IMPORTANCE OF ELECTRODE DESIGN, LEAD CONFIGURATION AND IMPEDANCE FOR SUCCESSFUL LOW-ENERGY TRANSCATHETER ATRIAL DEFIBRILLATION IN DOGS

Objectives. We assessed the feasibility of low energy endocardial defi brillation in a canine model of atrial fibrillation, comparing cathete rs with large surface area electrodes and standard electrode catheters , and evaluated the effects of lead configuration and circuit impedanc e on defibrillation energy requirements. Background. Although recent a nimal studies have demonstrated the feasibility of low energy endocard ial atrial defibrillation, their results have been conflicting with re gard to important methodologic aspects. Methods. In 14 anesthetized gr eyhounds, atrial fibrillation was induced by rapid atrial pacing and m aintained by vagal stimulation. Two large surface area braided electro de catheters and two standard electrode catheters were introduced perc utaneously, one of each, in the right atrial appendage and right ventr icular apex. A cutaneous patch electrode was placed on the left thorax . Biphasic shocks synchronized to the ventricular electrogram were use d to terminate atrial fibrillation. Seven configurations were evaluate d. Three used standard electrodes: proximal atrial cathode to distal a trial, ventricular or cutaneous anode. Four used braided electrodes: t hree with atrial cathode to ventricular, cutaneous or combined anode; one with ventricular cathode to atrial anode. Results. Defibrillation with standard electrode catheters was associated with high impedance ( 576 +/- 112 OMEGA) and low success rates for all configurations (28% s uccess at less-than-or-equal-to 40 J, no successes at 10 J). Low energ y defibrillation was readily achieved with the braided electrodes with significantly lower impedance (75 +/- 13 OMEGA, p < 0.0001). Ventricu lar fibrillation did not occur. The success rate of cardioversion incr eased in a dose-response manner, allowing fitting of a sigmoid curve a nd calculation of energy associated with 50% (ED50) and 90% (ED90) suc cess. The most successful configuration was ventricular cathode/atrial anode (ED50 1.5 +/- 0.4 J), and the least successful was atrial anode /cutaneous patch (ED50 6.5 +/- 3.2 J, p = 0.0001). Conclusions. Low en ergy atrial defibrillation is feasible using large surface area electr odes but not with standard electrode catheters owing to high impedance . An intracardiac anode provides lower impedance and higher success ra tes than are provided by a cutaneous anode.