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Research Papers

Mitral Valve Finite Element Modeling: Implications of Tissues’ Nonlinear Response and Annular Motion

[+] Author and Article Information
Marco Stevanella

Department of Bioengineering, Politecnico di Milano, Via Golgi 39, 20133 Milano, Italymarco.stevanella@mail.polimi.it

Emiliano Votta, Alberto Redaelli

Department of Bioengineering, Politecnico di Milano, Via Golgi 39, 20133 Milano, Italy

J Biomech Eng 131(12), 121010 (Nov 24, 2009) (9 pages) doi:10.1115/1.4000107 History: Received June 06, 2008; Revised July 31, 2009; Posted September 01, 2009; Published November 24, 2009; Online November 24, 2009

Finite element modeling represents an established method for the comprehension of the mitral function and for the simulation of interesting clinical scenarios. However, current models still do not include all the key aspects of the real system. We implemented a new structural finite element model that considers (i) an accurate morphological description of the valve, (ii) a description of the tissues’ mechanical properties that accounts for anisotropy and nonlinearity, and (iii) dynamic boundary conditions that mimic annulus and papillary muscles’ contraction. The influence of such contraction on valve biomechanics was assessed by comparing the computed results with the ones obtained through an auxiliary model with fixed annulus and papillary muscles. At the systolic peak, the leaflets’ maximum principal stress contour showed peak values in the anterior leaflet at the strut chordae insertion zone (300 kPa) and near the annulus (200–250 kPa), while much lower values were detected in the posterior leaflet. Both leaflets underwent larger tensile strains in the longitudinal direction, while in the circumferential one the anterior leaflet experienced nominal tensile strains up to 18% and the posterior one experienced compressive strains up to 23% associated with the folding of commissures and paracommissures, consistently with tissue redundancy. The force exerted by papillary muscles at the systolic peak was equal to 4.11 N, mainly borne by marginal chordae (76% of the force). Local reaction forces up to 45 mN were calculated on the annulus, leading to tensions of 89 N/m and 54 N/m for its anterior and posterior tracts, respectively. The comparison with the results of the auxiliary model showed that annular contraction mainly affects the leaflets’ circumferential strains. When it was suppressed, no more compressive strains could be observed and peak strain values were located in the belly of the anterior leaflet. Computational results agree to a great extent with experimental data from literature. They provided insight into some of the features characterizing normal mitral function, such as annular contraction and leaflets’ tissue anisotropy and nonlinearity. Some of the computed results may be useful in the design of surgical devices and techniques. In particular, forces applied on the annulus by the surrounding tissues could be considered as an indication for annular prostheses design.

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Copyright © 2009 by American Society of Mechanical Engineers
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Figures

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Figure 1

Finite element 3D model of the mitral valve: (a) atrial view, (b) commissural view, (c) posterior view, and (d) three-dimensional view

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Figure 2

Geometrical parameters of the annular profile in an atrial view (a) and in a lateral one (b). Lant=anterior annular portion length, Lpost=posterior annular portion length, ITL=intertrigonal length, IC=intercommissural distance, SLant=septolateral dimension of the anterior annular tract, SLpost=septolateral dimension of the posterior annular tract, c1 and c2=commissures, and t1 and t2=fibrous trigones.

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Figure 3

Pressure load applied to the ventricular surface of the leaflets (dashed line) and displacements, normalized to 1, imposed on annular nodes (continuous line) during valve closure

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Figure 4

Annulus and papillary muscles’ three-dimensional position at different pressure loads

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Figure 5

Mitral leaflets’ closure as computed by the main model: six configurations for increasing pressure values

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Figure 6

Leaflets’ maximum principal stress distribution at the systolic peak for the main model (left) and for the auxiliary one, characterized by fixed annulus and papillary muscles (right)

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Figure 7

Leaflets’ nominal strains in circumferential (ε11) and longitudinal (ε22) directions at the systolic peak for the main model (left) and for the auxiliary one, characterized by fixed annulus and papillary muscles (right)

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Figure 8

Papillary reaction force with (continuous black line) and without (continuous gray line) contraction. The dotted line depicts the time-dependent transvalvular pressure drop.

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Figure 9

Nodal reaction forces at the nodes belonging to the annulus as a function of node position, calculated in the main model (continuous black line) and in the auxiliary one (gray dashed line). Reference anatomical points are indicated on the horizontal axis and on sketch of the atrial view of the annular profile (top right): SH=saddle horn, Trig=trigone, Comm=commissure, Para=paracommissure, and MP=midposterior.

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