The influence of the aortic valve angle on the hemodynamic features of the thoracic aorta

Abstract

Since the first observation of a helical flow pattern in aortic blood flow, the existence of helical blood flow has been found to be associated with various pathological conditions such as bicuspid aortic valve, aortic stenosis, and aortic dilatation. However, an understanding of the development of helical blood flow and its clinical implications are still lacking. In our present study, we hypothesized that the direction and angle of aortic inflow can influence helical flow patterns and related hemodynamic features in the thoracic aorta. Therefore, we investigated the hemodynamic features in the thoracic aorta and various aortic inflow angles using patient-specific vascular phantoms that were generated using a 3D printer and time-resolved, 3D, phase-contrast magnetic resonance imaging (PC-MRI). The results show that the rotational direction and strength of helical blood flow in the thoracic aorta largely vary according to the inflow direction of the aorta, and a higher helical velocity results in higher wall shear stress distributions. In addition, right-handed rotational flow conditions with higher rotational velocities imply a larger total kinetic energy than left-handed rotational flow conditions with lower rotational velocities.

Figure 1. Representative helical flow pattern in the ascending aorta.

R indicates the right direction.

Figure 2. Streamlined visualization of aortic flows with various directional aortic valves.

Note that the helical flow directions varied depending on the aortic valve flows. The straight, posterior, and right directions of the aortic valve flows resulted in right-handed rotations in the aorta, while the anterior and left directions of the aortic valve flows resulted in left-handed rotations in the aorta. A indicates anterior; L, left; R, right; H, head.

Figure 3. Helical rotations of various aortic valve flows.

(A) Development of rotational flows in the ascending aorta, (B) rotational velocity in the ascending aorta, (C) comparison of rotational velocity in the ascending aorta depending on the helical rotation directions, and (D) average rotational velocity of the whole aortic flow. Note that the black solid line in (A) is the centerline axis of the thoracic aorta. *Statistical difference (p < 0.01, Bonferroni corrected) in comparison with the rotational velocity of straight aortic valve flow. ^†Statistical difference (p < 0.01, Bonferroni corrected) in comparison with the rotational velocity in the same aortic flow direction, but at 15°. The error bar indicates the mean + SD. Only positive errors are shown for clarity.

Figure 4. Comparison of λ_ci for aortic flows with various aortic valve directions.

(A) Volumetric visualization of λ_ci and representative cross-sectional velocity fields at high λ_ci regions. Note that λ_ci indicates the local intensity of rotational flow. (B) Plot of the average λ_ci in the thoracic aorta. *Indicates statistical differences (p < 0.01, Bonferroni corrected) in comparison with the rotational velocity of the straight aortic valve flow. ^†Indicates statistical differences (p < 0.01, Bonferroni corrected) in comparison with the rotational velocity in the same aortic flow direction, but at 15°. The error bar indicates the mean ± SE. L indicates the left direction.

Figure 5. Effect of the aortic flow direction and angle on WSS in the thoracic aorta.

(A) Colormap of WSS, (B) comparison with the top 5% percentile of WSS, (C) comparison with the top 5% percentile of WSS depending on the rotational direction, and (D) comparison of the maximum WSS at the thoracic aorta. The black arrows in (A) indicate the region of WSS in the ascending aorta. *Statistical difference (p < 0.01, Bonferroni corrected) in comparison with WSS at straight aortic valve flow. ^†Statistical difference (p < 0.01, Bonferroni corrected) in comparison with WSS in the same aortic flow direction, but at 15°. The error bar indicates mean + SD. Only the positive error is shown for clarity. L and R indicate left and right, respectively.

Figure 6. Low WSS distribution in the thoracic aorta.

(A) Colormap of WSS where WSS is <0.1 Pa, (B) comparison with the bottom 5% percentile of WSS. The black arrows in (A) indicate regions of WSS with <0.1 Pa in the descending aorta. *Statistical difference (p < 0.01, Bonferroni corrected) in comparison with WSS at straight aortic valve flow. ^†Statistical difference (p < 0.01, Bonferroni corrected) in comparison with WSS at the same aortic flow direction, but at 15°. The error bar indicates the mean + SD. Only the positive error is shown for clarity. L and R indicate left and right, respectively.

Figure 7. Effect of the aortic valve direction and angle on the impinging pressure at the aorta.

(A) Principle and basic parameters for estimating impinging pressure, and (B) flow impinging patterns and corresponding impinging parameters at various aortic valve flows. The white dashed arrows in (B) indicate the directions of the aortic valve flows.

Figure 8. Effect of the aortic valve direction and angle on TKE distribution.

(A) Volume-rendering of TKE in the thoracic aorta, (B) comparison with the top 5% percentile of TKE, (C) effect of the aortic valve angle, and (D) effect of helical rotation. *Statistical difference (p < 0.01, Bonferroni corrected) in comparison with TKE at the straight aortic valve flow. ^†Statistical difference (p < 0.01, Bonferroni corrected) in comparison with TKE at the same aortic flow direction, but at 15°. The error bar indicates the mean + SD. Only the positive error is shown for clarity.

Figure 9. Distributions of MKE, TKE, and total KE at various angles and the directions of the aortic valve flows.

L and A indicate left and anterior, respectively.