Abstract Body (Do not enter title and authors here): Background: Atrial fibrillation (AF) is one of the most common supraventricular arrhythmias in the general population and imposes significant risk for cerebral vascular events. Catheter ablation is one of the most effective approaches to achieve and maintain sinus rhythm. Left atrial appendage (LAA) is a common arrhythmogenic site for AF and targeting LAA for ablation has been proven to reduce AF recurrence. Nevertheless, LAA electrical isolation (LAAEI) is only performed in certain practices and in patients who have previously received a LAA occlusive (LAAO) device, LAAEI is difficult to achieve after the LAA is occluded.

Objective: The aim of this study is to investigate whether confirmed LAAEI prior to LAAO device implantation has an impact on AF recurrence.

Methods: Patients who received LAAO were included in this analysis. Demographics, co-morbidities, previous ablations, recurrence of AF or atrial arrhythmias, follow up duration and whether patients had confirmed LAAEI either through LAA ablation or electroanatomical mapping during ablation prior to LAAO implantation were summarized. Kaplan-Meier survival analysis for freedom from atrial arrhythmia recurrence was performed.

Results: A total of 613 patients were included in the study period and 63.6% were male. Among them 214 (34.9%) had confirmed LAAEI while 399 (65.1%) did not prior to implantation of LAAO device. Compared to patients without LAAEI, patients in the confirmed LAAEI group were more likely to have persistent and longstanding persistent AF (69.2% vs 46.6%), had higher percentage of diabetes (56.1% vs 40.3%) and heart failure (66.4% vs 33.3%) but were more likely to be male (72.9% vs 58.6%) and younger (70 vs 75 years old). At mean follow up period of 13 +/- 7.3 months, patients in the confirmed LAAEI group had 90.7% freedom from atrial arrhythmia recurrence compared to 81.5% in the no LAAEI group (P<0.001).

Conclusion: LAAEI prior to LAAO is associated with significantly reduced risk of AF recurrence after device implantation. LAAEI should be considered before LAAO in patients with LAA substrate given technical difficulty in LAAEI after LAAO.