Abstract Body (Do not enter title and authors here): Background: Recent clinical trials demonstrate the benefit of oral anticoagulation (OAC) for all device-recognized atrial fibrillation (AF) > 6 minutes. However, AF is not binary and those with greater AF burden generally have a higher risk of stroke. To date, there are limited data on a specific threshold of AF duration that is independently associated with the risk of ischemic stroke.

Objective: To assess the association between baseline maximum daily AF duration (MDAFD) and ischemic stroke among patients with cardiac implantable electronic devices (CIEDs) capable of continuous AF detection.

Methods: Using the Optum^® de-identified electronic health record (EHR) (2007-2021) linked with the Medtronic CareLink^® heart rhythm database, CIED patients with healthcare activity recorded in the EHR >12 months pre- and >6 months post-CIED implant were identified. Exclusion criteria included presence of a prescription for OAC. MDAFD was assessed during the first 30 days post-implant (baseline period). Associations between baseline MDAFD and ischemic stroke in follow-up were evaluated, adjusting for CHA₂DS₂-VASc and chronic kidney disease.

Results: Of 26,400 patients (68±13 years; 60% male) analyzed, 2,544 (9.6%) had AF at baseline. The distribution of maximum daily AF duration during baseline was as follows: 6 min-<1 hour: 734 (28.9%); 1 hour-<5.5 hours: 565 (22.2%); 5.5 hours-<23.5 hours: 519 (20.4%); >23.5 hours: 726 (28.5%). In total, 664 patients (2.5%) suffered an ischemic stroke through 2.6±1.6 years of follow-up. Presence, compared to absence, of AF at baseline was associated with a greater risk of ischemic stroke. Among those with AF, only patients with MDAFD>5.5 hours had an increased risk of stroke compared to those with no AF (Figure).

Conclusions: Within a large cohort of patients with CIEDs without a prescription for OAC, >5.5 hours of MDAFD was needed to increase the risk of ischemic stroke compared to those with no AF. These results suggest that there is a threshold of MDAFD, measured in hours, that may benefit from treatment with OAC.