Reduction of the Internal Atrial Defibrillation Threshold with Balanced Orthogonal Sequential Shocks.

Introduction: The aim of this study was to determine the atrial defibrillation threshold (ADFT) of a first shock across the standard right atrium (RA) to distal coronary sinus (dCS) configuration followed by a second shock along the atrial septum with a standard sequential waveform (the second shock leading edge equaled the first shock trailing edge) and a balanced sequential waveform (the leading edges of both shocks were equal). Methods and Results: In nine sheep atrial fibrillation was induced with acetyl-β-methylcholine and burst pacing. A catheter was placed with electrodes in the dCS, proximal coronary sinus (pCS), and RA. A J-shaped catheter was positioned with an electrode at Bachmann's bundle (BB) while another catheter was positioned with an electrode in the superior vena cava (SVC). The ADFTs of six single- and dual-pathway configurations were determined with single, standard sequential, or balanced sequential shocks. The ADFT of the RA→dCS configuration (0.86 ± 0.27 J, 159 ± 29 V, 2.42 ± 0.36 A) was significantly reduced when followed by an SVC→pCS (0.58 ± 0.17 J, 112 ± 20 V, 1.64 ± 0.39 A) or a BB→pCS shock (0.64 ± 0.16 J, 119 ± 18 V, 1.81 ± 0.38 A) with standard sequential shocks. With balanced sequential shocks, the peak voltage and current ADFTs were further significantly reduced (85 ± 11 V and 1.24 ± 0.21 A for second shock SVC→pCS, and 93 ± 13 V and 1.38 ± 0.27 A for second shock BB→pCS). Conclusion: The ADFT of the standard RA→dCS shock is significantly reduced when followed by a second shock along the atrial septum delivered between electrodes in the pCS and either SVC or BB and ADFT is further reduced with balanced sequential shocks. [ABSTRACT FROM AUTHOR]