Objective: To evaluate the racial differences in the efficacy and safety of ibutilide in patients with recent-onset (<2 weeks) atrial fibrillation and atrial flutter.
Methods: This study included 58 consecutive patients with recent-onset atrial fibrillation (n = 34) and atrial flutter (n = 24). The mean age was 65.7 +/- 14.6 years (range, 37-86 years), 47% were women (n = 27) and 34% (n = 20) were African Americans. The duration of arrhythmia ranged from 3 hours to 2 weeks. All patients had echocardiography, were on therapeutic anticoagulation, had a fairly well controlled ventricular rate, normal QTc interval on 12-lead electrocardiography, and normal serum electrolytes. Ibutilide was administered as an intravenous infusion with a maximal dose of 2 mg.
Results: The overall conversion rate to sinus rhythm was 66% (n = 38), with 62% (n = 21) with atrial fibrillation and 71% (n = 17) of atrial flutter. Most conversions (84%) occurred within 45 minutes of ibutilide infusion. The mean time to arrhythmia conversion was 37.4 +/- 59.8 minutes. Race had a significant impact on efficacy, with increased conversions seen in African Americans (P = 0.004) and increased nonconversion seen in whites (P = 0.02). Successful conversion was not affected by the left atrial size or the presence of valvular heart disease, hypertension, heart failure, coronary heart disease, and diabetes mellitus. QTc intervals were prolonged after drug administration, with a mean change of 24.6 milliseconds for all patients. The QTc prolongation after drug administration was greater in African Americans than in whites (27.4 vs. 23.3 milliseconds). Torsade de pointes occurred in 4 patients (3 African Americans) and was treated with intravenous magnesium sulfate and electrical cardioversion.
Conclusion: Ibutilide used for pharmacological cardioversion of atrial fibrillation and atrial flutter is more effective in African Americans but carries a higher risk of torsade de pointes.