## 4 Discussion  
Two tendon-like SCs, particularly strong and thick, are inserted in a fanlike manner into the ventricular side of the anterior MV leaflet and stretched toward the annulus. The importance of the roles of the SC in maintaining an appropriate anatomical valvular shape is obviously inferred from their anatomical location and bigger size when compared to other chordae. The SC endure tensional stresses three times larger than the marginal chordae but do not affect the existence of mitral regurgitation. Removing the SC tethering would cause the central region of the anterior leaflet to extend further towards the mitral annulus, resulting in flexible leaflet tissue around the coaptating leaflet margin [6, 34]. In the present study, we utilized parametric MV modeling and finite element simulation to evaluate the biomechanics and function of the anatomical alteration of the SC insertion location based on clinical data. Figure 6: Morphologic features and quantitative assessment of the MV leaflets at peak systole. For the narrow MV group, the cross-sectional views of the A2-P2 leaflet edges are presented in blue (anterior leaflet) and red (posterior leaflet) lines. Quantitative morphologic assessment includes (**A**) coaptation lengths, (**B**) coaptation angles, and (**C**) anterior bulging heights. A—anterior; P—posterior. Figure 7: Anterior leaflet bulging distance with respect to alteration of the SC insertion location during the diastolic phase. The shortest distance is found in the narrow–top MV model. A—anterior; Al—anterioral; P—posterior. Alteration of the SC insertion location demonstrated the smallest maximum leaflet stress (0.514 MPa) in the top-narrow MV model and the largest maximum leaflet stress (0.740 MPa) in the bottom-wide MV model at peak systole (Figures 4 and 5). The overall pattern of leaflet stress distribution was similar for all nine MV models, and large stresses near the anterior annular saddle-horn region increased in proportion to the width of the SC insertion location. In all nine MV models, the maximum stresses were found in the anterior annular trigone region. It is speculated that a wide width of the SC insertion location would not provide the central area of the anterior leaflet with sufficient tensional support, resulting in increased leaflet stresses near the anterior annular saddle-horn region. In addition, the maximum stress value was found to decrease as the SC insertion location was close to the mitral annulus. With the SC insertion location close to the annulus, the anterior leaflet displayed more leaflet bulging, indicating increased stresses in the central and marginal zone of the anterior leaflet. As the SC can maintain three times larger chordal stresses than the marginal chordae, lower leaflet stress values were observed in the region from the central to marginal zone when the SC was inserted far from the mitral annulus, reducing a considerable amount of overall leaflet stresses in the zone. Consistent with previous studies suggesting that the presence of the SC does not affect coaptation, all nine MV models exhibited full coaptation and similar leaflet contact distribution (Figure 3). The MV models with a wider SC insertion location displayed further spread distribution of leaflet coaptation. A narrower SC insertion location resulted in a longer coaptation length and hence a smaller anterior coaptation angle (Figure 6). In the center and bottom groups, as the width increased, the coaptation length decreased proportionally while the coaptation angle increased. However, in the top group, the middle and wide MV models revealed similar values of the coaptation length and anterior coaptation angle. In the wide group, all three locations along the apical direction showed comparable coaptation lengths, anterior coaptation angles, and anterior bulging heights. Particularly in the wide group, little difference was found in the leaflet stress and contact distributions (coaptation length and coaptation angle) as well as the anterior bulging height and bulging distance.