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Year : 2020  |  Volume : 6  |  Issue : 3  |  Page : 244-252

A Neonatal Echocardiographic Z-Score Nomogram for a Developing Country

Department of Cardiology, SBKS Medical Institute and Research Centre, Sumandeep Vidyapeeth University, Vadodara, Gujarat, India

Date of Submission28-Jun-2020
Date of Decision02-Jul-2020
Date of Acceptance15-Sep-2020
Date of Web Publication23-Dec-2020

Correspondence Address:
Cinosh Mathew
B-17, Saket Society, Sussen Tarsali Road, Vadodara - 390 010, Gujarat
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/jpcs.jpcs_52_20

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Background: Currently used pediatric Echocardiographic Z scores are mostly founded on western data and have restricted applicability for newborns in developing nations. Since biological parameters may vary in different populations the data from those studies cannot be applied to the Indian neonates directly. Aims & Objectives: This study was directed to obtain echocardiographic data of various routinely measured cardiovascular structures using 2D and M mode echocardiography in Indian newborns up to 24 hours after birth and to derive Z-Score graphs for those parameters. Materials and Methods: This was a prospective observational study of a cohort of normal newborns conducted at a tertiary care hospital in western India. Neonates with congenital heart disease on screening echo were excluded and 100 normal neonates were included in the study with the intention of obtaining echocardiographic data of various routinely assessed cardiac parameters and to obtain a Z - score graph for each parameter. Echocardiographic evaluation was done utilizing a GE vivid S6 system. For the assessment of the relationship of an individual parameter with respect to BSA, regression equation was applied. Results: 22 parameters were assessed and using polynomial regression model relation to Body surface area was assessed and Z score charts were derived. Conclusion: Majority of the Z score values and reference ranges in our study were lower compared to the western standards thus it emphasizes the need for such a Z score in a developing country and hence these Z score values obtained from our study could be useful as compared to western charts for use in developing countries for planning the appropriate cardiac intervention and surgery in the neonatal population. However, large-scale studies with heterogenicity of age groups will be needed before they can become clinically applicable in the general population.

Keywords: Echocardiography, neonates, Z-score

How to cite this article:
Jain R, Mathew C, Rawal J, Shah T, Padhi B, Saxena N. A Neonatal Echocardiographic Z-Score Nomogram for a Developing Country. J Pract Cardiovasc Sci 2020;6:244-52

How to cite this URL:
Jain R, Mathew C, Rawal J, Shah T, Padhi B, Saxena N. A Neonatal Echocardiographic Z-Score Nomogram for a Developing Country. J Pract Cardiovasc Sci [serial online] 2020 [cited 2022 Aug 17];6:244-52. Available from: https://www.j-pcs.org/text.asp?2020/6/3/244/304525

  Introduction Top

The echocardiogram is considered one of the most important investigations for cardiac evaluation and has reduced the number of invasive hemodynamic studies to a great extent which were frequently used before its invention. It aids in assessing various congenital heart diseases (CHDs) in new-born and also assists in quantifying the various cardiac anatomical structures and their proportions.[1] The growth of a child changes the dimensions of its heart structures along with its hemodynamics.[1],[2],[3] There are various methods by which we can assess the abnormality in the dimension of a particular heart structure out of which the graphical or nomographic is commonly used method to do so. To describe cardiac structures such as atrial and ventricular chambers, atrioventricular and semilunar valves, and great vessels with respect to Z-score is vital in the assessment of CHD and thus planning for further interventions and surgeries.[4],[5] The method which is currently applied to assess the extent of deviation of a particular cardiac structure's value from any given population mean is Z-score. This scoring method has now been extensively used for the calculation and comparison of a particular cardiac structural dimension in children undergoing successive echocardiographic studies. The Z-score of every cardiac structure can be calculated from the available charts or formulas, which are given on the Internet and as well as various mobile apps.[6]

Most of these charts or graphs are derived from studies done in the Western population.[7],[8],[9],[10],[11] Thus, important decisions, for example, the timing and type of surgery in neonates with CHDs coming from low socio-economic countries are made based on studies which are done in developed countries. Since biological parameters vary in different populations depending upon the ethnicity and environmental factors, it has been mentioned in various articles the data from those studies cannot be applied to the Indian neonates/pediatric population as such.[1],[12] Due to these issues, growth charts have drawn on an individual basis by the pediatric authority of our country,[13] which are applicable in our country since many years. The purpose of this study was to collect the echocardiographic data of various routinely measured various cardiovascular structures using echocardiography in healthy Indian new-borns up to 24 h after birth and to derive Z-score nomograms for each.

  Materials and Methodology Top

This was a prospective, observational study conducted at SBKS Medical Institute and Research Center, Dhiraj Hospital, Vadodara, Gujarat, India, with the aim of obtaining echocardiographic data of various routinely assessed cardiac parameters in a cohort of normal neonates aged up to 24 h and to obtain Z-score graph for each parameter. One hundred neonates who satisfied the eligibility criteria were included in the study. Written and informed consent was obtained from the parents. Approval for conducting the study was received from the Institutional Ethics Committee. The neonates were evaluated clinically to look for obvious cardiac abnormalities followed by echocardiographic screening. New-borns with any known CHD or those were detected with CHD on screening ECHO were excluded from the study.

