Association of coronary artery calcium score with qualitatively and quantitatively assessed adverse plaque on coronary CT angiography in the SCOT-HEART trial

Introduction Coronary artery calcification is a marker of cardiovascular risk, but its association with qualitatively and quantitatively assessed plaque subtypes is unknown. Methods In this post-hoc analysis, CT images and 5-year clinical outcomes were assessed in SCOT-HEART trial participants. Agatston coronary artery calcium score (CACS) was measured on non-contrast CT and was stratified as zero (0 Agatston units, AU), minimal (1-9AU), low (10-99AU), moderate (100-399AU), high (400-999AU) and very high (1000AU). Adverse plaques were investigated by qualitative (visual categorization of positive remodeling, low-attenuation plaque, spotty calcification, napkin ring sign) and quantitative (calcified, non-calcified, low-attenuation and total plaque burden; Autoplaque) assessments. Results Of 1769 patients, 36% had a zero, 9% minimal, 20% low, 17% moderate, 10% high and 8% very high CACS. Amongst patients with a zero CACS, 14% had non-obstructive disease, 2% had obstructive disease, 2% had visually assessed adverse plaques and 13% had low-attenuation plaque burden >4%. Non-calcified and low-attenuation plaque burden increased between patients with zero, minimal and low CACS (p<0.001), but there was no statistically significant difference between those with medium, high and very high CACS. Myocardial infarction occurred in 41 patients, 10% of whom had zero CACS. CACS >1000AU and low-attenuation plaque burden were the only predictors of myocardial infarction, independent of obstructive disease and 10-year cardiovascular risk score. Conclusions In patients with stable chest pain, zero CACS is associated with a good but not perfect prognosis, and CACS cannot rule out obstructive coronary artery disease, non-obstructive plaque or adverse plaque phenotypes, including low-attenuation plaque.