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) 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 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 in NOCAD in the right coronary artery (RCA).

Methods: A total of 443 patients who underwent both FFR and invasive coronary angiography, with < 50% RCA stenosis, were evaluated. Enrolled RCA vessels were classified into two groups according to distal FFR: FFR ≤ 0.80 (n = 60) and FFR > 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 ≤ 0.80 and > 0.80, lumen volume and V/L ratio were significantly lower in FFR ≤ 0.80. Distal FFR 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 (r = 0.61, p < 0.0001). Multivariable analysis showed that calcified plaque volume was the strongest predictor of distal FFR, followed by V/L ratio (β-coefficient = 0.48, p = 0.03). V/L ratio was the strongest predictor of a distal FFR ≤ 0.80 (cut-off 8.1 mm/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) and may have the potential to improve the diagnostic accuracy of FFR.

Key Points: • Physiological FFR 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 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 and an optimal cut-off value of 8.1 mm/mm.