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Thebesian sinusoids: forgotten collaterals to papillary muscles
1Department of Pathology, Health Sciences Centre, Winnipeg, Manitoba, Canada. taylorjr@cc.umanitoba.ca
Insights
Thebesian sinusoids, primitive blood vessels, extend to the tips of papillary muscles in the human heart, especially during ischemia. This sinusoidal network may protect papillary muscles from ischemic damage by supplementing arterial blood flow.
Area of Science:
- Cardiovascular Anatomy
- Vascular Biology
- Cardiac Physiology
Background:
- Papillary muscles of the left ventricle are vulnerable to ischemic damage.
- Thebesian sinusoids are primitive vessels that supply nutrients to the embryonic heart.
- Sinusoids may offer protection to papillary muscles against ischemia.
Purpose of the Study:
- To investigate the presence and extent of sinusoids within the papillary muscles of the adult human heart.
- To determine if sinusoids reach the apex of the papillary muscles.
Main Methods:
- Adult human hearts, both healthy and with ischemic lesions, were analyzed.
- Papillary muscle sinusoids were visualized using black ink perfusion from the left ventricular apex.
- Specimens were examined macroscopically, microscopically, and stereoscopically after clearing.
Main Results:
- A network of intertrabecular spaces connects the left ventricular apex to the papillary muscle bases.
- Sinusoids were observed extending from the papillary muscle bases to their tips in most hearts.
- Sinusoidal presence was more pronounced in papillary muscles from ischemic hearts compared to the adjacent ventricular free wall.
Conclusions:
- Thebesian sinusoids may provide a supplementary blood supply to papillary muscles, potentially mitigating ischemic damage.
- The apex of the human left ventricle appears adapted to facilitate sinusoidal blood flow to the papillary muscles.
- This vascular adaptation could play a crucial role in the resilience of papillary muscles to coronary occlusion.
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.