The antiplatelet effects of aspirin vary among individuals. In a single-center, blinded, prospective study, researchers assessed the clinical consequences of aspirin resistance by following 326 aspirin users with stable cardiovascular disease (all had been taking 325 mg/day of aspirin for at least 7 days). Seventeen patients (5.2%) met predefined criteria for aspirin resistance, as measured by optical platelet aggregation. Mean follow-up was 23 months.
Compared with patients not resistant to aspirin, those with aspirin resistance were more often female and had a lower hemoglobin count; otherwise, the 2 groups had similar baseline characteristics and medication-use profiles. During follow-up, patients with aspirin resistance had a significantly higher composite rate of death, MI, or stroke (24%) than nonresistant patients (10%). After adjustment for other clinical factors, aspirin resistance remained a significant independent predictor of adverse outcome (hazard ratio, 4.14, compared with no resistance).
Comment: In stable cardiovascular patients, aspirin resistance independently predicted adverse events in the long term. Strengths of this study include its prospective, blinded design; use of optical aggregation to identify aspirin resistance; and 97% subject retention. The mechanisms for resistance, which are likely multiple, were not addressed. Future studies are needed to clarify these mechanisms, to standardize the definition of aspirin resistance, to develop and validate simple methods of measuring resistance, and to assess the potential benefit of alternative antiplatelet therapies for aspirin-resistant patients.
— Howard C. Herrmann, MD
Published in Journal Watch Cardiology May 9, 2003
Gum PA et al. A prospective, blinded determination of the natural history of aspirin resistance among stable patients with cardiovascular disease. J Am Coll Cardiol 2003 Mar 19; 41:961-5.