People with atrial fibrillation (AF) have an increased risk of thromboembolic events including stroke and myocardial infarction (MI). While the use of oral anticoagulation is an established strategy in the prevention of stroke in AF patients, the optimal antithrombotic treatment to prevent MI has not been established.
In a recently published Danish registry study, Lee et al identified 71,959 patients hospitalized with first-time AF and with no history of coronary artery disease (CAD) between January 1, 1997, and December 31, 2012, Of these, the baseline treatment was vitamin K antagonist (VKA) monotherapy in 52%, acetylsalicylic acid (ASA) in 35% monotherapy and dual-therapy (VKA plus ASA) in 13%. The primary outcome was incidence of first-time MI, and occurred in 3% of participants, which was similar to that reported in other observational studies of AF patients. The risk of MI was significantly higher for patients taking ASA (incidence rate ratio [IRR]: 1.54; 95% confidence interval [CI] 1.40 to 1.68) and dual-therapy (IRR: 1.22; 95% CI: 1.06 to 1.40) compared with VKA. Secondary outcome measures were bleeding risk and stroke. The bleeding risk was significantly higher for dual-therapy (IRR: 1.93; 95% CI: 1.81 to 2.07) but not ASA monotherapy compared with VKA monotherapy. The risk of stroke was significantly higher for both ASA (IRR: 2.00; 95% CI: 1.88 to 2.12) and dual-therapy (IRR: 1.30; 95% CI: 1.18 to 1.43) compared with VKA monotherapy.
This real-world study included high-risk patient subgroups, which are often excluded in randomized clinical trials. However, its observational design allowed the possibility of residual confounding where clinical information such as body-mass index and blood pressure were not available. The study did not account for patients with undiagnosed AF or monitor adherence. Furthermore, in the last 5 years, direct oral anticoagulants (DOACs) that inhibit thrombin or factor Xa have been increasingly used in preference to VKA for the prevention of stroke in AF patients. Further studies comparing the efficacy of DOACs and VKAs in prevention of MI in AF patients are warranted. Nevertheless, the study has provided valuable evidence that, in patients with AF, VKA monotherapy is preferable to ASA monotherapy and ASA plus VKA dual-therapy in the prevention of MI.
KEYWORDS: anticoagulation; antiplatelet therapy; aspirin; atrial fibrillation; myocardial infarction; thromboembolism; warfarin