The functional and clinical anatomy of the mitral valve.

This paper is based largely on personal observations of normal and stenosed mitral valves. Some aspects that are new and some that are not in keeping with present-day concepts will be discussed. The mitral valve is a unit that consists of a so-called fibrous "ring," of two unequal cusps, of two sets of papillary muscles, and of numerous chorde tendinee. When two triangular leaflets are attached at their bases to the whole circumference of a ring and their corresponding free margins are brought into apposition, then a cone is formed. The mitral valve consisting, as it does, of two cusps, each somewhat triangular and each attached at its base to the mitral ring, is, therefore, when the cusp margins are in contact, cone-shaped. The significance of and the necessity for an "elongated" mitral "cone" was appreciated by William Harvey in 1628. In a cone-shaped valve, marginal contact alone would not give the same firm and complete valve closure as would total obliteration of the lumen of the cone when there is complete contact between the inner surfaces of the cusps. To obtain such surface contact a force is required to act on the cone from below. This force is the intraventricular systolic pressure. The mitral valve is a flat cone. Had it been a circular cone, then considerable excursion of the cusps, with more wear and tear, and an unduly high subvalvular pressure, and therefore a high systemic pressure, would have been required to close the lumen of the valve-cone during systole. The antero-medial cusp is a hinged extension into the cavity of the left ventricle of the postero-lateral aortic root. The hinge is the corresponding antero-medial half of the mitral "ring" and is formed by the common fibrous origins of the postero-lateral half of the aortic root, of the antero-medial cusp, and the major part of two aortic cusps. As the base of this mitral cusp is attached to the origin from the aortic root of two adjacent aortic cusps, the antero-medial half of the mitral "ring" is bi-concave (Fig. 1). Had the antero-medial half of the mitral "ring" been semi-circular or semi-ovoid, then the entire base of the antero-medial cusp could not have hinged on the entire postero-lateral half of the root of the aorta. The postero-lateral half of the mitral "ring" is formed by the common fibrous origins of the postero-lateral cusp and of the corresponding part …