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J Thorac Cardiovasc Surg 2007;134:1562-1568
© 2007 The American Association for Thoracic Surgery

Surgery for Acquired Cardiovascular Disease

A saddle-shaped annulus reduces systolic strain on the central region of the mitral valve anterior leaflet

^a Wallace H. Coulter Department of Biomedical Engineering, Georgia Institute of Technology and Emory University, Atlanta, Ga
^b Harrison Department of Surgical Research, University of Pennsylvania School of Medicine, Philadelphia, Pa
^c Department of Mechanical Engineering, Texas Tech University, Lubbock, Tex
^d Engineered Tissue Mechanics Laboratory, Department of Bioengineering, University of Pittsburgh, Pittsburgh, Pa.

Received for publication February 13, 2007; revisions received August 1, 2007; accepted for publication August 14, 2007.

^_* Address for reprints: Ajit P. Yoganathan, School of Biomedical Engineering, Suite 1126, IBB Building, 313 Ferst Dr, Georgia Institute of Technology, Atlanta, GA 30332-0535 (Email: ajit.yoganathan{at}bme.gatech.edu).

Objectives: Mitral valve repair for degenerative diseases has shown suboptimal results in selected patients. Improved postinterventional mitral valve mechanics are essential to increase repair durability.

Methods: Eight porcine mitral valves were tested in a physiologic left heart simulator under normal hemodynamic conditions. Leaflet strain was measured by tracking the displacement of a 5 x 8 marker array located on the central region of the anterior leaflet. Local leaflet strain and strain rates were calculated from measured displacements. The experiments were conducted in 4 different annular configurations associated with saddle height/commissural diameter ratios of 0%, 10%, 20%, and 30%. All experiments were conducted in the normal papillary muscle position.

Results: For all annular configurations, the anterior leaflet material showed anisotropy, with the major principal strain in the radial direction and the minor principal strain in the circumferential direction. The peak major principal strain was 0.22 ± 0.07, whereas the peak minor principal strain was 0.11 ± 0.049 in the normal annular configuration (saddle height/commissural diameter ratio of 20%). The peak major principal strain was reduced by 13.52% ± 12.79%, 27.53% ± 13.65%, and 29.72% ± 29.79% for the 10%, 20%, and 30% saddle height/commissural diameter ratio configurations, respectively, when compared with reduction for the flat annular configuration. Peak strain in the circumferential direction was unaffected by annular curvature. Reduction in areal strain of 18.62% ± 18.98% and 27.97% ± 35.01% were observed for the 20% and 30% saddle height/commissural diameter ratio configurations, respectively.

Conclusion: The strain in the central region of the anterior leaflet is reduced with increasing annular saddle curvature. Decreased leaflet strain and associated stress might improve mitral valve repair durability.

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