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 ofaction potential duration induced by blockade of the delayedrectifier potassium current. We examined whether acute administrationof beta-blocker could enhance ibutilide (IB) efficacy in conversionof atrial fibrillation (AF) with a rapid ventricular rate. Methods and results: Ninety patients (aged 63 ± 13.5 years) with rapidly conductingAF were randomized in to two groups. Group A (n = 44) receivedesmolol titrated to achieve a heart rate of <100 bpm followedby IB co-administration, while Group B (n = 46) were treatedwith IB as monotherapy. In Group A, 29 patients (67%) convertedto sinus rhythm (SR) compared with 21 (46%) in Group B (P =0.04). The use of esmolol was the most important predictor forcardioversion (P = 0.009). The slower the heart rate at thetime of IB initiation, the higher the likelihood for cardioversion(P = 0.015). Patients in Group A had significantly shorter correctedQT interval (QTc) at the time of conversion than those in GroupB (433 vs. 501 ms, P = 0.003). Two patients in Group A developedsevere bradycardia, whereas three patients in Group B developedsevere ventricular tachycardia (VT). Conclusion: Compared with IB monotherapy, the combination therapy of esmololand IB appears to be more effective in conversion of rapidlyconducting AF back to SR. The addition of beta-blocker reducesQTc prolongation and diminishes the risk of VT at the expense,however, of increased bradycardic events.