Marked reduction in internal atrial defibrillation thresholds with dual-current pathways and sequential shocks in humans

Background-This study tested the ability of sequential shocks delivered through dual-current pathways to lower the atrial defibrillation threshold (ADFT) compared with a biphasic shock through a standard single-current pathway. Methods and Results-Electrodes were positioned in the right atrial appendage (RA), left subclavian vein (LSV), proximal coronary sinus (CSos), and distal coronary sinus (DCS) in 14 patients with chronic atrial fibrillation (170 +/- 185 days). Using a step-up protocol, we compared ADFTs for a single-current pathway (RA --> DCS) that used a single 7.5/2.5-ms biphasic shock from a 150-mu F capacitor with those for a dual-current pathway system (RA --> DCS followed by CSos --> LSV) using sequential 7.5/2.5-ms biphasic shocks with capacitor discharge waveforms for 150-mu F and 600-mu F capacitors. Both dual-current pathway configurations (2.0 +/- 0.4 J for 150-mu F capacitance, 2.4 +/- 0.5 J for 600-mu F capacitance) had a significantly lower ADFT than the single-current pathway (5.1 +/- 1.8 J). Whereas the dual-current pathway with 150-mu F capacitor shocks had a significantly lower energy threshold, there was no statistical difference in terms of leading-edge voltage compared with the dual-current pathway with 600-mu F capacitance shocks. There were no ventricular arrhythmias induced with appropriately synchronized shocks. Conclusions-For internal atrial defibrillation in humans, sequential biphasic waveforms delivered over dual-current pathways resulted in a markedly reduced (>50% reduction) ADFT compared with a single shock over a single-current pathway.