Transthoracic monophasic and biphasic defibrillation in a swine model: a comparison of efficacy, ST segment changes, and postshock hemodynamics

Objective: Biphasic waveforms for transthoracic defibrillation (DF) have be en tested extensively after brief (15 s) episodes of VF in animal models an d in patients undergoing electrophysiologic testing. The purpose of this st udy was to compare the effects mono- and biphasic waveforms for DF on postd efibrillation ST segments and left ventricular pressure, markers of myocard ial injury, after more extended periods of VF (30 and 90 s). Methods: 21 an esthetized and instrumented swine were randomized to truncated exponential monophasic or biphasic waveform DF. VF was induced electrically and 30 s la ter, DF with the designated waveform was attempted with a shock dose of 200 J. If unsuccessful, 300 J and then 360 J were administered if necessary. F ollowing return to control hemodynamic values and normalization of the surf ace EGG, VF was again induced and, after 90 s, DF was attempted as in the 3 0 s VF period. CPR was not performed during VF and each animal was counters hocked with only one waveform for both VF episodes. Waveforms were compared for frequency of first shock defibrillation success, surface ECG indicator s of myocardial injury (ST segment changes at 10, 20, and 30 s after counte rshock) and time to return to pre-VF hemodynamics after successful DF, an i ndicator of postshock ventricular function. Results: Successful first shock conversion rates at 30 and 90 s were 60 and 63% for monophasic and 64 and 82% for biphasic (NS). Biphasic DF after 30 a produced ST segment changes ( measured 10 s after DF) in 1/10 animals while six of eight animals in the m onophasic group showed ST segment changes (P = 0.013). After 90 s of VF, ST segment changes were observed in 6/8 in the monophasic group and 2/10 in t he biphasic group (P = 0.054). Differences in the time to hemodynamic recov ery (return to control peak left ventricular pressure) were not observed be tween biphasic and monophasic waveforms after 30 or 90 s of VF. Conclusions : Monophasic and biphasic transthoracic defibrillation are equally effectiv e in terminating VF of 30 and 90 s duration and restoring a perfusing rhyth m. The biphasic waveform produced less ECG evidence of transient myocardial injury. However, there was no difference in the rate of return to control. hemodynamics. ST segment changes following countershock of VF of brief dur ation are transient and of questionable significance. (C) 2000 Elsevier Sci ence Ireland Ltd. All rights reserved.