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P86. Effects of Papillary Muscle Position on the In Vitro Dynamic Strain on the Porcine Mitral Valve Zhaoming He Georgia Institute of Technology, Atlanta, Georgia, United States OBJECTIVES: To understand the in-vitro dynamic strain on the anterior leaflet of the porcine mitral valve. METHODS: Fresh porcine valves were mounted in an in-vitro physiological flow loop. Two papillary muscles (PMs) were set to normal, taut, and slack positions to simulate pathological PM displacements. Dual camera stereo photogrammetry was used to monitor the motion of the mitral valve anterior leaflet. Tissue deformation was measured by tracking the displacements of sixteen markers placed in the central region of the anterior leaflet. Local leaflet tissue strain and strain rates were calculated from the measured displacements under dynamic loading conditions. A total of 11 mitral valves were studied. RESULTS: 1) There was a rapid rise in anterior leaflet strain during valve closure, followed by a plateau, where no additional strains occurred. Furthermore, the strain field was highly anisotropic with larger strains in the radial direction. 2) The averaged areal strain rate during valve closure was typically ~750% per second in the normal PM position. 3) The anterior leaflet showed the highest areal strain rate during valve closure when the PM was in the slack position. Furthermore, the slack PM position led to a delay in the transition and rapid leaflet stiffening in late systole, compared to the other two PM positions. CONCLUSIONS: The mitral valve exhibited a pronounced mechanically anisotropic behavior. PM position influenced the loading process in the central area of the anterior leaflet, with slack PM position causing rapid sudden stiffening in late systole.
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