The dynamic shape of the normal adult mitral annulus has been shown to be important to mitral valve function. However, annular dynamics of the healthy mitral valve in children have yet to be explored. We sought to model and quantify the shape and major modes of variation of pediatric mitral valve annuli at four phases in the cardiac cycle using transthoracic echocardiograms.

The mitral valve annuli of 100 children and young adults with normal 3D echocardiograms were modeled in four different cardiac phases using the SlicerHeart extension for 3DSlicer. Annular metrics were quantified using SlicerHeart and optimal normalization to BSA was explored. Mean annular shapes and the principal components of variation were computed using custom code implemented in a new SlicerHeart module (Annulus Shape Analyzer). Shape was regressed over metrics of age and body surface area (BSA) and the mean shapes for five age-stratified groups were generated.

The annular height to commissural width ratio (AHCWR) of the mitral valve (“saddle shape”) changed significantly through age for systolic phases (p<0.001) but within a narrow range (Medians 0.20-0.25). Annular metrics change statistically between the diastolic and systolic phases of the cardiac cycle. Visually, the annular shape was maintained with respect to age and BSA. Principal component analysis revealed that the pediatric mitral annulus primarily varies in size (Mode 1), AHCWR (Mode 2) and sphericity (Mode 3).

The saddle shaped mitral annulus is maintained throughout childhood but varies significantly throughout the cardiac cycle. The major modes of variation in the pediatric mitral annulus are due to size, AHCWR, and sphericity. The generation of age- and size-specific mitral annular shapes may inform the development of appropriately scaled absorbable or expandable mitral annuloplasty rings for children.