Cardioversion of Atrial Tachyarrhythmias by Low-Energy Transvenous Technique

Summary

This study assessed the feasibility of terminating atrial tachyarrhythmias by low-energy DC shock delivered through an electrode catheter positioned within the right atrial appendage. A modified defibrillator provided low stored-energy levels (0.16–6.1 joules) in calibrated increments of 0.1–0.2 joules. Six chloralose anesthetized open chest dogs were studied using four standard electrode catheters with differing stimulation surface electrode areas (SEA), or electrode configurations, but with similar ring-to-tip interelectrode (R/T) distances: (1) Medtronic 5816 (SEA 85 mm² R/T 16 mm), (2) Medtronic 5818 (SEA 53 mm², R/T 16mm), (3) Medtronic 6904A (SEA 20 mm², R/T 22 mm), and (4) USCI quadpolar with the two proximal terminals and the two distal terminals paired (approximate SEA 26 mm², approximate R/T 20 mm). Efficacy of each electrode configuration for cardioversion of pacing-induced atrial tachyarrhythmias (atrial cycle lengths 120–200 ms) was assessed sequentially. Shocks were delivered at random during the atrial cycle, and in 16/70 (23%) trials, the atrial tachyarrhythmia was terminated. In 7/16 successful trials termination was successful at stored energies less than 0.3 joules (approximately 0.2 joules delivered energy). Leads 6904A and USCI quadpolar failed to terminate tachyarrhythmias. Successful termination was associated with shocks delivered within 40 ms of the preceding atrial electrogram, while failure to terminate tachycardia was associated with arrhythmia present for longer than five minutes. Thus, if relatively large surface area electrodes are employed, transvenous cardioversion of atrial tachyarrhythmias is feasible and may be useful during recent onset tachyarrhythmias such as occur postoperatively or during invasive electrophysiological testing.