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Role of annulus tension in annular dilatation.

BACKGROUND AND AIM OF THE STUDY
Mitral annulus mechanics are related to annular dilatation, and are not well understood. The study aim was to develop a method to measure regional annulus tension (AT) during valve closure, and to understand its role in annular dilatation.


METHODS
A porcine mitral valve was harvested and mounted on a mitral valve closure test rig with the papillary muscles held in the normal position. The mitral valve annulus tissue rested on a plastic ring on which it was able to slide freely, there being no restriction in the interface between the annulus and the ring. The annulus was pulled by strings in the periphery during valve closure under a hydrostatic trans-mitral pressure. The string tensions were measured and further divided by string spacing to obtain the AT. A total of 10 mitral valves was tested.


RESULTS
The AT distribution along the anterolateral annulus exhibited a concave curve. The anterior, commissural and posterior ATs were 40.0, 17.8, and 30.6 N/m, respectively, and the trans-mitral pressure 120 mmHg. The ATs in the three sections of the annulus were significantly different.


CONCLUSION
A novel method to measure AT has been developed successfully. The AT was lower in the commissural section of the annulus than in the anterior or posterior sections. This finding may suggest that the potential for annular dilatation in the commissural section is high.