Relationship of coronary artery plaque composition to coronary artery stenosis severity: Results from the prospective multicenter ACCURACY trial

Objectives: The purpose of this study was to determine the relationship of coronary artery plaque composition as detected by coronary computed tomographic angiography (CCTA) to luminal diameter stenosis severity quantified by quantitative coronary angiography (QCA) in individuals without known coronary artery disease (CAD) presenting with stable chest pain syndrome. Background: While CCTA has been previously evaluated for its ability to detect and exclude coronary artery stenosis, CCTA also permits assessment of other important plaque characteristics, including plaque composition. Identification of the relationship between plaque composition by CCTA and plaque severity by invasive angiography may provide valuable insight into the pathophysiology of coronary artery plaque. Methods: Patients enrolled in the ACCURACY trial, a 16-site multicenter study of patients with stable chest pain syndrome but without known CAD undergoing both CCTA and invasive coronary angiography (ICA), comprised the study population. CCTAs were scored on a per-segment basis for plaque composition and graded as non-calcified (>70% non-calcified), calcified (>70% calcified) or "mixed" (30-70% non-calcified or calcified) by concordance of ≥2 of 3 readers. CCTAs were also scored on a per-patient basis, and individuals were categorized as possessing primarily non-calcified plaques, primarily calcified plaques or primarily mixed plaques. Quantitative coronary angiography (QCA) was performed in all patients, used as the reference standard for stenosis severity, and interpreted blinded to patient characteristics and CCTA results. Results: 230 subjects comprised the study population (59.1% male, 57 ± 10 years). QCA was performed in all subjects following CCTA (mean inter-test interval 5.9 ± 4.3 days), and demonstrated obstructive CAD in 24.8% and 13.9% at the 50% and 70% stenosis severity threshold, respectively. On a per-segment based analysis, obstruction by QCA at both the 50% and 70% stenoses thresholds was more often for mixed composition plaques by CCTA (69.1% and 67.9%, respectively), as compared to non-calcified plaques (24.7% and 28.6%, respectively) and calcified plaques (6.1% and 3.6%, respectively) [p< 0.01 for comparisons]. On a per-patient basis, patients with mixed plaque or mixtures of plaque types more often exhibited obstructive coronary stenosis by QCA at the 50% level (39/96; 40.6%) compared to those with primarily non-calcified (12/43; 27.9%) or primarily calcified (4/29; 13.8%) plaques [p= 0.02]. Conclusions: In this multicenter trial of chest pain patients without known CAD, QCA-confirmed obstructive coronary stenosis was associated with mixed plaque composition by CCTA at both the per-segment and the per-patient levels. Coronary artery segments exhibiting calcified plaque were rarely associated with obstructive coronary stenosis.