Methods

Consecutive patients with coronary artery disease undergoing invasive treatment were enrolled in this study from March through December 2010. According to previously published data, indications for prasugrel therapy in our patients were (1) ST-elevation acute myocardial infarction (STEMI), (2) drug-eluting stent (DES) implantation in diabetics, (3) stent thrombosis during clopidogrel therapy, (4) left main coronary artery DES-supported PCI, and (5) PCI in patients with high residual platelet reactivity on clopidogrel therapy. Contraindications to prasugrel therapy were (1) recent (<30 days) bleeding event or major surgery and (2) previous transient ischemic attack or stroke. All patients received a loading dose of prasugrel 60 mg. Patients ≥75 years old and with body weight ≤60 kg received a maintenance dose of 5 mg/day (10 mg/day for all other patients). Dual antiplatelet therapy was recommended for 12 months. All interventions were performed according to current standards and type of stent implanted, and use of glycoprotein IIb/IIIa inhibitors was at discretion of the operator.

All patients underwent platelet reactivity assessment by light transmittance aggregometry (APACT4, Helena Laboratories, Milan, Italy) 7 to 30 days after the index stenting procedure using adenosine diphosphate (ADP) 10 μmol as an agonist. Blood samples anticoagulated with sodium citrate 0.109 mmol (ratio 9:1) were obtained ≥7 days after loading with prasugrel 60 mg. Platelet-rich plasma, obtained by centrifuging whole blood for 10 minutes at 200 g , was stimulated with ADP 10 μmol. The 100% line was set using platelet-poor plasma and the 0 baseline was established with platelet-rich plasma (adjusted from 180 to 300 × 10 ⁹ /L). Platelet aggregation (according to the Born method) was evaluated considering maximal percent platelet aggregation in response to the stimulus. The coefficient of variation of ADP platelet aggregation was 6.8%. High residual platelet reactivity by ADP was defined as platelet aggregation ≥70%.

The primary end point of the study was occurrence of any bleeding event (major, minor, or minimal) according to TIMI criteria. Secondary end points were all-cause death, MI, definite or probable stent thrombosis, and stroke.

All patients were interviewed by trained researchers using a questionnaire to ascertain (1) vital status and clinical events, (2) rehospitalizations, (3) current medications, and (4) days and reasons for temporary or permanent discontinuation of the drug. All possible information derived from hospital readmissions or by the referring physician, relatives, or municipality live registries were entered into the prospective database. All events were adjudicated by an event adjudication committee whose members were blinded to platelet function data and current therapy (N.C., B.B., and F.V.). The study was approved by the Careggi Hospital ethics committee and all patients provided informed consent.

Discrete data were summarized as frequencies and continuous data were expressed as mean ± SD. Chi-square test was used for comparison of categorical variables and unpaired 2-tailed Student’s t test was used to test differences among continuous variables. Multivariable analyses to evaluate the independent contribution of clinical, angiographic, procedural, and platelet reactivity variables to bleeding events were performed by forward stepwise Cox proportional hazards model. Variables entered into the model were the age (years), female gender, body mass index, smoking, diabetes mellitus, hypertension, hypercholesterolemia, history of MI, history of renal insufficiency, STEMI at presentation, left ventricular ejection fraction, Killip class on admission, multivessel coronary disease, and associated use of aspirin, warfarin, or abciximab. A p value <0.05 was considered statistically significant. Analyses were performed using SPSS 19 (IBM Corporation, Somers, New York).