Atherosclerotic plaque characteristics by CT angiography identify coronary lesions that cause ischemia: a direct comparison to fractional flow reserve

Abstract

Objectives: This study evaluated the association between atherosclerotic plaque characteristics (APCs) by coronary computed tomographic angiography (CTA), and lesion ischemia by fractional flow reserve (FFR).

Background: FFR is the gold standard for determining lesion ischemia. Although APCs by CTA-including aggregate plaque volume % (%APV), positive remodeling (PR), low attenuation plaque (LAP), and spotty calcification (SC)-are associated with future coronary syndromes, their relationship to lesion ischemia is unclear.

Methods: 252 patients (17 centers, 5 countries; mean age 63 years; 71% males) underwent coronary CTA, with FFR performed for 407 coronary lesions. Coronary CTA was interpreted for <50% and ≥50% stenosis, with the latter considered obstructive. APCs by coronary CTA were defined as: 1) PR, lesion diameter/reference diameter >1.10; 2) LAP, any voxel <30 Hounsfield units; and 3) SC, nodular calcified plaque <3 mm. Odds ratios (OR) and net reclassification improvement of APCs for lesion ischemia, defined by FFR ≤0.8, were analyzed.

Results: By FFR, ischemia was present in 151 lesions (37%). %APV was associated with a 50% increased risk of ischemia per 5% additional APV. PR, LAP, and SC were associated with ischemia, with a 3 to 5 times higher prevalence than in nonischemic lesions. In multivariable analyses, a stepwise increased risk of ischemia was observed for 1 (OR: 4.0, p < 0.001) and ≥2 (OR: 12.1, p < 0.001) APCs. These findings were APC dependent, with PR (OR: 5.3, p < 0.001) and LAP (OR: 2.1, p = 0.038) associated with ischemia, but not SC. When examined by stenosis severity, PR remained a predictor of ischemia for all lesions, whereas %APV and LAP were associated with ischemia for only ≥50%, but not for <50%, stenosis.

Conclusions: %APV and APCs by coronary CTA improve identification of coronary lesions that cause ischemia. PR is associated with all ischemia-causing lesions, whereas %APV and LAP are only associated with ischemia-causing lesions ≥50%. (Determination of Fractional Flow Reserve by Anatomic Computed Tomographic Angiography; NCT01233518).

Keywords: coronary artery disease; coronary computed tomography angiography; coronary plaque; fractional flow reserve; myocardial ischemia.

Figure 1. Global chi-square values

Incremental risk prediction beyond CT stenosis ≥50% when adding spotty calcification (SC); SC and low attenuation plaque (LAP); and SC, PR and positive arterial remodeling (PR).

Figure 2. AUC for detecting FFR

AUC values gradually improving up to 0.79 (AS+%APV, p<0.001), and 0.86 (AS+%APV+APCs, p<0.001) respectively when %APV and APCs combined serially into AS. AUC = Area under the receiver operating curves, FFR = fractional flow reserve, AS = lumen area stenosis (%), %APV = percent aggregate plaque volume, APCs = atherosclerotic plaque characteristics.

Figure 3. Non-obstructive coronary stenosis causing ischemia

(A) Arterial segment demonstrating no luminal compromise but significant atherosclerosis. (B) Multiplanar reformat demonstrating positive remodeling and spotty calcification. (C) CT cross section demonstrating low attenuation plaque [22 Hounsfield Units (HU)]. (D) Corresponding invasive angiogram demonstrating a 36% stenosis in the left anterior descending artery. The FFR value was 0.76 indicating ischemia. FFR = fractional flow reserve, QCA = quantitative coronary angiography.

Figure 4. Obstructive coronary stenosis does not cause ischemia

(A) Arterial segment demonstrating significant luminal compromise. (B) Multiplanar reformat demonstrating no positive remodeling (remodeling index 1.08) and no spotty calcification. (C) CT cross section demonstrating no low attenuation plaque (>30 HU). (D) Corresponding invasive angiogram demonstrating a 70% stenosis in obtuse marginal branch of the circumflex artery. The FFR value was 0.89 indicating no ischemia. Abbreviations as in Figure 3.