0090-6689/88/281-285/$02.00/0
`MEDICAL INSTRUMENTATION
`Copyright © 1988 by the Association for the Advancement of Medical Instrumentation
`
`Vol. 22. No. 6
`
`Comparison of Effectiveness of Relay-Switched,
`One-Cycle Quasisinusoidal Waveform with Critically
`Damped Sinusoid Waveform in Transthoracic
`Defibrillation of lOO-Kilogram Calves
`
`JOHN C. SCHUDER, PHD, WAYNE C. McDANIEL, PHD, HARRY STOECKLE, MD, AND
`DAN YERKOVICH
`
`Studies of 240 transthoracic fibrillation-defibrillation episodes in calves
`of 91—108 kg are reported. The waveform in 120 of the episodes was
`a one-cycle, quasisinusoidal waveform having peak currents of 64 and
`-32 A and half-cycle durations of 4 and 6 ms. The episodes were
`interlaced with 120 others involving critically damped sinusoid wave-
`forms having a 70.2-A peak current at 1.1 ms to peak. Applied after
`30 s of fibrillation, the biphasic shock (201 j of delivered energy) was
`successful on the initial attempt in 106 of 120 episodes (88%), and the
`uniphasic shock (206]) was successful in only 44 of 120 episodes (37%).
`The biphasic waveform, producible by a simple relay-armature shift
`in a passive circuit, yielded significantly better results (p <0.001) and
`should be evaluated clinically.
`
`'
`
`A general belief is that ventricular fibrillation in pa-
`tients with potential for survival can usually be reversed
`by electric shock from widely used defibrillators deliv-
`ering a uniphasic or near-uniphasic waveform. Interest
`in the development of improved devices continues, how-
`ever, partially because the patient load is so large.
`Experimental evidence indicates that 1) both sym-
`metric and asymmetric biphasic rectangular waveforms
`are
`superior
`to
`uniphasic
`rectangular wave-
`forms“; 2) both symmetric and asymmetric biphasic,
`truncated exponential waveforms are superior to uni-
`phasic, truncated exponential waveforms”; and 3) a va-
`riety of biphasic waveforms considerably out perform the
`critically damped, uniphasic shock in transthoracic de—
`fibrillation in the 100—kg-calf model.7 Uniphasic or near-
`uniphasic defibrillators continue to be dominant in the
`clinical environment.
`‘
`
`In this article, we use a circuit having the topology
`described by Negovsky et al.8 that can deliverbiphasic
`waveforms reasonably close to the asymmetric biphasic
`waveforms we have found to be so successful. The wave—
`
`form can be generated by a relay—armature shift in a
`passive circuit instead of with high-current electronic
`devices such as silicon—controlled rectifiers (SCRs).
`
`From the Departments of Surgery and Child Health, University of
`Missouri, Columbia, Missouri and Physio Control Corporation, Red-
`mond, Washington.
`Address correspondence and reprint requests to Dr. John C. Schu-
`der, Department of Surgery. University of Missouri, Columbia, MO
`65212.
`
`281
`
`METHODS
`
`Apparatus
`
`The defibrillator used in this research is a modified
`
`version of one that can provide ultrahigh-energy, uni-
`phasic/biphasic,
`rectangular/truncated exponential
`waveforms. That defibrillator, previously described,9 uses
`hydrogen thyratron/SCR switching. The modifications
`involved replacing two of three electronically controlled
`pulse generators with electromechanical relays and pas-
`sive circuits for generating the waveforms to be tested.
`The operator could easily select the fibrillatory shock,
`the critically damped uniphasic waveform,
`the quasi-
`sinusoidal biphasic waveform, or an electronically gen-
`erated uniphasic rectangular backup waveform of almost
`any desired pulse width or pulse amplitude by front—
`panel controls.
`Circuits used in generating the quasisinusoidal bi-
`phasic and critically damped uniphasic waveforms are
`shown in Figures 1 and 2, respectively. In both circuits,
`the calf chest resistance (average value of some 20 Q with
`the 13-cm diameter electrodes employed) was trimmed
`with a variable resistance in such a way that the combined
`trimmer and calf resistance remained substantially in-
`variant at 25 Q from animal to animal and from episode
`to episode, thus permitting any shifts in delivered energy
`attributable to changes in electrode-skin interface re—
`sistance to be absorbed in the interface region rather
`than in the regions of both the heart and the interface.
`The component values and initial voltage on the ca-
`pacitor used in the circuit of Figure 1 were derived by
`one of us (D.Y.) so as to (a) yield a current waveform
`similar to a biphasic rectangular waveform that had been
`found to be effective in an earlier study,3 (b) be practical,
`component—wise,
`to scale and implement in apparatus
`designed for use on humans, (c) be appropriately scaled
`for use with the 20-0 resistance presented by the chest
`of the calf, and (d) deliver about 200 ] to the subject.
`The waveform of current, as shown in Figure 3, had a
`maximum amplitude of 64 A and a minimum amplitude
`of —32 A; the half-cycle durations were approximately
`
`L|FECOR454-1014
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`1
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`LIFECOR454-1014
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`

