Impact of left coronary artery bifurcation angle on computed tomography derived fractional flow reserve in normal coronary artery disease

Funding Acknowledgements Type of funding sources: None. Background Computed-tomography (CT) derived fractional-flow-reserve (FFRCT) decreases from the proximal to the distal part of vessel due to the influence of various factors. The energy loss due to the bifurcation angle may potentially contribute to a progressive FFRCT decline. However, the association of the bifurcation angle with FFRCT is still not entirely understood. Purpose This study aimed to investigate the impact of various bifurcation angles on FFRCT decline below the clinically crucial pathological value of 0.80 in normal coronary arteries. Methods A total of 83 consecutive patients who underwent both CT angiography including FFRCT and invasive coronary angiography, resulting in normal coronary arteries were evaluated. ΔFFRCT was defined as the magnitude of the change in FFRCT from the proximal to the distal vessel in the left anterior descending (LAD) and left circumflex (LCX). Both LAD angle and LCX bifurcation angle were measured as the crossing angle between the centrelines of the left main trunk and each coronary artery (LAD or LCX) on the 3-dimensional volume rendered image of the coronary artery tree (Figure 1). Vessel length, lumen volume, non-calcified plaque volume, and calcified plaque volume were assessed. Results Bifurcation angle was significantly lower in LAD angle (LAD angle, 31.1 ± 6.6°; LCX angle, 42.8 ± 14.9°, p < 0.0001). FFRCT showed a continuous gradual decline from the proximal to the distal in both LAD (from 0.95 ± 0.03 to 0.81 ± 0.06) and LCX (from 0.96 ± 0.03 to 0.88 ± 0.06). ΔFFRCT was significantly greater in LAD angle (LAD angle, 0.13 ± 0.06; LCX angle, 0.08 ± 0.05, p < 0.0001) ΔFFRCT was significantly correlated with each bifurcation angle (LAD angle, r = 0.35, p = 0.001; LCX angle, r = 0.26, p = 0.02) and vessel length (LAD angle, r = 0.30, p = 0.005; LCX angle, r = 0.49, p < 0.0001) (Figure 2A). In LAD, vessel length was the strongest predictor for distal FFRCT of ≤ 0.80 (β-coefficient = 0.56, p = 0.0002), immediately followed by the bifurcation angle (β-coefficient = 0.24, p = 0.02). The bifurcation angle was a good predictor for a distal FFRCT ≤ 0.80 (LAD angle, cut-off 31.0°, AUC 0.70, 95% CI 0.58–0.83, sensitivity 74%, specificity 68%; LCX angle, cut-off 52.6°, AUC 0.86, 95% CI 0.76–0.96, sensitivity 88%, specificity 85%) (Figure 2B). Conclusions The change in FFRCT depended on the bifurcation angle. In normal coronary arteries, vessel length was the most influential factor on FFRCT, immediately followed by the bifurcation angle.