Resuscitation after prolonged ventricular fibrillation with use of monophasic and biphasic waveform pulses for external defibrillation

Background-Survival after prolonged ventricular fibrillation (VF) appears s everely limited by 2 major factors: (1) low defibrillation success rates an d (2) persistent post-countershock myocardial dysfunction, Biphasic (BP) wa veforms may prove capable of favorably modifying these limitations. However , they have not been rigorously tested against monophasic (MP) waveforms in clinical models of external defibrillation, particularly where rescue from prolonged VF is the general rule. Methods and Results-We randomized 26 dogs to external countershocks with ei ther MP or BP waveforms, Hemodynamics were assessed after shocks applied du ring sinus rhythm, after brief VF (>10 seconds), and after resuscitation fr om prolonged VF (>10 minutes). Short-term differences in percent change in left ventricular +dP/dt(max) (MP -16+/-28%, BP +9.1+/-24%; P=0.03) and left ventricular --dP/dt(max) (MP -37+/-26%, BP -18+/-20%; P=0.05) were present after rescue from brief VF, with BP animals exhibiting less countershock-i nduced dysfunction. After prolonged VF, the BP group had lower mean defibri llation thresholds (107+/-57 versus 172+/-88 J for MP, P=0.04) and signific antly shorter resuscitation times (397+/-73.7 versus 488+/-74.3 seconds for MP, P=0.03), Conclusions-External defibrillation is more efficacious with BP countershoc ks than with MP countershocks. The lower defibrillation thresholds and shor ter resuscitation times associated with BP waveform defibrillation may impr ove survival after prolonged VF arrest.