The purpose of this study is to compare the clinical outcomes depending on catheter ablation strategy for repeat ablation procedure among the patients with recurred atrial fibrillation after de novo catheter ablation. After randomization, we will conduct circumferential pulmonary vein isolation alone in a group, and additional posterior box isolation in the other group. Non-pulmonary vein foci ablation will be done in all patients. We will compare clinical recurrence rate, complication rate, and procedure time, etc.

Inclusion Criteria:

1. Patients with AF aged between 20 and 80 years old.
2. Patients possible to anticoagulation and anti arrhythmic drug
3. Patients who had undergone de novo ablation procedures based on circumferential pulmonary vein isolation with no additional linear ablations
4. Patients undergoing a second ablation procedure due to clinical recurrence resistant to antiarrhythmic drugs with findings of PV reconnections

Exclusion Criteria:

1. Structural cardiac disease 2. Contraindication to brain perfusion CT 3. Catheter ablation history for AF, Cardiac surgery for AF 4. active internal bleeding 5. Impossible to anticoagulation or antiarrhythmic drug 6. valvular AF ((MA> GII, Mechanical valve, Mitral valve raplacement) 7. Patients with severe medical disease 8. Expected survival < 1year 9. Severe alcoholics, drug addiction 10. Pregnancy 11. LA diameter>60mm