Anatomical variations of the coronary sinus ostium area of the human heart.

Classic anatomical dissection of 150 heart specimens from adults aged 18 - 80 years was performed. The Thebesian valve was absent in 20% of cases and, in these, 4% had a large ostial valve of the middle cardiac vein in front of the coronary sinus ostium. Fibres of Chiari were found in 10% of cases. Ostia of the middle cardiac vein, posterior veins of the left ventricle, small cardiac vein and deep cardiac veins were present in the distal 10 mm of the coronary sinus. Some samples had ostial and/or parietal valves or antivalves that sometimes contained muscular fibres. Distal accessory parietal valves (2%) and antivalves (1%) of the coronary sinus wall were found at a distance of 4 - 7 mm from its ostium. The frequency and variability of anatomical structures in the area of the coronary sinus ostium probably influence the haemodynamics of this area. Knowledge of and being able to identify these anatomical variations may help in identifying and overcoming potential difficulties in treating arrythmias and in cardiosurgery.