Effects of papillary muscle position on anterior leaflet stretches under mitral valve edge-to-edge repair

Background and aim of the study: The mitral valve edge-to-edge repair (ETER) procedure inevitably alters mitral valve leaflet mechanics. The study aim was to quantify the effects of papillary muscle (PM) position on stretches in the central area of the anterior leaflet after mitral valve ETER. Methods: Sixteen markers of a 4×4 array were attached onto the central area of the mitral valve anterior leaflet. The free edges of the mitral valve leaflets were sutured together with a single stitch to mimic the ETER. The mitral valve was then mounted in an in-vitro flow loop that was capable of simulating physiological loading conditions. The PM of the mitral valve was set in slack, normal, and taut positions. Displacements of the markers were obtained from the images of the markers, in order to calculate the stretches and stretch rates. Results: The major principal stretch during systole was significantly greater than that during diastole in the three PM positions. The major principal (radial) stretch was significantly greater in the taut PM position than in the normal and slack PM positions during diastole. However, there was no significant difference in the minor principal (circumferential) stretch during diastole in the three PM positions. The loading and unloading stretch rates were not affected by the PM position, except for the major principal stretch rate during loading. Conclusion: With regards to the central region of the mitral valve anterior leaflet, the radial stretch during diastole was significantly less than that during systole. Therefore, the load on the anterior leaflet during systole, rather than that during diastole, should be considered when evaluating ETER durability, especially in the taut PM position. The circumferential stretch during diastole was not influenced by the PM positions.