The effects of biphasic and conventional monophasic defibrillation on postresuscitation myocardial function

OBJECTIVES The purpose of this study was to compare the effects of biphasic defibrillation waveforms and conventional monophasic defibrillation wavefo rms on the success of initial defibrillation, postresuscitation myocardial function and duration of survival after prolonged ventricular fibrillation (VF). BACKGROUND We have recently demonstrated that the severity of postresuscita tion myocardial, dysfunction was closely related to the magnitude of the el ectrical energy of the delivered defibrillation shock. In the present study , the effects of fixed 150-J low-energy biphasic waveform shocks were compa red with conventional monophasic waveform shocks after prolonged VF. METHODS Twenty anesthetized, mechanically ventilated domestic pigs were inv estigated. VF was induced with an AC current delivered to the right ventric ular endocardium. After either 4 or 7 min of untreated ventricular fibrilla tion (VF), the animals were randomized for attempted defibrillation with up to three 150-J biphasic waveform shocks or conventional sequence of 200-, 300- or 360-J monophasic waveform shocks. If VF was not reversed, a 1-min i nterval of precordial compression preceded a second sequence of up to three shocks. The protocol was repeated until spontaneous circulation was restor ed or for a total of 15 min. RESULTS Monophasic waveform defibrillation after 4 or 7 min of untreated VF resuscitated eight of 10 pigs. All 10 pigs treated with biphasic waveform defibrillation were successfully resuscitated. Transesophageal echo-Doppler , arterial pressure and heart rate measurements demonstrated significantly less impairment of cardiovascular function after biphasic defibrillation. CONCLUSIONS Lower-energy biphasic waveform shocks were as effective as conv entional higher energy monophasic waveform shocks for restoration of sponta neous circulation after 4 and 7 min of untreated VF. Significantly better p ostresuscitation myocardial function was observed after biphasic waveform d efibrillation. (J Am Coil Cardiol 1999;34:815-22) (C) 1999 by the American College of Cardiology.