Anatomy and clinical significance of ventricular Thebesian veins.

An injection study was carried out in sheep hearts to compare the anatomy and distribution of Thebesian veins (venae cordis minimae) in the ventricles. The left azygos, middle cardiac, small cardiac, and anterior cardiac veins were ligated in 36 hearts, and India ink was injected into the right coronary artery or the left coronary artery or the coronary sinus. Examination revealed foramina Thebesii in both of these cardiac chambers. Myocardial tissue samples were taken, and 12 were subsequently studied histologically to confirm the presence of Thebesian veins. A greater number of Thebesian veins were observed in the right ventricle than in the left (P < 0.05). To identify any larger communications between the coronary arteries and cardiac chambers (arterioluminal), and between the coronary veins and cardiac chambers (venoluminal), gelatine was injected in 16 hearts. Arterioluminal vessels were identified only in the right ventricle, whereas venoluminal vessels were present in both ventricles. Venoluminal vessels are most likely responsible for the non-nutritive shunting of cardioplegic solutions delivered via the coronary sinus during surgery. Thebesian veins play a role in the drainage of blood, contributing towards right to left shunting of deoxygenated blood. It has also been suggested, although not proven, that they are able to supply blood to the myocardium in coronary arterial occlusion, thus acting as a natural form of nutrient channel. Thebesian veins may be confused with artificial nutrient channels constructed by transmyocardial laser revascularization, a possibility that should be considered during histological evaluation of this technique.