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(Circulation. 1999;100:826-831.)
© 1999 American Heart Association, Inc.

Clinical Investigation and Reports

Fully Discharging Phases

A New Approach to Biphasic Waveforms for External Defibrillation

Yoshio Yamanouchi, MD; James E. Brewer, MS; Kenneth F. Olson, BS; Kent A. Mowrey, MS; Todor N. Mazgalev, PhD; 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., K.F.O.).

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—Phase-2 voltage and maximum pulse width are dependent on phase-1 pulse characteristics in a single-capacitor biphasic waveform. The use of 2 separate output capacitors avoids these limitations and may allow waveforms with lower defibrillation thresholds. A previous report also suggested that the optimal tilt may be >70%. This study was designed to determine an optimal biphasic waveform by use of a combination of 2 separate and fully (95% tilt) discharging capacitors.

Methods and Results—We performed 2 external defibrillation studies in a pig ventricular fibrillation model. In group 1, 9 waveforms from a combination of 3 phase-1 capacitor values (30, 60, and 120 µF) and 3 phase-2 capacitor values (0=monophasic, 1/3, and 1.0 times the phase-1 capacitor) were tested. Biphasic waveforms with phase-2 capacitors of 1/3 times that of phase 1 provided the highest defibrillation efficacy (stored energy and voltage) compared with corresponding monophasic and biphasic waveforms with the same capacitors in both phases except for waveforms with a 30-µF phase-1 capacitor. In group 2, 10 biphasic waveforms from a combination of 2 phase-1 capacitor values (30 and 60 µF) and 5 phase-2 capacitor values (10, 20, 30, 40, and 50 µF) were tested. In this range, phase-2 capacitor size was more critical for the 30-µF phase-1 than for the 60-µF phase-1 capacitor. The optimal combinations of fully discharging capacitors for defibrillation were 60/20 and 60/30 µF.

Conclusions—Phase-2 capacitor size plays an important role in reducing defibrillation energy in biphasic waveforms when 2 separate and fully discharging capacitors are used.

Key Words: defibrillation • death, sudden • ventricles

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