Abstract
The bicuspid aortic valve (BAV) is a major risk factor for secondary aortopathy such as aortic dilation. The heterogeneous BAV morphotypes [left-right-coronary cusp fusion (LR), right-non-coronary cusp fusion (RN), and left-non-coronary cusp fusion (LN)] are associated with different dilation patterns, suggesting a role for hemodynamics in BAV aortopathogenesis. However, assessment of this theory is still hampered by the limited knowledge of the hemodynamic abnormalities generated by the distinct BAV morphotypes. The objective of this study was to compare experimentally the hemodynamics of a normal (i.e., non-dilated) ascending aorta (AA) subjected to tricuspid aortic valve (TAV), LR-BAV, RN-BAV, and NL-BAV flow. Tissue BAVs reconstructed from porcine TAVs were subjected to physiologic pulsatile flow conditions in a left-heart simulator featuring a realistic aortic root and compliant aorta. Phase-locked particle image velocimetry experiments were carried out to characterize the flow in the aortic root and in the tubular AA in terms of jet skewness and displacement, as well as mean velocity, viscous shear stress and Reynolds shear stress fields. While all three BAVs generated skewed and asymmetrical orifice jets (up to 1.7- and 4.0-fold increase in flow angle and displacement, respectively, relative to the TAV at the sinotubular junction), the RN-BAV jet was out of the plane of observation. The LR- and NL-BAV exhibited a 71% increase in peak-systolic orifice jet velocity relative to the TAV, suggesting an inherent degree of stenosis in BAVs. While these two BAV morphotypes subjected the convexity of the aortic wall to viscous shear stress overloads (1.7-fold increase in maximum peak-systolic viscous shear stress relative to the TAV-AA), the affected sites were morphotype-dependent (LR-BAV: proximal AA, NL-BAV: distal AA). Lastly, the LR- and NL-BAV generated high degrees of turbulence in the AA (up to 2.3-fold increase in peak-systolic Reynolds shear stress relative to the TAV) that were sustained from peak systole throughout the deceleration phase. This in vitro study reveals substantial flow abnormalities (increased jet skewness, asymmetry, jet velocity, turbulence, and shear stress overloads) in non-dilated BAV aortas, which differ from those observed in dilated aortas but still coincide with aortic wall regions prone to dilation.
Highlights
With an incidence rate between 0.5 and 2.0%, the bicuspid aortic valve (BAV) is the most common congenital heart defect and is characterized by the presence of two functional leaflets instead of three in the normal tricuspid aortic valve (TAV) (Roberts, 1970; Ward, 2000)
The data presented in this study suggests that the elucidation of the shear stress environment in BAV AAs might be critical toward the development of improved clinical guidelines for the management of BAV patients (Atkins et al, 2016a)
While LR-BAV flow abnormalities were mostly contained within the proximal AA and progressively attenuated as the flow developed in the distal AA (16% and 12% reduction in flow angle and displacement, respectively), RN- and NL-BAV flow abnormalities amplified as the flow developed from the proximal to the distal section
Summary
With an incidence rate between 0.5 and 2.0%, the bicuspid aortic valve (BAV) is the most common congenital heart defect and is characterized by the presence of two functional leaflets instead of three in the normal tricuspid aortic valve (TAV) (Roberts, 1970; Ward, 2000). The demonstration of the skewness of the BAV orifice jet (Robicsek et al, 2004; Della Corte et al, 2011) and of its impingement on the anterolateral aortic wall (Robicsek et al, 2004; Hope et al, 2008, 2010), which correlate with the asymmetric formation of calcific nodules on BAV leaflets (Thubrikar et al, 1986; Sabet et al, 1999) and the asymmetric dilation patterns in BAV ascending aortas (AAs) (Fazel et al, 2008; Schaefer et al, 2008), has generated renewed support for the involvement of hemodynamic stresses in BAV disease and for the investigation of the flow in BAV aortas
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