Use and associated risks of concomitant aspirin therapy with oral anticoagulation in patients with atrial fibrillation: insights from the Outcomes Registry for Better Informed Treatment of Atrial Fibrillation (ORBIT-AF) Registry

Abstract

Background: The role of concomitant aspirin (ASA) therapy in patients with atrial fibrillation (AF) receiving oral anticoagulation (OAC) is unclear. We assessed concomitant ASA use and its association with clinical outcomes among AF patients treated with OAC.

Methods and results: The Outcomes Registry for Better Informed Treatment of Atrial Fibrillation (ORBIT-AF) registry enrolled 10 126 AF patients from 176 US practices from June 2010 through August 2011. The study population was limited to those on OAC (n=7347). Hierarchical multivariable logistic regression models were used to assess factors associated with concomitant ASA therapy. Primary outcomes were 6-month bleeding, hospitalization, ischemic events, and mortality. Overall, 35% of AF patients (n=2543) on OAC also received ASA (OAC+ASA). Patients receiving OAC+ASA were more likely to be male (66% versus 53%; P<0.0001) and had more comorbid illness than those on OAC alone. More than one third of patients (39%) receiving OAC+ASA did not have a history of atherosclerotic disease, yet 17% had elevated Anticoagulation and Risk Factors in Atrial Fibrillation (ATRIA) bleeding risk scores (≥5). Major bleeding (adjusted hazard ratio, 1.53; 95% confidence interval, 1.20-1.96) and bleeding hospitalizations (adjusted hazard ratio, 1.52; 95% confidence interval, 1.17-1.97) were significantly higher in those on OAC+ASA compared with those on OAC alone. Rates of ischemic events were low.

Conclusions: Patients with AF receiving OAC are often treated with concomitant ASA, even when they do not have cardiovascular disease. Use of OAC+ASA was associated with significantly increased risk for bleeding, emphasizing the need to carefully determine if and when the benefits of concomitant ASA outweigh the risks in AF patients already on OAC.

Clinical trial registration: URL: http://www.clinicaltrials.gov. UNIQUE IDENTIFIER: NCT01165710.

Keywords: anticoagulants; aspirin; atrial fibrillation; hemorrhage; outcome assessment (health care).

Figure 1

Flow diagram of exclusion criteria in the current study, yielding the final analysis population of 7,347 patients. OAC: oral anticoagulation; ASA: aspirin.

Figure 2

Factors associated with OAC+ASA (versus OAC alone) in multivariable analysis. References groups are new onset AF (for AF type), some school (for education), cardiologist (for provider type), and Northeast (for region). OAC: oral anticoagulation; ASA: aspirin; OR: odds ratio; CAD: coronary artery disease; DES: drug-eluting stent; TIA: transient ischemic attack; PCI: percutaneous coronary intervention; AF: atrial fibrillation; ECG: electrocardiogram; CABG: coronary artery bypass grafting; AAD: antiarrhythmic drug; LVH: left-ventricular hypertrophy; GI: gastrointestinal; AS: aortic stenosis; AR: aortic regurgitation; TR: tricuspid regurgitation.

Figure 3

Unadjusted, 6-month major bleeding rates among high-risk subgroups are shown with absolute numbers of events per group noted above. OAC: oral anticoagulation; ASA: aspirin; GI: gastrointestinal.