Risks and benefits of anticoagulation in atrial fibrillation: insights from the Outcomes Registry for Better Informed Treatment of Atrial Fibrillation (ORBIT-AF) registry.

BACKGROUND Patients with atrial fibrillation (AF) at the highest stroke risk derive the largest benefit from oral anticoagulation (OAC). Those with the highest stroke risk have been paradoxically less likely to receive OAC. This study assessed the association between stroke and bleeding risk on rates of OAC. METHODS AND RESULTS We analyzed OAC use among 10,098 patients with AF from 174 community-based outpatient practices enrolled in 2010-2011 in the Outcomes Registry for Better Informed Treatment of Atrial Fibrillation (ORBIT-AF). OAC was defined as warfarin or dabigatran use at study enrollment. Stroke and bleeding risk were calculated using congestive heart failure, hypertension, age, diabetes mellitus, prior stroke (CHADS₂), and anticoagulation and risk factors in AF (ATRIA) scores, respectively. The mean subject age was 73 years; 58% were men. Overall, 76% of patients received OAC (71% warfarin and 5% dabigatran). The use of OAC increased among those with higher CHADS₂ scores, from 53% for CHADS₂=0 to 80% for CHADS₂≥2 (P<0.001). OAC use fell slightly with increasing ATRIA bleeding risk score, from 81% for ATRIA=3 to 73% for ATRIA≥5 (P<0.001). A significant interaction existed between ATRIA and CHADS₂ scores (P=0.021). Among those with low bleeding risk, use of OAC increased significantly with increasing stroke risk. Among those with high bleeding risk, CHADS₂ stroke risk had a smaller impact on use of OAC. CONCLUSIONS In community-based outpatients with AF, use of OAC was high and driven by not only predominantly stroke but also bleeding risk. Stroke risk significantly affects OAC use among those with low bleeding risk, whereas those with high bleeding risk demonstrate consistently lower use of OAC regardless of stroke risk.