Pathologic insights into tricuspid valve morphology: impact on the standard echocardiographic nomenclature

Abstract Background Once underestimated, the tricuspid valve (TV) is now recognized for its critical prognostic impact. In recent years, tricuspid regurgitation has gained attention as a major cause of morbidity and mortality, igniting the development of transcatheter therapies. Detailed leaflet anatomy evaluation is key to determining both the feasibility and effectiveness of these interventions. Purpose To assess the normal TV apparatus anatomy and provide guidance for tricuspid interventions. Methods The TV apparatus was assessed in a consecutive series of 100 formalin-fixed hearts without structural disease. The following morphological data were obtained: number of scallops for each leaflet, anulus circumference, anterior leaflet (AL), septal leaflet (SL) and posterior leaflet (PL) width and length (Fig.), leaflet width/annulus ratio, location and number of papillary muscles (PM) and number of PM heads. Presence and length of chordal-free zones (CFZs) were also assessed. Results Mean TV annulus circumference was 11.6 ± 0.1 cm, with no significant difference between males and females. In all cases, three commissures and three leaflet were identified. The mean width and length were 4.4 cm and 2.3 cm for the AL, 4.0 cm and 2.0 cm for the posterior (PL), 3.2 cm and 1.7 cm for the septal (SL), respectively. Commissural accessory tissue was present in 27% of the antero-septal and 10% of the antero-posterior commissures. A single scallop leaflet was present in 97% of AL, 44% of PL and 95% of SL. The most frequent leaflet pattern was single scallop AL and SL with two scallops PL (45% of cases). The mean [interquartile range (IQR)] of the ratio of leaflet: TV annulus circumference were: AL/TV ratio 37.7 [IQR 33.3, 40.5], SL/TV ratio 27.4 [IQR 23.2, 30.6], PL/TV ratio 34.9 [IQR 23.2,30.6] The septal PM was absent or rudimentary in 65%. The anterior PM (APM) was a single muscular bundle in 94% of cases, while the posterior PM (PPM) was the most variable ranging from one in 45% to five heads in 2% of cases. In 16% of cases, the APM was not centered in the antero-posterior commissure but positioned in the middle of the AL. At least one CFZ was present in all cases in the AL, in 66% in the PL and in 57% in the SL. Conclusion The anatomy of the TV is highly variable. The most frequent leaflet pattern is the four scallop TV. In nearly half of cases, the TV consists of single scallop AL and SL and two scallops PL. The APM is not always the landmark for the antero-posterior commissure and the AL/anulus ratio is variable. These results contribute to a better understanding of the anatomy of the TV, which is essential for the successful management of transcatheter TV repair.