Utilization of Anticoagulation Therapy in Medicare Patients with Nonvalvular Atrial Fibrillation

Background: Clinical guidelines recommend oral anticoagulation for stroke prevention in patients with atrial fibrillation (AF) at moderate or high risk for stroke but not at high risk for bleeding; however, studies consistently report suboptimal use of such therapy. This study used Medicare Part D claims data to assess the use of warfarin in the Medicare population. Objectives: To compare real-world warfarin utilization with current treatment guideline recommendations, and to assess the effect of warfarin exposure level on patient outcomes in Medicare beneficiaries with nonvalvular AF (NVAF). Methods: Patients who were recently diagnosed with NVAF were identified using a random 5% sample of Research Identifiable Files of Medicare beneficiaries in 2006 or 2007. Individuals with moderate-to-high stroke risk per CHADS2 but not at high bleeding risk per ATRIA (Anticoagulation and Risk Factors in Atrial Fibrillation) bleeding risk score were evaluated for warfarin use, as identified by the presence of >= 1 warfarin prescription claims within 12 months after the index diagnosis. Warfarin exposure level was assessed by the proportion of days covered during the 12-month follow-up period. The effect of warfarin exposure on ischemic stroke and major bleeding event rates during the 12-month follow-up period were assessed using multivariate logistic regression. Results: Data from 14,149 newly diagnosed patients with NVAF (mean age, 79 years; 58.7% female) were analyzed, and of these, 7524 (53.2%) patients were identified as having moderate-to-high stroke risk and not being at high bleeding risk. Of these patients, 3110 (41.3%) did not receive warfarin within 12 months of the index diagnosis. The risk for ischemic stroke was significantly lower in those with warfarin exposure versus no warfarin exposure (adjusted odds ratio [OR], 0.51; confidence interval [CI], 0.43-0.61; P <.001) and in patients with warfarin proportion of days covered >= 80% versus those with proportion of days covered <80% (adjusted OR, 0.59; 95% CI, 0.48-0.72; P<.001). Warfarin exposure was associated with a significantly higher major bleeding rate (adjusted OR, 1.19; 95% CI, 1.04-1.36; P =.013), with this significant difference being driven by patients aged > 65 years. Conclusions: Based on a risk-stratification scheme composed of previously published tools, such as CHADS(2) and the ATRIA bleeding risk index, a significant proportion of Medicare beneficiaries with AF are not receiving guideline-recommended anticoagulation therapy, which leads to an excess rate of ischemic stroke in this patient population. These findings highlight quality-of-care issues for patients with AF and the need to improve compliance with anticoagulation guidelines in the Medicare population.