title: A structural basis for the size-related mechanical properties of mitral valve chordae tendineae.
abstract: It has been reported previously that the mechanical properties of mitral valve chordae tendineae vary with chordal size and type. The popularity of mitral valve repair and chordal transposition warrant a better understanding of this phenomenon. The objectives of this study were to characterize the size- and type-related variations in chordal mechanics and explain them from the ultra-structural viewpoint. A total of 52 porcine mitral valve chordae from eight hearts were mechanically tested. We found that thicker chordae were more extensible than thinner chordae (4.2+/-1.5%, 8.1+/-2.5%, 15.7+/-3.9% and 18.4+/-2.8% strain corresponding to chordae with cross-sectional areas of 0.1-0.5, 0.5-1.0, 1.0-2.0, and 2.0-3.0mm(2), respectively), and had lower moduli (90.1+/-22.3, 83.7+/-18.5, 66.3+/-13.5 and 61.7+/-13.3 MPa corresponding to the same chordae groups). Polarized light microscopy was used to measure collagen fibril crimp. Thicker chordae had smaller crimp period than thinner chordae (11.3+/-1.4 microm vs. 14.8+/-3.0 microm), and were thus more highly crimped. Thicker chordae could therefore extend to greater strain before lock-up. Transmission electron microscopy (TEM) was used to measure choral fibril ultra-structure. Thinner chordae had lower average fibril diameter than thicker chordae but greater average fibril density. The cross-sectional area occupied by fibrils, however, was found to be constant at 49+/-2% regardless of chordal size or type. The difference in moduli between thick and thin chordae can therefore be explained by differences in fibril packaging and hence fibril-to-fibril interactions. According to a simple fibril interaction model, chordae with smaller diameter fibrils will have a greater number of fibril-to-fibril interactions, and hence a greater modulus.
authors.affiliation: Department of Biomedical Engineering, Lerner Research Institute, The Cleveland Clinic Foundation, 9500 Euclid Avenue, Cleveland, OH 44195, USA.
authors.forename: Jun
authors.initials: J
authors.lastname: Liao
authors.forename: Ivan
authors.initials: I
authors.lastname: Vesely
mesh_terms: D019412:Anatomy, Cross-Sectional / Q000379:methods; D000818:Animals; D002815:Chordae Tendineae / Q000502:physiology* / Q000648:ultrastructure*; D003094:Collagen / Q000502:physiology* / Q000648:ultrastructure*; D003198:Computer Simulation; D004548:Elasticity; D066298:In Vitro Techniques; D008943:Mitral Valve / Q000502:physiology* / Q000648:ultrastructure*; D008954:Models, Biological; D009038:Motion; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D013223:Statistics as Topic; D013314:Stress, Mechanical; D013552:Swine
chemical_list: D003094:Collagen