Normal Tricuspid Valve Annulus Dimensions
The normal tricuspid annulus in healthy adults measures approximately 28-30 mm in the minor dimension and 36 mm in the major dimension on 3D echocardiography, with an area of 8.6 ± 2.0 cm² and perimeter of 10.5 ± 1.2 cm at end-diastole. 1
Key Measurement Parameters
Three-Dimensional Echocardiographic Values (Reference Standard)
3D transthoracic echocardiography provides the most accurate assessment of tricuspid annular dimensions, as 2D measurements consistently underestimate the true annular size due to the complex, non-planar geometry of the tricuspid annulus. 1, 2
Normal values at end-diastole (tricuspid valve closure):
- Area: 8.6 ± 2.0 cm² 1
- Perimeter: 10.5 ± 1.2 cm 1
- Major (longest) dimension: 36 ± 4 mm 1
- Minor (shortest) dimension: 30 ± 4 mm 1
- Circularity index: 0.83 ± 0.10 1
Two-Dimensional Measurements (Systematically Underestimate)
Traditional 2D measurements from apical four-chamber views underestimate the true annular dimensions because they cannot capture the longest dimension of the elliptical, saddle-shaped annulus. 2, 3 The 2D measurements are view-dependent and assume symmetrical enlargement, which is a significant limitation. 4
Common pitfall: Using 2D measurements alone will lead to underestimation of annular size by approximately 3-4 mm compared to 3D measurements. 3 This has critical implications for surgical planning, as current guideline recommendations for tricuspid valve repair (≥40 mm diameter threshold) are based on 2D measurements. 2
Dynamic Changes Throughout Cardiac Cycle
The tricuspid annulus is a dynamic structure that changes significantly during the cardiac cycle:
- Largest dimensions: Late diastole 1, 5
- Smallest dimensions: Mid-systole to end-systole 1, 5
- Fractional area change: 35 ± 10% 1
- Fractional changes in perimeter and dimensions: ≥20% 1
Measurement timing is critical: Measurements should be obtained at end-diastole (at tricuspid valve closure) for standardization and reproducibility. 1, 5
Sex and Body Size Considerations
Women have significantly larger indexed tricuspid annular perimeter and longer long-axis dimensions compared to men, even after indexing to body surface area. 1 This finding emphasizes that gender-specific reference values should be applied when assessing annular dimensions. 1, 5
No significant age-related changes in tricuspid annular parameters have been identified in healthy adults. 1
Measurement Methodology Recommendations
Preferred Approach: 3D Echocardiography with Dedicated Software
Semiautomated 3D analysis software provides superior accuracy and reproducibility compared to multiplanar reconstruction (MPR), with intraclass correlation coefficients of 0.94-0.96 versus 0.82-0.90 for MPR. 5 This methodology accounts for the non-planar, saddle-shaped geometry of the tricuspid annulus, which cannot be accurately captured by 2D imaging or simple MPR techniques. 2, 5
Transthoracic vs. Transesophageal Approach
3D transthoracic echocardiography can be used instead of 3D transesophageal echocardiography for tricuspid annular measurements, as there are no significant differences between the two approaches when adequate image quality is obtained. 2 This is advantageous because it avoids the need for sedation and the invasive nature of TEE. 2
Clinical Implications for Pathology
Significant tricuspid annular dilatation requiring intervention consideration is defined differently depending on measurement technique:
- Traditional 2D guideline threshold: ≥40 mm diameter 2
- However, this threshold likely underestimates true annular size and a higher 3D-based cutoff value needs to be established 2
The tricuspid annulus correlates with both right atrial and right ventricular volumes, suggesting that both chambers are determinants of annular size. 1 This relationship is important when evaluating secondary tricuspid regurgitation. 6
Measurement Technique Specifics
When performing 3D measurements, the analysis should include:
- Major and minor axes at the hinge points of the tricuspid leaflets 1, 5
- Annular area by direct planimetry accounting for non-planarity 2, 5
- Perimeter measurement 1, 5
- Circularity index (shortest/longest dimension ratio) 1, 3
Critical technical point: The tricuspid annulus orientation varies significantly in patients with tricuspid regurgitation, with posterior displacement most common in atrial fibrillation. 3 This orientation affects the accuracy of 2D measurements and explains inconsistencies between 2D and 3D values. 3