Stent Thrombosis Is Associated With an Impaired Response to Antiplatelet Therapy

We sought to evaluate the response to antiplatelet therapy in patients with stent thrombosis (ST). Stent thrombosis is associated with considerable morbidity and mortality. An impaired response to antiplatelet therapy might be related to an increased risk for ST. Eighty-two patients were included in the present study: 23 patients with previous ST, 50 matched controls (coronary stenting without ST), and 9 healthy volunteers. Platelet aggregation (PA) was studied (optical aggregometry) under monotherapy with acetylsalicylic acid (ASA) 100 mg daily for one month, followed by dual therapy with ASA 100 mg and clopidogrel 75 mg daily (loading dose 300 mg) for another month. Maximal (5 and 20 μmol) adenosine diphosphate-induced PA was significantly higher in patients with ST compared with controls (5 μmol, p < 0.005; 20 μmol, p < 0.05) and volunteers (5 μmol, p < 0.005; 20 μmol, p < 0.05). Resistance to ASA (>20% aggregation with 0.5 mg/ml arachidonic acid) was more prevalent in patients with ST (48%) compared with control patients (32%, p = ns) and volunteers (0%, p = 0.01). Clopidogrel significantly reduced PA in all three groups, but intergroup differences persisted. Clopidogrel resistance (