Prevalence of high-risk plaque features on cardiac computed tomography scans in patients with a coronary artery calcium score of zero

Abstract Introduction Coronary artery calcium (CAC) score of zero (so-called "power of zero") is associated with a very low rate of major adverse cardiac events (MACE), especially during short and midterm follow-up. However, a CAC score of zero does not definitively exclude the presence of atherosclerotic plaques or obstructive coronary artery disease (CAD). The composition of atherosclerotic plaques and the frequency of high-risk plaque features in this population are not well described. Purpose We sought to characterize the composition of atherosclerotic plaques and assess the frequency of high-risk plaque features on contrast-enhanced computed tomography (CT) images in patients with a zero CAC score. Methods The study enrolled patients with stable chest pain suspected of CAD referred for coronary CT imaging and having a CAC score of zero. Coronary CT angiography images were assessed by an expert reader to identify atherosclerotic plaques and high-risk plaque features in all coronary arteries with a diameter ≥1.5mm. The coronary artery lumen and plaques were manually segmented, and the degree of stenosis was evaluated following the Coronary Artery Disease Reporting and Data System (CAD-RADS) criteria. The presence of four high-risk plaque features was identified: positive remodeling, spotty calcification, low-attenuation plaque, and napkin ring sign. Total plaque volume, percent atheroma volume, and plaque composition were quantified using dedicated software (Figure 1). Results A total of 145 patients (mean age 54.2±12.1 years, 35.9% males) were included in the analysis. At least one coronary artery plaque was identified in 30 individuals (20.7%). 22 (15.2%), 7 (4.8%), and 1 (0.7%) patients were categorized into CAD-RADS 1, CAD-RADS 2, and CAD-RADS 3 categories, respectively. Among 30 patients with any coronary artery plaque, at least one high-risk feature was found in 10 individuals (33.3%), while 3 individuals (10.0%) had two features. Positive remodeling was found in 7 (23.3%), spotty calcification in 3 (10.0%), low-attenuation plaque in 3 (10.0%), and napkin ring sign in 0 patients, respectively (Figure 1). The mean total plaque volume was 48.2±54.3mm³, and the mean percent atheroma volume was 1.2±0.8%. Total plaque volume comprised low-attenuation (0.4%), fibro-fatty (58.9%), fibrous (39.4%), and calcified (1.3%) plaque volumes. Notably, in 3 (10.0%) individuals, the presence of calcified plaque was identified, which on non-contrast CT images did not meet the Agatston criteria for the CAC score. Conclusions Our study demonstrates a significant prevalence of atherosclerotic plaques and high-risk plaque features in patients with a CAC score of zero. Specifically, one in every five study participants had identifiable atherosclerotic plaque, with one in every three of those exhibiting one or more high-risk plaque features. The prognostic significance of these findings warrants further evaluation in studies with longitudinal follow-up.