Association between first anticoagulant prescription and embolic and hemorrhagic events among older adults with atrial fibrillation.

BACKGROUND: The impact of first prescription of oral anticoagulation on ischemic stroke and major bleeding events among Medicare beneficiaries with atrial fibrillation (AF) is not known. METHODS: A retrospective, observational, cohort study was performed based on a 5% sample of United States fee-for-service Medicare beneficiaries aged ≥66 years who developed AF from 2007 to 2020. The principal exposure was first prescription of an oral anticoagulant. The primary effectiveness end point was ischemic stroke (including cerebral or retinal ischemic stroke [central retinal artery occlusion]). The primary safety end point was major bleeding. To reduce the impact of selection bias and immortal time bias, unadjusted and adjusted hazard ratios (HRs) and rate differences were computed in a dataset comprised of pooled, sequential clinical trial replicates starting 1 month apart. RESULTS: In total, 144,969 patients (60.8% female; mean age 77.7 years [standard deviation (SD) 7.1]) were included in the study. First prescription of oral anticoagulation was not associated with a reduced hazard of ischemic stroke (adjusted HR [aHR] 1.01 [95% confidence interval (CI): 0.97-1.05]). However, first prescription of oral anticoagulation was associated with an increased hazard of a major bleeding event (aHR 1.38 [95% CI: 1.36-1.40]) and increased hazards of intracerebral hemorrhage (ICH) and major gastrointestinal hemorrhage. CONCLUSIONS: In this cohort study of Medicare beneficiaries aged 66 years and older with incident AF, the first anticoagulant prescription was not associated with a reduced hazard of ischemic stroke. Furthermore, unadjusted models suggested that clinicians are likely appropriately selecting patients for anticoagulation in routine clinical practice.