Ultrastructural changes in spontaneous rupture of mitral chordae tendineae.

Mitral valves from ten patients with spontaneous rupture of mitral chordae were examined by light, scanning and transmission electron microscopy. Changes identified at rupture sites included oedema and necrosis of collagen, endothelial loss and, in some cases, partial or complete re-endothelialisation of the disrupted ends. With a solitary exception these abnormalities were confined to chordae which had actually ruptured. Some non-ruptured chordae were irregularly thinned and stretched but were normal by light and electron microscopy. Mucoid degeneration was almost invariable in mitral valve leaflets. These results suggest that spontaneous chordal rupture is more likely to be the result of abnormal mechanical strain rather than a diffuse connective tissue abnormality affecting multiple chordae. They may also provide theoretical justification for reconstruction rather than replacement of mitral valves in this condition.