Mitral valve apparatus. A spectrum of normality relevant to mitral valve prolapse.

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Abstract
The intricate anatomy of the mitral valve apparatus suggests that variations in its architecture may have functional significance. Deviations from a basic scheme of normality of chordal support were documented, with particular reference to the occurrence of deficient chordae. Chordae were considered deficient when they had an irregular branching pattern, not compensated by neighboring chordae, leaving parts of the valve leaflets less well supported than others. One hundred normal heart specimens were studied, in which the mitral valve in the unopened state showed a regular appearance, and compared with 40 hearts in which the valve showed a deformity, classified as ballooning in 38 cases and as prolapse in two. Deficient chordae were identified in 8 of the 100 normal hearts and in 36 of the 40 hearts with a valve deformity. In the latter group the chordal deficiency was directly related to the leaflet deformity present. Deficiencies in chordal branching and distribution affected commissural chordae and rough zone chordae, showing a particular preference for the posteromedial commissural area and the middle scallop of the posterior leaflet. The latter abnormalities showed a tendency to be associated with finger-like posteromedial papillary muscle groups and a haphazard arrangement of chordal take-off. Both specimens with necropsy evidence of prolapse had such an arrangement. There is evidently a spectrum of normality regarding the anatomy of the mitral valve chordal apparatus. It provides an anatomical basis for echocardiographic recordings of disharmonious mitral valve movements, frequently recorded among otherwise healthy individuals. Such minor variations may play a role in the pathogenesis of the syndrome of mitral valve, prolapse, by rendering unsupported parts of leaflets particularly vulnerable to high pressures.