Simulations of morphotype-dependent hemodynamics in non-dilated bicuspid aortic valve aortas

Abstract

Bicuspid aortic valves (BAVs) generate flow abnormalities that may promote aortopathy. While positive helix fraction (PHF) index, flow angle (θ), flow displacement (d) and wall shear stress (WSS) exhibit abnormalities in dilated BAV aortas, it is unclear whether those anomalies stem from the abnormal valve anatomy or the dilated aorta. Therefore, the objective of this study was to quantify the early impact of different BAV morphotypes on aorta hemodynamics prior to dilation. Fluid-structure interaction models were designed to quantify standard peak-systolic flow metrics and temporal WSS characteristics in a realistic non-dilated aorta connected to functional tricuspid aortic valve (TAV) and type-I BAVs. While BAVs generated increased helicity (PHF>0.68) in the middle ascending aorta (AA), larger systolic flow skewness (θ>11.2°) and displacement (d>6.8mm) relative to the TAV (PHF=0.51; θ<5.5°; d<3.3mm), no distinct pattern was observed between morphotypes. In contrast, WSS magnitude and directionality abnormalities were BAV morphotype- and site-dependent. Type-I BAVs subjected the AA convexity to peak-systolic WSS overloads (up to 1014% difference vs. TAV). While all BAVs increased WSS unidirectionality on the proximal AA relative to the TAV, the most significant abnormality was achieved by the BAV with left-right-coronary cusp fusion on the wall convexity (up to 0.26 decrease in oscillatory shear index vs. TAV). The results indicate the existence of strong hemodynamic abnormalities in non-dilated type-I BAV AAs, their colocalization with sites vulnerable to dilation and the superior specificity of WSS metrics over global hemodynamic metrics to the valve anatomy.

4D Flow Analysis of BAV-Related Fluid-Dynamic Alterations: Evidences of Wall Shear Stress Alterations in Absence of Clinically-Relevant Aortic Anatomical Remodeling

“…Indeed, recent studies investigated the effects of BAV-related fluid-dynamic alterations in non-dilated and initially healthy aortas, isolating these alterations from possible concomitant pathophysiological factors (Atkins et al, 2014; Atkins, 2016; Cao et al, 2017; McNally et al, 2017). Morphotype-dependent flow alterations in the aorta proved to generate different mechanical stimuli on the aortic wall in terms of $\overrightarrow{WSS}$ magnitude and directionality (Cao et al, 2017). These BAV-specific mechanical stimuli were different on the convexity and on the concavity of the ascending aorta.…”

“…Cao et al (2017) used CFD to quantify the WSS acting on the wall of a non-dilated aorta in presence of healthy aortic valve and of BAV with different fusion patterns. That analysis highlighted the alterations in terms of WSS magnitude and time-oscillations induced by the different BAV morphotypes.…”

Bicuspid aortic valve aortopathies: An hemodynamics characterization in dilated aortas

“…Characteristics impossible to observe in these images (e.g. shape of the raphe) were retrieved from previous computational works (Cao et al 2016a(Cao et al , 2017, including the use of uniform thickness of 0.5 mm for all configurations. Leaflets were created using SOLIDWORKS 2016 (Dassault Systemes, Inc, Velizy-Villacoublay, France) ( Fig.…”

“…Velocity vectors and vorticity fields were captured at sections A2 and A3. Aortic flow helicity was quantified using the positive helix fraction (PHF) index (Cao et al 2017;Bonomi et al 2015),…”

“…According to this, research studies have tried to underline mechanisms associated with dilation onset and progression in the presence of a BAV. Computational works have provided further insight on the hemodynamic aspects of ascending aortic blood flow in this disease: flow eccentricity, skewness, helical patterns and abnormally elevated wall shear stress (WSS) have been reported by computational (Cao et al 2017;Bonomi et al 2015;Kimura et al 2017) and in vivo studies (Mahadevia et al 2014;Rodriguez-Palomares et al 2018). Nonetheless, further hemodynamics characterization of blood patterns in the ascending aorta in cases of dilation is necessary.…”