Pediatric echocardiographic nomograms: What has been done and what still needs to be done.

Nomograms are essential tools for quantification in pediatric echocardiography. In the last few years, multiple sources highlight that nomograms employed for decades presented significant numerical and methodological limitations. As a result, widely different ranges of normality were generated, thus creating confusion in estimation of several cardiac diseases. New nomograms have recently been generated, overcoming some of the gaps of previous research: wider sample sizes (including neonates/infants), solid statistical/methodological plan, and availability of new data (chamber dimensions, many functional parameters). In particular, robust two-dimensional nomograms covering a wide spectrum of cardiac measurements have recently become available. Significant advances have been made for functional data (i.e. diastolic and deformation indexes) but a few limitations still exist. These include numerical issues (sample size of below 400 subjects) and methodological pitfalls (heterogeneous data normalization/expression). Despite these limitations, however, actual nomograms for functional data present quite reproducible intervals of normality with the exception of neonates and infants. In conclusion, great advances have been made during the last years. A few basic rules for the building of nomograms have been established (i.e. inclusion/exclusion criteria, measurement standardization), while others (i.e. the sample size, the way to express/normalize data, statistical requirements) are basically defined but still require standardization. New pediatric echocardiographic nomograms of good quality are easily accessible due to new electronic tools (online calculators, apps for smart-phone/tablets). Studies are ongoing to generate wider, comprehensive and multi-ethnic nomograms and to evaluate new parameters (e.g. three-dimensional parameters).