Introduction: Although the recurrence rate of atrial fibrillation has been reported to be similar to that after external and internal cardioversion, little is known about immediate reinitiation of atrial fibrillation (IRAF) following internal cardioversion.
Methods and results: Thirty-eight patients (24 men; mean age 63 +/- 13 years) underwent internal atrial defibrillation. Catheter-based defibrillation electrodes were positioned in the anterolateral right atrium and the coronary sinus. All patients were cardioverted at a mean threshold of 4.6 +/- 3.4 J. Five of 38 patients (13%) had 1 to 4 episodes of IRAF. No difference in clinical and echocardiographic characteristics were observed when patients with and without IRAF were compared. Atrial fibrillation was always reinitiated by an atrial premature beat. When the earliest atrial endocardial activation time on the defibrillation catheters was analyzed, these atrial premature beats did not seem to originate from the defibrillation catheters. Twenty-one patients had atrial premature beats without IRAF. When the coupling intervals of the first atrial premature beat in patients without and with IRAF after conversion were compared, a significant difference was found (661 +/- 229 vs 418 +/- 79 msec, P < 0.05). IRAF was successfully treated with repeated shock delivery after the administration of atropine in 1 patient and intravenous flecainide in 2. Only repeated shock delivery was sufficient to treat IRAF in another 2 patients. Late recurrences of atrial fibrillation occurred in 3 of 5 with IRAF and in 19 of 33 patients without IRAF (P = NS).
Conclusion: IRAF after internal atrial defibrillation occurred in 13% of patients, was always initiated by an atrial premature beat having a short coupling interval not originating from the defibrillation catheters, and was prevented by repeated shock delivery with or without preceding administration of pharmacologic agents. IRAF did not predict early recurrences of the arrhythmia after discharge from the hospital, emphasizing the necessity to treat immediate reinitiation promptly to achieve a successful cardioversion.