CTI Block in Persistent AF that a CTI block plays a critical role in preventing AF recur- rence in patients with drug-induced atrial flutter. A previous randomized study on the effects of CTI ablation in patients with typical atrial flutter and atrial fibrillation revealed that CTI block reduced only the early postablation recurrence of arrhythmias, and that pulmonary vein isolation might be sufficient to control both arrhythmias.21 However, in drug- induced atrial flutter, the CTI block had a different signifi- cant meaning. In an animal model, the spontaneous trans- formation of AF was related to the development of a line of functional block between the vena cavae.22 This process was enhanced by the administration of antiarrhythmic medica- tion. Recently, Waldo and Feld23 described an inter-relation- ship between atrial fibrillation and atrial flutter; a transient period preceding atrial fibrillation prior to atrial flutter is present in humans. During the short period of AF, a func- tional line of block developed and fibrillatory waves evolved to regular macro-reentrant waves. The antiarrhythmic med- ications with sodium channel blocking properties have been associated with significant conversion of AF to atrial flutter, suggesting that these drugs make it possible for a functional line of block to form between the vena cavae during the ini- tial atrial fibrillation rhythm. The depression of atrial conduc- tion velocity with a consecutive transformation of conduc- tion delay into a conduction block, caused by antiarrhythmic medications, prevents the simultaneous occurrence of the multiple reentrant circuits necessary for the perpetuation of atrial fibrillation, resulting in a single atrial flutter reentrant circuit with an area of slow conduction. Therefore, block of the slow conduction of atrial flutter, with continuation of antiarrhythmic medication, can be an alternative treatment for patients with persistent AF, especially in cases with mini- mal atrial remodeling. However, in patients with persistent AF and severe atrial remodeling, rhythm control could not be maintained, and AF recurrence frequently occurred. There- fore, rate control without antiarrhythmics might be a more reasonable approach for long term treatment in these pa- tients. Preprocedural evaluation of patients, including imag- ing study, is essential to choose the type of treatement and predict the prognosis of the clinical outcome. Study limitations This study was not planned as a randomized prospective study. Although all data on the hybrid therapy performed previously were collected retrospectively, the documented atrial flutter was induced after anti-arrhythmic drug therapy for atrial fibrillation. In addition, the incidence of atrial flut- ter caused by atrial fibrillation after anti-arrhythmic drug use could not be estimated. Although the general incidence of atrial flutter transformed from atrial fibrillation has been reported to be 10 to 20%, this data were collected, based on a Western study; there are no data on Asian populations. Even though standard 12 lead ECG was regularly performed re- gardless of symptom, Holter and event monitors were only available for symptomatic recurrences; therefore, it is possi- ble that some asymptomatic recurrences of atrial fibrillation were missed. The lack of significant differences in the long- term follow-up is probably related to a too small number of patients in each group. Another factor that could explain the lack of differences is the longer duration of AF in the group treated by ablation. In conclusion, hybrid therapy might be a reasonable ther- apy for patients with anti-arrhythmic drug induced atrial flutter. The left atrial size was the strongest predictor of post- ablation recurrence of atrial fibrillation. Careful patient se- lection for hybrid therapy of atrial fibrillation may provide long term stable sinus rhythm. However, in patients with se- vere atrial remodeling, rhythm control could not be main- tained in prolonged period. Therefore, rate control without AAD might be a more reasonable approach for long term treatment in these patients. ACKNOWLEDGEMENTS This work was supported in part by Yonsei University Re- search Fund of 6-2008-0009 (JB Kim). REFERENCES 1. Fuster V, Rydén LE, Cannom DS, Crijns HJ, Curtis AB, Ellenbo- gen KA, et al. 2011 ACCF/AHA/HRS focused updates incorporat- ed into the ACC/AHA/ESC 2006 guidelines for the management of patients with atrial fibrillation: a report of the American College of Cardiology Foundation/American Heart Association Task Force on practice guidelines. Circulation 2011;123:e269-367. 2. Oral H, Pappone C, Chugh A, Good E, Bogun F, Pelosi F Jr, et al. Circumferential pulmonary-vein ablation for chronic atrial fibrilla- tion. N Engl J Med 2006;354:934-41. 3. Knecht S, Hocini M, Wright M, Lellouche N, O’Neill MD, Matsuo S, et al. Left atrial linear lesions are required for successful treat- ment of persistent atrial fibrillation. Eur Heart J 2008;29:2359-66. 4. Stabile G, Bertaglia E, Turco P, Zoppo F, Iuliano A, Zerbo F, et al. Role of pulmonary veins isolation in persistent atrial fibrillation ab- lation: the pulmonary vein isolation in persistent atrial fibrillation (PIPA) study. Pacing Clin Electrophysiol 2009;32 Suppl 1:S116-9. 5. Huang DT, Monahan KM, Zimetbaum P, Papageorgiou P, Epstein Yonsei Med J http://www.eymj.org Volume 53 Number 1 January 2012 81