Thebesian valve: the guard dog of the coronary sinus?

When the Silesian physician Adam Christian Thebesius described the valve guarding the ostium of the coronary sinus, he could hardly imagine that this structure would attract attention of many researchers and clinicians more than 300 years later. 1 However, the advent of novel therapeutic techniques such as catheter ablation of cardiac arrhythmias, cardiac resynchronization therapy, and most recently percutaneous mitral repair have turned interest to this structure as an integral part of anatomy of the coronary sinus. The Thebesian valve is a caudal remnant of the embryonic sinoatrial valves. Whether it has any role in normal physiology is not known and some believe that it may prevent the regurgitation of blood into the sinus during the contraction of the atrium. However, experience from clinical practice suggests that the valve may pose difficulties in cannulation of the coronary sinus. Therefore, studies on anatomy of the Thebesian valve have potential practical implications. The paper by Mak et al. , 2 published in the current issue of the journal, provides another piece of knowledge in a mosaic. In a series of 75 autopsied human hearts (54 with organic heart disease), these authors confirmed a wide variety of Thebesian valve patterns. The valve was present in 73% of examined hearts. Most of these valves were membranous in composition (46%), followed by fibrous (24%), fibromuscular (11%), and muscular composition (18%). Fenestrations were noted in 26% of valves. Importantly, 16% of hearts showed a valve that covered more than 75% of the ostium and some were devoid of any fenestrations. Such morphology could make such variants potentially complicating the cannulation of the coronary sinus. The described data are in concordance with another large, recently published autopsy study by Pejković et al.3 who analysed 150 human heart specimens. They found Thebesian valve in 80% of cases. It covered one-third of the ostium in 29% of cases, one-half in another 27%, and two-thirds in 14%. The whole ostium was covered in 5% of cases. In 3% of cases, no ostium was revealed and large ostial valve of the middle cardiac veins was described. The middle cardiac vein entered the proximal coronary sinus in 92% of specimens. These are additional drawbacks for smooth catheterization of the coronary sinus. Both studies expanded previous knowledge from smaller anatomical series that documented significant variability in the presence and arrangement of a Thebesian valve. 4–6 Therefore, we can conclude that Thebesian valves are present in 65–95% of heart specimens. In about 5–20% of cases, potentially complicating Thebesian valves can be found. However, the first attempt to demonstrate how the Thebesian valve could interfere with cannulation of the coronary sinus was made on isolated heart apparatus filled with modified Krebs–Henseleit buffer. 7 Such a model enables direct visualization of internal structures of the functioning heart, including the Thebesian valve. In a recent study on 15 heart specimens, some difficulties to enter coronary sinus via obstructing Thebesian valve were documented. More recently, a special fiberoptic endocardial technique was used in vivo to visualize coronary sinus ostium during implantation of the left ventricular lead for cardiac resynchronization therapy. 8 In this study, coronary sinus anatomy was evaluated in 100 consecutive heart failure patients planned for implant procedure. An 8F steerable catheter with a balloon at tip and an embedded light-emiting diode as the light source was used. Fiberoptic endoscope located within the balloon enabled visualization of endocardial structures. The coronary sinus ostium was successfully displayed in 98 patients and Thebesian valve was observed in 53 of them (54%). This relatively low prevalence of the valves compared with anatomical postmortem studies may reflect limitation of the fiberoptic technique for visualization of very small valves. The most common morphology in vivo was a semilunar valve in 26 patients followed by valves characterized by fibrous strands and bands in 18 patients, and fenestrated valves were seen in 9 patients. Most of the valves originated from inferior (61%) or posterior (33%) aspect of the ostium. Anterior insertion of the valve was found in three patients (6%). The degree of coverage of the ostium was estimated as severe in 11% of subjects, while moderate in 47%, and mild in 42% of cases. However, the success of left ventricular lead implantation was not impaired by the extent of Thebesian valve coverage of the ostium. On the other hand, direct visualization of the valve anatomy could help adjust the strategy of cannulation. What conclusions for clinical practice can we draw from the above studies on the Thebesian valve? First, there is tremendous variability in the presence and arrangement of the Thebesian valve and large extent of coverage or other complicating anatomical variants can be found in 5–16% of cases. However, despite such a high prevalence of anatomical patterns that could result in low probability of cannulation of the coronary sinus, the real-life success of cannulation of the coronary sinus does not seem to be impaired. Dynamic studies showed that there is no clear relationship between cannulation success and the pattern of the Thebesian valve. Most probably, it is the continuous blood flow from the coronary sinus that keeps the valve opened and allows introduction of the catheter or delivery system into the coronary sinus even in cases of extensive coverage of the ostium by the valve. The success rate in cannulation of coronary sinus, especially in patients undergoing cardiac resynchronization therapy, is probably more influenced by distortion of the position and course of the coronary sinus and its ostium rather than by the pattern of Thebesian vein (see Figure 2 in Ref. 9). Second, Thebesian valve may consist of many fenestrations and/or fibrous strands. This may have an important implication for introduction of the delivery system for the left ventricular lead placement. Some operators often use the so-called haemodynamic approach to engage the coronary sinus and introduce a delivery system for the left ventricular lead. This strategy includes engagement of the coronary sinus with a wire and subsequent sliding of the delivery system over the wire in. Provided the wire enters the coronary sinus through the small fenestration in the Thebesian valve, introduction of the sheath may lead to damage of the coronary sinus ostium. The probability of such damage seems to be lower when using an electrophysiological approach to cannulation of the coronary sinus. 9 , 10 This strategy consists of introduction of a diagnostic electrophysiologic catheter into the coronary sinus and in subsequent sliding of the delivery sheath over the catheter. Since there is less or no mismatch between the diameter of the catheter and the sheath, there seems to be lower potential for damage of the proximal coronary sinus. In addition, the recordings of intracardiac electrograms from the distal bipole of the catheter provide immediate information about the location of the catheter tip, and prevent inadvertent manipulation inside the right ventricle. Our experience and the results of recently published randomized study suggest that the analysis of electrograms appears to facilitate cannulation of the coronary sinus and results in very low fluoroscopic times for implantation procedure. 9 , 10 Conflict of interest: none declared.