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.