The aortomitral angle is suspended by the anterior mitral basal "stay" chords.

OBJECTIVES The function of the anterior mitral basal "stay" chords (SC) is not yet known. Collagen fiber orientation of the anterior mitral leaflet (AML) suggests that local stress is directed from papillary muscles (PM) over SC and AML to fibrous trigones (FT), maintaining the aortomitral angle (AMA). It has been shown that narrowing of AMA increases risk of systolic anterior movement (SAM). METHODS Sonomicrometry crystals were implanted in six sheep at the left ventricular (LV) apex, PM tips (M1, M2), FT (T1, T2), posterior mitral annulus (PMA), and base of aortic right coronary sinus (RCS). The retracting force of ascending aorta was measured. RESULTS Transection of SC resulted in an increase of distance M1-T1 and M2-T2. Consequently, the AMA narrowed at end systole by -3.26+/-0.85 degrees (p<0.05) and at end diastole by -4.16+/-1.28 degrees (p<0.05). A force of 1.8+/-0.2 N was needed to pull the recoiling ascending aorta back to its original position. CONCLUSIONS The elastic recoil of ascending aorta is balanced by SC, which connect PM to FT and constitute the center of the LV base. Transection of SC narrows AMA and increases the risk of SAM.

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