Aspirin resistance in patients with stable coronary artery disease with and without a history of myocardial infarction

BACKGROUND: Aspirin therapy is a cornerstone in the prevention of atherothrombotic events, but recurrent vascular events are estimated to occur in 8-18% of patients taking aspirin for secondary prevention after 2 years. Estimates of biologic aspirin resistance vary from 5% to 60%, depending on the assay used. However, the relationship between biologic measurements of aspirin resistance and adverse clinical events remains unclear. OBJECTIVE: To determine whether patients with documented myocardial infarction (MI) while on aspirin therapy (cases) were more likely to be aspirin resistant than were patients with coronary artery disease (CAD) who had no history of MI (controls) and to assess clinical predictors of aspirin resistance in patients with stable CAD. METHODS: This case-control study examined aspirin responses using the VerifyNow Aspirin Assay system in 50 cases and 50 controls who had taken a dose of aspirin within 48 hours of presentation to the clinic visit. Odds ratios were estimated to determine the association between aspirin resistance and Mi. Independent predictors of aspirin resistance were determined using univariate and multivariate analyses. RESULTS: An increase in the prevalence of aspirin resistance among cases (16% vs 12% in controls) was not observed (OR 1.40; 95% Cl 0.45 to 4.37; p = 0.566). In the overall CAD population, female sex was independently associated with aspirin resistance (OR 4.01; 95% Cl 1. 15 to 13.92; p = 0.029). CONCLUSIONS: Additional large studies are required to understand whether biologically defined aspirin resistance is associated with increased risk for cardiovascular events, with special attention paid to sex differences.