Non obstructive high-risk plaque but not calcified by coronary CTA, and the G-score predict ischemia.

BACKGROUND: The association of plaque morphology with ischemia in non-obstructive lesions has not been fully eludicated: Calcium density and high-risk plaque features have not been explored.

OBJECTIVES: to assess whether high-risk plaque or calcified, and global mixed including non-calcified plaque burden (G-score) by coronary CTA predict ischemia in non-obstructive lesions using non-invasive fractional flow reserve (FFRCT ).

METHODS: In 106 patients with low-to-intermediate pre-test probability referred to coronary 128-slice dual source CTA, lesion-based and distal FFRCT were computated. The 4 high-risk-plaque criteria: Low-attenuation-plaque, Napkin Ring Sign, positive remodelling and spotty calcification were recorded. Plaque density (HU) and stenosis (MLA,MLD,%area,%diameter stenosis) were quantified. Plaque composition was classified as type 1-4:1 = calcified, 2 = mixed (calcified > non-calcified), 3 = mixed (non-calcified > calcified), 4 = non-calcified, and expressed by the G-score: Z = Sum of type 1-4 per segment. The total plaque segment involvement score (SIS) and the Coronary Calcium Score (Agatston) were calculated.

RESULTS: 89 non-obstructive lesions were included. Both lesion-based and distal FFRCT were lower in high-risk-plaque as compared to calcified (0.85 vs 0.93, p < 0.001 and 0.79 vs 0.86, p = 0.002). The prevalence of lesion-based ischemia (FFRCT <0.8) was higher in high-risk-plaque as compared to calcified (25% vs. 2.5%, p = 0.007). Similarly, the rate of distal ischemia (40% vs 17.5%) was higher, respectively. Lower plaque density (HU) indicating higher lipid plaque component (p = 0.024) predicted lesion based FFRCT in low attenuation plaque. For all lesions (n = 89) including calcified (p = 0.003), the correlation enhanced. Positive remodelling and an increasing non-calcified plaque burden (G-score) in relation to calcified were associated with lower FFRCT distal (p = 0.042), but not the SIS and calcium score.

CONCLUSION: High-risk-plaque but not calcified, an increasing lipid-necrotic-core component and non-calcified mixed plaque burden (G-score) predict ischemia in non-obstructive lesions (INOCA), while an increasing calcium compactness acts contrary.