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(Circulation. 1998;98:2487-2493.)
© 1998 American Heart Association, Inc.

Basic Science Reports

Optimal Small-Capacitor Biphasic Waveform for External Defibrillation

Influence of Phase-1 Tilt and Phase-2 Voltage

Yoshio Yamanouchi, MD; James E. Brewer, MS; Kent A. Mowrey, MS; Ann M. Donohoo, MS; Bruce L. Wilkoff, MD; ; Patrick J. Tchou, MD

From the Department of Cardiology, Cleveland Clinic Foundation, Cleveland, Ohio, and SurVivaLink Corp, Minneapolis, Minn (J.E.B., A.M.D.).

Correspondence to Patrick J. Tchou, MD, Director, Clinical Cardiac Electrophysiology, Department of Cardiology/F15, Cleveland Clinic Foundation, 9500 Euclid Ave, Cleveland, OH 44195. E-mail tchoup{at}cesmtp.ccf.org

Background—Biphasic waveforms have been reported to be more efficacious than monophasic waveforms for external defibrillation. This study examined the optimal phase-1 tilts and phase-2 leading-edge voltages with small capacitors (60 and 20 µF) for external defibrillation. We also assessed the ability of the "charge-burping" model to predict the optimal waveforms.

Methods and Results—Two groups of studies were performed. In group 1, 9 biphasic waveforms from a combination of 3 phase-1 tilt values (30%, 50%, and 70%) and 3 phase-2 leading-edge voltage values (0.5, 1.0, and 1.5 times the phase-1 leading-edge voltage, V₁) were tested. Phase-2 pulse width was held constant at 3 ms in all waveforms. Two separate 60-µF capacitors were used in each phase. The energy value that would produce a 50% likelihood of successful defibrillation (E₅₀) decreased with increasing phase-1 tilt and increased with increasing phase-2 leading-edge voltage except for the 30% phase-1 tilt waveforms. In group 2, 9 waveforms were identical to the waveforms in group 1, except for a 20-µF capacitor for phase 2. E₅₀ decreased with increasing phase-1 tilt. Phase-2 leading-edge voltage of 1.0 to 1.5 V₁ appeared to minimize E₅₀ for phase-1 tilt of 50% and 70% but worsened E₅₀ for phase-1 tilt of 30%. There was a significant correlation between E₅₀ and residual membrane voltage at the end of phase 2, as calculated by the charge-burping model in both groups (group 1, R²=0.47, P<0.001; group 2, R²=0.42, P<0.001).

Conclusions—The waveforms with 70% phase-1 tilt were more efficacious than those with 30% and 50%. The relationship of phase-2 leading-edge voltage to defibrillation efficacy depended on phase-2 capacitance. The charge-burping model predicted the optimal external biphasic waveform.

Key Words: defibrillation • ventricles • death, sudden

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