External exponential biphasic versus monophasic shock waveform: Efficacy in ventricular fibrillation of longer duration

Ventricular fibrillation (VF) duration may be a factor in determining the d efibrillation energy for successful defibrillation. Exponential biphasic wa veforms have been shown to defibrillate with less energy than do monophasic waveforms when used for external defibrillation. However, it is unknown wh ether this advantage persists with longer VF duration. We tested the hypoth esis that exponential biphasic waveforms have lower defibrillation energy a s compared to exponential monophasic waveforms even with longer VF duration up to 1 minute. In a swine model of external defibrillation (n = 12, 35 +/ - 6 kg), we determined the stored energy at 50% defibrillation success (E50 ) after both 10 seconds and 1 minute of VF duration. A single exponential m onophasic (M) and two exponential biphasic (B1 and B2)waveforms were tested with the following characteristics: M (60 mu F, 70% tilt), B2 (60/60 mu F, 70% tilt/3 ms pulse width), and B2 (60/20 mu F, 70% tilt/3 ms pulse width) where the ratio of the phase 2 leading edge voltage to that of phase 1 was 0.5 for B1 and 1.0 for B2. E50 was measured by a Bayesian technique with a total of ten defibrillation shocks in each waveform and VF duration random ly. The E50 (J) for M, B1, and B2 were 131 +/- 41, 57 +/- 18,* and 60 +/- 2 6* with 10 seconds of VF duration, respectively, and 114 +/- 62, 77 +/- 45, * and 72 +/- 53* with 1 minute of VF duration, respectively (*P < 0.05 vs M ). There was no significant difference in the E50 between 10 seconds and 2 minute of VF durations for each waveform. We conclude that (1) the E50 does not significantly increase with lengthening VF durations up to 2 minute re gardless of the shock waveform, and (2) external exponential biphasic shock s are more effective than monophasic waveforms even with longer VF duration s.