摘要Background Extensive atrial fibrillation (AF) ablation is associated with an increased success rate of catheter ablation in chronic AF patients and an increased rate of atrial tachycardia (AT) during the procedure. The mechanism of these Ats varies in previous studies. Our study aimed to report the mechanism of organized AT occurring during the stepwise ablation procedure of chronic AF.Methods A prospective cohort of 86 consecutive patients who underwent an ablation procedure for chronic atrial fibrillation (CAF) was investigated. The stepwise procedure was performed in the following order: circumferential pulmonary vein ablation, complex fractionated atrial electrograms ablation, mapping and ablation of AT. The endpoint was noninducibility of AF/AT after sinus rhythm (SR) was restored or the procedure time was beyond 6 hours.Results Sixty-nine (80%) of patients converted to SR via AT. A total of 179 sustained ATs were observed in 69 patients during the procedure. There were 81% (n=145) macroreentrant ATs which included 65 perimitral circuits, 48 peritricuspid tachycardia and 32 roof dependent circuits, 12% (n=21) localized reentrant and 7% (n=13) focal ATs. Thirty (15%) patients experienced significant left atrium (LA) and LA appendage (LAA) conduction delay or dissociation in the procedure or during the follow-up period.Conclusions Most CAF patients converted to SR via ablation of organized AT occurring during the stepwise procedure. The mechanism of most of these ATs was macro-reentry.