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Research Papers

Mechanics of the Mitral Valve Strut Chordae Insertion Region

[+] Author and Article Information
Muralidhar Padala

Wallace H. Coulter Department of Biomedical Engineering, Georgia Institute of Technology and Emory University, 315 Ferst Drive, Atlanta, GA 30332-0535mpadala@gatech.edu

Michael S. Sacks

Department of Bioengineering, University of Pittsburgh, Pittsburgh, PA 15219; McGowan Institute for Regenerative Medicine, University of Pittsburgh, Pittsburgh, PA 15219msacks@pitt.edu

Shasan W. Liou

Wallace H. Coulter Department of Biomedical Engineering, Georgia Institute of Technology and Emory University, 315 Ferst Drive, Atlanta, GA 30332-0535gtg113g@mail.gatech.edu

Kartik Balachandran

Wallace H. Coulter Department of Biomedical Engineering, Georgia Institute of Technology and Emory University, 315 Ferst Drive, Atlanta, GA 30332-0535gtg977v@mail.gatech.edu

Zhaoming He

Department of Mechanical Engineering, Texas Tech University, P.O. Box 41021, Lubbock, TX 79409-1021zhaoming.he@ttu.edu

Ajit P. Yoganathan

Wallace H. Coulter Department of Biomedical Engineering, Georgia Institute of Technology and Emory University, 315 Ferst Drive, Atlanta, GA 30332-0535ajit.yoganathan@bme.gatech.edu

J Biomech Eng 132(8), 081004 (Jun 15, 2010) (9 pages) doi:10.1115/1.4001682 History: Received September 03, 2009; Revised April 14, 2010; Posted April 28, 2010; Published June 15, 2010; Online June 15, 2010

Interest in developing durable mitral valve repair methods is growing, underscoring the need to better understand the native mitral valve mechanics. In this study, the authors investigate the dynamic deformation of the mitral valve strut chordae-to-anterior leaflet transition zone using a novel stretch mapping method and report the complex mechanics of this region for the first time. Eight structurally normal porcine mitral valves were studied in a pulsatile left heart simulator under physiological hemodynamic conditions −120 mm peak transvalvular pressure, 5 l/min cardiac output at 70 bpm. The chordal insertion region was marked with a structured array of 31 miniature markers, and their motions throughout the cardiac cycle were tracked using two high speed cameras. 3D marker coordinates were calculated using direct linear transformation, and a second order continuous surface was fit to the marker cloud at each time frame. Average areal stretch, principal stretch magnitudes and directions, and stretch rates were computed, and temporal changes in each parameter were mapped over the insertion region. Stretch distribution was heterogeneous over the entire strut chordae insertion region, with the highest magnitudes along the edges of the chordal insertion region and the least along the axis of the strut chordae. At early systole, radial stretch was predominant, but by mid systole, significant stretch was observed in both radial and circumferential directions. The compressive stretches measured during systole indicate a strong coupling between the two principal directions, explaining the small magnitude of the systolic areal stretch. This study for the first time provides the dynamic kinematics of the strut chordae insertion region in the functioning mitral valve. A heterogeneous stretch pattern was measured, with the mechanics of this region governed by the complex underlying collagen architecture. The insertion region seemed to be under stretch during both systole and diastole, indicating a transfer of forces from the leaflets to the chordae and vice versa throughout the cardiac cycle, and demonstrating its role in optimal valve function.

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Copyright © 2010 by American Society of Mechanical Engineers
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Figures

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Figure 1

(a) An intact mitral valve in a sectioned heart showing the mitral annular plane, anterior leaflet, chordae tendineae, antero-lateral papillary muscle (ALPM), and postero-medial papillary muscle (PMPM); (b) an excised mitral valve with intact annular and subvalvular components with the red arrows showing the strut chordae insertion regions

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Figure 2

(a) Schematic of the Georgia Tech left heart simulator; (b) a native mitral valve sutured onto a silicone annulus with two plastic rings attached onto the papillary muscles, ready for mounting into the simulator; and (c) functional mitral valve in the simulator

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Figure 3

(a) Photograph of the mitral valve with the anterior strut chordal insertion region marked using tissue dye; (b) schematic of the subzones in the chordal insertion region that were used for data processing. The left ridge is closer to the A2 cusp of the anterior leaflet while the right ridge is closer to the commissures.

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Figure 4

(a) Deformation of the 3D mesh during different phases of the cardiac cycle, demonstrating the out-of-plane motion of the nodes near the edges of the chordal insertion region; (b) areal stretch mapping on the entire marked region of the anterior strut chordae insertion region. The red dots represent the 31 markers that were used for the three dimensional surface fitting using triangular finite elements and for stretch computation. The X-axis represents the circumferential direction along the anterior leaflet, the Y-axis represents the radial direction and also the axis of the strut chordae, and the Z-axis represents the normal to the region of interest. The region to the left of the center line is closest to the A2 cusp of the anterior leaflet, while the region on the right is closer to the commissural sections.

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Figure 5

The averaged areal stretch plotted at subregions in the chordal insertion region. The peak stretch was significantly higher along the edge than compared with the centerline, where the stretch magnitude was small at the strut chordal region and diminished basally along the center line.

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Figure 6

Temporal changes in the areal stretch at different points in the chordal insertion zone, demonstrating the heterogeneity in the surface strains

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Figure 7

(Top gallery) The series of images demonstrate the changes in the major principal stretch magnitude and direction during systole; (bottom gallery) changes in the minor principal magnitude and direction during systolic loading of the valve

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Figure 8

Temporal changes in the major principal stretch at different points in the chordal insertion zone, demonstrating the heterogeneity in the surface strains

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Figure 9

Temporal changes in the minor principal stretch at different points in the chordal insertion zone demonstrating the heterogeneity in the surface strains

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Figure 10

(a) Image of an ovine MVAL fixed at 5 mm Hg showing the chordae; (b) corresponding SALS data showing detailed maps of the collagen fiber orientation. Inset-high resolution data of a chordal insertion region. The color legend represents the angular distribution of collagen fibers, defined by a normalized orientation index (NOI), which is defined as NOI=[(90−OI)/90]∗100%. The blue scale represents least oriented fibers with the NOI, and the red scale represents good alignment of fibers with the NOI.

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