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`282
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`MEDICAL INSTRUMENTATION
`
`Volume 22, No. 6, December 1988
`
`RELAY
`
`l-_————— -—— ..
`
`20 mH
`
`TRIMMER
`
`
`
`FROM
`
`CHARGING
`
`CIRCUIT
`
`
`
`
`
`
`E NERGY STORAGE CAPACITOR
`
`
`CHEST
`
`Figure 1. Circuit for generating biphasic waveform.
`
`4—6 ms, respectively. That this waveform will deliver 200
`] to a 20-!) chest can be demonstrated easily by graphic
`integration of the corresponding current-squared curve,
`and multiplication by 20 Q.
`The component values and initial capacitor voltage of
`the circuit of Figure 2 were derived so as to deliver some
`200 ] to a 20-0 chest; the critically damped sinusoid
`would peak at 70.2 A in 1.1 ms, as shown in Figure 4.
`That this waveform will deliver 200 I to a 20—0 chest
`follows analytically from a simple manipulation of the
`current equation for critically damped waveforms using
`the specified values of peak current and time required
`to reach the peak current. In both circuits, the resistance
`shown in series with the inductive element was primarily
`that of the inductor.
`
`A double-throw, electromechanical relay was used in
`the circuit of Figure l to prevent shunting by the charg-
`ing circuit, which would occur when the storage capacitor
`reversed its polarity during discharge. Because polarity
`reversal does not occur in the circuit shown in Figure
`2, a single—throw relay was adequate.
`The initial polarity of the capacitors differs in the two
`circuits, but this is compensated by the connections to
`the chest electrodes—with the result that in both the
`
`uniphasic shock and in the leading portion of the biphasic
`shock, the lower left electrode was positive with respect
`to the upper right electrode on the chest.
`
`Procedure
`
`Anesthesia was induced with 110 mg of glyceryl guia-
`colate/kg and 4.4 mg of thiopental sodium/kg injected
`
`2
`
`intravenously. The calf was intubated and then main-
`tained in anesthesia with methoxyflurane in 50% N20
`and 50% Oz. Fibrillation was induced with a 1—s, 60-Hz,
`lOO—V (rms) shock applied through the chest electrodes;
`after 30 s, one of the two waveforms being studied was
`applied.
`If defibrillation was accomplished on the first attempt,
`the episode was recorded as a success, and the lead II
`electrocardiogram was observed on an oscilloscope and
`recorded for 21/2 min. Otherwise, the episode was re—
`corded as a failure, and a shock of known high effective-
`ness was used to salvage the animal. With not less than
`3 min between the start of successive episodes, the pro—
`cedure was repeated—but with the other waveform being
`evaluated.
`In a given session, animals were carried
`through not more than 20 episodes (10 episodes involving
`one of the waveforms interlaced with 10 involving the
`other). The waveforms of both current and voltage of the
`shocks being studied were observed on a dual-beam stor-
`age oscilloscope (model 5113, Tektronix, Beaverton, Or-
`egon). The chest resistance associated with each biphasic
`shock was calculated as the mean of the voltage-to-cur-
`rent ratios at the positive and negative peaks. The chest
`resistance to each uniphasic shock was calculated as the
`ratio of the peak voltage to peak current. For both wave-
`forms, and to the extent that the current waveforms were
`
`maintained invariant, the actual delivered energy in joules
`in any episode was given by the calculated resistance for
`the episode divided by 20 and multiplied by 200. The
`mean delivered energy was calculated from the mean
`resistance by the same procedure.
`In addition to the alternating of the waveforms being
`
`2
`
`

