Hemodynamic Abnormalities in the Aorta of Turner Syndrome Girls

Abstract

Congenital abnormalities in girls and women with Turner syndrome (TS), alongside an underlying predisposition to obesity and hypertension, contribute to an increased risk of cardiovascular disease and ultimately reduced life expectancy. We observe that children with TS present a greater variance in aortic arch morphology than their healthy counterparts, and hypothesize that their hemodynamics is also different. In this study, computational fluid dynamic (CFD) simulations were performed for four TS girls, and three age-matched healthy girls, using patient-specific inlet boundary conditions, obtained from phase-contrast MRI data. The visualization of multidirectional blood flow revealed an increase in vortical flow in the arch, supra-aortic vessels, and descending aorta, and a correlation between the presence of aortic abnormalities and disturbed flow. Compared to the relatively homogeneous pattern of time-averaged wall shear stress (TAWSS) on the healthy aortae, a highly heterogeneous distribution with elevated TAWSS values was observed in the TS geometries. Visualization of further shear stress parameters, such as oscillatory shear index (OSI), normalized relative residence time (RRTn), and transverse WSS (transWSS), revealed dissimilar heterogeneity in the oscillatory and multidirectional nature of the aortic flow. Taking into account the young age of our TS cohort (average age 13 ± 2 years) and their obesity level (75% were obese or overweight), which is believed to accelerate the initiation and progression of endothelial dysfunction, these findings may be an indication of atherosclerotic disease manifesting earlier in life in TS patients. Age, obesity and aortic morphology may, therefore, play a key role in assessing cardiovascular risk in TS children.

Keywords: Turner syndrome; atherosclerosis; cardiovascular disease; computational fluid dynamics; disturbed flow; hemodynamics; patient-specific; pediatric medicine.

Figure 1

Anterior view of the reconstructed aortic models from the (H1-H3) healthy and (TS1-TS4) Turner syndrome (TS) girls. RSA, Right subclavian artery; RCCA, right common carotid artery; LCCA, left common carotid artery; LSA, left subclavian artery. Inset: Superior view of TS3 to highlight the origin of the aberrant RSA. Geometries are in scale.

Figure 2

STAR-CCM+ polyhedral mesh shown on a healthy (H1) model with zoomed views of the inlet mesh with a prism boundary layer (left) and the arch surface mesh (right).

Figure 3

PC-MRI derived (A) volumetric flow rate and (B) normalized waveforms at the aortic root during one cardiac cycle for healthy (H) and Turner syndrome (TS) girls. Insets: average data calculated from H1-H3 (black line) and TS1-TS4 (red line). Flow rate and time normalized by the mean flow rate and cardiac cycle period (see Table 2 for values).

Figure 4

Velocity streamlines in the aortic arch of the healthy (H1-H3) and Turner syndrome (TS1-TS4) girls at (A) peak velocity (t₁), (B) maximum deceleration (t₂), and (C) mid-diastole (t₃), colored by non-dimensional velocity magnitude that is normalized according to the average inlet velocity (U_mean), derived from patient PC-MRI data (anterior view). Note that the color legends in (B) and (C) were shifted compared to (A) to enhance visualization. For interpretation of the colored legends, please refer to the online version of the paper.

Figure 5

(Left) Through-plane velocity profiles and (Right) contours of through-plane velocity overlayed by vectors of in-plane velocity on seven cross-sections α-α′ to η-η′ along the aorta [locations shown on the 3D healthy (H1) model]. Contours colored by non-dimensional axial velocity at peak velocity for the healthy (H1–H3) and Turner syndrome (TS1–TS4) girls. Cross-sections are oriented looking downstream, with the top and bottom edges corresponding to the anterior and posterior sides of the aorta, respectively, and the left and right points as shown on the left. Cross-sections are not to scale.

Figure 6

(A,B) Instantaneous normalized wall shear stress (WSS_n), and (C) normalized time-averaged wall shear stress (TAWSS_n) distributions shown (anterior view) for the (H1-H3) healthy, and (TS1-T4) Turner syndrome cases. (A) Peak systole and (B) maximum deceleration. WSS and TAWSS were normalized with respect to the mean WSS at the inlet for each individual case.

Figure 7

(A) Oscillatory shear index (OSI), (B) normalized relative residence time (RRTn), based on the surface integral average for each individual case, and (C) transverse wall shear stress (transWSS) distributions shown (anterior view) for the (H1-H3) healthy and (TS1-T4) Turner syndrome cases.

Figure 8

Normalized time-averaged wall shear stress (TAWSS_n) values at seven cross-sections along the aorta of the healthy (black, dotted lines, as average of H1–H3) and Turner syndrome girls (red, solid lines, as average of TS1–TS4). Cross-sections are located as shown on the 3D model of a healthy (H1) case. Standard deviation shown as error bars at each point.