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. 2022 Jan;15(1):33-42.
doi: 10.1016/j.jcmg.2021.06.020. Epub 2021 Aug 18.

Association of Regional Wall Shear Stress and Progressive Ascending Aorta Dilation in Bicuspid Aortic Valve

Gilles Soulat  1 , Michael B Scott  2 , Bradley D Allen  1 , Ryan Avery  1 , Robert O Bonow  3 , S Chris Malaisrie  4 , Patrick McCarthy  4 , Paul W M Fedak  5 , Alex J Barker  6 , Michael Markl  7
Affiliations

Association of Regional Wall Shear Stress and Progressive Ascending Aorta Dilation in Bicuspid Aortic Valve

Gilles Soulat et al. JACC Cardiovasc Imaging. 2022 Jan.

Abstract

Objectives: The aim of this study was to evaluate the role of wall shear stress (WSS) as a predictor of ascending aorta (AAo) growth at 5 years or greater follow-up.

Background: Aortic 4-dimensional flow cardiac magnetic resonance (CMR) can quantify regions exposed to high WSS, a known stimulus for arterial wall dysfunction. However, its association with longitudinal changes in aortic dilation in patients with bicuspid aortic valve (BAV) is unknown.

Methods: This retrospective study identified 72 patients with BAV (age 45 ± 12 years) who underwent CMR for surveillance of aortic dilation at baseline and ≥5 years of follow-up. Four-dimensional flow CMR analysis included the calculation of WSS heat maps to compare regional WSS in individual patients with population averages of healthy age- and sex-matched subjects (database of 136 controls). The relative areas of the AAo and aorta (in %) exposed to elevated WSS (outside the 95% CI of healthy population averages) were quantified.

Results: At a median follow-up duration of 6.0 years, the mean AAo growth rate was 0.24 ± 0.20 mm/y. The fraction of the AAo exposed to elevated WSS at baseline was increased for patients with higher growth rates (>0.24 mm/y, n = 32) compared with those with growth rates <0.24 mm/y (19.9% [IQR: 10.2%-25.5%] vs 5.7% [IQR: 1.5%-21.3%]; P = 0.008). Larger areas of elevated WSS in the AAo and entire aorta were associated with higher rates of AAo dilation >0.24 mm/y (odds ratio: 1.51; 95% CI: 1.05-2.17; P = 0.026 and odds ratio: 1.70; 95% CI: 1.01-3.15; P = 0.046, respectively).

Conclusions: The area of elevated AAo WSS as assessed by 4-dimensional flow CMR identified BAV patients with higher rates of aortic dilation and thus might determine which patients require closer follow-up.

Keywords: 4-dimensional flow; aortic dilation; bicuspid aortic valve; wall shear stress.

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Conflict of interest statement

Funding Support and Author Disclosures Funding was provided by National Institutes of Health (grant nos. R01HL115828, R01HL133504, and F30HL145995). Dr Soulat received a grant support from the French College of Radiology Teachers and French Radiology Society. Additional support was provided by the Melman Bicuspid Aortic Valve Program, Bluhm Cardiovascular Institute. Dr Malaisrie has received honoraria and a research grant from Terumo Aortic. Dr McCarthy has received royalties and honoraria for speaking for Edwards Lifesciences. Dr Markl has received research support from Siemens Healthineers; a research grant and consulting fees from Circle Cardiovascular Imaging; and a research grant from Cryolife Inc. All other authors have reported that they have no relationships relevant to the contents of this paper to disclose.

Figures

Figure 1:
Figure 1:. WSS heatmaps and relative area of elevated WSS.
Left: For each patient, 4D flow data (top) were analyzed to calculate peak systolic 3D WSS mapped onto the 3D segmentation of the aorta (middle). Right: Peak systolic 3D aortic WSS was calculated for ≥10 healthy controls within 5 years of the target patient age to obtain a normal age and sex matched population average. Bottom: A patient specific WSS heatmap of the patient aorta was computed relative to a map of the population average. WSS regions outside the healthy 95% confidence intervals were classified as abnormal and mapped onto 3D visualizations of the patient-specific aorta (red = elevated, blue = reduced, gray = normal).
Figure 2:
Figure 2:. Regionally elevated WSS in patients with fast vs. slow rates of aortic dilation.
Aorta WSS heatmap examples for 2 patients, arranged by rate of aortic dilation (fast vs. slow, defined as greater or less than 0.24 mm/year, respectively). Each panel represents right anterior and left posterior views of the patient specific WSS heatmap illustrating abnormal WSS relative to individually age and sex matched WSS population averages. On the left: BAV patient with a slow rate of aortic dilation exhibiting mostly normal aortic WSS. On the right: BAV patient a high rate of aortic dilation demonstrating clearly visible areas of elevated WSS.
Figure 3:
Figure 3:. Incidence of elevated WSS in patients with high vs. low rates of aortic dilation
Histograms of the relative area of elevated WSS in the ascending aorta (AAo, left) and the entire thoracic aorta (right) for n=40 patients with lower rates of AAo growth <0.24mm/year (blue bars) compared to n=32 patients with higher rates of progressive AAo dilation >0.24mm/year (red bars).
CENTRAL ILLUSTRATION:
CENTRAL ILLUSTRATION:. Elevated WSS secondary to altered aortic flow is associated with higher rates of progressive dilation of the ascending aorta.
Top left: example of abnormal aortic flow patterns in the ascending aorta visualized using 4D flow MRI derived systolic 3D streamlines (higher velocities appear in red). Top right: WSS heatmap from the same patient, obtained using an age/gender matched population average of healthy volunteers showing areas of abnormally elevated WSS in red (outside the 95% confidence interval of the age/gender matched control population). Bottom: Histogram of the relative areas of elevated WSS in the ascending aorta for n=40 patients with low rates of aortic growth <0.24mm/year (blue bars) compared to n=32 patients with higher rates of progressive aortic dilation >0.24mm/year (red bars).
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Comment in

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