Regional analysis of dynamic deformation characteristics of native aortic valve leaflets

Abstract

Background The mechanical environment of the aortic valve (AV) has a significant impact on valve cellular biology and disease progression, but the regional variation in stretch across the AV leaflet is not well understood. This study, therefore, sought to quantify the regional variation in dynamic deformation characteristics of AV leaflets in the native mechanical environment in order to link leaflet stretch variation to reported AV calcification patterns. Methods Whole porcine AVs (n=6) were sutured into a physiological left-heart simulator and subjected to pulsatile and physiologically normal hemodynamic conditions. A grid of ink dots was marked on the entire ventricular surface of the AV leaflet. Dual camera stereo photogrammetry was used to determine the stretch magnitudes across the entire ventricular surface over the entire diastolic duration. Results Elevated stretch magnitudes were observed along the leaflet base and coaptation line consistent with previously reported calcification patterns suggesting the higher mechanical stretch experienced by the leaflets in these regions may contribute to increased disease propensity. Transient stretch overloads were observed during diastolic closing, predominantly along the leaflet base, indicating the presence of a dynamic fluid hammer effect resulting from retrograde blood flow impacting the leaflet. We speculate the function of the leaflet base is to act in cooperation with the sinuses of Valsalva to dampen the fluid hammer effect and reduce stress levels imparted on the rest of the leaflet.

In-vivo heterogeneous functional and residual strains in human aortic valve leaflets

“…However, in general the results presented here are in good agreement with previous studies. For example, the radial stretches have been reported to be higher than the circumferential ones in porcine valves (Adamczyk et al, 2000; Weiler et al, 2011), with values of strains in the same range as our presented results. However, a direct comparison of strain values is not possible.…”

Cell-matrix mechanics and pattern formation in inflammatory cardiovascular calcification

“…Computational modelling by the Yoganathan group recently showed regional strain variations in aortic valve tissue subjected to physiological stresses, with the highest stretch magnitude seen in the base and along the coaptation lines of the valve cusps, which is, interestingly, also where calcification is most often seen. 56 Additionally, in vitro studies by the Merryman group have demonstrated the strain dependence of apoptosis and nodule formation in valvular cells. 57 58 These studies suggest an important role of tissue stretch in the pathogenesis of valvular calcification, and highlight the complexities of studying cardiovascular cells exposed to a dynamic biomechanical environment.…”

The living aortic valve: From molecules to function

“…It is possible that more than one of these components could be adversely affected in valve disease, with obvious consequences for the identification of an effective ameliorating strategy. Further compounding the challenge is the fact that the natural stretch environment in vivo is strongly anisotropic and heterogeneous 143 . We and other researchers have demonstrated that endothelial and interstitial cells respond differently to different patterns of cyclic stretch and shear stress, which exist in a localized geometry 101,144–147 .…”