Background: Early identification of nonresponders to clopidogrel may be important in identifying subgroups of patients that might be at risk for future thrombotic events.
Methods: We prospectively assessed postclopidogrel platelet reactivity in 250 consecutive patients scheduled for elective percutaneous coronary intervention (PCI). All patients received dual antiplatelet therapy with 160 mg aspirin and a 300 mg loading dose of clopidogrel >12 hours before PCI. A platelet aggregation test was performed at the time of the intervention using a point-of-care assay, the Platelet Function Assay (PFA-100C/ADP; Dade-Behring, Deerfield, IL). Nonresponders were defined as having a PFA closure time of <71 seconds under dual oral antiplatelet therapy, reflecting normal platelet reactivity. Myonecrosis post-PCI constituted the primary end point and was defined as the release of creatine kinase-MB >1x the upper limit of normal on a sample taken 12 to 24 hours after intervention. The secondary end point was a composite end point of major adverse cardiac events including death, myocardial infarction, and stent thrombosis after 6 months.
Results: The PFA closure time was available in 242 patients and ranged from 31 to 300 seconds with a mean value of 147 seconds. Nonresponders represented 7% (17/242) of the cases. Myonecrosis post-PCI occurred in 29 patients (12%) and was more common in nonresponders than in normal responders (29% vs 11%, respectively; P = .03 on multivariate analysis). Major adverse cardiac events at 6 months occurred in 13 patients (1 sudden death possibly related to stent thrombosis and 12 post-PCI myocardial infarctions) and were more common in the nonresponder group (12% vs 5%, respectively; P = .06 on multivariate analysis).
Conclusions: Unresponsiveness to clopidogrel as assessed by the point-of-care test PFA-100C/ADP is an independent major risk factor for thrombotic complications after coronary intervention.