Incidence of Atrial Fibrillation in Patients With Recent Ischemic Stroke Versus Matched Controls

Background and Purpose- It is unclear whether atrial fibrillation/flutter (AF) newly diagnosed after ischemic stroke represents a preexisting risk factor that led to stroke, an arrhythmia triggered by poststroke autonomic dysfunction, or an incidental finding. Methods- We compared AF incidence after hospitalizations for ischemic stroke, hemorrhagic stroke, and nonstroke conditions using inpatient and outpatient claims between 2008 and 2015 from a nationally representative 5% sample of Medicare beneficiaries. We used validated International Classification of Diseases, Ninth Revision, Clinical Modification ( ICD-9-CM) codes to identify AF-free patients hospitalized with ischemic or hemorrhagic stroke and matched them in a 1:1 ratio by age, sex, race, calendar year, vascular risk factors, and Charlson comorbidities. We then matched the combined stroke cohort in a 1:1 ratio to patients hospitalized for nonstroke diagnoses. We used survival statistics and Cox regression to compare postdischarge AF incidence among groups. Results- We matched 2580 patients with ischemic stroke, 2580 with hemorrhagic stroke, and 5160 patients with other conditions. The annual postdischarge AF incidence was 3.4% (95% CI, 3.1%-3.7%) after ischemic stroke, 2.2% (95% CI, 1.9%-2.4%) after hemorrhagic stroke, and 2.9% (95% CI, 2.6%-3.1%) after nonstroke hospitalization. Ischemic stroke was associated with a somewhat higher risk of AF than hemorrhagic stroke (hazard ratio, 1.5; 95% CI, 1.3-1.8) or nonstroke conditions (hazard ratio, 1.2; 95% CI, 1.1-1.3). The latter association attenuated in sensitivity analyses limiting the outcome to AF diagnoses made by cardiologists (hazard ratio, 1.1; 95% CI, 0.8-1.5) or limiting the outcome to a minimum of 2 AF claims on separate dates (hazard ratio, 1.2; 95% CI, 1.0-1.5; P=0.09). Conclusions- New diagnoses of AF were more common after hospitalization for ischemic stroke than after hospitalization for hemorrhagic stroke or nonstroke conditions, but all hospitalized patients had a substantial incidence of new AF diagnoses after discharge and differences were attenuated when using more stringent definitions.