TCT: Platelet function testing is still not ready for prime time
 |
While prior studies have emphasized the absolute level of platelet activation/aggregation to antiplatelet medications, the role of the baseline level of platelet activation and the percentage of platelet inhibition in response to these therapies have largely been unstudied prior to ADAPT-DES, according to the study’s lead author, Gregg Stone, MD, director of cardiovascular research and education at New York-Presbyterian Hospital/Columbia University Medical Center in New York City. In addition, the impact of poor platelet response to aspirin, and overall platelet aggregation while on dual antiplatelet therapy (DAPT) on the risk of stent thrombosis have not been fully examined.
In the registry, 8,575 patients undergoing PCI with drug-eluting stents (DES) were enrolled at 11 sites between January 2008 and September 2010. The researchers assessed platelet reactivity to aspirin and clopidogrel as well as overall platelet responsiveness with the VerifyNow Aspirin, P2Y12 and IIb/IIIa tests after successful implantation of drug-eluting stents (DES).
The researchers found that absolute and relative levels of platelet inhibition in response to ADP antagonists as assessed by the VerifyNow P2Y12 test are powerful independent predictors of stent thrombosis within 30 days, with a significant proportion of events independently attributable to clopidogrel hyporesponsivenes.
In contrast, the baseline level of platelet P2Y12 response, as well as aspirin and overall platelet responsiveness after DAPT loading as assessed by VerifyNow, were not shown to be related to the 30-day rate of stent thrombosis.
While platelet function was taken at baseline, the tests were correlative to events if the patient’s PRU was 230 or more or his or her inhibition was less than 11 percent. However, Stone said that because the events cannot pinpoint with any predictability, the routine use of the test cannot be justified.
“These results suggest that agents which more effectively inhibit ADP-induced platelet activation should reduce 30-day stent thrombosis when applied to large patient populations,” said Stone. “However, the modest sensitivity and specificity of platelet function testing, coupled with the low prevalence of events, implies that testing of platelet ADP antagonist responsiveness is unlikely to provide useful information to guide clinical decision-making in most individual patients for the prevention of stent thrombosis at 30 days.”
Based on these findings, Stone said that he has stopped using VerifyNow in clinical practice. Also, out of a nine-person panel reviewing the trial at the TCT press conference, not one of them said they are routinely using VerifyNow routinely in clinical practice. However, more than half said they are using the test selectively and in research, including Stone.
"There was a low stent thrombosis rate in patients with stable CAD, which coupled with the poor prognostic utility of platelet function testing in this setting, suggests that assessing DAPT response in patients without ACS undergoing PCI is unlikely to provide incremental clinical utility,” Stone said. “The relationship between platelet responsiveness testing and the occurrence of late and very late stent thrombosis in patients who have maintained and discontinued DAPT, will be assessed during the two-year clinical follow-up phase of the ADAPT-DES study."
The ADAPT-DES trial is sponsored by the Cardiovascular Research Foundation with research support from Boston Scientific, Abbott Vascular, Medtronic, Cordis, Biosensors, The Medicines Company, Daiichi Sankyo, Eli Lilly, Volcano and Accumetrics.