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Background Patients with persistent or permanent atrial fibrillation (AF) often need direct current cardioversion after radiofrequency ablation. The aim of this study was to investigate the effectiveness and safety of ibutilide for cardioversion of persistent or permanent atrial fibrillation after radiofrequency ablation and the factors related to conversion.Methods Patients with persistent or permanent atrial fibrillation were treated with combined ablation strategy including circumferential pulmonary vein isolation, linear ablation and CAFE potential ablation. If AF was not terminated after ablation, ibutilide was used for cardioversion (1 mg, intravenous injection in 10 minutes). These patients were divided into a conversion group and a non-conversion group according to whether AF was converted to sinus rhythm within 30 minutes after administration. ECG monitoring was performed during the injection of ibutilide. Atrial waves recorded by coronary sinus electrodes were measured for calculating average wavelength of AF waves in six seconds. The QT interval was measured immediately after conversion and 2 hours after injection of ibutilide.Results Forty patients whose AF was not converted to sinus rhythm after radiofrequency ablation were given an intravenous injection of ibutilide. Of the 40 patients, 29 cases were converted to sinus rhythm, with a conversion rate of 72.5%. The average conversion time was (13.2±5.5) minutes. Compared with the conversion group, patients in the non-conversion group had a longer history of AF (9.4±5.3) years vs. (4.3±2.8) years, P ＜0.05), and a markedly enlarged left atrium (47.3±2.9) mm vs. (42.1±4.5) mm, P ＜0.05). There were no significant differences in gender, age, body mass index and left ventricular function between the two groups. Ibutilide significantly prolonged the average wavelength of the AF wave (171.8±29.5) ms vs. (242.0±40.0) ms, P ＜0.001). Two hours after ibutilide treatment, the QT interval was significantly shortened (421.0±24.7) ms vs. (441.0±37.4) ms, P＜0.05). No cases of serious arrhythmias or other adverse reactions were found.Conclusions A single dose of ibutilide for conversion of persistent or permanent AF after radiofrequency ablation is safe and effective.