Abstract
The aim of the present research is to determine the influence of the calcification of human mitral valves on the mechanical properties of their marginal chordae tendineae. The study was performed on marginal chords obtained from thirteen human mitral valves, explanted at surgery, including six non-calcified, four moderately calcified and three strongly calcified valves. The mechanical response of the chords from the non-calcified and moderately calcified valves was determined by means of quasi-static tensile tests (the poor condition of the strongly calcified valves prevented them from being mechanically characterised). The material parameters that were obtained and analysed (the Young's modulus, the secant modulus, the proportional limit stress, the ultimate strength, the strain at fracture and the density of energy stored up to maximum load) revealed noticeable differences in mechanical behaviour between the two groups of mitral chordae tendineae. Large scatter was obtained in all cases, nevertheless, considering the mean values, it was observed that the normal chords are between three and seven times stiffer or more resistant than the moderately calcified ones. On the contrary, the results obtained for the strain at fracture showed a rather different picture as, in this case, no significant differences were observed between the two families of chords. A scanning electron microscopy study was conducted in order to find out the relevant features of the calcium deposits present in the calcified chordae tendineae. In addition, the general aspects appreciated in the stress vs. strain curves were correlated with the collagen morphological evidences determined microscopically. Finally, the calcium content present in the three groups of chords was quantitatively determined through atomic absorption spectroscopy; then, the relation between the mechanical properties of normal and moderately calcified chords as a function of its calcium content was obtained. This analysis confirmed the existence of a strong correlation between calcium content and stiffness or resistance whereas the influence on the ductility seems to be negligible.
Highlights
Observing the mean values of these parameters reveals that, on average, the normal mitral chordae tendineae (MCT) are between three and seven times stiffer or more resistant than the moderately calcified chords. ii) there is not enough information available to conduct a statistical analysis of the distribution of minimum values, the results clearly suggest that these are noticeably lower for the moderately calcified chords than for the functional ones, whenever the stiffness or resistant parameters (E, Es, σP, σR or Ea) are being considered. iii) The results obtained for the strain at fracture, εR show a rather different picture: in this case, see Fig. 5 (e), no significant differences can be seen between normal and moderately calcified MCT
Large scatter was systematically obtained, a great difference can be observed between functional and moderately calcified MCT when the mechanical parameters related with the stiffness (Young’s modulus, secant modulus) or the resistance are considered
The amount of calcium present in normal, moderately and strongly calcified chords was measured through AAS; noticeable differences in calcium content were detected between them, large scatter was present in the results
Summary
The mitral valve and the mitral chordae tendineae. The mitral valve (MV) is composed of four elements (see Fig. 1 (a)): the valve annulus, the valve leaflets (anterior and posterior), the mitral chordae tendineae (MCT) and the papillary muscles [23, 31, 13]. The MCT link the free edges and the ventricular surface of both leaflets of the MV to the papillary muscles, preventing the backflow of the blood into the left atrium during ventricular contraction. The MCTs are classified according to their insertion sites on the mitral leaflets. In this sense, the anterior leaflet includes: (i) marginal chordae and (ii) strut chordae.
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