Abstract 232: Effect of Oral Anticoagulation Use on Thromboembolic Risk and Bleeding in Women Compared with Men with Atrial Fibrillation: Findings from the PINNACLE Data Registry

Abstract

Background: Among those with atrial fibrillation (AF), women have a higher risk of thromboembolic events and lower use of oral anticoagulation (OAC) when compared to men. Whether the effect of gender on thromboembolic risk in patients with AF is mediated by lower use of OAC among women is unknown. We examined whether gender differences in OAC use mediated the relationship between gender and thromboembolic risk in patients with AF. Methods: Adults 65 years and older with AF in the PINNACLE Registry from October 2008 to December 2014 were identified. Adults with valvular AF and contraindications to OAC use were excluded. Thromboembolic events (stroke, systemic embolism) and major bleeding events were determined using linked Medicare claims data. Site-stratified proportional hazard models adjusting for patient and practice-level characteristics compared thromboembolic and bleeding events by gender, as well as the mediating effect of OAC use as a time-dependent covariate on these outcomes. Results: Among 667,287 patients, the mean ±standard deviation age was 77±8 years and 46% were women. Compared to men, women had higher CHA2DS2-Vasc scores (mean 4.8 vs. 3.8, p<0.001), had similar prevalence of bleeding risk factors, but were prescribed OAC less frequently (51.5% vs. 53.8%, p<0.001). Over a median 2 years of follow up (range 0-6 years), there were 25,947 thromboembolic events and 40,967 major bleeding events. Women had a higher risk of thromboembolic events compared to men (5-year cumulative incidence 8.3% vs. 6.0%, adjusted hazard ratio [HR] 1.24, 95% CI 1.16-1.33) and a slightly lower risk of major bleeding (5-year cumulative incidence 10.4% vs. 11.2%, adjusted HR 0.90, 95% CI 0.83-0.98). Among adult patients with AF, OAC use was associated with lower thromboembolic risk (HR 0.90, 95% CI 0.86-0.94) and greater bleeding risk (HR 1.51, 95% CI 1.42-1.60). Among women, OAC use did not mediate the relationship between gender and either thromboembolic or major bleeding events (HR 1.24 and 0.90 respectively, identical to the unmediated effects). Conclusions: In a national US sample of older adults with AF, women had lower rates of OAC use, higher risk of thromboembolic events and lower risk of major bleeding. However, the difference in OAC use did not explain the gender differences in these outcomes. These findings underscore that women with AF are independently at higher risk for thromboembolic events and lower OAC use among women does not significantly explain this higher risk.