Key result
Asymmetric papillary muscle displacement impairs lateral cleft coaptation, while symmetric displacement only causes tenting.
Why the study?
The mechanism of gapping formation of the mitral valve cleft is unknown.
Does asymmetric or symmetric papillary muscle displacement affect mitral valve cleft coaptation geometry in an in-vitro porcine model?
Does asymmetric or symmetric papillary muscle displacement affect mitral valve cleft coaptation geometry in an in-vitro porcine model?
Asymmetric papillary muscle displacement impairs lateral cleft coaptation, suggesting a mechanism for gap formation in functional mitral regurgitation beyond apical leaflet tenting.
May implicate asymmetric PM displacement in lateral cleft gap formation in functional MR; hypothesis-generating from porcine model, requires clinical validation.
Gapping formation of the mitral valve cleft is unknown. The objective of this study was to quantify the geometry of mitral valve cleft coaptation in the asymmetric and symmetric papillary muscles (PMs) positions in a dilated annulus in order to reveal mitral valve gapping mechanism. Nine fresh porcine mitral valves with the posterior leaflet clefts were sutured onto a saddle-shaped dilated annulus in an in-vitro experiment to simulate mitral valve closure at hydrostatic pressure. PMs were adjusted to the normal position, and subsequently to positions of asymmetric and symmetric PM displacement. Sonomicrometry was used to measure positions of the lateral and medial clefts. PM displacement tethered the leaflets. Both the opening angle and contact angle of the lateral cleft, but not of the medial cleft, increased in the asymmetric PM displacement. Neither the opening angle nor contact angle of both clefts increased in the symmetric PM displacement. Displacement of the postero-medial PM moves the posterior leaflet medially and impairs coaptation of the lateral cleft, but not medial cleft, which suggest that the medial cleft displacement in the asymmetric PM position is another mechanism of gap formation in addition to leaflet tenting due to apical leaflet displacement. Symmetric PM displacement cause leaflet tenting, but doesn’t impair the leaflet cleft coaptation, which suggest that the asymmetric PM position is even worse than the symmetric PM position.
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Gao et al. (2021) studied Functional mitral regurgitation (n=9). Asymmetric and symmetric papillary muscle displacement vs. Normal papillary muscle position was evaluated on Geometry of mitral valve cleft coaptation (opening angle and contact angle). Asymmetric papillary muscle displacement impaired coaptation of the lateral cleft by increasing its opening and contact angles, whereas symmetric displacement caused tenting without impairing coaptation.
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