Aspirin vs Oral Anticoagulants in Atrial Fibrillation With High Stroke Risk

Some patients with atrial fibrillation who have a moderate to high risk of stroke are still being prescribed aspirin only instead of oral anticoagulants or a combination of both, according to research published in the Journal of American College of Cardiology.

Researchers sought to identify factors associated with prescription of aspirin alone compared with oral anticoagulants in patients with atrial fibrillation at moderate to high thromboembolic risk (defined as CHADS₂ score ≥2 and CHA₂DS₂-VAS_C score ≥2). They selected 2 cohorts of outpatients who were enrolled in the American College of Cardiology PINNACLE (Practice Innovation and Clinical Excellence) registry between 2008 and 2012.

Of the total 210 380 patients who had CHADS₂ scores ≥2 on antithrombotic therapy, 80 371 were treated with aspirin alone while 130 009 were treated with warfarin or non-vitamin K antagonist oral anticoagulants (NOACS). Of the 294 642 patients who had CHA₂DS₂-VAS_C scores ≥2, 118 398 were treated with aspirin alone while 176 244 were treated with warfarin or NOACS.

The mean CHADS₂ score in the CHADS₂ score ≥2 cohort was 2.8 ± 1.0 and the mean CHA₂DS₂-VAS_C score in the CHA₂DS₂-VAS_C score ≥2 cohort was 2.2 ± 1.2.

In both cohorts, patients who were prescribed aspirin alone instead of oral anticoagulants were more likely to be younger, had lower BMI, more often female, and were more likely to have diabetes, hypertension, dyslipidemia, coronary artery disease, unstable or stable angina, prior myocardial infarction, prior coronary artery bypass graft surgery, and peripheral artery disease. Meanwhile, those patients who were prescribed oral anticoagulants were more likely male, had higher BMI, had prior stroke or transient ischemic attack, had prior systemic embolism, and had congestive heart failure.

Of the patients in the CHADS₂ score ≥2 cohort who were treated with oral anticoagulants (n=130 009), warfarin was the most commonly used therapy (n=118 178), followed by dabigatran (n=9363), and rivaroxaban (n=2468). Warfarin was also the most commonly used therapy in the CHA₂DS₂-VAS_C score ≥2 cohort (n=159 668), followed by dabigatran (n=13 122), and rivaroxaban (n=3454).

“Despite a well-established association of AF [atrial fibrillation] with stroke, significant lack of OAC [oral anticoagulant] prescription to reduce thromboembolism in at-risk candidates has been demonstrated in several large-scale studies, with aspirin prescription prevalence as high as 28% to 38% in patients who were prescribed an antithrombotic agent all,” researchers wrote.

In an evaluation of practice-level variation, researchers found that the median practice rate for oral anticoagulant prescription in the CHADS₂ score ≥2 cohort was 64.9% with significant variation in oral anticoagulant prescription (interquartile range: 56.4% to 69.9%). They also found that the median practice rate for oral anticoagulant prescription in the CHA₂DS₂-VAS_C score ≥2 cohort was 63.3% (interquartile range: 55.2% to 68.7%).

In both cohorts, researchers discovered concomitant use of any thienopyridine (mainly clopidogrel) was higher in patients who were prescribed aspirin, and concomitant prescription of aspirin alone (as well as aspirin plus thienopyridine) was not uncommon in patients who were prescribed an oral anticoagulant. Combination dual antiplatelet therapy with aspirin and a thienopyridine was far less common in patients prescribed an oral anticoagulant vs aspirin.

“These data indicate a gap in care, most prominent in patients with or at risk for coronary artery disease, and should draw attention to a high rate of prescription of aspirin therapy in AF patients at risk for stroke, despite previous data that show aspirin to be inferior to OAC in this population,” they concluded.

Reference

Hsu JC, Maddox TM, Kennedy K, et al. Aspirin instead of oral anticoagulant prescription in atrial fibrillation patients at risk for stroke. J Am Coll Cardiol. 2016;67(25):2913-2923. doi: 10.1016/j.jacc.2016.03.81.