Coronary plaque quantification and fractional flow reserve by coronary computed tomography angiography identify ischaemia-causing lesions

Abstract

Aims: Coronary plaque characteristics are associated with ischaemia. Differences in plaque volumes and composition may explain the discordance between coronary stenosis severity and ischaemia. We evaluated the association between coronary stenosis severity, plaque characteristics, coronary computed tomography angiography (CTA)-derived fractional flow reserve (FFRCT), and lesion-specific ischaemia identified by FFR in a substudy of the NXT trial (Analysis of Coronary Blood Flow Using CT Angiography: Next Steps).

Methods and results: Coronary CTA stenosis, plaque volumes, FFRCT, and FFR were assessed in 484 vessels from 254 patients. Stenosis >50% was considered obstructive. Plaque volumes (non-calcified plaque [NCP], low-density NCP [LD-NCP], and calcified plaque [CP]) were quantified using semi-automated software. Optimal thresholds of quantitative plaque variables were defined by area under the receiver-operating characteristics curve (AUC) analysis. Ischaemia was defined by FFR or FFRCT ≤0.80. Plaque volumes were inversely related to FFR irrespective of stenosis severity. Relative risk (95% confidence interval) for prediction of ischaemia for stenosis >50%, NCP ≥185 mm(3), LD-NCP ≥30 mm(3), CP ≥9 mm(3), and FFRCT ≤0.80 were 5.0 (3.0-8.3), 3.7 (2.4-5.6), 4.6 (2.9-7.4), 1.4 (1.0-2.0), and 13.6 (8.4-21.9), respectively. Low-density NCP predicted ischaemia independent of other plaque characteristics. Low-density NCP and FFRCT yielded diagnostic improvement over stenosis assessment with AUCs increasing from 0.71 by stenosis >50% to 0.79 and 0.90 when adding LD-NCP ≥30 mm(3) and LD-NCP ≥30 mm(3) + FFRCT ≤0.80, respectively.

Conclusion: Stenosis severity, plaque characteristics, and FFRCT predict lesion-specific ischaemia. Plaque assessment and FFRCT provide improved discrimination of ischaemia compared with stenosis assessment alone.

Keywords: Computational fluid dynamics; Computed tomography angiography; Coronary plaque; Fractional flow reserve; Ischaemia.

Figure 1

Case example. (A) Multiplanar reconstruction showing 50–70% stenosis (red arrow) in the left anterior descending artery. (B) Plaque analysis of the proximal portion of left anterior descending artery: non-calcified plaque 201 mm³ (red plus orange), low-density non-calcified plaque 35 mm³ (orange), and calcified plaque 41 mm³ (yellow). Total per-vessel plaque volumes: non-calcified plaque 454 mm³, low-density non-calcified plaque 85 mm³, and calcified plaque 50 mm³. (C) Fractional flow reserve derived from coronary computed tomography angiography in the distal left anterior descending artery was 0.75. (D) Invasive coronary angiogram with a 60% stenosis in the proximal portion of left anterior descending artery (red arrow). Measured fractional flow reserve was 0.71.

Figure 2

Distribution of coronary stenosis severity in relation to fractional flow reserve. N = 484 vessels. Values shown are percentages within the fractional flow reserve groups, P < 0.001 for <30% stenosis, 51–70% stenosis, and >70% stenosis and P = 0.006 for the 30–50% stenosis category.

Figure 3

Distribution of coronary plaque volumes (A + C) and fractional flow reserve derived from coronary computed tomography angiography values (B + D) in relation to fractional flow reserve. N = 484 vessels. Values shown are medians (interquartile range).

Figure 4

AUCs for discrimination of fractional flow reserve ≤0.80. AUC, area under the receiver-operating characteristics curve; CI, confidence interval; CTA, stenosis severity by coronary CTA; FFR_CT, fractional flow reserve derived from coronary computed tomography angiography; LD-NCP, low-density non-calcified plaque.