Electrophysiological effects of ibutilide in patients with accessory pathways.

BACKGROUND Atrial fibrillation (AF) may cause life-threatening ventricular arrhythmias in patients with Wolff-Parkinson-White syndrome. We prospectively evaluated the effects of ibutilide on the conduction system in patients with accessory pathways (AP). METHODS AND RESULTS In part I, we gave ibutilide to 22 patients (18 men, 31+/-13 years of age) who had AF during electrophysiology study, including 6 pediatric patients </=18 years of age. Ibutilide terminated AF in 21 of 22 patients (95%) during or 8+/-5 minutes after infusion and prolonged the shortest preexcited R-R interval during AF. Successful ablation was performed in all patients. In part II, ibutilide was given to 18 patients (14 men, 28+/-21 years) to assess its effects on the AP and conduction system. Ibutilide prolonged the antegrade atrioventricular node effective refractory period (ERP) (from 252+/-60 to 303+/-70 ms; P<0.02). Ibutilide caused transient loss of the delta wave in 1 patient and abolished inducible tachycardia in 2 patients, although retrograde mapping still allowed for successful AP ablation. The antegrade AP ERP prolonged from 275+/-40 to 320+/-60 ms (P<0.01), as did the antegrade AP block cycle length; the retrograde AP ERP and block cycle length similarly prolonged with ibutilide. The relative and effective refractory period of the His-Purkinje system increased in 61% of patients after ibutilide. There were no adverse side effects. CONCLUSIONS We report the use of ibutilide in terminating AP-mediated AF, including the first report in the pediatric population. Ibutilide prolonged refractoriness of the atrioventricular node, His-Purkinje system, and AP.