## 4 Computed Tomography and Tricuspid Valve
### CT Assessment of the Tricuspid Apparatus for Transcatheter Procedures
[110], in patients with TR \(\geq\) 3+, CT exhibited greater tricuspid annulus and RV dimensions and marked tethering of the anterior and septal tricuspid leaflets compared to those with mild valvular defects. Of note, the grade of functional TR was independently correlated with the anteroposterior annulus diameter. The features of leaflet tethering, including tenting height, angle, and area, can be obtained with CT scan and compared to the ones visualized with echocardiography. The edge-to-edge repair using the Triclip (Abbott Vascular, Santa Clara, CA, USA) or PASCAL systems (Edwards Lifesciences, Irvine, CA, USA) allows bringing the TV leaflets closer, thus reducing the grade of regurgitation. The role of CT in the edge-to-edge repair is less important than the other techniques, even if viable information about the coaptation gap, annulus, and right chamber remodeling can be obtained [111]. Moreover, as described for the mitral valve, measuring the anatomical regurgitant orifice area (AROA) by CT is also feasible. It may be an additional grading tool for TR severity in patients with contradictory echocardiographic parameters [112]. Notably, this flow-independent parameter of TR severity provided by CT has been reported to strongly correlate with the 3D measurement of vena contracta (thus with three-dimensional assessment of the narrowest flow region of the tricuspid regurgitant volume), using transesophageal echocardiography [108]. The dimensions of the RV and RA are also crucial for evaluating the anatomic feasibility of transcatheter therapies. RA must allocate the delivery catheter and be large enough for various maneuvers during the procedure [11]. Furthermore, with the promising results of the trials regarding transcatheter TV replacement, assessing the right chambers is more important than ever. Some valves are used in high-risk patients, such as NaviGate bio prosthesis (NaviGate Cardiac Structures, Lake Forest) or EVQQUE valve (Edwards Lifesciences). In this setting, RV volume, the distance between the RV apex and the tricuspid annular plane, the location of the papillary muscles, the moderator band, and the presence of prominent trabeculae must be assessed with regard to the protrusion of the prosthesis into the RV, most notably to avoid RV outflow tract obstruction [111]. Tricuspid valve replacement is also challenging due to the lack of calcifications at the level of the tricuspid annulus [113]. The Melody prosthesis (Medtronic, Minneapolis) is usually used in transcatheter tricuspid valve-in-valve and valve-in-ring procedures. In this setting, 3D CT measurement of the effective inner diameters of the ring is fundamental to bypass the differences reported in the nominal size documented by surgical report [114]. Annuloplasty devices, such as Cardioband(tm) (Valtech Cardio, OrYehuda, Israel), use a transfemoral ring or suture-based approach to reduce the diameter in cases where annular dilation is the major pathophysiological mechanism. Therefore, in this type of transcatheter repair procedures, it is also essential to evaluate the structures surrounding the tricuspid annulus, particularly the course of the right coronary artery, that could be damaged. The vessel course in relation to the annulus is variable. An RCA course at the annular level was shown in 65% of patients, a superior (i.e., atrial) course in 10%, and a crossing course in 25% [115]. Finally, measurement of the inferior vena cava plays a role in some interventional procedures aiming to reduce TR. In the heterotopic implantation of valves in the caval veins, balloon-expandable transcatheter aortic valve prostheses such as Sapien XT (Edwards Lifesciences) are placed to reduce blood backflow and prevention of venous congestion. Other systems, such as the TricValve system (P&F, Vienna) or the Tricento (NVT AG, Muri), are deployed top-down from the superior to the inferior vena cava, improving pressure's profile in the right atrium.