Abstract
The mitral valve (MV) apparatus is a complex mechanical structure including annulus, valve leaflets, papillary muscles (PMs) and connected chordae tendineae. Chordae anchor to the papillary muscles to help the valve open and close properly during one cardiac cycle. It is of paramount importance to understand the functional, mechanical, and microstructural properties of mitral valve chordae and connecting PMs. In particular, little is known about the biomechanical properties of the anterior and posterior papillary muscle and corresponding chords. In this work, we performed uniaxial and biaxial tensile tests on the anterolateral (APM) and posteromedial papillary muscle (PPM), and their respective corresponding chordae tendineae, chordaeAPM and chordaePPM, in porcine hearts. Histology was carried out to link the microstructure and macro-mechanical behavior of the chordae and PMs. Our results demonstrate that chordaePPM are less in number, but significantly longer and stiffer than chordaeAPM. These different biomechanical properties may be partially explained by the higher collagen core ratio and larger collagen fibril density of chordaePPM. No significant mechanical or microstructural differences were observed along the circumferential and longitudinal directions of APM and PPM samples. Data measured on chordae and PMs were further fitted with the Ogden and reduced Holzapfel - Ogden strain energy functions, respectively. This study presents the first comparative anatomical, mechanical, and structural dataset of porcine mitral valve chordae and related PMs. Results indicate that a PM based classification of chordae will need to be considered in the analysis of the MV function or planning a surgical treatment, which will also help developing more precise computational models of MV.
Highlights
The mitral valve (MV) is a complex structure including annulus, leaflets, papillary muscles (PMs), and chordae tendineae
STD: standard deviation; λmax: maximum stretch; Ulti mate tensile stress (UTS): ultimate tensile strength; p-value indicates difference between chordaeAPM and chordaePPM, statistically significant difference is annotated in bold, N indicates the number of samples
There are more chords connected to anterolateral papillary muscle (APM) than PPM, but neither the amount of chords connected to APM and PPM on the papillary muscle side (p = 0.83) nor on the leaflet side (p = 0.25) are statistically different
Summary
The mitral valve (MV) is a complex structure including annulus, leaflets, papillary muscles (PMs), and chordae tendineae. Chordal and PM rupture almost always results in flail leaflets and acute severe mitral regurgitation (Gabbay and Yosefy, 2010), which is a serious medical complication. A systematic clinical review by Gabbay and Yosefy analyzed and investigated the underlying major cause of chord rupture, identifying mitral valve prolapse and myxomatous degeneration as major causes (Gabbay and Yosefy, 2010). Rather than replacing the valve by a prosthesis, the therapy of choice is to surgically correct ruptured chords by repairing or replacement (Bortolotti et al, 2012; Gammie et al, 2018). It is of clinical interest to better understand the functional, mechanical and microstructural properties of mitral valve chordae and PMs
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