In Vivo Dynamic Deformation of the Mitral Valve Annulus

Abstract

Though mitral valve (MV) repair surgical procedures have increased in the United States [Gammie, J. S., et al. Ann. Thorac. Surg. 87(5):1431-1437, 2009 Nowicki, E. R., et al. Am. Heart J. 145(6):1058-1062], studies suggest that altering MV stress states may have an effect on tissue homeostasis, which could impact the long-term outcome [Accola, K. D., et al. Ann. Thorac. Surg. 79(4):1276-1283 Fasol, R., et al. Ann. Thorac. Surg. 77(6):1985-1988, 2004; Flameng, W., P. Herijgers, and K. Bogaerts. Circulation 107(12): 1609-1613 Gillinov, A. M., et al. Ann. Thorac. Surg. 69(3):717-721, 2000]. Improved computational modeling that incorporates structural and geometrical data as well as cellular components has the potential to predict such changes; however, the absence of important boundary condition information limits current efforts. In this study, novel high definition in vivo annular kinematic data collected from surgically implanted sonocrystals in sheep was fit to a contiguous 3D spline based on quinticorder hermite shape functions with C 2 continuity. From the interpolated displacements, the annular axial strain and strain rate, bending, and twist along the entire annulus were calculated over the cardiac cycle. Axial strain was shown to be regionally and temporally variant with minimum and maximum values of −10 and 4%, respectively, observed. Similarly, regionally and temporally variant strain rate values, up to 100%/s contraction and 120%/s elongation, were observed. Both annular bend and twist data showed little deviation from unity with limited regional variations, indicating that most of the energy for deformation was associated with annular axial strain. The regionally and temporally variant strain/strain rate behavior of the annulus are related to the varied fibrous-muscle structure and contractile behavior of the annulus and surrounding ventricular structures, although specific details are still unavailable. With the high resolution shape and displacement information described in this work, high fidelity boundary conditions can be prescribed in future MV finite element models, leading to new insights into MV function and strategies for repair.

Cellular and Extracellular Matrix Basis for Heterogeneity in Mitral Annular Contraction

“…This work agrees with a previous in vivo study showing that the lateral annulus contracts more than the septal region of the annulus, and we have now correlated this observed behavior with the extracellular matrix structure and cell behavior in these regions [19]. It should be noted that contraction in the commissures was reported as being limited in the previous study, whereas in this study commissural contraction was not significantly different from contraction of the lateral annulus.…”

Characterization of Mitral Valve Annular Dynamics in the Beating Heart

“…Eckert et al 13 previously reported strain and curvature in the ovine mitral annulus. Their peak strains in the septal and lateral regions are in excellent agreement with our findings both in systole and in diastole.…”

“…Linear interpolation has been widely used among clinical researchers to characterize the mitral annulus in humans and in animal models. 18,20,21,48 More sophisticated approaches use one-dimensional (1D) interpolating Hermitian finite elements 13 or Fourier series to approximate the mitral annulus from echo data. 36 An alternative method to reconstruct space curves that provides a variety of practical advantages is spline fitting.…”

Modeling active muscle contraction in mitral valve leaflets during systole: a first approach

“…Most studies on material models for mitral tissue are based on animal tissues and in-vitro tests (May-Newman and Yin 1995;Sacks et al 2002), but also some in-vivo studies have been published, mainly focusing of deformation patterns in different parts of the mitral complex (Sacks et al 2006;Eckert et al 2009;Göktepe et al 2009;Krishnamurthy et al 2008;Ryan et al 2008). Some initial in-vitro studies on human tissue constitutive modeling are provided by Prot et al (2010).…”