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Dr. Alessandro Giardini
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During a paediatric echocardiogram, the sonographer and cardiologist measure the dimensions of many structures: heart valves, the aorta, the pulmonary arteries, the coronary arteries, and the left ventricle itself. Raw measurements in millimetres or centimetres mean very little without context, because a child's heart grows in proportion to body size. A left ventricular diameter of 3.5 cm might be perfectly normal in a nine-year-old and markedly dilated in a two-year-old. Z-scores express every measurement as the number of standard deviations it sits above or below the mean expected value for a child of that body surface area, derived from a large population of healthy children. A Z-score of zero means the measurement is exactly at the population mean. A Z-score of +2 or above suggests enlargement; a Z-score of −2 or below suggests that a structure is smaller than expected.
This calculator covers all 34 cardiac structures included in the Lopez 2017 Pediatric Heart Network (PHN) normative dataset. Enter the child's height and weight (from which body surface area is calculated automatically using the Haycock formula) and then enter whichever echo measurements are available. Only structures with measurements entered will appear in the results. The calculator returns the Z-score, the predicted mean for that child's body surface area, and the 95% reference interval for each measurement entered.
The measurements and their units are as follows. All linear measurements are entered in centimetres (cm), except the three coronary artery diameters (LMCA, LAD, proximal RCA), which are entered in millimetres (mm) as is standard in coronary artery reporting. Valve areas (mitral and tricuspid) are in cm². Left ventricular volumes are in mL and LV mass is in grams. The three LV ratios: mass:volume ratio, thickness:dimension ratio, and sphericity index are dimensionless calculated ratios entered without BSA adjustment, as these parameters do not have a clinically significant relationship with body size.
About the reference. The Lopez 2017 study enrolled 3,566 healthy non-obese children and adolescents aged zero to 18 years at 19 North American centres participating in the Pediatric Heart Network. Echocardiographic images were submitted in standardised digital format and all measurements were performed offline by trained Core Laboratory sonographers, making this one of the most methodologically rigorous and reproducible paediatric echo normative datasets in existence. For each measurement, the study identified the optimal BSA scaling exponent (α) such that the indexed parameter X / BSA^α followed a normal distribution with no residual dependence on body size. Age, sex, race and ethnicity were tested and found to have statistically significant but clinically insignificant effects — meaning that Z-scores derived from this reference are independent of those factors and a single set of reference values applies across the entire paediatric population. The study is officially endorsed as the reference dataset for the Pediatric Heart Network's own online Z-score calculator.
Clinical applications. This is the broadest paediatric echo Z-score tool in clinical use, and it has applications across virtually every subspecialty of paediatric cardiology. In congenital heart disease, Z-scores of ventricular dimensions, valve annuli and great artery sizes inform decisions about surgical timing and the feasibility of biventricular repair. In Kawasaki disease, coronary artery Z-scores from this reference classify the severity of coronary involvement according to the AHA 2017 Scientific Statement. In inherited aortopathies : Marfan syndrome, Loeys-Dietz syndrome, bicuspid aortic valve aortic root Z-scores track dilatation over serial studies. In cardiomyopathies, LV end-diastolic diameter Z-scres classify left ventricular dilatation and guide referral for transplant assessment. In pulmonary hypertension, main and branch pulmonary artery Z-scores help quantify the degree of vascular remodelling, and LV wall thickness Z-scores assess the presence of right heart pressure effects on septal geometry. In inherited cardiac conditions including hypertrophic cardiomyopathy, LV wall thickness Z-scores, particularly of the interventricular septum, are central to the diagnosis in children, where a Z-score of 2 or above at the septum in a first-degree relative of an affected individual meets diagnostic criteria.
A Z-score of 2 or above (or −2 or below) does not automatically imply pathology. Clinical context, the pattern of involvement across multiple structures, the direction of change on serial studies, and the child's underlying diagnosis all matter. This tool is intended to support — not replace — clinical judgement.
Dr Alessandro Giardini is a Consultant Paediatric and Adolescent Cardiologist at Great Ormond Street Hospital and the Portland Hospital.