Testing different biphasic waveforms and capacitances: effect on atrial defibrillation threshold and pain perception

Electrophysiology Laboratory, Duke University, Veterans Affairs Medical Center, Durham, North Carolina 27705, USA.

OBJECTIVES: The goal of this study was to compare the effect of different tilts and capacitances for biphasic shocks on atrial defibrillation efficacy and pain threshold. BACKGROUND: Although biphasic shocks have been shown to be superior to monophasic shocks, the effect of tilt and capacitance on atrial defibrillation success and pain perception has not been studied in patients. METHODS: Atrial defibrillation threshold (DFT) testing was performed using a right atrial appendage/coronary sinus lead configuration in 38 patients with a history of paroxysmal atrial fibrillation undergoing an invasive electrophysiologic study. Biphasic waveforms with 40%, 50%, 65%, 80%, 30%/50% and 40%/50% were tested randomly in 22 patients (Group 1). In 16 patients (Group 2), a 65% tilt waveform with 50- and 120-microF capacitance was tested. Before sedation, pain sensation was graded by 15 patients in Group 1 after delivery of a 0.5-J shock and by 10 patients in Group 2 after two 1.5-J shocks with 50- and 120-microF capacitance were delivered. RESULTS: The DFT energy for the 50% tilt waveform was significantly lower than the 65%, 80% and 30%/50% tilt waveforms. The 40%/50% tilt waveform provided slightly lower energy requirements than the 50% tilt waveform. Nine patients (60%) described the 0.5-J shock as very painful, and four (26.6%) complained of slight pain. The 50-microF capacitor lowered energy requirements compared with the 120-microF capacitor. Six patients (60%) perceived the 1.5-J 50-microF capacitor shock as more painful, whereas three (30%) perceived both shocks as equally painful. CONCLUSIONS: Biphasic waveforms with 50% tilt in both phases and a smaller tilt in the positive phase than that in the negative phase (40%/50%) provided a decrease in energy requirements at atrial DFT. In addition, stored energy was reduced by biphasic shocks with 50-microF capacitance compared with 120-microF capacitance. Despite the reduction in energy requirements, shocks < 1 J continued to be perceived as painful in the majority of patients.

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