Concomitant aspirin common in afib patients taking oral anticoagulants

Concomitant aspirin use appears common in patients with atrial fibrillation (AF) who are taking oral anticoagulants and is associated with significantly increased bleeding risk, a new study has found.

Researchers used data from the Outcomes Registry for Better Informed Consent (ORBIT) of Atrial Fibrillation registry to examine concomitant aspirin use and its relationship to clinical outcomes among AF patients who were taking oral anticoagulants. Patients in ORBIT-AF were enrolled from 176 U.S. practices from June 2010 through August 2011. The researchers used hierarchical multivariable logistic regression models to analyze factors associated with concomitant aspirin use. Six-month bleeding, hospitalization, ischemic events and mortality were the primary outcomes. The study results were published early online July 16 by Circulation.

The study population included 7,347 AF patients who were taking oral anticoagulants. The median patient age was 75 years, 43% were women, and 89% were white. Thirty-five percent of AF patients taking oral anticoagulants (n=2,543) were also taking aspirin. Patients who were receiving both aspirin and oral anticoagulants were more likely to be men (66% vs. 53%; P<0.0001) and had more comorbidities than patients receiving oral anticoagulants alone. Among patients taking both aspirin and oral anticoagulants, 39% had no history of atherosclerotic disease and 17% had increased risk for bleeding (ATRIA bleeding risk score ≥5). Patients taking both aspirin and oral anticoagulants also had higher risk for major bleeding and bleeding hospitalizations compared with patients taking oral anticoagulants alone (adjusted hazard ratios, 1.53 [95% CI, 1.20 to 1.96] and 1.52 [95% CI, 1.17 to 1.97], respectively). Ischemic event rates were low in both of the study groups.

The researchers acknowledged that their data came from a prospective national registry and that the treatment groups were not randomly assigned. In addition, they pointed out that the overall rates of ischemic events were low and that data on aspirin use could have been affected by recall bias. However, they concluded that concomitant aspirin use is relatively common in AF patients who have been prescribed oral anticoagulant therapy, even when vascular disease is not present, and that patients with AF who do have cardiovascular disease often receive oral anticoagulants alone. Bleeding risk in patients taking oral anticoagulants and aspirin was independently associated with use of both agents compared with oral anticoagulants alone.

These data, along with those from other studies, appear to support the potential of a “less is more” strategy in AF patients taking oral anticoagulants, the researchers concluded. They called for additional studies to assess benefits and harms and determine optimal antithrombotic treatment in AF patients.

“In the interim, clinicians need to carefully weigh whether the potential benefits of adding aspirin is worth the risk among patients with AF on [oral anticoagulants],” the researchers wrote. “In lieu of clinical trials, automatic risk assessment tools that calculate ischemic risk and bleeding risk might help guide concomitant antiplatelet therapy.”

The authors of an accompanying editorial compared the differences between U.S. and European guidelines on this issue, pointing out that concomitant use of oral anticoagulants and low-dose aspirin in patients with nonvalvular atrial fibrillation and stable atherothrombotic vascular disease is under debate because the efficacy and safety of such combination therapy have not yet been definitively determined. They also recommended that other elements be included in this discussion, including availability of three new oral anticoagulants and two P2Y₁₂ blockers, the advent of drug-eluting stents with lower risk for thrombosis, and increased awareness of aspirin's potential long-term benefits in areas besides cardiovascular health.

“It is hoped that these novel therapeutic options and areas of knowledge will be integrated with more widespread assessment of the individual AF patient's ischemic and bleeding risks as well [as] his/her values and preferences to inform personalized antithrombotic therapy in this setting,” the editorialists concluded.