Normal Reference Values and Reproducibility of Tricuspid Annulus Dimensions Using Cardiovascular Magnetic Resonance

Tricuspid annular (TA) dilation is a key process in functional tricuspid regurgitation, but normal TA dimensions using cardiovascular magnetic resonance have not been established. We measured TA diameters in 66 healthy volunteers, aged 38 ± 11 years, during 3 different phases of the cardiac cycle (end-systole, early diastole, and end-diastole) and in 2 routinely acquired cardiovascular magnetic resonance imaging planes (4-chamber [4C] and right ventricular inflow-outflow [RVIO]). Three readers independently measured each value and 1 reader repeated measurements 1 month apart. The upper limit of normal (ULN) was calculated as 1.96 standard deviations above the mean. We assessed inter- and intraobserver reliability using the intraclass correlation coefficient (ICC) and Bland-Altman analysis. We found the TA diameter largest during early diastole in the 4C view with an ULN of 43 mm (22 mm/m²). Men had larger absolute TA diameters (36 mm, 95% CI 27 to 44 mm) than women (30 mm, 95% CI 23 to 37 mm) but not after indexing for body surface area (both 18 mm/m²). In the RVIO view, the largest TA diameter occurred during early diastole with a ULN value of 46 mm (27 mm/m²). In this view, females had a larger indexed TA than men (21 mm/m² vs 17 mm/m²). Reproducibility of measurements was excellent in all cardiac phases with an inter-rater ICC between 0.90 to 0.96 and an intrarater ICC 0.89 to 0.96. In conclusion, we have provided normative data regarding TA dimensions in routinely acquired 4C and RVIO views, and these values are larger than the current thresholds of annular dilation measured by echocardiography. Gender differences with the TA diameter in the RVIO view may be an important finding with consideration of future tricuspid devices.