ABSTRACT NUMBER: ESOC2026A673 TIMING OF INSERTABLE CARDIAC MONITOR IMPLANTATION AFTER ESUS AND ITS IMPACT ON ATRIAL FIBRILLATION DETECTION: A TARGET TRIAL EMULATION ANALYSIS

Abstract Background and aims A substantial proportion of ischemic strokes remain classified as embolic stroke of undetermined source (ESUS). Although prolonged monitoring with implantable cardiac monitors (ICMs) improves atrial fibrillation (AF) detection, the optimal timing of implantation remains uncertain. We evaluated whether early versus delayed ICM implantation affects AF detection and time to diagnosis. Methods We conducted a multicentre observational cohort study emulating a target trial. Consecutive ESUS patients undergoing ICM implantation were classified as ICMEARLY (≤30 days) or ICMDELAYED (31–365 days) implantation after the index event. Inverse probability weighting was applied to adjust for baseline confounding. Primary and secondary outcomes included AF detection within 30, 90, and 120 days after implantation, assessed using weighted logistic regression, Poisson models for detection rates per person-time, Cox proportional hazards models, and restricted mean survival time (RMST). Results Among 333 patients (90 ICMEARLY, 243 ICMDELAYED), early implantation was associated with significantly higher AF detection within 30 days (7.8% vs 1.6%; OR 4.49, 95% CI 1.17–17.27) and higher detection rates per person-time (IRR 4.26, 95% CI 1.16–15.60). Consistent associations were observed at 90 and 120 days. Time-to-event analyses showed higher hazards of AF detection with early implantation (HR 4.29 at 30 days; HR 2.97 at 90 days; HR 2.77 at 120 days). RMST analyses demonstrated progressively shorter time to AF diagnosis in the ICMEARLYgroup across multiple time horizons. Conclusions Early ICM implantation after ESUS is associated with higher and faster AF detection compared with delayed implantation. When ICM monitoring is indicated, avoiding unnecessary delays may substantially enhance diagnostic Conflict of interest nothing to disclose