**2. Tricuspid regurgitation**

#### **2.1 Anatomy of the tricuspid valve**

The TV is a complex structure composed of three leaflets (septal, anterior and posterior), a fibrous TV annulus (TVA) in which these leaflets are inserted, at least two papillary muscles with multiple tendinous cords and the adjacent atrial and RV myocardium. Despite these general considerations, anatomical interindividual variability is high, and it is not so rare to find four or even five TV leaflets instead of three [9–11]. The anterior leaflet is usually more prominent and extends from the infundibular region to the inferolateral wall. The posterior leaflet is smaller and, in some cases, hypoplastic, and it is inserted along the posterior margin of the TVA from the septum to the inferolateral basal segment. Lastly, the septal leaflet is fixed along the interventricular septum from the infundibulum to the posterior ventricular margin.

The fibrous TVA is not a flat structure but elliptic in shape under normal preloading conditions, with the posterolateral portion at a lower or more apical position and the anteroseptal portion in a higher or more atrial situation. Like the mitral valve annulus, the TVA is dynamic and changes shape and size during the cardiac cycle. TV is the largest and the most apically positioned heart valve, and can measure up to 9 cm2 in size in healthy subjects.

The subvalvular apparatus is composed of the tendinous cords and the papillary muscles. Usually, there are two different papillary muscles, anterior and posterior, but not infrequently, a third septal papillary muscle can be found. The anterior papillary muscle is the largest of these muscles and gives rise to cords that sustain the anterior and posterior leaflets, while the posterior papillary muscle supports mainly the posterior and the septal leaflets. The septal leaflet is normally directly fixed to the septal ventricular wall by third order tendinous cords, resulting in reduced displacement during the cardiac cycle.

From an interventional perspective, some issues should be highlighted that may pose technical difficulties for an invasive approach [12–14]:


*Percutaneous Treatment of Tricuspid Regurgitation DOI: http://dx.doi.org/10.5772/intechopen.95799*

