Efficacy and safety of repeated intravenous doses of ibutilide for rapid conversion of atrial flutter or fibrillation. Ibutilide Repeat Dose Study Investigators.

BACKGROUND: Currently available antiarrhythmic drugs have limited efficacy for acute termination of atrial fibrillation and flutter, especially if the arrhythmia is not of recent onset. The purpose of this multicenter study was to determine the efficacy and safety of repeated doses of intravenous ibutilide, a class III antiarrhythmic drug, in terminating atrial fibrillation or flutter.

METHODS AND RESULTS: Two hundred sixty-six patients with sustained atrial fibrillation (n = 133) or flutter (n = 133), with an arrhythmia duration of 3 hours to 45 days, were randomized to receive up to two 10-minute infusions, separated by 10 minutes, of ibutilide (1.0 and 0.5 mg or 1.0 and 1.0 mg) or placebo. The conversion rate was 47% after ibutilide and 2% after placebo (P < .0001). The two ibutilide dosing regimens did not differ in conversion efficacy (44% versus 49%). Efficacy was higher in atrial flutter than fibrillation (63% versus 31%, P < .0001). In atrial fibrillation but not flutter, conversion rates were higher in patients with a shorter arrhythmia duration or a normal left atrial size. Arrhythmia termination occurred a mean of 27 minutes after start of the infusion. Of 180 ibutilide-treated patients, 15 (8.3%) developed polymorphic ventricular tachycardia during or soon after the infusion. The arrhythmia required cardioversion in 3 patients (1.7%) and was nonsustained in 12 patients (6.7%).

CONCLUSIONS: Intravenous ibutilide given in repeated doses is effective in rapidly terminating atrial fibrillation and flutter and under monitored conditions is an alternative to current cardioversion options.