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Research Papers

Mechanics of Healthy and Functionally Diseased Mitral Valves: A Critical Review

[+] Author and Article Information
Ajit P. Yoganathan

e-mail: ajit.yoganathan@bme.gatech.edu
Wallace H. Coulter
Department of Biomedical Engineering,
Georgia Institute of Technology and Emory University,
Atlanta, GA 30332

1Corresponding author. Present address: Wallace H. Coulter Department of Biomedical Engineering, Georgia Institute of Technology, 313 Ferst Drive, Suite 2119, Atlanta, GA 30332-0535.

Contributed by the Bioengineering Division of ASME for publication in the JOURNAL OF BIOMECHANICAL ENGINEERING. Manuscript received November 5, 2012; final manuscript received December 20, 2012; accepted manuscript posted December 22, 2012; published online February 7, 2013. Editor: Victor H. Barocas.

J Biomech Eng 135(2), 021007 (Feb 07, 2013) (16 pages) Paper No: BIO-12-1539; doi: 10.1115/1.4023238 History: Received November 05, 2012; Revised December 20, 2012; Accepted December 22, 2012

The mitral valve is a complex apparatus with multiple constituents that work cohesively to ensure unidirectional flow between the left atrium and ventricle. Disruption to any or all of the components—the annulus, leaflets, chordae, and papillary muscles—can lead to backflow of blood, or regurgitation, into the left atrium, which deleteriously effects patient health. Through the years, a myriad of surgical repairs have been proposed; however, a careful appreciation for the underlying structural mechanics can help optimize long-term repair durability and inform medical device design. In this review, we aim to present the experimental methods and significant results that have shaped the current understanding of mitral valve mechanics. Data will be presented for all components of the mitral valve apparatus in control, pathological, and repaired conditions from human, animal, and in vitro studies. Finally, current strategies of patient specific and noninvasive surgical planning will be critically outlined.

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Figures

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Fig. 1

Mitral valve: The ventricular side of a porcine mitral valve is displayed, highlighting the mitral leaflets, chordae tendineae, and papillary muscles. The valve was excised from an explanted heart and cut in half at the P2 scallop of the posterior leaflet.

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Fig. 2

Forces acting on the mitral apparatus: Overall mitral force balance requires the structural interplay between each of the individual components. This is most commonly disrupted in functional mitral valve disease where left atrial and ventricular dilation lead to restricted leaflet closure and mitral regurgitation.

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Fig. 3

Mitral annular force transducers: (a) Instrumented bileaflet mechanical heart valve (adapted with permission from Hasenkam et al. [26]), (b) apical-basal annuloplasty force transducer (adapted with permission from Jensen et al. [32]), and (c) in-plane annular force transducer (adapted with permission from Siefert et al. [29])

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Fig. 4

Mitral leaflets: Atrial view of the mitral leaflets during systole shows the anterior leaflet extends to cover two-thirds of the mitral orifice. The posterior leaflet is comprised of three scallops P1, P2, and P3, which are opposed by similarly named regions of the anterior leaflet. AC: anterior commissure. PC: posterior commissure.

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Fig. 5

Histological cross-section of mitral leaflets: Histological cross-sections of the mitral leaflets reveal an organized layered structure. In addition to elastin, collagen (main load bearing element) and proteoglycans, the mitral leaflets are known to contain smooth muscle cells, nonmylenated nerve fibers, and vasculature at their base. (Images adapted with permission from Grande-Allen et al. [35]).

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Fig. 6

Typical leaflet stress-strain curve: Nonlinear stress strain curve of the mitral leaflets shows directionally dependent response and minimal hysteresis. There is minimal stress developed in the “toe” region due to the uncrimping of the collagen fibers. A nonlinear transition region (recruitment and alignment of collagen fibers) is followed by a linear, high tensile modulus regime (locking of collagen fibers). (Image adapted with permission from Grashow et al. [51]).

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Fig. 7

Leaflet strains: (Top Panel) Superficial grids marked on mitral leaflets include tissue marker dye (in vitro), sonomicrometry crystals (image courtesy of Dr. Gorman), and radio-opaque markers (image adapted with permission from Rausch et al. [69]). (Bottom Panel) Leaflet strains calculated over the cardiac cycle show large and rapid aniosotropic stretch. A plateau is observed during peak systole as the collagen fibers lock preventing further deformation. (Images adapted with permission from Sacks et al. [56]).

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Fig. 8

Leaflet strain distribution: in vivo ovine areal, circumferential, and radial strains are shown at maximum left ventricular pressure. The strain is anisotropic and largest in the radial direction due to the preferential alignment of collagen fibers. The largest stretch is observed at the free edge, which helps create redundant coaptation. (Image adapted with permission from Rausch et al. [58]).

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Fig. 9

Chordal and papillary muscle force transducers: Miniature C-arm force transducers selectively record chordal forces throughout the cardiac cycle (Image adapted with permission from Neilsen et al. [85]). Similarly, force transducers sutured between severed papillary muscles record forces throughout the cardiac cycle (Image adapted with permission from Askov et al. [110]).

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Fig. 10

Patient specific computational modeling: Patient specific anatomical mitral valve models derived from CT (left) and three-dimensional echocardiography (right) will ultimately be used for predictive surgical planning. CT imaging is better capable of capturing the detailed chordal structure. (Images adapted with permission from Wang et al. [120] and Mansi et al. [114]).

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