Morphologic classification of the mitral papillary muscles.

BACKGROUND AND AIMS OF THE STUDY

Mitral homograft replacement requires a good knowledge of the anatomy of the papillary muscles. Clinical experience with mitral homografts has revealed an as yet unexplored aspect of the morphology of the mitral subvalvular apparatus, that is correspondence between papillary muscle sub-divisions and chordal attachment to the leaflets.

METHODS

To further our understanding we subjected 65 normal hearts to close scrutiny which confirmed our perioperative observations.

RESULTS

We could establish a classification based on the ways that the papillary muscles relate to the leaflets via the chordae. Four types are described. In type I the papillary muscle is single. In type II the papillary muscle has two heads, one of which sends chordae exclusively to the posterior leaflet. In type III the papillary muscle is also divided, one head supporting the commissural area exclusively. Type IV PM resembles type III but is distinguished from it in the way that the head supporting the commissure is very short. In this type the different heads also originate at different levels on the ventricular wall from the apex to the base.