Left ventricular mass is underestimated in overweight children because of incorrect body size variable chosen for normalization

Abstract

Background: Left ventricular mass normalization for body size is recommended, but a question remains: what is the best body size variable for this normalization-body surface area, height or lean body mass computed based on a predictive equation? Since body surface area and computed lean body mass are derivatives of body mass, normalizing for them may result in underestimation of left ventricular mass in overweight children. The aim of this study is to indicate which of the body size variables normalize left ventricular mass without underestimating it in overweight children.

Methods: Left ventricular mass assessed by echocardiography, height and body mass were collected for 464 healthy boys, 5-18 years old. Lean body mass and body surface area were calculated. Left ventricular mass z-scores computed based on reference data, developed for height, body surface area and lean body mass, were compared between overweight and non-overweight children. The next step was a comparison of paired samples of expected left ventricular mass, estimated for each normalizing variable based on two allometric equations-the first developed for overweight children, the second for children of normal body mass.

Results: The mean of left ventricular mass z-scores is higher in overweight children compared to non-overweight children for normative data based on height (0.36 vs. 0.00) and lower for normative data based on body surface area (-0.64 vs. 0.00). Left ventricular mass estimated normalizing for height, based on the equation for overweight children, is higher in overweight children (128.12 vs. 118.40); however, masses estimated normalizing for body surface area and lean body mass, based on equations for overweight children, are lower in overweight children (109.71 vs. 122.08 and 118.46 vs. 120.56, respectively).

Conclusion: Normalization for body surface area and for computed lean body mass, but not for height, underestimates left ventricular mass in overweight children.

Fig 1. The pairs of the LVM-for-body size curves defined by the allometric equations, corresponding to the OVER (dashed line) and NORM (solid line) groups.

The upper graph presents the LVM-for-height curves, the middle LVM-for-BSA, and the lower graph the LVM-for-computed LBM curves.

Fig 2. Scatter graphs of paired LVM values corresponding to the OVER (square) and the NORM (circle) equations and of differences between these paired values (triangle) plotted against BMI z-score.

Respective graphs show data which correspond to different explanatory variables, i.e., height, BSA and computed LBM. On each graph regression lines for the expected values and the differences are fitted–the solid line corresponds to the data computed based on the NORM equation, the dashed line corresponds to the data computed based on the OVER equation, and the dot-dash line corresponds to the differences.