• William F McIntyre, Maria E Vadakken, Stuart J Connolly, Pablo A Mendoza, Alexandra P Lengyel, Anand S Rai, Nicole R Latendresse, Alex J Grinvalds, Chinthanie Ramasundarahettige, J Gabriel Acosta, Kevin J Um, Jason D Roberts, David Conen, Jorge A Wong, P J Devereaux, Emilie P Belley-Côté, Richard P Whitlock, and Jeff S Healey.
• Division of Cardiology, Department of Medicine, McMaster University; Department of Health Research Methods, Evidence, and Impact, McMaster University; and Population Health Research Institute, Hamilton, Ontario, Canada (W.F.M., S.J.C., D.C., J.A.W., P.J.D., J.S.H.).
• Ann. Intern. Med. 2023 Oct 1; 176 (10): 129913071299-1307.

BackgroundAtrial fibrillation (AF) is often detected for the first time in patients who are hospitalized for another reason. Long-term risks for AF recurrence in these patients are unclear.ObjectiveTo estimate risk for AF recurrence in patients with new-onset AF during a hospitalization for noncardiac surgery or medical illness compared with a matched population without AF.DesignMatched cohort study. (ClinicalTrials.gov: NCT03221777).SettingThree academic hospitals in Hamilton, Ontario, Canada.ParticipantsThe study enrolled patients hospitalized for noncardiac surgery or medical illness who had transient new-onset AF. For each participant, an age- and sex-matched control participant with no history of AF from the same hospital ward was recruited. All participants left the hospital in sinus rhythm.Measurements14-day electrocardiographic (ECG) monitor at 1 and 6 months and telephone assessment at 1, 6, and 12 months. The primary outcome was AF lasting at least 30 seconds on the monitor or captured by ECG 12-lead during routine care at 12 months.ResultsAmong 139 participants with transient new-onset AF (70 patients with medical illness and 69 surgical patients) and 139 matched control participants, the mean age was 71 years (SD, 10), the mean CHA2DS2-VASc score was 3.0 (SD, 1.5), and 59% were male. The median duration of AF during the index hospitalization was 15.8 hours (IQR, 6.4 to 49.6 hours). After 1 year, recurrent AF was detected in 33.1% (95% CI, 25.3% to 40.9%) of participants in the transient new-onset AF group and 5.0% (CI, 1.4% to 8.7%) of matched control participants; after adjustment for the number of ECG monitors worn and for baseline clinical differences, the adjusted relative risk was 6.6 (CI, 3.2 to 13.7). After exclusion of participants who had electrical or pharmacologic cardioversion during the index hospitalization (n = 40) and their matched control participants and limiting to AF events detected by the patch ECG monitor, recurrent AF was detected in 32.3% (CI, 23.1% to 41.5%) of participants with transient new-onset AF and 3.0% (CI, 0% to 6.4%) of matched control participants.LimitationsGeneralizability is limited, and the study was underpowered to evaluate subgroups and clinical predictors.ConclusionAmong patients who have transient new-onset AF during a hospitalization for noncardiac surgery or medical illness, approximately 1 in 3 will have recurrent AF within 1 year.Primary Funding SourcePeer-reviewed grants.

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