Antecedent Aspirin Therapy Inhibits Baseline Platelet Activity in Patients Presenting with Acute Myocardial Infarction

Aspirin therapy and platelet inhibition reduce the risk for the development of acute myocardial infarction (AMI). However, the effects of aspirin on baseline platelet activity in patients presenting with AMI are not known. We determined the effect of long-term aspirin use on baseline platelet activity in patients presenting with AMI, enrolled in the GUSTO-III Platelet Study. Platelet characteristics were investigated by aggregometry, flow cytometry and enzyme-linked immunosorbent assay in 23 patients before thrombolysis. Sixteen AMI patients were aspirin free, and 7 patients were using aspirin (81-500 mg/daily). The aspirin-treated patients exhibited a mild but consistent reduction of platelet activity which reached significance for 5 microM (p = 0.02), and 10 microM (p = 0.01) adenosine diphosphate induced aggregation. The surface expression of P-selectin (p = 0.02) and PECAM-1 (p = 0.03) and the plasma level of soluble P-selectin (p = 0.02) were also reduced. As previously observed in normal humans and patients with stable coronary artery disease, long-term aspirin therapy is also associated with diminished platelet activation in patients presenting with AMI. Long-term aspirin therapy mildly reduces baseline platelet activity; however, this degree of relative platelet inhibition does not appear to be cardioprotective.