• Carl van Walraven, Robert G Hart, George A Wells, Palle Petersen, Peter J Koudstaal, Annette L Gullov, Beppie S P Hellemons, Birgitte G Koefed, and Andreas Laupacis.
• Clinical Epidemiology Unit, Ottawa Health Research Institute, Ottawa Hospital, Ontario, Canada. carlv@ohri.ca
• Arch Intern Med. 2003 Apr 28;163(8):936-43.

BackgroundWe sought to derive and internally validate a simple and easily applied clinical prediction rule to identify patients with nonvalvular atrial fibrillation (AF) whose stroke risk while taking aspirin is, irrespective of age, low enough that oral anticoagulation therapy is unnecessary.MethodsWe included 2501 patients with AF treated with aspirin during participation in 6 clinical trials. Patients were randomly divided into derivation and validation sets. Recursive partitioning was used to identify patients in the derivation set whose risk for stroke (ischemic or hemorrhagic) or transient ischemic attack was comparable to that observed in an age- and sex-matched cohort from the Framingham Heart Study. The derived prediction rules were tested on the validation set.ResultsOverall, 166 patients (6.6%) had an event during 4688.6 person-years (PYs) of observation for an incident rate of 3.5 events per 100 PYs. Patients in the derivation set classified as low risk (no previous stroke or transient ischemic attack, no treated hypertension or systolic blood pressure equal to or exceeding 140 mm Hg, no symptomatic coronary artery disease, and no diabetes) experienced 1.0 events per 100 PYs, compared with an age- and sex-matched rate of 1.2 events per 100 PYs. In the validation set, low-risk patients experienced 1.1 events per 100 PYs (expected rate of 1.2 events per 100 PYs). Low-risk patients made up 24% of the cohort and 16% of patients older than 75 years. Low-risk patients who were randomized to therapeutic oral anticoagulation therapy experienced 1.5 events per 100 PYs.ConclusionIrrespective of age, patients with AF and none of these 4 clinical features and who take aspirin have stroke rates comparable to those of age-matched community cohorts and would not benefit substantially from anticoagulation.

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