TRANSTHORACIC DEFIBRILLATION OF SWINE WITH MONOPHASIC AND BIPHASIC WAVE-FORMS

Background Biphasic waveforms have had a favorable impact on internal defibrillation but have seen minimal use in transthoracic defibrillati on systems. The purpose of this study was to compare monophasic and bi phasic waveforms for transthoracic defibrillation in swine. Methods an d Results Three interrelated studies were per formed in 19 swine to es tablish the relative transthoracic defibrillation efficacy of biphasic shock waveforms. In study 1, we measured voltage (V-50) and energy (E (50)) strength-duration curves for monophasic and biphasic truncated e xponential waveforms. We then independently examined the effects of ph ase duration and tilt on biphasic waveform defibrillation with a total waveform duration from study 1 that provided the minimum V-50 (study 2) and the minimum E(50) (study 3). At each pulse duration tested in s tudy 1, biphasic waveforms defibrillated with significantly less volta ge and energy than monophasic waveforms. At a duration of 12 ms, there was a voltage minimum for biphasic waveform defibrillation. At this d uration, V-50 was 1378+/-505 V for the biphasic waveform compared with 2185+/-361 V for the monophasic waveform, P=.01. For both monophasic and biphasic waveforms, E(50) increased with pulse duration. With a to tal pulse duration of 12 ms, E(50) was 169+/-101 J for the biphasic wa veform compared with 414+/-114 J for the monophasic waveform, P=.003. In study 2, optimization of phase duration and total tilt reduced the defibrillation requirements of the 12-ms ''minimum voltage'' biphasic waveform to 1284+/-187 V and 129+/-36 J. In study 3, the 8-ms ''minimu m energy'' biphasic waveform had an E(50) of 115+/-35 J that was 11% l ess than the 12-ms biphasic waveform, P=.11; however, voltage requirem ents of 1476+/-239 V were 15% higher, P=.005. Conclusions This study d emonstrates the superiority of truncated biphasic waveforms over trunc ated monophasic waveforms for transthoracic defibrillation of swine, B iphasic waveforms should prove as advantageous at reducing voltage and energy requirements for transthoracic defibrillation as they have for internal defibrillation.