Patients With Previous Definite Stent Thrombosis Have a Reduced Antiplatelet Effect of Aspirin and a Larger Fraction of Immature Platelets

ObjectivesThis study sought to evaluate the platelet response to aspirin and the immature platelet fraction in patients with previous stent thrombosis (ST).BackgroundST is a potentially fatal complication of coronary stenting. A reduced platelet response to aspirin increases the risk of cardiovascular events.MethodsWe included 117 patients previously undergoing percutaneous coronary intervention. A total of 39 patients had suffered ST and 78 patients served as controls matched at a 1:2 ratio with respect to age, sex, stent type, and percutaneous coronary intervention indication. All patients were treated with aspirin 75 mg once daily. Platelet function was assessed by multiple electrode aggregometry in citrated and hirudinized blood and by VerifyNow Aspirin Assay (Accumetrics, San Diego, California). Flow cytometric determination of the immature platelet fraction was performed to evaluate platelet turnover. Platelet activation was evaluated by soluble serum P-selectin. Compliance was confirmed by serum thromboxane B2.ResultsAll patients were fully compliant, which was confirmed by suppressed levels of serum thromboxane B2. Platelet aggregation was increased in patients with previous ST when assessed by multiple electrode aggregometry induced by collagen (pcitrated blood = 0.003; phirudinized blood < 0.0001) and by arachidonic acid (pcitrated blood = 0.16; phirudinized blood = 0.04), respectively. Similarly, platelet aggregation assessed by VerifyNow was higher in ST cases (p = 0.12). A trend toward an increased immature platelet fraction among cases was seen (p = 0.13), whereas P-selectin levels (p = 0.56) did not differ between groups.ConclusionsOverall, patients with previous ST had a reduced antiplatelet effect of aspirin, which might be explained by an increased platelet turnover.