The prevalence of atrial fibrillation (AF) has increased substantially in the aging population. Drug therapies for maintaining sinus rhythm have been tried, but antiarrhythmic drug (AAD) responsiveness is relatively low in AF patients [1,2]. Guidelines recommend radiofrequency catheter ablation (RFCA) as a class I indication for drug resistant paroxyamal atrial fibrillation (PAF) and a class IIa indication for persistent AF (PeAF) [3]. Although the superiority of RFCA over AAD has been documented in clinical trials [4], the long-term recurrence rate is still substantial after AF catheter ablation [5]. There is little information on the efficacy of AAD in patients with recurrent AF after catheter ablation. Therefore, we evaluated the type and timing of recurrent atrial tachyarrhythmias after AF catheter ablation, to determine their responsiveness to AAD and the long-term clinical results of this treatment. This study included 397 consecutive patients with AAD refractory AF (77.1% males, 56.0±10.9 years old) who underwent RFCA. Among them, 69.5% of patients had PAFand 30.5% had PeAF. All patients initially underwent a circumferential pulmonary vein isolation (CPVI) and a bidirectionalblockof the cavo-tricuspid isthmus. InpatientswithPeAF,we conducted roof line, and posterior inferior line as a routine lesion set in all patients. We defined AF recurrence as any episode of AF or atrial tachycardia of at least 30 s in duration [6]. If any ECG documented an AF episode within the first three months of follow-up, the patient was diagnosed with an early recurrence (ER), and any AF recurrence thereafter was diagnosed as chronic recurrence (CR) [6] and AAD medications were prescribed. AAD was prescribed when AF recurrence was documented after RFCA. Oral flecainidewas given at a dose of 100– 200 mg per day (n=75, 18.9%), oral propafenone at 300–600 mg per day (n=1, 0.3%), oral pilsicainide at 150 mg per day (n=3, 0.8%), and oral amiodarone at an initial dose of 400 mg a day (n=103, 25.9%) for the first 2 weeks. The study protocol was approved by the Institutional ReviewBoardof YonseiUniversityHealthSystemand informed consents were obtained from patients. Of the total 397 patients, 130 patients (32.7%) experienced AF recurrence within 3 months after RFCA, and 98 patients (24.7%) experienced AF recurrence after the third month post-RFCA during the 16.1±5.0 months of follow-up. 60 patients (46.2%) out of 130 patients with ER experienced CR. Of the recurrent atrial tachyarrhythmias, 31.3% were atrial tachycardias (AT), and the remainder experienced AF. Patients with ER or CR had a greater left atrial size (p=0.001) or longer ablation time (pb0.001), and were more likely to be PeAF (p=0.003) than those who remained in sinus rhythm (Table 1). The use of additional ablation lines did not affect the incidences of ER or CR. Independent predictors for CR among the patients with ER were slower heart rate at recurrent presentation (odds ratio 0.984; 95% CI 0.971–0.998, p=0.029) and later timing of recurrencewithin 3 months post-RFCA (odds ratio 1.015; 95% CI 1.000–1.030, p=0.049). Within 2 weeks of AADprescription, 74.8% of the patientswith ER and 64.2% of CR converted to sinus rhythm without cardioversion. Sinus conversion rates of AT vs. AF (71.0% vs. 70.0%, p=0.891) and class IC AAD vs. amiodarone (69.6% vs. 71.8%, p=0.745) were not significantly different. The proportion of PeAF was significantly lower in AAD responders, who were converted to sinus rhythm within 2 weeks after AAD therapy (31.8%), than in non-responders (56.6%, p=0.003). Table 2 compares responders and non-responders in terms of class IC AAD and amiodarone. 34 (33.0%) out of 103 patients who took amiodarone were resistant to amiodarone before RFCA, and their sinus conversion rate was 55.9%. Among 79 patients who were prescribed class IC AAD, 63 patients (79.7%) took the same class IC AADs that were resistant before RFCA, and sinus conversion ratewas 69.8%. After pharmacologic cardioversion, sinus rhythmmaintenance rates with AAD were 55.3% with class IC and 52.2% with amiodarone during the 16.1±5.0 months of follow-up period