Impact of vessel morphology on CT-derived fractional-flow-reserve in non-obstructive coronary artery disease in right coronary artery

Objectives Computed tomography (CT)–derived fractional flow reserve (FFR CT ) decreases continuously from proximal to distal segments of the vessel due to the influence of various factors even in non-obstructive coronary artery disease (NOCAD). It is known that FFR CT is dependent on vessel-length, but the relationship with other vessel morphologies remains to be explained. Purpose To investigate morphological aspects of the vessels that influence FFR CT in NOCAD in the right coronary artery (RCA). Methods A total of 443 patients who underwent both FFR CT and invasive coronary angiography, with < 50% RCA stenosis, were evaluated. Enrolled RCA vessels were classified into two groups according to distal FFR CT : FFR CT ≤ 0.80 ( n = 60) and FFR CT > 0.80 ( n = 383). Vessel morphology (vessel length, lumen diameter, lumen volume, and plaque volume) and left-ventricular mass were assessed. The ratio of lumen volume and vessel length was defined as V/L ratio. Results Whereas vessel-length was almost the same between FFR CT ≤ 0.80 and > 0.80, lumen volume and V/L ratio were significantly lower in FFR CT ≤ 0.80. Distal FFR CT correlated with plaque-related parameters (low-attenuation plaque, intermediate-attenuation plaque, and calcified plaque) and vessel-related parameters (proximal and distal vessel diameter, vessel length, lumen volume, and V/L ratio). Among all vessel-related parameters, V/L ratio showed the highest correlation with distal FFR CT ( r = 0.61, p < 0.0001). Multivariable analysis showed that calcified plaque volume was the strongest predictor of distal FFR CT , followed by V/L ratio (β-coefficient = 0.48, p = 0.03). V/L ratio was the strongest predictor of a distal FFR CT ≤ 0.80 (cut-off 8.1 mm 3 /mm, AUC 0.88, sensitivity 90.0%, specificity 76.7%, 95% CI 0.84–0.93, p < 0.0001). Conclusions Our study suggests that V/L ratio can be a measure to predict subclinical coronary perfusion disturbance. Clinical relevance statement A novel marker of the ratio of lumen volume to vessel length (V/L ratio) is the strongest predictor of a distal CT-derived fractional flow reserve (FFR CT ) and may have the potential to improve the diagnostic accuracy of FFR CT . Key Points • Physiological FFR CT decline depends not only on vessel length but also on the lumen volume in non-obstructive coronary artery disease in the right coronary artery. • FFR CT correlates with plaque-related parameters (low-attenuation plaque, intermediate-attenuation plaque, and calcified plaque) and vessel-related parameters (proximal and distal vessel diameter, vessel length, lumen volume, and V/L ratio). • Of vessel-related parameters, V/L ratio is the strongest predictor of a distal FFR CT and an optimal cut-off value of 8.1 mm 3 /mm.