Background. Delivery of shocks within the right atrium has been reported to be more effective than conventional external shocks in converting atrial fibrillation (AF), but these two cardioversion techniques have never been compared prospectively. The purpose of this study was to compare the efficacies of external and internal cardioversion in patients with chronic AF unresponsive to prior attempts at electrical and/or pharmacological cardioversion. Low-dose amiodarone was used in all patients after cardioversion to suppress recurrences of AF. Methods and Results. One hundred twelve patients with AF of at least 1 month in duration were randomly assigned to undergo external cardioversion with 300-360-J shocks or internal cardioversion with 200-300-J shocks delivered through a standard electrode catheter within the right atrium. The patients were treated with amiodarone (200 mg/day 5-7 days/week) for 1 month before electrical cardioversion and afterward if the cardioversion was successful. The patients were evaluated at regular intervals during 1 year of follow-up. The efficacy of internal cardioversion was significantly greater than that of external cardioversion (91% versus 67%, p=0.002). The only variable that was associated with the outcome of cardioversion was body weight. Among patients in whom sinus rhythm was restored, AF recurred as often after internal and external cardioversion; at 1 year of follow-up, 37% of patients in whom external or internal cardioversion had been effective were still in sinus rhythm. Patients who had undergone an attempt at electrical cardioversion before entry into this study were less likely to remain in sinus rhythm after cardioversion. The only complications of cardioversion were one instance of cerebral thromboembolism after external cardioversion and one instance of transient pulmonary edema after internal cardioversion. Therapy with amiodarone was discontinued because of an adverse drug effect in only three patients. Conclusions. Internal cardioversion is more effective than external cardioversion in restoring sinus rhythm and is as safe as external cardioversion in patients with chronic AF. The recurrence rate of AF is the same after both types of cardioversion. If conventional electrical cardioversion is ineffective, internal cardioversion should be attempted. The combination of low-dose amiodarone and external or internal cardioversion may result in maintaining sinus rhythm long-term in patients with refractory AF.
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