• Interventional Techniques & Devices Clinical Trials
• Thrombotic Disorders

Three tests of platelet reactivity were able to predict one-year risk of thrombotic events in patients who were undergoing elective percutaneous coronary intervention (PCI), according to new findings from the POPular study.

Dual antiplatelet therapy with aspirin and clopidogrel is the standard of care for patients who are undergoing PCI with stent implantation; yet, up to 36% of patients show decreased responsiveness to clopidogrel. These patients exhibit high on-treatment platelet reactivity, which is associated with an increased risk of thromboischemic events. Today, Nicoline J. Breet, MD, St. Antonius Hospital, Nieuwegein, the Netherlands (lead investigator JM ten Berg, MD, PhD), presented results from the POPular study, which was designed to identify which platelet function tests predict thrombotic risk in patients who receive antiplatelet therapy following PCI.

The POPular trial included 1069 consecutive patients who were treated with aspirin and clopidogrel after undergoing elective PCI with stent implantation. In a head-to-head comparison, investigators evaluated seven platelet reactivity tests in parallel:

• Light transmittance aggregometry (LTA) 5 μmol/L adenosine diphosphate (ADP) and 20 μmol/L ADP

• VerifyNow® P2Y12

• Plateletworks®

• Impact-R

• Impact-R ADP

• PFA-100 COL/ADP

• INNOVANCE® PFA P2Y®

The primary endpoint was a composite of death, myocardial infarction, stent thrombosis, and stroke at 1 year. Primary safety endpoints included TIMI major and minor bleeding at 1 year.

Three platelet function tests were able to correlate high platelet reactivity with an increased risk of thrombotic complications at 1 year, including both versions of the LTA test, the VerifyNow® P2Y12 assay, and the Plateletworks® assay.

When the LTA test was used with 5 μmol/L ADP, 6% of patients with normal reactivity and 11.7% of patients with high reactivity reached the primary endpoint (p<0.0001). When used with 20 μmol/L ADP, the risk of complications was 6.2% in the normal reactivity group and 12% in the high reactivity group (p<0.0001). The LTA test is the most labor-intensive and time-consuming of the platelet reactivity tests and can not be performed at the patient's bedside, Dr. Breet said.

Patients with normal and high platelet reactivity according to the VerifyNow® P2Y12 assay had a 5.7% and 13.3% risk of reaching the primary endpoint, respectively (p<0.0001). The VerifyNow® test is fully automated and can be performed at the bedside in the cardiac catheterization laboratory.

Using the Plateletworks® assay, normal and high platelet reactivity corresponded with a 1-year risk of thrombotic events of 6.7% and 12.6%, respectively (p=0.002). The Plateletworks® assay is a semiautomated test that can be performed at the bedside, but it is limited by the requirement that it must be performed within 10 minutes of drawing blood.

The four remaining tests — Impact-R, Impact-R ADP, PFA-100 COL/ADP, and INNOVANCE® PFA P2Y® — were not able to identify an association between high platelet reactivity and thrombotic complications at 1 year. None of the tests that were included in the analysis was able to identify patients with an increased risk of TIMI major or minor bleeding.

Currently, platelet reactivity tests are used primarily in research rather than in the clinical setting. However, large randomized trials are currently underway to evaluate whether these tests can guide clinical decision-making for patients who receive antiplatelet therapy following PCI, Dr. Breet said.

• © 2009 MD Conference Express