Relationship between age and platelet activation in patients with stable and unstable angina.

The objective of this study was to examine platelet reactivity and activation as a function of age in patients with both stable and unstable angina. This was a retrospective cohort study to compare platelet function in older patients with and without acute coronary syndromes. Participants were 55 individuals presenting with acute coronary syndromes and 54 with stable angina whose age ranged from 38 to 92 years. Platelet reactivity was assessed by ADP-induced aggregation and activation was measured by p-selectin, total and active GPIIb/IIIa expression, and platelet-leukocyte aggregates in. Multiple regression was used to identify independent predictors for each platelet variable. Aggregation and receptor expression decreased with advancing age only among patients with acute coronary syndromes. In multivariate analyses, age was the strongest predictor of decreased aggregation (beta=-0.558, R(2)=0.353, p<0.0001), reduced labeling with PAC-1 (beta=-0.561, R(2)=0.276, p<0.0001) and reduced p-selectin (beta=-0.442, R(2)=0.240, p<0.0001). However, age did not predict total GPIIb/IIIa labeling or platelet-leukocyte aggregates in either acute coronary syndrome or stable patients. In conclusion, older patients with acute coronary syndromes demonstrate decreased platelet reactivity and activation at presentation. These findings may provide a mechanism to explain increased bleeding observed in elderly patients treated with GPIIb/IIIa inhibitors and fibrinolytic therapy for unstable coronary syndromes.