How to Use This Calculator

The aortic root is the section of the main body artery that sits immediately above the heart. It comprises four distinct anatomical points measured routinely during a paediatric echocardiogram: the aortic valve annulus (the ring formed by the base of the aortic valve leaflets), the sinuses of Valsalva (the widest part of the root, where the coronary arteries originate), the sinotubular junction (where the root narrows into the tubular ascending aorta), and the ascending aorta itself. Because children vary enormously in body size, a measurement of  25 mm means something very different in a five-year-old weighing 18 kg compared with a teenager weighing 60 kg. Z-scores solve this problem by expressing how far any given measurement sits from the mean expected value for a child of that particular body surface area, in units of standard deviation.

To use the calculator, enter the child's height, weight and sex, then type in whichever aortic root measurements are available from the echocardiogram. All measurements should be in millimetres. The calculator returns a Z-score, predicted mean and 95% reference interval simultaneously from every applicable normative dataset, allowing direct side-by-side comparison. Where a reference does not cover a particular site, for example, Pettersen 2008 does not include the ascending aorta, and Colan 2006 and Daubeney 1999 cover the annulus and sinuses only, the cell is marked accordingly rather than producing an erroneous result.

Aortic root dilatation in children is a finding of clinical significance in several conditions seen in a specialist paediatric cardiology practice. In Marfan syndrome (a connective tissue disorder caused by mutations in the FBN1 gene) progressive dilatation of the aortic root at the level of the sinuses of Valsalva is the primary cardiovascular concern and the main driver of surgical decision-making. A Z-score of 2 or greater at the sinuses of Valsalva in a child with Marfan syndrome is generally considered abnormal and typically triggers enhanced surveillance; a Z-score of 3 or above in a symptomatic child, or one with a rapidly rising trend, prompts discussion of prophylactic surgery. In children with a bicuspid aortic valve, aortopathy (progressive dilatation involving any or all of the four aortic root segments) is a recognised long-term risk, and serial Z-score tracking identifies those whose aorta is enlarging at a rate that warrants closer follow-up. Z-scores are similarly used in the surveillance of Loeys-Dietz syndrome, Turner syndrome, Kawasaki disease, and familial thoracic aortic aneurysm syndromes.

About the six reference equations in this calculator. Each reference differs in study population, BSA formula, statistical model and the specific sites it covers. Understanding these differences is essential for correct interpretation.

Lopez et al., Circ Cardiovasc Imaging 2017 is the largest and most ethnically diverse paediatric echocardiographic normative dataset published to date, derived from 3,566 healthy non-obese children aged zero to 18 years across 19 North American centres (Pediatric Heart Network). This reference covers all four aortic root sites.

Pettersen et al., JASE 2008 derives Z-scores from 782 patients at the Children's Hospital of Michigan using a second-order polynomial regression of ln(diameter in cm) on ln(BSA) (Haycock). It covers the aortic annulus, sinuses of Valsalva and sinotubular junction. The ascending aorta was not published in this study.

Colan et al., JACC 2006 provides the widely used Boston Children's Hospital equations derived from a log-log regression of diameter (cm) on BSA (Haycock). It covers the aortic valve annulus and sinuses of Valsalva only, and forms the basis of the Marfan Foundation's online calculator.

Daubeney et al., Cardiol Young 1999 provides ln(cm) ~ ln(BSA) equations from 125 children at the Wessex Cardiothoracic Unit, Southampton, using DuBois BSA. It covers the aortic annulus and sinuses of Valsalva only.

Z-scores for the same measurement can vary meaningfully across references. This reflects genuine differences in methodology, not errors. Where most references agree that a measurement is abnormal, confidence in that conclusion is high. Where results are discordant, particularly near the Z = 2 threshold, clinical context, trend over serial studies, and the reference most commonly used at your institution should all inform interpretation.

References

1. Lopez L, Colan S, Stylianou M, et al.; Pediatric Heart Network Investigators. Relationship of echocardiographic Z scores adjusted for body surface area to age, sex, race, and ethnicity: the Pediatric Heart Network Normal Echocardiogram Database. Circ Cardiovasc Imaging. 2017;10(11):e006979. doi:10.1161/CIRCIMAGING.117.006979
2. Pettersen MD, Du W, Skeens ME, Humes RA. Regression equations for calculation of z scores of cardiac structures in a large cohort of healthy infants, children, and adolescents: an echocardiographic study. J Am Soc Echocardiogr. 2008;21(8):922–934. doi:10.1016/j.echo.2008.05.005
3. Colan SD, McElhinney DB, Crawford EC, Keane JF, Lock JE. Validation and re-evaluation of a discriminant model predicting anatomic suitability for biventricular repair in neonates with aortic stenosis. J Am Coll Cardiol. 2006;47(9):1858–1865. doi:10.1016/j.jacc.2005.12.050
4. Daubeney PE, Blackstone EH, Weintraub RG, Slavik Z, Scanlon J, Webber SA. Relationship of the dimension of cardiac structures to body size: an echocardiographic study in normal infants and children. Cardiol Young. 1999;9(4):402–410. doi:10.1017/S1047951100005217
5. Haycock GB, Schwartz GJ, Wisotsky DH. Geometric method for measuring body surface area: a height-weight formula validated in infants, children, and adults. J Pediatr. 1978;93(1):62–66.

Author: Dr. Alessandro Giardini, MD, PhD, Consultant Paediatric Cardiologist

Written: 27/06/2026

Last reviewed: 27/06/2026