From Population Health Research Institute, Hamilton, ON, Canada (J.S.H., J.W., D.L., H.D., K.S., S.R.M., S.J.C.); McMaster University, Hamilton, ON, Canada (J.S.H., J.W., D.L., H.D., W.F.M., S.R.M., A.S.P., S.J.C.); Amphia Ziekenhuis, Breda, the Netherlands (M.A.); WCN–Dutch Network for Cardiovascular Research (M.A.); University of Toronto, ON, Canada (A.H., A.V.); University of Western Ontario, London, Canada (P.L.-S.); University of Ottawa Heart Institute, ON, Canada (D.H.B.); Nij Smellinghe Hospital, Drachten, the Netherlands (J.J.d.G.); Ikazia Ziekenhuis, Rotterdam, the Netherlands (M.F.); Institut Universitaire de Cardiologie et de Pneumologie de Québec, QC, Canada (F.P.); University of Alberta, Edmonton, Canada (W.B.); University of Calgary, AB, Canada (M.D.H.); St. Jude Medical, Sylmar, CA (M.C.); Slingeland Ziekenhuis, Doetinchem, the Netherlands (F.S.); and Cambridge Cardiac Care Centre, ON, Canada (A.S.P.).
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Background:Long-term continuous electrocardiographic monitoring shows a substantial prevalence of asymptomatic, subclinical atrial fibrillation (SCAF) in patients with pacemakers and patients with cryptogenic stroke. Whether SCAF is also common in other patients without these conditions is unknown.Methods:We implanted subcutaneous electrocardiographic monitors (St. Jude CONFIRM-AF) in patients ≥65 years of age attending cardiovascular or neurology outpatient clinics if they had no history of atrial fibrillation but had any of the following: CHA2DS2-VASc score of ≥2, sleep apnea, or body mass index >30 kg/m2. Eligibility also required either left atrial enlargement (≥4.4 cm or volume ≥58 mL) or increased (≥290 pg/mL) serum NT-proBNP (N-terminal pro–B-type natriuretic peptide). Patients were monitored for SCAF lasting ≥5 minutes.Results:Two hundred fifty-six patients were followed up for 16.3±3.8 months. Baseline age was 74±6 years; mean CHA2DS2-VASc score was 4.1±1.4; left atrial diameter averaged 4.7±0.8 cm; and 48% had a prior stroke, transient ischemic attack, or systemic embolism. SCAF ≥5 minutes was detected in 90 patients (detection rate, 34.4%/y; 95% confidence interval [CI], 27.7–42.3). Baseline predictors of SCAF were increased age (hazard ratio [HR] per decade, 1.55; 95% CI, 1.11–2.15), left atrial dimension (HR per centimeter diameter, 1.43; 95% CI, 1.09–1.86), and blood pressure (HR per 10 mm Hg, 0.87; 95% CI, 0.78–0.98), but not prior stroke. The rate of occurrence of SCAF in those with a history of stroke, systemic embolism, or transient ischemic attack was 39.4%/y versus 30.3%/y without (P=0.32). The cumulative SCAF detection rate was higher (51.9%/y) in those with left atrial volume above the median value of 73.5 mL.Conclusions:SCAF is frequently detected by continuous electrocardiographic monitoring in older patients without a history of atrial fibrillation who are attending outpatient cardiology and neurology clinics. Its clinical significance is unclear.Clinical Trial Registration:URL: http://www.clinicaltrials.gov. Unique identifier: NCT01694394.