Role of chordae tendineae in mitral valve opening: two-dimensional echocardiographic evidence.

Study of 16 normal and 33 flail mitral valves provides evidence of the active participation of chordae tendineae in mitral valve opening. The normal valves have straight chordae at all phases of opening. During isovolumic relaxation and progressive opening phases, the smooth configuration of the mid-anterior mitral leaflet is broken by a sharp outward "tenting." This tenting is localized at chordal insertions, reflecting significant tension at these points. Flail mitral valves allow comparison of opening motion between mitral segments with normal chordal attachment and flail segments without chordal support. Posterior flail leaflets demonstrate delay in initiation of opening motion relative to the normal anterior leaflet. The most dramatic examples of this delay reveal a maximal opening excursion of the anterior leaflet before the flail posterior leaflet initiates opening motion. The untethered free margins of opening flail anterior leaflets produce the appearance of the flail segment trailing the body of the anterior leaflet with a sharp break in leaflet contour between the supported and unsupported segments. These configurational expressions of mitral valve opening are inconsistent with a passive hemogenic mechanism. They support an active myogenic process mediated through direct traction on the valve by the chordae tendineae.