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. 2018 Dec;156(6):2112-2120.e2.
doi: 10.1016/j.jtcvs.2018.05.095. Epub 2018 Jun 12.

Aortic valve-mediated wall shear stress is heterogeneous and predicts regional aortic elastic fiber thinning in bicuspid aortic valve-associated aortopathy

Emilie Bollache  1 , David G Guzzardi  2 , Samaneh Sattari  3 , Katherine E Olsen  3 , Elena S Di Martino  4 , S Chris Malaisrie  5 , Pim van Ooij  6 , Jeremy Collins  1 , James Carr  1 , Patrick M McCarthy  5 , Michael Markl  7 , Alex J Barker  1 , Paul W M Fedak  8
Affiliations

Aortic valve-mediated wall shear stress is heterogeneous and predicts regional aortic elastic fiber thinning in bicuspid aortic valve-associated aortopathy

Emilie Bollache et al. J Thorac Cardiovasc Surg. 2018 Dec.

Abstract

Objectives: The objectives of this study were to investigate an association between the magnitude of flow-mediated aortic wall shear stress (WSS) and medial wall histopathology in patients with bicuspid aortic valve (BAV) with aortopathy.

Methods: Patients with BAV (n = 27; 52 ± 15 years; 3 women; proximal thoracic aorta diameter = 4.4 ± 0.7 and 4.6 ± 0.5 cm) who underwent prophylactic aortic resection received preoperative 3-dimensional time-resolved phase-contrast magnetic resonance imaging with 3-dimensional velocity encoding to quantify WSS relative to a population of healthy age- and sex-matched tricuspid aortic valve control participants (n = 20). Quantitative histopathology was conducted on BAV aorta tissue samples resected at surgery (n = 93), and correlation was performed between elastic fiber thickness and in vivo aortic WSS as continuous variables. Validation of elastic fiber thickness was achieved by correlation relative to tissue stiffness determined using biaxial biomechanical testing (n = 22 samples).

Results: Elastic fibers were thinner and WSS was higher along the greater curvature compared with other circumferential regions (vs anterior wall: P = .003 and P = .0001, respectively; lesser curvature: both P = .001). Increased regional WSS was associated with decreased elastic fiber thickness (r = -0.25; P = .02). Patient stratification with subanalysis showed an increase in the correlation between WSS and histopathology with aortic valve stenosis (r = -0.36; P = .002) and smaller aortic diameters (<4.5 cm: r = -0.39; P = .03). Elastic fiber thinning was associated with circumferential stiffness (r = -0.41; P = .06).

Conclusions: For patients with BAV, increased aortic valve-mediated WSS is significantly associated with elastic fiber thinning, particularly with aortic valve stenosis and in earlier stages of aortopathy. Elastic fiber thinning correlates with impaired tissue biomechanics. These novel findings further implicate valve-mediated hemodynamics in the progression of BAV aortopathy.

Keywords: 4D flow MRI; aortopathy; bicuspid aortic valve; wall shear stress.

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Conflict of interest statement

Conflict of interest statement

The authors have no conflict of interest to disclose.

Figures

Figure 1
Figure 1
Example of 4D flow MRI-derived aortic wall shear stress map in a BAV patient and definition of aortic regions of interest matching resected tissue sample location. a) Two longitudinal zones were defined as the proximal (AAprox) and distal (AAdist) ascending aorta, using anatomical landmarks from magnitude images (details in text). b) Circumferential regions (A: anterior; P: posterior: GC: greater and LC: lesser curvature) were defined using the sagittal, coronal and axial views.
Figure 2
Figure 2
Aortic elastic fiber thickness assessed using histology in BAV patients according to the circumferential location, while pooling the proximal and distal ascending aorta (A: anterior; P: posterior: GC: greater and LC: lesser curvature). Columns illustrate median values while error bars indicate interquartile ranges. *: p<0.05 for comparison against A; ‡: against LC.
Figure 3
Figure 3
Aortic wall shear stress (WSS) assessed using 4D flow MRI in BAV patients (blue) and healthy volunteers (grey) according to the circumferential location, while pooling the proximal and distal ascending aorta (A: anterior; P: posterior: GC: greater and LC: lesser curvature). Columns illustrate median values while error bars indicate interquartile ranges. Hashed regions: p<0.05 against BAV patients. *: p<0.05 for comparison against A; ‡: against LC, within each group.
Figure 4
Figure 4
Correlations for comparison between aortic elastic fiber thickness and wall shear stress (WSS): a) over all patients and all locations (A: anterior; P: posterior: GC: greater and LC: lesser curvature); b) in patients with aortic valve stenosis (AS, squares); c) in longitudinal ascending aortic locations with a diameter <4.5 cm (circles). Correlation coefficients r, p-values and lines of best fit are provided.
Figure 5
Figure 5
Correlations for comparison between aortic elastic fiber thickness and circumferential maximum tangential stiffness (MTS). Correlation coefficient r, p-values and line of best fit are provided.
Figure 6
Figure 6. Central picture
In vivo wall shear stress correlates with local elastic fiber thinning in the BAV aorta.
See this image and copyright information in PMC

Comment in

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