Table 1.

Anatomic considerations for transcatheter tricuspid valve intervention (TTVI).

Anatomic findings	Considerations for TTVI
Leaflets and commissure
- Three leaflets, but variable for deep clefts, scallops and folds. - Very thin leaflets - Larger anterior leaflet with the greatest motion - Posterior leaflet with a variable number of scallops - Short and less mobile septal leaflets - Commissures supported by numerous fan-shaped chords - Commissures usually do not reach the annulus, but several millimeters of leaflet tissue remain sometimes in the form of small scallops	- Imaging leaflet anatomy may be challenging - Thin leaflets are not ideal for anchoring devices - Greater leaflet motion (especially anterior leaflet) may cause high leaflet stress - Maneuvering to capture short and multiscallops leaflet may be difficult - Edge-to-edge devices positioned in commissural region may interfere with the coaptation due to fan-shaped chords distortion.
Tricuspid annulus
- Large valve orifice (normal orifice area of 7–9 cm2, increased in TR) - Saddle-shaped/flat structure - Dynamic along the cardiac cycle - Discontinuous fibrous support - Usual absence of calcification	- Stenosis is unlikely with central orifice devices - Stability of devices within the tricuspid annulus may be challenging - Disadvantageous landing zone for prosthesis - Suboptimal anchoring - Risk of paravalvular regurgitation
Chordae and papillary muscles
- The anterior papillary muscle is the largest, supplying chords to the anterior and posterior leaflets - Septal leaflet chords insert directly into the septum or with multiple, small papillary muscles - A large number of chords with various patterns composed of straight collagen bundles, which make chords little distensible	- Papillary muscles serve as an imaging landmark for leaflets and commissures - Marked tethering results from dilation of the right ventricle or displacement of papillary muscles - Catheters and devices may imping with chordae - Location of the moderator band and prominent trabeculae regarding protrusion of the prosthesis into the RV should be assessed
Surrounding structures
- Thin-walled and markedly dilated RA - Dilated RV - SVC: mean length ~7 cm, maximum diameter ~2 cm, funnel-shaped ostium in case of large RA - IVC: extremely dilated and distorted - Coronary sinus enters RA at PS commissure - No continuity between inflow and outflow tract - RCA runs within the AV groove (variable transverse distance from annulus) - AVN, bundle of His crosses the septal leaflet attachment 3–5 mm posterior to the AS commissure - Non-coronary sinus of Valsalva is close to anterior/superior annulus and AS commissure - Pacemaker leads may interfere with leaflet mobility	- Large space to maneuver devices but more difficult for imaging - Adequate distance between the RV apex and the annular plane is mandatory in spacer device and orthotopic prosthesis implantation - Venous access may be limited by SVC diameters and irregular shape. - IVC-annular angle regard the TV plane may pose issues for device placement - Anatomic landmarks (coronary sinus, non-coronary aortic sinus, RCA) - Little risk for outflow tract obstruction - Risk of RCA injury - Risk for heart block with devices in AVN region - Intracardiac leads can create significant artifacts in CT and CMR imaging study, compromising image quality and interpretation - Intracardiac leads can interfere with device implantation

AVN, atrioventricular node; AS, anteroseptal; CMR, cardiac magnetic resonance; IVC, inferior vena cava; PS, post-eroseptal; RA, right atrium; RCA, right coronary artery; RV, right ventricle; SVC, superior vena cava; TR, tricuspid regurgitation; TV, tricuspid valve.