Structure-specific variation in pediatric echocardiographic Z scores across the nutritional spectrum: four body-surface-area nomograms and a BMI-adjusted GAMLSS model

Abstract Purpose Z score nomograms, the standard for interpreting pediatric echocardiographic dimensions, derive mostly from eutrophic populations. We assessed whether cardiac structure Z scores vary with body mass index Z score (BMIz) across four body-surface-area (BSA)-based nomograms, and whether a BMI-adjusted reference mitigates this bias. Methods Retrospective study of 1883 children aged 5–18 years with structurally normal echocardiograms (2016–2021). Eleven cardiac structure diameters were analyzed and Z scores computed with four nomograms (Pediatric Heart Network, Detroit, Toronto, Italy) and, for ten structures, with a fifth based on generalized additive models for location, scale and shape (GAMLSS) adjusted for body size, BMI and age. Associations with BMIz used linear regression in three nested models with false discovery rate correction. Results Overall, 25.8% were overweight and 15.8% had obesity. Absolute diameters increased with BMIz in every structure (p < 0.001), yet Z scores of most left-sided structures were inversely associated with it, most strongly for the four aortic levels (β − 0.325 to − 0.182, significant in all 45 nomogram-by-model comparisons) and for left ventricular end-diastolic diameter. Ventricular walls showed no consistent pattern; right-sided annuli varied non-monotonically. Under GAMLSS these associations were abolished in the most affected structures, persisted in the sinotubular junction and walls, and reversed in sign in the pulmonary annulus. Conclusion Z scores of most left-sided structures were lower in obesity than their absolute dimensions suggest, so interpretation must account for nutritional status and the reference. Persisting bias follows model construction: the three structures whose GAMLSS equations omit BMI are exactly those still biased.