses, with a heart-to-body-weight percentage of about 0.85, required much

1 .52W higher energy per kilogram of body weight. In the caseONRANGE of the current requirement, as shown in Fig. 5, it can be

seen that all species and weights required essentially thesame current per kilogram of body weight, despite thewide range of heart to body weight percentage (0.22-

50 00 2001.2), indicating again that current is a better descriptorfor the electrical dose for ventricular defibrillation.

Beyond the desire to obtain beating ventricles there is,/

B/

/

//

//

/,

,/I= 1.87 WO.88DURATION3 - 10 ms

1 2 5 10 20 50 100 200BODYWEIGHT (W), kg

FIGURE 6 Energy (A) and peak current (B) requiredfor defibrillation using the duration of current pulse em-ployed in clinical medicine (3-10 ms).

The fact that disproportionately more energy per kilo-gram is required to defibrillate the ventricles of largeanimals than those of small animals is difficult to ex-

100

90

80

70

60

4

I 504

X. 40

30

20

10

0

RESISTANCE, a

FIGURE 7 Measured output current capabilities of threecommercially available defibrillators connected to variousresistive loads. None of these defibrillators delivered theirrated energy, yet all are capable of providing enough cur-rent for the defibrillation of a 70 kg subject using the 1A/kg criterion providing the electrode subject resistance is

low enough. The numbers in the illustration refer to thenumbered figures in the original paper by Ewy et al. (6).

318 L. A. Geddes, W. A. Tacker, J. P. Rosborough, A. G. Moore, and P. S. Cabler

1000

Sono

500

200

100

fn 50

3 2

Iz

z

520ad

z

ad 10

u-j

5

500

200

100

50

20

10

1-z

V

.5

at present, really no agreement on the best criterion forthe specification of optimum defibrillation. Mackay andLeeds (11), on the basis of a study of dogs weighing8-12 kg, showed that electrical energy was the appro-priate electrical parameter for indicating the requirementfor defibrillation. Others (12-14, 16) have proposed thatthe current that flows is a better descriptor for the elec-trical dose required for defibrillation. Without arguingthe issue of the superiority of current over energy forspecifying the dose for ventricular defibrillation, Fig. 6shows that for subjects up to about 7 kg, the energy doseis 2 W*s/kg; from 7 to 40 kg the dose ranges from 2 to5 W- s/kg. Above 40 kg, the dose is 5-10 W- s/kg. Thecorresponding current dose level is between 1 and 2 A/kgfor all weights up to about 100 kg; slightly less cur-rent/kg is needed for heavier subjects. The authors wishto emphasize the fact that the data provided herein referto the presently used capacitor-inductor waveform ofcurrent and other current waveforms may require moreor less energy and current for defibrillation.

ACKNOWLEDGMENTSThis study was supported by grant FD 00044-02 from theFood and Drug Administration, Washington, D. C.

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