Fully discharging phases - A new approach to biphasic waveforms for external defibrillation

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 wavefor ms with lower defibrillation thresholds. A previous report also suggested t hat the optimal tilt may be >70%. This study was designed to determine an o ptimal biphasic waveform by use of a combination of 2 separate and fully (9 5% tilt) discharging capacitors. Methods and Results-We performed 2 external defibrillation studies in a pig ventricular fibrillation model. In group I, 9 waveforms from a combination of 3 phase-1 capacitor values (30, 60, and 120 mu F) and 3 phase-2 capacit or values (0=monophasic, 1/3, and 1.0 times the phase-1 capacitor) were tes ted. 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-mu F phase-1 cap acitor. In group 2, 10 biphasic waveforms from a combination of 2 phase-1 c apacitor values (30 and 60 mu F) and 5 phase-2 capacitor values (10, 20, 30 , 40, and 50 mu F) were tested. In this range, phase-2 capacitor size was m ore critical for the 30-mu F phase-1 than for the 60-mu F phase-1 capacitor . The optimal combinations of fully discharging capacitors for defibrillati on were 60/20 and 60/30 mu F Conclusions-Phase-2 capacitor size plays an important role in reducing defi brillation energy in biphasic waveforms when 2 separate and fully dischargi ng capacitors are used.