Use of catheter ablation for persistent atrial fibrillation (PerAF) remains controversial due to unsatisfactory long-term success rates (15% - 28.4%). The investigators' previous study indicated that the upper area of the left atrium (LA) plays an important role in PerAF, with the LA roof and mitral isthmus appearing to serve as main substrate in progression from PAF to PerAF and maintenance of fibrillatory activities. The investigators therefore hypothesized that AF should not be initiated or sustained if the latter crucial regions for AF maintenance are abolished. This study aimed to describe the efficacy and safety of additional linear ablation on the left atrial anterior wall for PerAF.