Thransthoracic defibrillation of short lasting ventricular fibrillation

BACKGROUND: Biphasic rectilinear shocks are more effective than monophasic shocks for transthoracic atrial defibrillation and for ventricular arrhythmias during electrophysiological testing. We undertook the present study to compare the efficacy of 100 J rectilinear biphasic waveform shocks with 150 J monophasic damped sine waveform shocks for transthoracic defibrillation of true ventricular fibrillation during defibrillation threshold testing (DFT). The second aim of the study was to analyse the influence of patch positions on the efficacy of defibrillation. METHODS: 50 episodes of 14 patients (age ranging from 37 to 82 years) who underwent DFT testing were randomised for back-up shocks with either a sequence of 100 and 200 J biphasic waveform, or a sequence of 150 and 360 J conventional monophasic shocks. A binary search protocol was used at implantation and before hospital discharge. Patients were also randomised to an anteroposterior position versus a right-anterior-apical position. A crossover was performed between implantation and pre-hospital discharge for biphasic versus monophasic sequence as well as for the 2 different positions. RESULTS: After failed internal shocks, 27 episodes were treated with biphasic, and 23 with monophasic shocks. The first attempt by the external device did not terminate II episodes (2 biphasic, 9 monophasic). The first shock efficacy was significantly greater with biphasic than with monophasic shocks (p < 0.02). The overall success rate was 93% with biphasic shocks and 64% with monophasic shocks. In multivariate regression analysis including patch position, arrhythmia duration, type of waveform, testing order and session, only waveform was associated with successful defibrillation (p < 0.02). CONCLUSION: For transthoracic defibrillation of ventricular fibrillation, low-energy rectilinear biphasic shocks are more effective than monophasic shocks. The position of the defibrillation shock pads has no influence on the biphasic shock efficacy, but anteroposterior pad position is more effective using monophasic shocks.