Anterior Mitral Basal 'Stay' Chords are Essential for Left Ventricular Geometry and Function

Background and aim of the study: Among the anterior mitral basal chords, two particularly strong and thick stay chords (SC) remain under tension during the entire cardiac cycle. Collagen fibers of the anterior mitral leaflet (AML) are oriented from insertion of the SC on the AML to the fibrous trigones (FT), suggesting that local stress is directed from the papillary muscles (PM) over the SC and AML to the FT, maintaining left ventricular (LV) geometry. Methods: Sonomicrometry crystals were implanted in sheep at the LV apex (A), the anterior (AW) and septal (SW) LV wall, the PM tips (M1 and M2), the SC insertion into the AML (S1 and S2), the posterior (PMA) and lateral (P1 and P2) mitral annulus, the FT (T1 and T2), the tips of the anterior (AL) and posterior (PL) mitral leaflets, and the base of the aortic right coronary sinus (RCS). Changes in distances, areas, and volume were time-related to aortic flow and LV and ascending aorta pressures. Recordings were taken at baseline and after transection of the SC. Results: After transection of the SC, the systolic distance from M1-T1 increased by +0.96 ± 0.41 mm (p <0.05) and from M2-T2 by +0.97 ± 0.42 mm (p <0.05). The LV length increased at T1-A by +1.14 ± 0.60 mm (p <0.05) and at T2-A by +0.97 ± 0.37 mm (p <0.05). The aortomitral angle narrowed at end-systole by ‐3.26 ± 0.85° (p <0.05). Transection of the SC reduced dP/dt by ‐11.20 ± 5.29% (p <0.05), maximum aortic flow by ‐16.89 ± 7.86% (p <0.05), and maximum pressure-volume ratio by -10.83 ± 3.36% (p <0.05). Conclusion: Transection of the anterior mitral SC did not result in mitral regurgitation but induced significant changes in LV geometry, including narrowing of the aortomitral angle and subsequent deterioration of LV function. The SC are essential for maintaining normal LV geometry and function.