Can We Predict the Failure of Electrical Cardioversion of Acute Atrial Fibrillation? The FinCV Study TONI GR ¨ ONBERG, B.M.,* JUHA E. K. HARTIKAINEN, M.D., PH.D.,† ILPO NUOTIO, M.D., PH.D.,‡ FAUSTO BIANCARI, M.D., PH.D.,§ TUIJA VASANKARI, R.N.,* MARKO NIKKINEN, M.D.,† ANTTI YLITALO, M.D., PH.D.,¶ and K. E. JUHANI AIRAKSINEN, M.D., PH.D.* From the *Heart Center, Turku University Hospital and University of Turku, Turku, Finland; †Heart Center, Kuopio University Hospital, Kuopio, Finland; ‡Division of Medicine, Department of Acute Internal Medicine, Turku University Hospital, Turku, Finland; §Department of Surgery, Oulu University Hospital, Oulu, Finland; and ¶Heart Center, Satakunta Central Hospital, Pori, Finland Background: Data on predictors of failure of electrical cardioversion of acute atrial fibrillation are scarce. Methods: We explored 6,906 electrical cardioversions of acute (<48 hours) atrial fibrillation in 2,868 patients in a retrospective multicenter study. Results: The success rate of electrical cardioversion was 94.2%. In 26% of unsuccessful cardioversions, the cardioversion was performed successfully later. Antiarrhythmic drug therapy, short (<12 hours) duration of atrial fibrillation episode, advanced age, permanent pacemaker, history of atrial fibrillation episodes within 30 days before cardioversion, and β -blockers were independent predictors of unsuccessful electrical cardioversion. In the subgroup of patients with cardioversion of the first atrial fibrillation episode (N = 1,411), the short duration of episode (odds ratio [OR] = 2.28; 95% confidence interval [CI] 1.34–3.90, P = 0.003) and advanced age (OR = 1.03; 95% CI 1.02–1.05, P < 0.001) were the only independent predictors of unsuccessful cardioversion. After successful cardioversion, the rate of early (<30 days) clinical recurrence of atrial fibrillation was 17.3%. The index cardioversion being performed due to the first atrial fibrillation episode was the only predictor of remaining in the sinus rhythm. Conclusion: A short (<12 hours) duration of acute atrial fibrillation is a significant predictor of unsuccessful cardioversion, especially during the first attack. First atrial fibrillation episode was the only predictor of remaining in the sinus rhythm. (PACE 2015; 38:368–375) atrial fibrillation, cardioversion, failure rate, clinical recurrence, antiarrhythmic drug therapy Introduction Electrical cardioversion (ECV) of atrial fibril- lation (AF) is an efficient and safe procedure to restore sinus rhythm. The success rate has been reported to range from 66% to 98% 1,2 with higher success rate in acute AF. 3 This work was supported by The Finnish Foundation for Cardiovascular Research, Helsinki, Finland; Clinical Research Fund (EVO) of Turku University Hospital, Turku, Finland. Conflicts of interest: None declared. Authors’ Contributions: Concept and design: K.E.J. Airaksinen, J.E.K. Hartikainen; analysis and interpretation: all authors; Drafting of manuscript: T. Gr ¨ onberg, K.E.J. Airaksinen, I. Nuotio; Critical revision of article: all authors; Approval of article: all authors. Address for reprints: K. E. Juhani Airaksinen, M.D., PH.D., Heart Center, Turku University Hospital, P.O. Box 52, FI-20521 Turku, Finland. Fax: 358 2 3138651; e-mail: juhani.airaksinen@tyks.fi Received May 29, 2014; revised September 21, 2014; accepted October 29, 2014. doi: 10.1111/pace.12561 Numerous studies have evaluated predictors of successful cardioversion in persistent, long- standing (duration >7 days) AF. Clinical risk factors for failure have been long duration of AF 1,4–11 and obesity. 7,12,13 However, only a few small studies have studied cardioversion of an acute (duration of arrhythmia < 48 hours) AF 3,14–16 and none of them have focused on identifying predictors for ECV failure. The aim of this study was to determine the success rate of ECV and explore the predictors of unsuccessful ECV in acute AF in a large multicenter patient cohort. Second, we evaluated the rate and risk factors for clinical recurrences of AF within 30 days after successful ECV. Methods This study is a part of the multicen- ter FinCV study (ClinicalTrials.gov Identifier: NCT01380574) assessing the thromboembolic and arrhythmic complications after cardioversion of acute (<48 hours) AF. 17–19 ©2014 Wiley Periodicals, Inc. 368 March 2015 PACE, Vol. 38