Patients demonstrating high platelet reactivity (HPR) on clopidogrel are more likely to suffer stent thrombosis (ST) or MI within two years of stent implantation, according to a new study in JACC: Cardiovascular Interventions.

A research team studied two-year outcomes of 8,582 patients undergoing routine platelet function testing following implantation of drug-eluting stents via PCI. Definite or probable ST occurred in 1.07 percent of the patients, and HPR to clopidogrel at baseline was independently associated with more than double the risk.

The same patient population showed a 35 percent increased risk of MI and a 26 percent decreased risk of clinically relevant bleeding. In contrast, HPR to aspirin was not associated with any adverse outcomes.

The study’s authors noted their findings were largely confirmatory, but they sought to stretch the previous one-year research of the ADAPT-DES (Assessment of Dual AntiPlatelet Therapy with Drug-Eluting Stents) study an additional year.

“The fact that baseline HPR on clopidogrel was predictive of ischemic events and mortality and inversely related to clinically relevant bleeding through two years of follow-up after successful drug-eluting stents implantation is notable, although the majority of probable or definite ST occurred within the first year, and adverse events were most frequent among patients with ACS (acute coronary syndrome),” wrote the authors, including lead researcher Thomas D. Stuckey, of the LeBauer-Brodie Center for Cardiovascular Research and Education/Cone Health in Greensboro, North Carolina.

According to the researchers, the low rate (0.23 percent) of very late ST—occurring in patients between one and two years—could partially be attributed to the use of second-generation drug-eluting stents, which are safer than the previous versions.

“Recent studies have demonstrated that patients treated with second-generation drug-eluting stents who were event free at one year and thereafter maintained on ASA (aspirin) alone have a low subsequent rate of ST, and data from the present study confirm these findings,” Stuckey et al. wrote.