Objective To investigate the impact and clinical significance of interatrial block（IAB） on paroxysmal atrial fibrillation（PAF） in patients after catheter ablation. Methods Two hundred and forty eight consecutive patients with PAF who hospitalized in our hospital and received catheter ablation were followed up for 2 years from January 2013 to December 2018. In all patients

P wave duration

the presence of advance IAB（a IAB）

defined as a P-wave duration>120 ms and biphasic（+/-） morphology in the inferior leads

were analyzed pre-ablation under sinus rhythm from surface electrocardiogram（ECG）. Multivariate Logistics was used to analyze the risk factors of AF recurrence

and Kaplan-Meier survival analysis was used to evaluate the impact of IAB on AF recurrence. Results A total of 64 patients had recurrence of AF during follow-up（25.8%）. The incidence of IAB in the group of AF recurrence was significantly higher than that in the no-recurrence group（a-IAB: 43.7%vs. 17.3%; p<0.001）. Multivariate Logistics analysis showed that a IAB was an independent relevant factor for AF recurrence（OR=3.188

95%CI 1.378-7.378

p=0.007）. Kaplan-Meier survival analysis showed a IAB in ECG from preoperative ablation significantly increased the recurrence of AF（ p<0.001）. Conclusions Patients with PAF and advanced IAB in surface ECG preoperative ablation had increased risk of AF recurrence rate after catheter ablation. Thus

IAB analysis from ECG can be acted as a valuable clinical predictor of PAF recurrence after catheter ablation.