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Ann Thorac Surg 2006;82:1369-1377
© 2006 The Society of Thoracic Surgeons

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Original Articles: Cardiovascular

In-Vivo Dynamic Deformation of the Mitral Valve Anterior Leaflet

^a Engineered Tissue Mechanics Laboratory, Department of Bioengineering, University of Pittsburgh, Pittsburgh, Pennsylvania
^b Harrison Department of Surgical Research, University Pennsylvania School of Medicine, Philadelphia, Pennsylvania
^c Cardiovascular Fluid Mechanics Laboratory, Wallace H. Coulter Department of Biomedical Engineering, Georgia Institute of Technology and Emory University, Atlanta, Georgia
^d Division of Cardiology, Children's Hospital of Philadelphia, Philadelphia, Pennsylvania

Accepted for publication March 21, 2006.

^_* Address correspondence to Dr Sacks, Engineered Tissue Mechanics Laboratory, McGowan Institute for Regenerative Medicine, 100 Technology Dr, Room 234, University of Pittsburgh, Pittsburgh, PA 15219 (Email: msacks{at}pitt.edu).

BACKGROUND: Surgical techniques have been developed for mitral valve repair for a wide range of pathologies. However, excessive tissue stress and damage have been identified as etiologic factors limiting long-term durability. Before computational models to optimize valve repair can be realistically developed, in-vivo dynamic mitral valve leaflet strain data are required. However, these data do not presently exist. In the present study, a sheep model and sonomicrometry were used to compute the in-surface Eulerian strain tensor of the anterior leaflet over the cardiac cycle at varying afterloads.

METHODS: The anterior leaflet of nine Dorsett sheep (35 kg to 45 kg) was instrumented with nine 1-mm hemispherical piezoelectric transducers in a 15-mm square array. Three-dimensional crystal spatial positions were recorded at 250 Hz over several cardiac cycles, with peak left ventricular pressures varying from 90 mm Hg to 200 mm Hg. The in-surface Eulerian strain tensor was computed from the crystal displacements.

RESULTS: The mitral valve anterior leaflet experiences large anisotropic strains and peak strain rates of 400%/s, followed by an absolute cessation of any deformation during systole. Increasing left ventricular pressure also increased the effective leaflet stiffness but not the peak strains.

CONCLUSIONS: We report the first data on the dynamic in-vivo strain tensor of a functioning mitral valve anterior leaflet, which indicated large anisotropic strains and very high strain rates. Our observations also suggest that changes in left ventricular pressure and annular geometry result in altered effective leaflet stiffness, and may be an important factor in reducing leaflet stress and as such potentially affect mitral valve repair longevity.

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