Muscularization of the chordae tendinea of the mitral anterior papillary muscle.

The chordae tendineae, described as fibro-collagenous structures, support the leaflets of the atrioventricular valves of the heart in various ways. The chordae tendineae are composed of collagen and elastic fibers. They connect to the ventricular side of the valve leaflets' free border and hinder the leaflets from swinging back into the atrial cavity during systole. Mitral valve chordae tendineae have been classified using a variety of classification systems. To our knowledge, we report a variant chordae tendinea that has yet to be described in the literature. The variant, present only on the mitral anterior papillary muscle, did not show the characteristic appearance of the chorda tendineae. Muscular fibers were observed extending from a larger than usual mitral anterior papillary muscle, inserting into the rough zone of the anterior leaflet. Several tendinous primary and secondary true leaflet chordae emerge from the apical portion of the anterior papillary muscle, inserting into the anterior leaflet's free edge and rough zone. Contraction of this muscular chorda during systole could disrupt the mechanics of valvular closure and result in possible regurgitation across the mitral valve. Additionally, this structure may be subject to rupture during myocardial infarction, leading to valvular dysfunction. The developmental connection between the chordae and papillary muscles could explain the anomalous muscularization of the chordae tendineae observed in this case.