Wall Shear Stress Directional Abnormalities in BAV Aortas: Toward a New Hemodynamic Predictor of Aortopathy?

Abstract

The bicuspid aortic valve (BAV) generates wall shear stress (WSS) abnormalities in the ascending aorta (AA) that may be responsible for the high prevalence of aortopathy in BAV patients. While previous studies have analyzed the magnitude and oscillatory characteristics of the total or streamwise WSS in BAV AAs, the assessment of the circumferential component is lacking despite its expected significance in this highly helical flow environment. This gap may have hampered the identification of a robust hemodynamic predictor of BAV aortopathy. The objective of this study was to perform a global and component-specific assessment of WSS magnitude, oscillatory and directional characteristics in BAV AAs. The WSS environments were computed in the proximal and middle convexity of tricuspid aortic valve (TAV) and BAV AAs using our previous valve-aorta fluid-structure interaction (FSI) models. Component-specific WSS characteristics were investigated in terms of temporal shear magnitude (TSM) and oscillatory shear index (OSI). WSS directionality was quantified in terms of mean WSS vector magnitude and angle, and angular dispersion index (Dα). Local WSS magnitude and multidirectionality were captured in a new shear magnitude and directionality index (SMDI) calculated as the product of the mean WSS magnitude and Dα. BAVs subjected the AA to circumferential TSM overloads (2.4-fold increase vs. TAV). TAV and BAV AAs exhibited a unidirectional circumferential WSS (OSI < 0.04) and an increasingly unidirectional longitudinal WSS between the proximal (OSI > 0.21) and middle (OSI < 0.07) sections. BAVs generated mean WSS vectors skewed toward the anterior wall and WSS angular distributions exhibiting decreased uniformity in the proximal AA (0.27-point increase in Dα vs. TAV). SMDI was elevated in all BAV AAs but peaked in the proximal LR-BAV AA (3.6-fold increase vs. TAV) and in the middle RN-BAV AA (1.6-fold increase vs. TAV). This analysis demonstrates the significance of the circumferential WSS component and the existence of substantial WSS directional abnormalities in BAV AAs. SMDI abnormality distributions in BAV AAs follow the morphotype-dependent occurrence of dilation in BAV AAs, suggesting the predictive potential of this metric for BAV aortopathy.

Aortic Wall Elastic Properties in Case of Bicuspid Aortic Valve

“…The pathophysiological process leading to the medial layer remodeling in the case of BAV is poorly understood. Two assumptions have been formulated and are not necessarily conflicting: on the one hand, a constitutive aortic wall alteration due to genetic predisposition, on the other hand an acquired aortic wall alteration due to the modified amplitude and direction of the flow wall shear stress, generated by the BAV (Girdauskas et al, 2011; Sievers and Sievers, 2011; Piatti et al, 2017; Liu et al, 2018). The presence of matrix degeneration is thus emphasized in areas with high shear stress (Gore and Seiwert, 1952; Gosline et al, 2002).…”

Wall Shear Stress Directional Abnormalities in BAV Aortas: Toward a New Hemodynamic Predictor of Aortopathy?

“…A correlation was further observed between the distal ascending aorta diameter in BAV patients with fusion of the right and non-coronary cusps (RN-BAV) but not in BAV patients with fusion of the right and left coronary cusps (RL-BAV) (Youssefi et al, 2017 ; Raghav et al, 2018 ). Flow displacement correlates with both type 1 aortopathy (involvement of the aortic root) and type 3 aortopathy (distal ascending aorta) which are more common in RN-BAV, whereas type 2 aortopathy (mid-ascending aorta) is more common in RL-BAV (Della Corte et al, 2012 ; Della Corte, 2014 ; Mahadevia et al, 2014b ) as confirmed by Liu et al ( 2018 ). In the current study the WSS data are not directly correlated to histopathologic investigation of the aortic tissue.…”

“…We read with interest the study by Liu and coworkers in which they have addressed the role of hemodynamics in the development of aortopathy in bicuspid aortic valve (BAV) patients (Liu et al, 2018 ). BAV is the most common congenital cardiac malformation, with a prevalence of 1–2% in the general population (Michelena et al, 2015 ).…”

Identification of Aorta-Specific DNA Methylation Patterns in Cell-Free DNA from Patients with Bicuspid Aortic Valve-Associated Aortopathy and Correlation with Aortic Wall Cell Death

“…Although our candidate DMRs showed no significant correlation with several histological markers associated with elastin degradation and dysregulation of ECM proteins known to occur in aortopathy, the integrity of the aortic wall is impacted by many factors, including apoptosis that leads to the depletion of vascular smooth muscle cells. [32][33][34] Regardless of the mechanism of cell death, DNA fragmentation and its release into the circulation is a common endpoint. Thus, the level of aortaspecific cfDNA is potentially an independent and end-stage measure of aortic cell death, regardless of mechanism.…”