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Dr. Alessandro Giardini
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Clinical Tool · Kawasaki Disease & Coronary Assessment
Calculate echocardiographic Z-scores for the left main coronary artery (LMCA), proximal left anterior descending artery (LAD), and proximal right coronary artery (RCA) in children, using two rigorously validated normative datasets from the Pediatric Heart Network.
The coronary arteries supply the heart muscle itself with oxygen and nutrients. In children, the inner diameters of these vessels are tiny (typically between one and four millimetres in an infant or toddler) and they vary considerably with body size. A measurement that appears reassuringly small in absolute terms in a large teenager may represent significant dilatation in a three-year-old. Z-scores solve this problem by expressing a measured diameter as a number of standard deviations above or below the mean expected value for a child of that body surface area (BSA), derived from large populations of healthy children who underwent standardised echocardiography.
To use the calculator, enter the child's height and weight, which are used to calculate the body surface area (BSA) by the Haycock formula, then enter whichever coronary diameters are available from the echocardiogram. Results from both reference datasets are returned simultaneously, showing the Z-score, the predicted mean for that child's BSA, and the 95% reference interval.
The primary clinical application of coronary artery Z-scores is in Kawasaki disease, an acute systemic vasculitis of unknown aetiology that predominantly affects children under five years of age and remains the leading cause of acquired heart disease in children in high-income countries. Kawasaki disease causes inflammation that has a predilection for the coronary arteries: without prompt treatment with intravenous immunoglobulin (IVIG), up to a quarter of affected children develop coronary artery aneurysms. Even with appropriate treatment, a subset of children will develop some degree of coronary dilatation. Serial echocardiographic assessment with Z-score reporting forms the backbone of monitoring, and the Z-score at each time point directly drives management decisions. The AHA 2017 Scientific Statement defines a Z-score of 2.0 or greater as abnormal: 2.0 to 2.49 constitutes dilation, 2.5 to 4.99 a small aneurysm, 5.0 to 9.99 a medium aneurysm, and 10.0 or above a giant aneurysm, the highest-risk category, carrying a lifelong risk of thrombosis and myocardial ischaemia and requiring systemic anticoagulation. The same Z-score framework is now applied in Multisystem Inflammatory Syndrome in Children (MIS-C), recognised during the COVID-19 pandemic as a Kawasaki-like illness that can also cause coronary artery involvement.
About the two reference equations used in this calculator. This tool implements only the Lopez 2017 and McCrindle 2007 equations, both of which are grounded in Pediatric Heart Network data and use Haycock BSA, making them methodologically consistent with each other and the most appropriate for use in UK and North American clinical practice.
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. The coronary artery model uses a BSA-indexed approach in which the measured diameter in mm is divided by BSA raised to the power of 0.45 (BSA^0.45), producing an indexed parameter that is normally distributed and independent of age, sex, race, and ethnicity. This is the reference currently recommended by many paediatric cardiology centres for Kawasaki disease surveillance and is used by the Pediatric Heart Network's own online Z-score calculator.
McCrindle et al., Circulation 2007 derived normative coronary equations from 221 healthy children as part of a Pediatric Heart Network study of Kawasaki disease. This reference has been widely used in clinical trials and published series of Kawasaki disease for nearly two decades and remains a standard comparator.
It is important to note that the two references can produce meaningfully different Z-scores for the same measurement, particularly for the LAD, where Lopez 2017 typically yields higher Z-scores than McCrindle 2007. This is not an error but reflects genuine differences in study population, statistical methodology, and the era in which measurements were acquired. The AHA 2017 guidelines acknowledge this variability and recommend that individual institutions adopt a single Z-score system and apply it consistently rather than switching between references. Where Z-scores from the two equations agree, especially when both exceed 2.5, confidence in the finding of coronary abnormality is high.
Measurement technique is critical. Coronary diameters for Z-score reporting should be obtained in end-diastole, using a zoomed two-dimensional image in the parasternal short-axis view, from inner edge to inner edge at the point of maximum diameter and perpendicular to the vessel long axis. The left main coronary artery (LMCA) is measured at its mid-point, distal to the apparent flaring near the aortic orifice and before the first bifurcation. The left anterior descending coronary artery ((LAD) is measured at its largest diameter distal to the bifurcation and before the first marginal branch. The right coronary artery (RCA) is measured in the relatively straight proximal segment just after the initial rightward turn from the anterior-facing sinus of Valsalva. A measurement taken with a different technique applied to these normative equations will produce an unreliable Z-score regardless of which formula is used.
Author: Dr. Alessandro Giardini, MD, PhD, Consultant Paediatric Cardiologist
Written: 27/06/2026
Last reviewed: 27/06/2026