Acute beta-adrenoceptor blockade improves efficacy of ibutilide in conversion of atrial fibrillation with a rapid ventricular rate.

Aims: Activation of beta-adrenoceptors attenuates prolongation of action potential duration induced by blockade of the delayed rectifier potassium current. We examined whether acute administration of beta-blocker could enhance ibutilide (IB) efficacy in conversion of atrial fibrillation (AF) with a rapid ventricular rate.

Methods And Results: Ninety patients (aged 63 +/- 13.5 years) with rapidly conducting AF were randomized in to two groups. Group A (n = 44) received esmolol titrated to achieve a heart rate of <100 bpm followed by IB co-administration, while Group B (n = 46) were treated with IB as monotherapy. In Group A, 29 patients (67%) converted to sinus rhythm (SR) compared with 21 (46%) in Group B (P = 0.04). The use of esmolol was the most important predictor for cardioversion (P = 0.009). The slower the heart rate at the time of IB initiation, the higher the likelihood for cardioversion (P = 0.015). Patients in Group A had significantly shorter corrected QT interval (QTc) at the time of conversion than those in Group B (433 vs. 501 ms, P = 0.003). Two patients in Group A developed severe bradycardia, whereas three patients in Group B developed severe ventricular tachycardia (VT).

Conclusion: Compared with IB monotherapy, the combination therapy of esmolol and IB appears to be more effective in conversion of rapidly conducting AF back to SR. The addition of beta-blocker reduces QTc prolongation and diminishes the risk of VT at the expense, however, of increased bradycardic events.