Antithrombotic Therapy and First Myocardial Infarction in Patients With Atrial Fibrillation.

BACKGROUND:Patients with atrial fibrillation (AF) have increased risk of thromboembolic events such as stroke and myocardial infarction (MI). Although it has been established that the efficacy of anticoagulation is superior to that of antiplatelet agents for stroke prophylaxis in AF, the optimal antithrombotic treatment remains uncertain for primary protection against MI. OBJECTIVES:The authors investigated the incidence of first-time MI in patients with AF according to antithrombotic treatment and estimated the risk of stroke and bleeding. METHODS:Subjects with first-time AF diagnosed from 1997 to 2012 without history of coronary artery disease were identified using Danish nationwide administrative registries. Subjects were divided into time varying exposure groups according to antithrombotic treatment. The relative risks of outcomes were estimated by Poisson regression models. RESULTS:A total of 71,959 patients (median 75 years of age; females: 47%). At baseline, 37,539 patients (52%) were treated with vitamin K antagonist (VKA) monotherapy, 25,458 (35%) with acetylsalicylic acid (ASA) monotherapy and 8,962 (13%) with dual-therapy (VKA + ASA). The incidence of MI was 3% (n = 2,275). Relative to the VKA-treated group, the associated risk of MI was significantly higher for 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). The bleeding risk was significantly higher for dual-therapy (IRR: 1.93; 95% CI: 1.81 to 2.07). The risk of stroke relative to that of VKA therapy 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). CONCLUSIONS:VKA monotherapy in patients with AF was associated with a lower risk of first-time MI and stroke than ASA monotherapy. Combination of ASA and VKA therapy was not associated with a lower risk of MI but was associated with increased bleeding risk.