Monophasic versus biphasic transthoracic countershock after prolonged ventricular fibrillation in a swine model

Objective We sought to compare the defibrillation efficacy of a low-energy biphasic truncated exponential (BTE) waveform and a conventional higher-ene rgy monophasic truncated exponential (MTE) waveform after prolonged ventric ular fibrillation (VF). Background Low energy biphasic countershocks have been shown to be effectiv e after brief episodes of VF (15 to 30 s) and to produce few postshock elec trocardiogram abnormalities. Methods Swine were randomized to MTE (n = 18) or BTE (n = 20) after 5 min o f VF. The first MTE shock dose was 200 J, and first BTE dose 150 J. If requ ired, up to two additional shocks were administered (300, 360 J MTE; 150, 1 50 J BTE). If VF persisted manual cardiopulmonary resuscitation (CPR) was b egun, and shocks were administered until VF was terminated. Successful defi brillation was defined as termination of VF regardless of postshock rhythm. if countershock terminated VF but was followed by a nonperfusing rhythm, C PR was performed until a perfusing rhythm developed. Arterial pressure, lef t ventricular (LV) pressure, first derivative of LV pressure and cardiac ou tput were measured at intervals for 60 min postresuscitation. Results The odds ratio of first-shock success with BTE versus MTE was 0.67 (p = 0.55). The rate of termination of VF with the second or third shocks w as similar between groups, as was the incidence of postshock pulseless elec trical activity (15/18 MTE, 18/20 BTE) and CPR time for those animals that were resuscitated. Hemodynamic variables were not significantly different b etween groups at 15, 30 and 60 min after resuscitation. Conclusions Monophasic and biphasic waveforms were equally effective in ter minating prolonged VF with the first shock, and there was no apparent clini cal disadvantage of subsequent low-energy biphasic shocks compared with pro gressive energy monophasic shocks. Lower-energy shocks were not associated with less postresuscitation myocardial dysfunction. (C) 2000 by the America n College of Cardiology.