Impact of coronary bifurcation angle on computed tomography derived fractional flow reserve in coronary vessels with no apparent coronary artery disease

Computed tomography (CT) derived fractional flow reserve (FFR${}_{CT}$) decreases from the proximal to the distal part due to a variety of factors. The energy loss due to the bifurcation angle may potentially contribute to a progressive decline in FFR${}_{CT}$. However, the association of the bifurcation angle with FFR${}_{CT}$ is still not entirely understood. This study aimed to investigate the impact of various bifurcation angles on FFR${}_{CT}$ decline below the clinically crucial relevance of 0.80 in vessels with no apparent coronary artery disease (CAD). A total of 83 patients who underwent both CT angiography including FFR${}_{CT}$ and invasive coronary angiography, exhibiting no apparent CAD were evaluated. ΔFFR${}_{CT}$ was defined as the change in FFR${}_{CT}$ from the proximal to the distal in the left anterior descending artery (LAD) and left circumflex artery (LCX). The bifurcation angle was calculated from three-dimensional volume rendered images. Vessel morphology and plaque characteristics were also assessed. ΔFFR${}_{CT}$ significantly correlated with the 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). In LAD, vessel length was the strongest predictor for distal FFR${}_{CT}$ of ≤ 0.80 (β-coefficient = 0.55, p = 0.0003), immediately followed by the bifurcation angle (β-coefficient = 0.24, p = 0.02). The bifurcation angle was a good predictor for a distal FFR${}_{CT}$ ≤ 0.80 (LAD angle, cut-off 31.0°, AUC 0.70, sensitivity 74%, specificity 68%; LCX angle, cut-off 52.6°, AUC 0.86, sensitivity 88%, specificity 85%). In vessels with no apparent CAD, vessel length was the most influential factor on FFR${}_{CT}$, directly followed by the bifurcation angle. Both LAD and LCX bifurcation angles are factors influencing FFR${}_{CT}$. Bifurcation angle is one of the predictors of a distal FFR${}_{CT}$ of ≤ 0.80 and an optimal cut-off value of 31.0° for the LAD and 52.6° for the LCX. Bifurcation angle should be taken into consideration when interpreting numerical values of FFR${}_{CT}$.