Incidence of ischemic stroke or transient ischemic attack in patients with multiple risk factors with or without atrial fibrillation: a retrospective cohort study

Background: The risk of stroke in atrial fibrillation (AF) increases with number of risk factors (RFs). However, the combined effect from multiple RFs on the incidence of ischemic stroke and transient ischemic attack (TIA) among US patients without AF has not been fully examined. Methods and results: Truven MarketScan Medicare Supplemental database was used to establish cohorts of patients >= 65 years old with and without AF. Index date was first occurrence of AF diagnosis (AF patients) or first medical encounter (non-AF patients) during the inception period from 2010 through 2011. Incidences of ischemic stroke/TIA in relation to number of baseline RFs (congestive heart failure, hypertension, advanced age, diabetes, and prior stroke/TIA, myocardial infarction) were determined during the follow-up period from the index date through March 2013. A total of 158,199 patients were included in the AF cohort and 1,181,273 patients in the non-AF cohort. Approximately 51% of AF patients had >= 3 RFs versus 18% in non-AF patients. Ischemic stroke/TIA were observed in 24,680 and 104,154 patients in the AF and non-AF cohorts, yielding incidence rate (SD) of 7.3 (0.05) and 3.2 (0.01) per 100 person-years, respectively. In the AF cohort, incidence rate of ischemic stroke/TIA was 2.3, 4.9, 9.4, and 16.9 per 100-person years for 0, 1-2, 3-4, and 5-6 RFs, respectively, compared with the corresponding rate of 1.3, 2.8, 6.4, and 12.3 per 100 person-years for the non-AF cohort. This positive association between the number of risk factors and incidence rates within each cohort was consistently observed in sensitivity analyses. Conclusion: In a large cohort of elderly patients without AF, the risk of ischemic stroke/TIA increased substantially in the presence of multiple RFs, highlighting potentially unmet medical needs. This observation implies that future studies may be warranted to investigate the effect of prophylactic anticoagulation in high risk non-AF patients.