Comparison of Oral Anticoagulant Use and Stroke Risk Among Older Adults Newly-Diagnosed Atrial Fibrillation Living in Urban-Versus-Rural Areas.

We aimed to assess the association between urban/rural residence and the risk of ischemic stroke in individuals with newly diagnosed atrial fibrillation (AF), and to quantify the role of oral anticoagulation (OAC) initiation in the variation in stroke risk between urban and rural residents with AF. Using 5% random samples of Medicare claims, we identified fee-for-service beneficiaries who were diagnosed with AF between January 2014 and December 2015. Beneficiaries were followed for 1 year since their AF diagnosis, and were categorized according to their initiation of OAC within the year. We used the Rural-Urban Continuum Codes to define urban (levels 1 to 3) and rural (levels 4 to 9) areas. We applied marginal structural models to examine to what extent the difference in stroke risk between rural and urban areas were attributable to the difference in OAC initiation. In the year of AF diagnosis, 52% of those residing in urban areas and 56% residing in rural areas initiated an OAC (p <0.001). Urban residence, compared with rural residence, was associated with a 22% (hazard ratio and 95% confidence interval: 1.22 [1.13, 1.31]) increased risk of stroke. The hazard ratio attributed to urban residence decreased to 1.14 (1.01, 1.30) after accounting for the mediating role of lack of OAC initiation. Lack of OAC initiation explained 34% of the increased stroke risk observed in urban areas. In conclusion, urban residents with newly diagnosed AF were less likely to initiate OAC than rural counterparts, which explained one third of the increased risk of stroke observed in urban areas.