Post-treatment Platelet Activity Predicts Ischemic Event
Post-treatment platelet function may be a better predictor of ischemic events than platelet inhibition or responsiveness after a stenting procedure, according to Paul A. Gurbel, MD, from the Sinai Center for Thrombosis Research in Baltimore.
In a session Monday morning, Gurbel said a common misperception is that lack of platelet inhibition or responsiveness is predictive of high risk for ischemic events and that pretreatment function and inhibition are predictive of post-treatment markers. This may lead to overestimation of risk in patients with low pretreatment markers and underestimation of risk in patients with high pretreatment markers.
Although pre-clopidgrel and post-clopidogrel treatment aggregation may correlate in the short term, percent aggregation tends to drop off; the difference is even more dramatic in patients with high pretreatment aggregation, Gurbel said.
Risk factor for events
In a series of studies at the Sinai Center for Thrombosis Research, post-treatment platelet reactivity was a risk factor for poststenting ischemic events. In one trial, patients assigned either 300 mg or 600 mg clopidogrel (Plavix, Sanofi) and eptifibatide (Integrilin, Schering) had a higher relative inhibition of platelet activity that correlated with periprocedural infarction, as measured by CK-MB or troponin.
Evidence from a retrospective trial showed a correlation between post-treatment aggregation and stent thrombosis, Gurbel said. Stent thrombosis tended to develop in patients with a higher percentage of platelet aggregation.
A third trial examined the relation of pre-percutaneous coronary intervention (PCI) aggregation to ischemic events in patients presenting to the catheterization lab who had been assigned chronic clopidogrel therapy. The study “demonstrated clearly that those patients who suffer events who come to the cath lab already loaded on clopidogrel have higher platelet reactivity,” Gurbel said.
Periprocedural platelet reactivity is a predictor of six-month ischemic events in these types of patients, he said.
Post-treatment function
Several recent studies have correlated post-treatment platelet function with clinical outcomes. According to Gurbel, these studies tend to look at post-treatment platelet function in isolation and ignore the role of platelet-fibrin clot formation as a main contributor to adverse events.
A 2005 study by Gurbel examined this correlation between platelet function and maximum clot strength and six-month post-stenting ischemic events. High aggregation alone was as predictive of ischemic events as high platelet-fibrin clot strength, he said.