CTI Block in Persistent AF been long-term AAD even though persistent AF is poorly controlled by AAD therapy. Furthermore, in the latest guideline,1 longterm AAD therapy is indicated in patients who have troublesome symptoms related to paroxysmal AF or recurrent AF after cardioversion who can tolerate antiar- rhythmic drugs and have a good chance of remaining in si- nus rhythm over an extended period (e.g., young patients without organic heart disease or hypertension, a short dura- tion of AF, and normal LA size). In some patients, AF evolves to typical atrial flutter after the initiation of anti-ar- rhythmic drug therapy. Previously, catheter ablation of the inferior vena cava-tricuspid annulus isthmus along with continuation of anti-arrhythmic medication therapy (hybrid therapy) has been shown to be effective treatment for anti- arrhythmic drug-induced atrial flutter.5-8 Although a high initial success rate establishing a stable sinus rhythm has been described in patients with hybrid therapy, post-abla- tion atrial fibrillation can recur during follow-up, despite the continuation of anti-arrhythmic medication. Most pa- tients have good immediate and intermediate outcomes with hybrid therapy in regard to their paroxysmal AF. Hybrid therapy may be effective in patients with conversion to typ- ical atrial flutter occurring in 10 to 15% of patients with persistent AF who are undergoing antiarrhythmic medica- tion. However, the long term clinical outcome of hybrid ther- apy in patients with chronic persistent AF has not yet been evaluated and the risk factors associated with the recur- rence of AF have not been identified. Furthermore, there is few data comparing hybrid therapy and drug therapy after electrical cardioversion. Therefore, the goal of this study was to assess the long term success rate of hybrid therapy for persistent AF com- pared to sole antiarrhythmic medication therapy after elec- trical cardioversion and identify the independent risk fac- tors associated with recurrence after hybrid therapy in patients with persistent AF. MATERIALS AND METHODS Patient population Persistent AF was defined as AF lasting more than 7 days. It was considered to be highly likely if two electrocardio- graphic studies, including 24 hour Holter monitoring, were without an episode of sinus rhythm. From January 1999 to December 2007, 250 patients underwent catheter ablation for atrial flutter at our institution. Among these patients, we identified 32 patients who developed atrial flutter after anti- arrhythmic drug therapy for chronic persistent AF without evidence of pre-drug atrial flutter (hybrid group). The clini- cal outcomes and echocardiographic data from this group were compared to those of 33 persistent AF patients that underwent successful electrical cardioversion with antiar- rhythmics during the same period electrocardioversion group (EC group). Demographic, clinical and procedural variables were col- lected retrospectively by review of the medical records. All patients underwent non-invasive cardiac examination in- cluding M-mode and two dimensional echocardiography with color Doppler flow analysis. Valvular heart disease was defined as existence of moderate to severe regurgitation or stenosis of valve in echocardiography. Left atrial enlarge- ment was defined as a left atrial anterior-posterior diameter more than 44 mm. This study received approval from the institutional ethics committee, and the procedures followed were in accordance with the institutional guideline. Electrophysiological studies and catheter ablation of atrial flutter All patients in the hybrid group received electrophysiological studies and radiofrequency ablation after informed consent was obtained. Antiarrhythmics were continued. Three multi- polar electrode catheters were inserted percutaneously into the left femoral vein. Two quadripolar catheters (2-5-2 mm spacing, DAIG, St Jude Medical Inc., St. Paul, MN, USA) were positioned at the his bundle and right atrium. A decap- olar catheter (2-5-2 mm spacing, DAIG, St Jude Medical Inc., St. Paul, MN, USA) was positioned in the coronary si- nus via the left subclavian vein. Activation sequence of atri- al flutter or entrapment mapping was assessed by a 20-pole electrode halo catheter (2-10-2 mm spacing, Biosense- Webster, Diamond Bar, CA, USA). The position of the catheters was checked in the 45° left anterior oblique view and the 30° right anterior oblique view. A deflectable 5 mm- tipped quadripolar catheter or irrigation catheter was used as the ablation catheter. The electrophysiological definition of isthmus dependent atrial flutter was demonstrated by the standard criteria9 for entrainment mapping. A 500 kHz ra- diofrequency (RF) ablation unit (Stockert, Biosense-web- ster, Diamond Bar, CA, USA) was used for the ablation. RF ablation started at the ventricular side of inferolateral tricus- pid annulus and the end point was bidirectional block of isthmic conduction. Yonsei Med J http://www.eymj.org Volume 53 Number 1 January 2012 77