Trends in warfarin use and its associations with thromboembolic and bleeding rates in a population with atrial fibrillation between 1996 and 2011

AIM: Warfarin is a cornerstone for the prevention of thromboembolism in atrial fibrillation (AF), and several efforts have been taken to increase its usage and safety, including risk stratification schemes. Our aim was to investigate the temporal trends in initiation of warfarin and its effects on incidence of bleeding and thromboembolism in patients with new-onset atrial fibrillation 1996-2011. METHODS: All patients with a first-time diagnosis of non-valvular atrial fibrillation were identified from nationwide administrative registries. Trends were determined by linear regression. RESULTS: In total 153,682 patients were included. Initiation of warfarin increased from 14% to 41% (p<0.0001). Events of thromboembolism decreased from 3.9% to 2.6% annually (p<0.0001). The greatest decline in thromboembolic events was observed for patients with a CHA2DS2VASc score >1, where the annual decline was -0.12% (95%CI: -0.161; -0.084)) for those treated with warfarin and -0.073% (95%CI: -0.116;-0.030)) for those not treated with warfarin. Bleeding increased from 3.3% to 3.9% (p = 0.043). For those with a CHA2DS2VASc score >1 annual bleeding rates increased by 0.095% (95%CI: -0.025; -0.165) in warfarin treated and by 0.056% (95%CI: -0.013; -0.100) in patients not treated with warfarin. CONCLUSION: Warfarin use increased by nearly a 3-fold between 1996 and 2011. During the same period, thromboembolic events declined by a third and bleeding increased by a fifth, suggesting a beneficial effect associated with higher warfarin use. Notably, a small decline in thromboembolic events and increase in bleeding events was observed for the untreated population, suggesting a changing risk profile of AF patients.