The purpose of this study is to evaluate the efficacy of additional ablation targeting complex fractionated atrial electrogram area within low voltage zone identified by high resolution mapping in patients with persistent atrial fibrillation.

Fifty patients with persistent atrial fibrillation will be randomized a 1:1 ratio to each group. A test group includes those who undergoing ablation targeting low voltage areas which contains complex fractionated trial electrogram in addition to pulmonary vein isolation and a control group includes who undergoing pulmonary vein isolation only.

Inclusion Criteria:

1. Age over 20 years old and under 80 years old
2. Patients with non-valvular atrial fibrillation
3. Patients having atrial fibrillation even after receiving continued treatment with at least 1 antiarrhythmic drug for more than 6 weeks
4. Patients who can understand the information sheet and consent form on the need and procedure of catheter ablation and submitted them
5. Patients who are available of follow-up at least for more than three months after catheter ablation

Exclusion Criteria:

1. Patients unsuitable for catheter ablation because the size of left atrium is over 6.0 cm
2. Patients unsuitable for catheter ablation due to previous history of pulmonary surgery or structural heat disease.
3. Patients who cannot receive standard treatments such as anticoagulation therapy which need to be continuously performed prior to radiofrequency catheter ablation
4. Patients in the subject group vulnerable to clinical study
5. Patients who had undergone a prior catheter ablation for atrial fibrillation