Profile and prevalence of aspirin resistance in patients with cardiovascular disease

We determined the prevalence and clinical predictors of aspirin resistance by prospectively studying 325 patients with stable cardiovascular disease w ho were receiving aspirin (325 mg/day for greater than or equal to7 days) b ut no other antiplatelet agents. We also compared the detection of aspirin resistance with optical platelet aggregation, a widely accepted method, wit h a newer, more rapid method, the platelet function analyzer (PFA)-100, a w hole blood test that measures platelet adhesion and aggregation ex vivo. Bl ood samples were analyzed in a blinded fashion for aspirin resistance by op tical aggregation using adenosine diphosphate (ADP) and arachidonic acid, a nd by PFA-100 using collagen and/or epinephrine and collagen and/or ADP car tridges to measure aperture closure time. Aspirin resistance was defined as a mean aggregation of greater than or equal to 70% with 10 muM ADP and a m ean aggregation of greater than or equal to 20% with 0.5 mg/ml arachidonic acid. Aspirin semiresponders were defined as meeting one, but not both of t he above criteria. Aspirin resistance by PFA-100 was defined as having a no rmal collagen and/or epinephrine closure time (less than or equal to 193 se conds). By optical aggregation, 5.5% of the patients were aspirin resistant and 23.8% were aspirin semiresponders. By PFA-100, 9.5% of patients were a spirin resistant. Of the 18 patients who were aspirin resistant by aggregat ion, 4 were also aspirin resistant by PFA-100. Patients who were either asp irin resistant or aspirin semiresponders were more likely to be women (34.4 % vs 17.3%, p = 0.001) and less likely to be smokers (0% vs 8.3%, p = 0.004 ) compared with aspirin-sensitive patients. There was a trend toward increa sed age in patients with aspirin resistance or aspirin semiresponders (65.7 vs 61.3 years, p = 0.06). There were no differences in aspirin sensitivity by race, diabetes, platelet count, renal disease, or liver disease. (C) 20 01 by Excerpta Medica, Inc.