Determination of the mechanical properties of the Tricuspid Valve Annulus within the surrounding myocardium and leaflets

The Tricuspid valve (TV) annulus is a heterogeneous structure located at the intersection of the leaflets of the TV and the myocardium. The TV annulus provides structural stability and assists in leaflet coaptation for the TV. This study helps to understand the mechanical properties of the TV annulus within the surrounding myocardium and leaflets. Since the annulus structure is intertwined within the myocardium and leaflets, incorporating these tissue components were important to get a comprehensive analysis of the mechanical properties for TV annulus mechanics. There are 3 leaflets (septal, posterior, and anterior) of the TV and there were 3 different annulus segments regions. Each segment had 30 mm length, 8 mm width, and 2 mm thickness. Eleven TVs were tested up to a 20% strain for all 3 TV annulus segments. Young’s Modulus (E) and extensibility (εT) values were calculated. Subsequent western blots for collagen I and III content along each annulus segment as well as histological analyses were conducted. GAG concentration was estimated along each annulus segment. All 3 TV annulus segments had many non-linear characteristics based on stress-strain curve outputs. The results show that the septal annulus E value (200 ± 70.5 kPa) was the greatest value out of all the 3 segments. The septal annulus segment is statistically greater (p < 0.02) than the anterior (109.6 ± 86.2 kPa), but not for the posterior (147.7 ± 56.2 kPa). Western blotting and histological analysis indicated that collagen I content was greatest along the septal annulus segment. Collagen III content was greatest along the posterior annulus segment, followed by the septal and anterior annulus segments. The εT values were 0.0607 ± 0.025, 0.0614 ± 0.016, and 0.0789 ± 0.033 for septal, posterior, and anterior annulus segments and showed no statistical difference. GAG concentration was 36.5 ± 30 µg/ml, 30 ± 31 µg/ml, and 33 ± 31 µg/ml for the septal, posterior, and anterior annulus segments, respectively. The collagen I and III content is directly related to the E and εT values along each annulus segment based on degree of stiffness. GAG concentrations for each segment suggest a counteracting mechanism to the high E values along each annulus segment to increase flexibility along the region. The septal annulus segment is able to withstand the effects of annulus dilation in comparison to the other annulus segments as shown from E and εT values. The E, εT, and GAG concentrations provide a new understanding of TV annulus mechanical properties which can be used to improve annuloplasty design in the future.