Journal of Interventional Cardiac Electrophysiology 9, 15–20, 2003 C  2003 Kluwer Academic Publishers. Manufactured in The Netherlands. Effectiveness of Ibutilide in Cardioversion of Persistent Atrial Fibrillation in Patients with Dual Chamber Stimulation Massimo Santini, Carlo Pignalberi, Renato Ricci, Leonardo Cal ` o, and Luca Santini Department of Cardiology, S. Filippo Neri Hospital, Rome, Italy Abstract. Aim of the study: To evaluate the effective- ness of Ibutilide in cardioversion of persistent atrial fibrillation in patients with sinus node disease wear- ing a dual chamber pacemaker and to assess the poten- tial role of overdrive ventricular pacing in prevention of drug related proarrhythmia. Methods and Results: Fifty-three sinus node disease patients (35 males; mean age 75 ± 9.5 years), implanted with a dual chamber pacing system, with persistent atrial fibrillation, lasting for 328 ± 416 days, received 1–2 mg of intravenous Ibutilide. Pacing mode was pro- grammed in VVI at 90 ppm, in order to suppress sponta- neous ventricular activity. All patients were monitored for 4 hours. Late occurrence of ventricular arrhythmias was evaluated using the pacemaker memory. Ventricu- lar pacing threshold, spontaneous electrogram ampli- tude and pacing impedance were measured before and after Ibutilide infusion. Cardioversion to sinus rhythm occurred in twenty-two patients (41.5%). Treatment suc- cess was significantly related to shorter atrial fibril- lation duration. Paced QT interval duration increased from 412 ± 36 ms to 481 ± 40 ms ( p < 0.0001), without dif- ferences between responders and non responders; QRS width did not change significantly (from 152 ± 25 ms to 161 ± 25 ms; p = n.s.). No early or late episodes of sus- tained or non sustained polymorphic ventricular tachy- cardia were observed. Pacing and sensing threshold did not show any significant variation. Conclusions: Ibutilide showed a good effectiveness in treating persistent atrial fibrillation in paced patients. Overdrive ventricular pacing may have played a role in preventing drug induced ventricular proarrhythmia. No adverse effect on pacing threshold was observed. Key Words. Ibutilide, persistent atrial fibrillation, si- nus node disease, dual chamber pacing, proarrhythmia Introduction Recurrence of persistent atrial fibrillation is a quite common event in patients with sinus node disease after dual chamber pacemaker implanta- tion and may require electrical cardioversion. Ibu- tilide fumarate is a class III antiarrhythmic agent, effective in terminating atrial flutter and fibrilla- tion and in preventing their re-induction [1,2]. The electrophysiological mechanism, by which this antiarrhythmic action is obtained, is directly re- lated with the action potential and refractory pe- riod durations [3]. Such effects, leading to the pro- longation of the QT interval, may be responsible for ventricular proarrhythmia [4,5]. We investigated the effectiveness of Ibutilide administration in patients with sinus node disease and persistent atrial fibrillation wearing a dual chamber pacemaker with the aims: (1) to evalu- ate the actual drug efficacy in such clinical set- ting, (2) to verify if overdrive ventricular pacing may be effective in preventing ventricular proar- rhythmia, (3) to quantify, if any, the effects of Ibu- tilide on atrial and ventricular pacing and sensing thresholds. Methods Patient Population We enrolled a population of fifty-three patients (35 males; mean age 75 ± 9.5 years) affected by sinus node disease and persistent atrial fibril- lation lasting for 328 ± 416 days with a prior implanted dual chamber pacing system. Clini- cal characteristics of the study population are summarised in Table 1. Left atrium size was on average 40 ± 12 mm; mean left ventricular ejection fraction was 45 ± 17%. Implanted units were Medtronic Thera DR 7940–7944, 7960–7964 (Medtronic Inc., Minneapolis, USA) in 47 (89%) and Guidant Discovery DR 1273 (Guidant Inc., St. Paul, USA) in six (11%). All devices were equipped with diagnostic function capable of collecting data on atrial and ventricular tachyarrhythmias. All patients met the following eligibility criteria: sus- tained atrial fibrillation persisting for at least Address for correspondence: Prof. M. Santini, Department of Cardiology, San Filippo Neri Hospital, via Martinotti, 20; 00135 Rome, Italy. E-mail: m.santini@rmnet.it Received 11 July 2002; accepted 29 January 2003 15