Usefulness of platelet reactivity before percutaneous coronary intervention in determining cardiac risk one year later

Abstract

F low cytometric analysis of platelets with the use of epitope-dependent monoclonal antibodies or fluorochrome-labeled ligands provides sensitive and specific assessment of platelet activation.1,2 Assessment of platelet function has not yet been implemented to direct antiplatelet therapy. In contrast, analogous methods are used extensively in the diagnosis and classification of malignancies, as well as to guide antineoplastic therapy.3–5 We have previously reported that flow cytometric analysis of platelet reactivity prospectively identifies those patients at high and low risk of cardiac events during the first 90 days after percutaneous coronary intervention (PCI).6 The aim of the present report was to determine whether this method provides an outcome measure at 6 months and 1 year of follow-up in patients who underwent PCI. • • • The institutional review board of the University of Vermont approved the protocol. All patients provided informed consent. Eligible nonconsecutive patients included those with symptomatic coronary artery disease, a normal creatine kinase and creatine kinase-MB at the time of the procedure, and no pretreatment with intravenous glycoprotein (GP) IIb/IIIa inhibitors. Blood was obtained shortly before PCI for assay of platelet reactivity by flow cytometry. Patients were classified into 1 of 2 groups, high reactivity and low reactivity based on the percentage of platelets capable of binding fibrinogen in response to adenosine diphosphate 0.2 M (activation of platelet GP IIb/IIIa). The median value for all patients was used to stratify the subjects. PCI was performed as clinically mandated. All patients were treated with aspirin 325 mg/daily in addition to clopidogrel 75 mg/daily for 4 weeks. The composite of myocardial infarction (MI), urgent revascularization, and repeat vascularization was assessed after 6 months and 1 year. Follow-up was obtained by telephone calls and chart review at 3, 6, and 12 months. Follow-up was completed in all but 3 of the 112 patients studied ([97.3%] 2 deaths, 1 lost to follow-up). Platelet reactivity was assessed as previously described.6 In brief, blood was anticoagulated with corn trypsin inhibitor. Platelet reactivity was determined with respect to the activation of GP IIb/IIIa. Blood in 5l aliquots was added to microcentrifuge tubes containing HEPES-Tyrodes buffer and fluorochrome-labeled ligands. Adenosine diphosphate (0.2 and 1 M) was used to activate platelets. A peridinin chlorophyll protein conjugated antibody to GP IIIa was used as an activation-independent marker of platelets. Fluorescein isothiocyanate conjugated fibrinogen was used to assess the activation of GP IIb/IIIa. The reaction mixture was incubated at room temperature for 15 minutes. Subsequently, platelets were fixed and red blood cells were lysed with Optilyse-C (Immunotech, Marseille, France). Association of ligands with platelets was determined with a fluorescence-activated cell sorter. Platelets were identified on the basis of particle size and on association with CD61 antibody. Descriptive statistics were implemented for all measures. Comparison of the cumulative incidence of events in high and low reactivity groups was conducted using 2 2 contingency table methods and Fisher’s exact test for dichotomous measures. Comparison of the incidence of clinical outcomes over time in the high and low reactivity groups were From the University of Vermont College of Medicine, Burlington, Vermont. Dr. Kabbani’s address is: 111 Colchester Avenue, Cardiology Unit—Fletcher Allen Health Care—McClure 1, Burlington, Vermont 05401. E-mail: Samer.Kabbani@vtmednet.org. Manuscript received September 13, 2002; revised manuscript received and accepted December 4, 2002. FIGURE 1. Kaplan-Meier curves of the probability of freedom from the composite end point at 1 year. Platelet reactivity was assessed by flow cytometric determination of the capacity of platelets to bind fibrinogen in response to adenosine diphosphate 0.2 M. The divergence of the curves during the initial 24 hours predominantly reflects a higher incidence of periprocedural MI in those with high platelet reactivity. The highest incidence of cardiac events occurred during the first 6 months after PCI.