Plaque distribution in clopidogrel responders and low responders as determined by multislice computed tomography

Via multidetector computed tomography (MDCT) with retrospective electrographic gating, we sought to evaluate whether plaque distribution differs between responders and low responders to clopidogrel treatment. Low response was defined as a post-treatment aggregation of 35% to 70%. In this observational study, we enrolled 62 patients (mean age, 64.8 ± 8.9 yr; 51 men). In addition to determining coronary calcium scores, we performed noninvasive coronary angiography with MDCT before stent implantation. Plaques were visually classified as calcified, mixed, or completely noncalcified. Mean density was measured. Residual platelet aggregation (RPA) was evaluated by aggregometry 6 hr after administration of a 600-mg loading dose of clopidogrel. Patients with an RPA of less than 35% were defined as responders.The median calcium score was 736 Agatston score equivalent (ASE) (range, 0-5,772) and mean platelet inhibition was 35% ± 19% (range, 0-70%). A total of 494 coronary plaques were detected (responders: calcified, 197; mixed, 47, noncalcified, 5; and low responders: calcified, 177; mixed, 65; noncalcified, 3). Responders (n = 35) had significantly lower ASEs and fewer mixed but more calcified plaques than did low responders. In mean plaque density (measured within the noncalcified part of the plaques), no statistically significant difference existed between the 2 patient groups. By use of MDCT, we showed that ASE and plaque distribution were associated with RPA after clopidogrel treatment. Patients with a low coronary plaque burden and a small proportion of mixed plaques were more likely to have low RPA after administration of clopidogrel.