Optimization of biphasic waveforms for human nonthoracotomy defibrillation.

BACKGROUND Biphasic waveforms reduce defibrillation threshold (DFT) in a wide variety of models. Although there are several human studies of long-duration, high-tilt biphasic waveform defibrillation, the specific biphasic waveform shape required to achieve optimal DFT reduction is unknown. METHODS AND RESULTS This study tested the effect of single capacitor biphasic waveform tilt modification on DFT using a paired study design in 18 patients undergoing nonthoracotomy defibrillator implantation. Baseline DFT was obtained using a 65% tilt, simultaneous pulse, bidirectional monophasic shock from a right ventricular cathode to a coronary sinus or superior vena cava lead and a subscapular patch. The single-capacitor biphasic waveform shocks, delivered over the same pathways, consisted of either both phases at 65% tilt (65/65 biphasic waveform) to produce an overall tilt of 88% and a delivered energy 11% greater than monophasic shock or both phases at 42% tilt (42/42 biphasic waveform) to produce an overall tilt of 66% and delivered energy equal to monophasic shock. The 65/65 biphasic waveform reduced stored energy DFT 25%, from 16.2 +/- 4.4 J with monophasic shock to 12.1 +/- 5.3 J (P < .02); however, it did not significantly reduce the delivered energy DFT. In contrast, the 42/42 biphasic waveform required 49% less stored energy (16.2 +/- 4.4 J, monophasic shock, vs 8.3 +/- 3.3 J, biphasic waveform; P < .001) and 49% less delivered energy (14.2 +/- 3.8 J, monophasic shock, vs 7.3 +/- 2.9 J, biphasic waveform; P < .001) than monophasic shock for successful defibrillation. The 42/42 biphasic waveform delivered energy DFT was 4.6 +/- 5.2 J (39%) less than 65/65 biphasic waveform DFT (P < .002). CONCLUSIONS DFT reduction is an inherent electrophysiological property of biphasic waveforms that is independent of delivered energy. Overall biphasic waveform tilt and the relative amplitudes of the waveform phases are important factors in defibrillation efficacy. Defibrillation with a 42/42 biphasic waveform is more efficacious than 65/65 biphasic waveform defibrillation; however, the optimal biphasic waveform remains unknown.