Predictors of high on-treatment platelet reactivity early after clopidogrel loading in ST-elevation myocardial infarction.

Background: Given that platelet inhibition is crucial when ST-elevation myocardial infarction (STEMI) patients undergo primary PCI (PPCI), the identification of factors associated with early high on-treatment platelet reactivity may be important.
Methods and Results: Consecutive STEMI patients admitted for PPCI were considered for platelet reactivity assessment 2 h after loading with 600 mg clopidogrel using the VerifyNow point-of-care P2Y12 assay. A cut-off of ≥235 P2Y12 reaction units indicated high on-treatment platelet reactivity. Out of 92 STEMI patients, 63 (68.5%) were found to have high on-treatment platelet reactivity. Patients with high on-treatment platelet reactivity had received upstream clopidogrel loading and pantoprazol more frequently, had lower admission hemoglobin and tended to have an impaired renal function compared to those with an adequate response to clopidogrel. On multivariate analysis, upstream clopidogrel loading and creatinine clearance <60 ml/min were independently associated with higher risk for high on-treatment platelet reactivity (relative risk [RR]=1.55, 95% confidence interval [CI]: 1.11-2.17, P=0.01; RR=1.31, 95% CI: 1.008-1.71, P=0.04, respectively).
Conclusions: In patients with STEMI undergoing PPCI, use of upstream clopidogrel and impaired renal function independently predict high on-treatment platelet reactivity assessed as early as 2h following 600 mg of clopidogrel loading dose on point-of-care P2Y12 function assay.