Alterations in Mechanical Properties and In Vivo Geometry of the Mitral Valve Following Myocardial Infarction
Bruno V. Rego1, Salma Ayoub1, Amir H. Khalighi1, Andrew Drach1, Joseph H. Gorman, III2, Robert C. Gorman2, Michael S. Sacks1.
1University of Texas at Austin, Austin, TX, USA, 2University of Pennsylvania, Philadelphia, PA, USA.
BACKGROUND: Mitral valve (MV) repair failure following myocardial infarction (MI) is a major problem, with 30% of patients experiencing a recurrence of ischemic regurgitation within 6 months of surgery. In the present study, we examined how the mechanical properties and in vivo geometry of the MV change after MI, in an effort to gain a deeper understanding of the driving factors behind post-MI valvular remodeling.
METHODS: MI was induced in three Dorsett sheep, and 3D ultrasound scans were collected pre-MI, immediately post-MI, and at 8 weeks post-MI. At 8 weeks, animals were sacrificed and MV tissues were explanted for biaxial mechanical testing. Additionally, each 3D ultrasound scan was traced to separately label the annulus, leaflets, coapted region, and commissure points. The ultrasound tracings were then computationally analyzed to identify significant changes in in vivo MV geometry and function following MI.
RESULTS: Biaxial testing results showed that at 8 weeks post-MI, the mechanical properties of the MV anterior leaflet are severely disturbed. While normal MVs are approximately 6x more extensible in the radial direction than in the circumferential direction (Fig. 1a), this anisotropy is entirely reversed post-MI (Fig. 1b), indicating that the fiber structure of the leaflet undergoes dramatic changes following infarction. Moreover, ultrasound scans showed that the MV annulus is substantially flattened post-MI and that the MV leaflets lose their normal tenting behavior during closure (Fig. 1c-f).
CONCLUSIONS: Our results shed significant light on the post-MI mechanical and geometric properties of the MV. These findings are highly relevant to the design of MV repair devices and the optimization of surgical strategies, as they directly elucidate the state of the valve at the time of surgery. While current MV repair endeavors largely seek to return the valve to its pre-MI state, our results suggest that this approach may not be favorable, and that an effort to place the MV in an alternative homeostatic state may lead to decreased repair failure.
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