Residual arachidonic acid-induced platelet activation in aspirin-treated patients occurs largely via a COX-1 and COX-2 independent pathway, mediated in part by ADP-induced platelet activation.
Observational (n=700)
What is the mechanism of residual arachidonic acid-induced platelet activation in aspirin-treated patients undergoing cardiac catheterization?
Residual platelet activation in most aspirin-treated patients is not due to noncompliance but occurs via a COX-independent, ADP-mediated pathway, highlighting the mechanistic rationale for dual antiplatelet therapy.
BACKGROUND: Thrombotic events still occur in aspirin-treated patients with coronary artery disease. METHODS AND RESULTS: To better understand aspirin "resistance," serum thromboxane B2 (TXB2) and flow cytometric measures of arachidonic acid-induced platelet activation (before and after the ex vivo addition of aspirin and indomethacin) were analyzed in 700 consecutive aspirin-treated patients undergoing cardiac catheterization. In 680 of 682 evaluable patients, serum TXB2 concentrations were reduced compared with nonaspirinated healthy donors. Twelve patients had serum TXB2 that was lower than nonaspirinated healthy donors but >10 ng/mL. Arachidonic acid stimulated greater platelet activation in patients with high serum TXB2 (>10 ng/mL) than in patients with low serum TXB2. Addition of ex vivo aspirin reduced arachidonic acid-induced platelet activation to similar levels regardless of serum TXB2 concentrations, which suggests that patients with high residual serum TXB2 concentrations were either noncompliant or underdosed with aspirin. Among the remaining 98% of patients, ex vivo administration of either aspirin or indomethacin failed to prevent platelet activation across all degrees of arachidonic acid-induced platelet activation and aspirin doses. Although the patients were not randomized with respect to clopidogrel treatment, multivariate analysis showed that arachidonic acid-induced platelet activation was less in patients receiving clopidogrel. CONCLUSIONS: There is a residual arachidonic acid-induced platelet activation in aspirin-treated patients that (1) is caused by underdosing and/or noncompliance in only approximately 2% of patients and (2) in the remaining patients, occurs via a cyclooxygenase-1 and cyclooxygenase-2 independent pathway, in direct proportion to the degree of baseline platelet activation, and is mediated in part by adenosine diphosphate-induced platelet activation.
Frelinger et al. (2006) conducted an observational in Coronary artery disease (n=700). Aspirin therapy vs. Nonaspirinated healthy donors was evaluated on Serum thromboxane B2 (TXB2) and arachidonic acid-induced platelet activation. Residual arachidonic acid-induced platelet activation in aspirin-treated patients occurs largely via a COX-1 and COX-2 independent pathway, mediated in part by ADP-induced platelet activation.