Thebesian sinusoids: forgotten collaterals to papillary muscles

Abstract

Background: Papillary muscles of the left ventricle are prone to ischemic damage but seldom rupture, perhaps because they are protected by transendocardial diffusion and thebesian sinusoids as well as by arteries. Sinusoids are primitive vessels that precede coronary arteries as nutrient suppliers to all parts of the embryonic heart.

Objectives: To determine whether sinusoids penetrate to the tips of papillary muscles.

Materials and methods: Adult hearts with and without evidence of acute and chronic ischemic lesions were selected. Papillary muscle sinusoids were perfused by black ink from the apex of the left ventricle. Papillary muscles and the adjacent ventricular free walls were then excised and fixed before gross and microscopic examination for inked sinusoids. Some fixed specimens were cleared through methyl salicylate and examined stereoscopically.

Results: The meshwork of trabeculae and, importantly, intertrabecular spaces lining the apex of the left ventricle continue into the deeply undercut bases of papillary muscles. In most hearts, sinusoids can be shown to extend from the undercut bases to the tips of human papillary muscles, especially in ischemic hearts. The compact myocardium of the adjacent ventricular free wall contains few sinusoids.

Conclusions: Sinusoids may supplement normal arterial flow to papillary muscles and mitigate the effects of coronary occlusion. The authors hypothesize that the apex of the human left ventricle is adapted for sinusoidal flow to papillary muscles.