Obstructive Thebesian valve: anatomical study and implications for invasive cardiologic procedures.

Thebesian valve is the embryological remnant of the right sinoatrial valve, guarding the coronary sinus (CS) ostium. Advanced invasive and interventional cardiac diagnostic and management tools involve cannulation of the CS ostium. The presence of obstructive Thebesian valves has been reported to lead to unsuccessful cannulation of the CS. We studied the morphology of the Thebesian valve and CS ostium to assess the possible impact of these structures on invasive cardiological procedures. One hundred fifty randomly selected human cadaveric heart specimens fixed in 10% formalin were dissected in the customary routine manner. The Thebesian valves were classified according to their shape as semilunar/fenestrated/biconcave band like and according to their composition as membranous/fibromuscular/fibrous/muscular, and the extent to which the valve covered the CS ostium was also noted. An obstructive Thebesian valve that could interfere with the cannulation of the CS was defined as non-fenestrated (semilunar/biconcave band like) and non-membranous (fibromuscular/fibrous/muscular) valves covering >75% of the CS ostium. Thebesian valves were present in 118 (79%) heart specimens, of which 27 (18%) met the criteria of being obstructive. Semilunar was the most common type of Thebesian valve in terms of shape and was observed in 65 (65/118; 55%) hearts. This type was associated with the least mean craniocaudal (7.9±0.6 mm) and mean transverse (6.25±0.6 mm) diameters of the CS ostium. The mean craniocaudal diameter of the CS ostium (9.4±2.1 mm) was significantly larger (p=0.004) than the mean transverse diameter (7.15±1.5 mm) in specimens with Thebesian valves, and the cranial margin of the CS ostium was free from any attachment of the Thebesian valve in all the types observed (in terms of shape). Hence, attempts to direct the tip of the catheter toward the cranial margin of the CS ostium under direct vision may lead to successful cannulation of the same when conventional techniques have been unsuccessful because of the presence of an obstructive Thebesian valve.