Circadian patterns of atrial fibrillation and disease progression assessed by implanted loop recorders

BACKGROUND AND AIMS: The heterogeneity of atrial fibrillation (AF) necessitates better phenotyping. This study aimed to explore circadian patterns of AF and their impact on AF characteristics and progression. METHODS: Post hoc analysis of the LOOP study randomizing 6004 older, AF-naïve persons with risk factors for AF and stroke 1:3 to receive implantable loop recorder screening or usual care. Implantable loop recorder data were extracted from 1410 participants to obtain AF episode characteristics. RESULTS: A total of 41 713 AF episodes lasting at least 6 min were identified among 430 patients undergoing 39 (37-41) months of monitoring. The most frequent onset hour was 9 a.m., which was twice as likely as 9 p.m. Night-time AF episodes (onset 10 p.m.-7 a.m., 40% of all episodes) lasted longer 28 (10-104) vs 14 (8-44) min and had slower ventricular rate 75 (60-86) vs 85 (75-100) b.p.m. compared with daytime episodes. K-means clustering revealed two distinct groups of patients with mostly midnight-morning median 6 a.m. (3 a.m.-11 a.m.) and daytime median 12 p.m. (9 a.m.-5 p.m.), onset respectively. Patients in the midnight-morning cluster had higher AF burden 0.2 (0.1-1.2) vs 0.1 (0.0-0.4)%, P < .001 and more progression (28% vs 18% progressed to ≥24-h episodes, P = .019) compared to those in the daytime cluster. CONCLUSIONS: A circadian pattern was observed for ILR-detected AF, with onset most often before noon. Cluster analyses revealed distinct AF phenotypes with different patterns of onset and progression over time. These exploratory findings warrant studies investigating the timing of AF screening and the selection of patients for rhythm control vs more conservative strategies.