`

`WAVEFORM COMPARISON (Schuder et 3/.)
`
`283
`
`TRIMMER
`
`
`
`
`FROM
`
`CHARGING
`
`CIRCUIT
`
`TIME IN MILLISECONDS
`
`64
`
`32
`
`l
`
`I
`
`\
`
`\?
`
`8
`
`I2
`
`
`
`
`
`Figure 3. Quasisinusoidal biphasic waveform.
`
`evaluated in successive episodes as described above, the
`initial episode in animals as they were successively en—
`tered into the study alternated between the two wave-
`forms. With no animal being carried through more than
`20 episodes with a particular waveform (nor more than
`40 episodes in total),
`the sessions were ordinarily re-
`peated with at least one day between sessions. A total
`of 7 calves of 91—108 kg were used in the 240—episode
`study.
`
`3
`
`RESULTS
`
`In 120 episodes with each waveform, our study yielded
`chest resistances of20. 1 i- 3.5 0 (mean : SD) with the
`biphasic waveform and 20.6 i 3.1 Q with the uniphasic
`one. The biphasic shock generated by the circuit of Fig—
`ure 1 and sketched in Figure 3 was successful in 106 of
`120 episodes (88%) at an average delivered energy of 201
`J. The uniphasic shock generated by the circuit of Figure
`
`3
`
`

`

`284
`
`0CURRENTINAMPERES O)
`
`MEDICAL INSTRUMENTATION
`
`Volume 22, No. 6, December 1988
`
`
`
`TIME IN MILLISECONDS
`
`Flgure 4. Critically damped uniphasic waveform.
`
`2 and shown in Figure 4 yielded 44 successes in 120
`episodes (37%) at an average delivered energy of 206 J.
`The difference is large, and an unpaired x2 test shows it
`is significant (p < 0.001).
`In terms of the electrocardiographic findings, 28 :t
`1.1 5 (mean : SD) were required for the appearance of
`the first ventricular complex following a successful bi-
`phasic shock, and 6.8 t 4.2 s were required after a
`successful uniphasic shock. An unpaired Student's t test
`showed that this difference is significant (p < 0.05). Sim-
`ilarly, 4.3 t 2.8 s were needed for the return of normal
`sinus rhythm after the biphasic shock, compared with
`12.0 1- 6.8 s after the uniphasic shock (p < 0.05). Thus,
`the electrocardiographic disturbances caused by suc-
`cessful shocks were significantly less severe with biphasic
`than with uniphasic waveforms.
`
`bination of the diode and 135-0 resistor. For example,
`with essentially the same delivered energy, the stored
`energy is 2.73 times as large in the biphasic circuit of
`Figure 1 as in the uniphasic circuit of Figure 2. We
`anticipate that the efficiency of the circuit of Figure 1
`would also compare poorly with that of a defibrillator
`circuit using SCRs or similar switches in providing bi-
`phasic defibrillation.
`
`CONCLUSION
`
`The significantly better defibrillation results in calves
`with the relay-generated biphasic waveform of Figure 1
`compared with the uniphasic waveform of Figure 2 sup-
`port the conclusion that clinical trials should be per-
`formed to see if the results from the calf model translate
`
`DISCUSSION
`
`to human patients.
`
`The results of this study are seen as further confir-
`mation of what seems to be a general superiority of hi-
`phasic over uniphasic waveforms in the defibrillation of
`calves. A series of studies in cultured chicken-embryo
`myocardial cells by Iones et al.“Hz have furnished some
`hypotheses for the superiority of biphasic shocks and can
`be broadly interpreted as compatible with our previous
`results with a biphasic waveform applied to calves, thus
`suggesting that the findings in calves may extend to other
`spec1es.
`
`Although the simplicity of relay switching for gener-
`ating biphasic waveforms may be attractive in many ap-
`plications, a shortcoming of the biphasic circuit of Figure
`1 is the power loss and consequent loss of efiiciency
`associated with the shunt consisting of the series com-
`
`This work was supported by a grant from the Physio Control
`Corporation and was presented in part at the 23rd Annual
`Meeting of the Association for the Advancement of Medical
`Instrumentation, Washington, DC, May 14—18, 1988.
`
`REFERENCES
`
`1. Gold JH, Schuder JC, Stoeckle H, Granberg TA, Hamdani SZ:
`Transthoracic ventricular defibrillation in the 100 kg calf with
`unidirectional rectangular pulses. Circulation 56: 745—750. 1977
`2. Schuder JC. Gold JH, Stoeckle H, McDaniel WC, Cheung KN:
`Transthoracic ventricular defibrillation in the 100 kg calf with
`symmetrical one-cycle bidirectional rectangular wave stilmuli.
`IEEE Trans Biomed Eng 30: 415—422, 1983
`3. Schuder JC, McDaniel WC, Stoeckle H: Defibrillation of 100 kg
`claves with asymmetrical, bidirectional rectangular pulses.
`Cardiovasc Res 18: 419—426, 1984
`4 4. Schuder JC. Gold JH, Stoeckle H, Granberg TA, Dettmer JC,
`
`4
`
`

