EFFICACY AND TOLERABILITY OF TRANSVENOUS LOW-ENERGY CARDIOVERSION OF PAROXYSMAL ATRIAL-FIBRILLATION IN HUMANS

Objectives. This study investigated the efficacy and tolerability of l ow energy shocks for termination of atrial fibrillation in patients, u sing an endocardial electrode configuration that embraced both atria. Background. In animals, low energy biphasic shocks delivered between e lectrodes in the coronary sinus and right atrium have effectively term inated atrial fibrillation. If human defibrillation thresholds are suf ficiently low, atrial defibrillation could be achieved in conscious pa tients using an implanted device. Methods. Twenty-two consecutive pati ents with stable atrial fibrillation were studied during electrophysio logic testing. Biphasic R wave synchronous shocks were delivered betwe en 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 in creasing to a maximum of 400 V. Patients were conscious at the start o f the study and were asked to report on symptoms but were sedated late r 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 2.1 6 +/- 1.02 J (range 0.7 to 4.4). The mean maximal shock delivered with out sedation was 116 +/- 51 V (range 60 to 180). No proarrhythmia or m echanical complications occurred. Conclusions. The delivery of biphasi c R wave synchronous shocks between the high right atrium and coronary sinus can terminate atrial fibrillation with very low energies, Gener al anaesthesia is not required, and a minority of fully conscious pati ents are able to tolerate this method of cardioversion.