Size and Function of the Right Atrium in Healthy Children by Three-Dimensional Echocardiography

Right atrial volume (RAV) and function have proven prognostic value in the assessment of cardiac disease and may be more accurately assessed using three-dimensional echocardiography (3DE). Normal 3DE reference values for the right atrial (RA) volume and function in healthy children have not yet been published. Furthermore, current methods of indexing cardiac measurements to body surface area (BSA) alone may be insufficient. We aimed to develop reference values for 3DE-derived RAV and function in the pediatric population, to provide a comparison of regression methods using BSA, height, weight, and sex, and to compare 3DE values to two-dimensional echocardiography (2DE) derived volumes.

We retrospectively analyzed 187 3DE datasets acquired for a multi-center study on healthy children at two international centers. 3DE volumes were measured with vendor-agnostic software (Tomtec), and 2DE endo-diastolic volume (EDV) using the area-length single-plane approach. Regression curve-fitting of height (Ht), weight (Wt), BSA, and sex were explored to optimize Pearson coefficient and homoscedasticity.

The relationship of 3DE RAVs to BSA alone was heteroscedastic, with a residual positive relationship on indexing (R² = 0.2506). Optimal regression of Ln (Volume) = b0 + x*Ln (Ht) + y*Ln (Wt) + z*Sex was homoscedastic. Total RA emptying fraction (EF) did not vary across age or sex, however active and passive emptying was best fit by a spline curve with a knot at approximately BSA = 1 m². Strong agreement with 2DE-derived EDV was present (r² = 0.83).

We provide reference values for RA size and function in the pediatric population and provide a comparison of methods for indexing these values.