Mitral isthmus block is associated with favorable outcomes after reablation for long‐standing persistent atrial fibrillation

BACKGROUND: Mitral isthmus (MI) ablation was limited due to technical challenges in the index ablation for long‐standing persistent atrial fibrillation (LPeAF). The role of adjunctive MI ablation was controversial. HYPOTHESIS: MI block could be achieved in most patients undergoing repeat LPeAF ablation and was associated with favorable clinical outcomes. METHODS: Of 87 consecutively patients undergoing reablation for recurrent atrial tachyarrhythmias (ATa), 41 patients with residual MI conduction but without pulmonary vein reconnection or left atrial roof conduction were enrolled to treat recurrent atrial flutter (AFL) (n = 20) and AF (n = 21). After AFL ablation and AF cardioversion, MI conduction gaps (CGs) were mapped and closed. RESULTS: MI line was successfully blocked in 37 (90.2%) of 41 patients after closing 1.4 ± 0.5 CGs (31 endocardial CGs and 16 epicardial ones) in the initial MI lines. CGs were more often located at the endocardial sites close to the lateral ridge between left atrial appendage and left‐sided PVs, midportion of MI and at the epicardial breakthroughs within coronary sinus. At the end of 16.0 ± 1.9 months' follow‐up, 31 (83.8%) of 37 patients with MI block and 1 of 4 patients without MI block were free of further recurrence of ATa off anti‐arrhythmic drugs. MI block was positively associated with ATa‐free survival by Cox's regression analysis (hazard ratio [HR]: 0.012, 95% confidence interval [CI]: 0.000‐0.456, P = .02). CONCLUSIONS: MI block could be achieved in the majority of patients during repeat ablation for LPeAF. MI block was associated with favorable clinical outcomes after LPeAF reablation.