RELATIVE EFFICACY OF MONOPHASIC AND BIPHASIC WAVE-FORMS FOR TRANSTHORACIC DEFIBRILLATION AFTER SHORT AND LONG DURATIONS OF VENTRICULAR-FIBRILLATION

Background-Recently, interest has arisen in using biphasic waveforms f or external defibrillation. Little work has been done, however, in mea suring transthoracic defibrillation efficacy after long periods of ven tricular fibrillation. In protocol 1, we compared the efficacy of a qu asi-sinusoidal biphasic waveform (QSBW), a truncated exponential bipha sic waveform (TEBW), and a critically damped sinusoidal monophasic wav eform (CDSMW) after 15 seconds of fibrillation. In protocol 2, we comp ared the efficacy of the more efficacious biphasic waveform from proto col I, QSBW, with CDSMW after 15 seconds and 5 minutes of fibrillation . Methods and Results-In protocol 1, 50% success levels, ED50, were me asured after 15 seconds of fibrillation for the 3 waveforms in 6 dogs. In protocol 2, defibrillation thresholds were measured for QSBW and C DSMW after 15 seconds of fibrillation and after 3 minutes of unsupport ed fibrillation followed by 2 minutes of fibrillation with femoral-fem oral cross-circulation. In protocol 1, QSBW had a lower ED50, 16.0+/-4 .9 J, than TEBW, 20.3+/-4.4 J, or CDSMW, 27.4+/-6.0 J. In protocol 2, QSBW had a lower defibrillation threshold after 15 seconds, 38+/-10 J, and after 5 minutes, 41.5+/-5 J, than CDSMW after 15 seconds, 54+/-19 J, and 5 minutes, 80+/-30 J, of fibrillation. The defibrillation thre shold remained statistically the same for QSBW for the 2 fibrillation durations but rose significantly for CDSMW. Conclusions-In this animal model of sudden death and resuscitation, these 2 biphasic waveforms a re more efficacious than the CDSMW at short durations of fibrillation. Furthermore, the QSBW is even more efficacious than the CDSMW at long er durations of fibrillation.