Efficacy and tolerability of transvenous low energy cardioversion of paroxysmal atrial fibrillation in humans.

Objectives: This study investigated the efficacy and tolerability of low energy shocks for termination of atrial fibrillation in patients, using an endocardial electrode configuration that embraced both atria.

Background: In animals, low energy biphasic shocks delivered between electrodes in the coronary sinus and right atrium have effectively terminated atrial fibrillation. If human defibrillation thresholds are sufficiently low, atrial defibrillation could be achieved in conscious patients using an implanted device.

Methods: Twenty-two consecutive patients with stable atrial fibrillation were studied during electrophysiologic testing. Biphasic R wave synchronous shocks were delivered between large surface area electrodes in the coronary sinus and high right atrium, using a step-up voltage protocol starting at 10 or 20 V and increasing to a maximum of 400 V. Patients were conscious at the start of the study and were asked to report on symptoms but were sedated later if shocks were not tolerated.

Results: Cardioversion was achieved in all 19 patients who completed the study, with a mean (+/- SD) leading-edge voltage of 237 +/- 55 V (range 140 to 340) and mean energy of 2.16 +/- 1.02 J (range 0.7 to 4.4). The mean maximal shock delivered without sedation was 116 +/- 51 V (range 60 to 180). No proarrhythmia or mechanical complications occurred.

Conclusions: The delivery of biphasic R wave synchronous shocks between the high right atrium and coronary sinus can terminate atrial fibrillation with very low energies. General anaesthesia is not required, and a minority of fully conscious patients are able to tolerate this method of cardioversion.