Improved internal defibrillation efficacy with a biphasic waveform.

Abstract

Clinically available automatic implantable defibrillators use a monophasic truncated exponential waveform shock; after delivery the charge remaining on the device's capacitors is "dumped" internally and wasted. The efficacy of a monophasic and biphasic truncated exponential defibrillation waveform produced by a single capacitor discharge was compared in seven closed-chest, pentobarbital-anesthetized dogs. Defibrillation leads consisted of a new deployable intrapericardial electrode system. The monophasic waveform was positive and 6 msec in duration. The biphasic waveform had a positive phase identical to that of the monophasic waveform and a negative phase of equal duration with its initial voltage equal to 50% of the final voltage of the positive phase. Defibrillation shocks of varying initial voltage were delivered to construct curves of the percentage of successful defibrillation versus initial voltage and delivered energy, and the voltage and energy required for 50% (V50 and E50, respectively) and 80% (V80 and E80, respectively) success were compared. The biphasic waveform had significantly lower initial voltage (V50: 194 +/- 48 volts vs 227 +/- 48 volts, p less than 0.001; V80: 217 +/- 55 volts vs 256 +/- 66 volts, p less than 0.02) and energy (E50: 2.7 +/- 1.3 joules vs 3.4 +/- 1.5 joules, p less than 0.01; E80: 3.4 +/- 1.6 joules vs 4.3 +/- 2.2 joules, p less than 0.05) requirements than the monophasic waveform. It is concluded that a biphasic waveform produced by a single discharge that uses the "free" energy remaining on the capacitors significantly reduces the initial voltage and energy requirements for successful defibrillation and may improve the efficacy of future automatic implantable defibrillators.