The influence of ventricular fibrillation duration on defibrillation efficacy using biphasic waveforms in humans

Objectives. The purpose of this study was to prospectively investigate the influence of ventricular fibrillation (VF) durations of 5, 10 and 20 s on t he defibrillation threshold (DFT) during implantable cardioverter-defibrill ator (ICD) implantation. Background. Although the DFT using monophasic waveforms has been shown to i ncrease with VF duration in humans, the effect of VF duration on defibrilla tion efficacy using biphasic waveforms in humans is not known. Methods. Thirty patients undergoing primary ICD implantation or pulse gener ator replacement were randomly assigned to have the DFT determined using bi phasic shocks at two durations of VF each (5 and 10 s, 10 and 20 s or 5 and 20 s). Results. There was no statistically significant difference in the mean DET comparing VF durations of 5 s (9.5 +/- 6.0 J) and 10 s (10.8 +/- 7.0 J) (p = 0.4). The mean DFT significantly increased from 10.9 +/- 6.1 J at 10 s of VF to 12.6 +/- 5.6 J (p = 0.03) at 20 s of VF, and from 7.0 +/- 3.5 J at 5 s of VF to 10.5 +/- 6.3 J (p = 0.04) at 20 s of VF. An increase in the DFT was observed in 14 patients as VF duration increased. There were no clinic al characteristics that differentiated patients with and without an increas e in the DFT. Conclusions. Defibrillation efficacy decreases with increasing VF duration using biphasic waveforms in humans. Ventricular fibrillation durations grea ter than 10 s may negatively affect the effectiveness of ICD therapy. (C) 1 998 by the American College of Cardiology.