Atrial fibrillation as a risk factor for stroke: A retrospective cohort study of hospitalized medicare beneficiaries

Abstract

Objectives. This study examined the relationship between atrial fibrillation and (1) stroke and (2) all-cause mortality. Methods. All eligible Medicare patients older than 65 years of age hospitalized in 1985 were followed up for 4 years. Kaplan-Meier and Cox proportional hazards models were used for assessment of risk of stroke and mortality. Results. A total of 4 282 607 eligible Medicare patients were hospitalized in 1985. The mean age was 76.1 (±7.7) years; 58.7% were female; 7.2% were Black; and 8.4% had a diagnosis of atrial fibrillation. During the follow-up period, 66 063 patients (32.6/1000 person-years) developed nonembolic stroke and 7285 (3.6- 1000 person-years) developed embolic stroke. After adjustment for age, race, sex, and comorbid conditions, atrial fibrillation remained a significant risk factor for both nonembolic stroke (relative risk [RR] = 1.56) and embolic stroke (RR = 5.80) and for mortality (RR = 1.31). Approximately 4.5% of nonembolic and 28.7% of embolic strokes among hospitalized Medicare patients aged 65 years and older were attributable to atrial fibrillation. Conclusions. This study demonstrates that atrial fibrillation is associated with an appreciable increase in the risk of stroke (both embolic and nonembolic) and in the risk of mortality from all causes.