Residual platelet activity is increased in clopidogrel- and ASA-treated patients with coronary stenting for acute coronary syndromes compared with stable coronary artery disease

Objective: To evaluate residual platelet activity in a consecutive cohort of patients treated with dual antiplatelet therapy after coronary stent implantation Design: Prospective single-centre cohort study. Setting: University hospital in Germany. Patients: 480 patients with symptomatic coronary artery disease (n = 221 (46%) or acute coronary syndrome (ACS; n = 259 (54%) stable angina) were studied. Platelet activity was measured by collagen- (5 mg/ml) and adenosine diphosphate- (ADP; 20 mu mol/l) induced platelet aggregation to assess post-treatment activity in patients treated with acetylsalicylic acid (500 mg bolus intravenously followed by 100 mg once a day) and clopidogrel (600 mg loading dose followed by 75 mg once a day). Main outcome measures: Increased residual platelet activity (IRPA) was defined if platelet aggregation was in the upper tertile of values in the patient collective. Association of epidemiological factors with IRPA was evaluated in a multivariate logistic regression analysis. Results: IRPA-ADP was found in 53 patients (11.0%) and IRPA-collagen in 42 patients (8.8%). ACS was associated with IRPA independently from other factors (for IRPA-collagen: odds ratio (OR) = 2.3, 95% confidence interval (CI) 1.2 to 4.5, p<0.05; for IRPA-ADP: OR = 2.4; 95% CI 1.3 to 4.4, p<0.01; for IRPA-ADP/collagen: OR = 4.5, 95% CI 1.2 to 16.9, p<0.05). Conclusions: The data suggest that ACS is independently associated with IRPA despite conventional antiplatelet therapy. Further studies are warranted to demonstrate the effects of intensified antiplatelet therapy for patients with acute coronary events.