`

`WAVEFOFIM COMPARISON (Schuder et al.)
`
`285
`
`Larwill MH: Transthoracic ventricular defibrillation in the 100
`kg calf with untruncated and truncated exponential stimuli.
`lEEE Trans Biomed Eng 27: 37—43, 1980
`5. Schuder JC, McDaniel WC. Stoeckle H: Transthoracic defibril-
`lation of 100 kg calves with bidirectional tmncated exponential
`shocks. Trans Am Soc Artif Intern Organs 30: 520—525, 1984
`6. Schuder JC, McDaniel WC, Stoeckle H: Bidirectional truncated
`exponential shocks of extended current range in the trans-
`thoracic defibrillation of 100 kg calves. Am Soc Artif Intern
`Organs Abstracts 15: 76. 1986
`7. Schuder JC. McDaniel WC, Stoeckle H: Transthoracic ventric-
`ular defibrillation of 100 kilogram calves with critically damped
`sinusoidal shocks. Proceedings of the Association for the Ad-
`vancement of Medical Instrumentation, 21 st Annual Meeting,
`p 67, 1986
`
`8. Negovsky VA, Smerdov AA. Tabak VY, Venin IV. Bogushevich
`MS: Criteria of efficiency and safety of the defibrillating im-
`pulse. Resuscitation 8: 53—67, 1980
`9. SchuderJC. Gold JH, McDaniel WC: Ultrahigh-energy hydrogen
`thyratron/SCFl bidirectional waveform defibrillator. Med Biol
`Eng Comput 20: 419—424. 1982
`10. Jones JL, Jones FtE: Improved defibrillator waveform safety fac-
`tor with biphasic waveforms. Am J Physiol 245: H60—H65,
`1983
`11. Jones JL, Jones RE: Decreased defibrillator-induced dysfunction
`with biphasic rectangular waveforms. Am J Physiol 247: H792—
`H796, 1984
`12. Jones JL, Jones RE, Balasky G: Improved cardiac cell excitation
`with symmetrical biphasic defibrillator waveforms. Am J Phys-
`iol 253: H1418—H1424. 1987
`
`5
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