Echocardiographic evaluation was performed utilizing a GE vivid S6 system with dedicated neonatal and pediatric probes by a senior experienced cardiologist. The observed values of all the parameters mentioned were recorded for each new-born. Echocardiographic images were assessed in the standard positions which are currently practiced by 2D ECHO and M-mode. We followed the standard recommendations for measuring the data made from echocardiograms as described in the studies.[3],[4] The following 22 parameters were assessed in all of the 100 new-borns. The views and the methods, which are used in the study for measuring the echocardiographic parameters, are shown in [Table 1].
Table 1: Views and phase of cardiac cycle applied in various assessed parameters

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The data which we get from our study were expressed with respect to body surface area (BSA). Height (length) and weight of the new-borns were measured as per standard practice and BSA was calculated by the following formula: Haycock's formula (BSA = weight 0.5378 × height 0.3964 × 0.024265).[4],[14]

Statistical analysis

For the assessment of the relationship of an individual parameter with respect to BSA, regression equation was applied.

We chose 2nd degree polynomial regression model: Y = a + b1x + b2x2.

Graphs were drawn up for all the assessed echocardiographic parameter [Graph 1],[Graph 2],[Graph 3],[Graph 4],[Graph 5],[Graph 6],[Graph 7],[Graph 8],[Graph 9],[Graph 10],[Graph 11],[Graph 12],[Graph 13],[Graph 14],[Graph 15],[Graph 16],[Graph 17],[Graph 18],[Graph 19],[Graph 20],[Graph 21],[Graph 22]. The dependent variable, the regression equation, and its R2 values are presented in the tabular form under.

The calculation statistics was done with StataCorp. 2013. Stata Statistical Software: Release 13. College Station, TX: StataCorp LP.

Z-scores for each studied subject for all dependent variables are obtained using below formula.

Z = (X − XB)/Error.

Where, XB for a subject is obtained using the regression equations given in [Table 2], i.e., the BSA value of subject and values of regression co-efficient as given in equation. X is observed value of the dependent variable for a subject and error is mean square error of the regression.
Table 2: Parameters assessed, the regression equation and corresponding R2 values for each

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  Results Top

The present study included 100 healthy new-borns up to 24 h after birth, of which 54 new-borns were boys and 46 were girls. The BSA ranged from 0.176 m2 to 0.219 m2. The weight ranged from 2.5 kg to 3.4 kg.

R2 coefficient is the standard statistic used to measure whether the calculated data fit into our selected regression model. The value of R2 ranges from 0 to 1, with 1 denotes perfect and 0 denotes null.

[Table 2] showing R2 values for our parameters to be <0.10 which shows the weaker the correlation between BSA and the dependent variable. The lower R2 value of our study can be justified by to small study group or less variation in the age group of the participants.

[Graph 1],[Graph 2],[Graph 3],[Graph 4],[Graph 5],[Graph 6],[Graph 7],[Graph 8],[Graph 9],[Graph 10],[Graph 11],[Graph 12],[Graph 13],[Graph 14],[Graph 15],[Graph 16],[Graph 17],[Graph 18],[Graph 19],[Graph 20],[Graph 21],[Graph 22] show the graphical representation of the correlation of individual parameters with BSA. These graphs also depict the approximate regression line corresponding to the Z-scores of 0 (red line).[6]

[Table 3] shows the mean, standard deviation, maximum and minimum values of various assessed dependent parameters and independent variables.
Table 3: Descriptive statistics of various parameters of the present study

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  Discussion Top

The World Health Organization growth charts for the pediatric population[6] are mainly based on the Western population,[4],[15],[16],[17],[18] and they grossly underestimate the growth in children of developing countries.[19] Similarly, using Western Z-score values to derive Z-score values in Indian neonates may lead to incorrect values and erroneous decisions.[4] The adult echocardiographic measurements are reported with respect to a single “normal range,” but this approach is not feasible in neonates because the normal range of measurements will be impacted by its weight and/or length. Therefore, the interpretation of these measurements in neonates presents a unique challenge, in determining whether a given measurement is within the expected range. In addition, if a measurement deviates from normality, it is necessary for the cardiologist to gauge the magnitude of such deviation.

Currently, Z-scores are the standard way for the presentation of pediatric echocardiographic and physiological data. The Z-score describes the standard deviations above or below a size or age-specific population mean a given measurement lies.[20] This approach is now routinely practiced in the pediatric cardiology. For instance, the left ventricle will increase in dimension in all children as they grow. However, if a patient with chronic aortic or mitral valve regurgitation is being followed through serial assessment then clearly it is an abnormal and inappropriate dilation of the left ventricle that must be excluded. The use of Z-scores facilitates the detection of pathological increases in left ventricular dimensions, over and above that expected due to normal growth, by showing an increased Z-score over time. Z-score charts are helpful not only for chamber dimensions and valves, but even for the evaluation of great vessels like aorta in aortic arch hypoplasia or coronary artery dilatation in diseases such as Kawasaki disease.[21],[22] Z-score values also help for follow-up and prognosis of children with repaired CHD.[23],[24],[25]

These values will serve as normal Z-scores for the parameters mentioned for a healthy new-born. In a new-born without any apparent CHD or if some CHD is missed on screening ECHO, values outside the normal range will raise the suspicion for a detailed ECHO for CHD. Frequently good ECHO window and acquisition may be a hurdle or lack of proper neonatal probes may hamper appropriate imaging then values outside the Z-score will provide indirect clues to guide us to look for specific anomalies. In a new born, in whom tricuspid annulus or right ventricular size is smaller than Z-score range, then tricuspid atresia may be suspected or an enlarged RA above the Z-score range should suggested to assess for a shunt lesion like partial anomalous pulmonary venous connection (PAPVC) which may be missed on screening ECHO.

The measurements of cardiac structures and their comparison with the available standard graphs or charts are essential for the preoperative assessment of various CHD.[20],[26],[27] Majority of pediatric cardiac centers in the world have developed their own charts.[22],[28],[29],[30] Currently, available under-5 growth charts[31] are designed after extensive studies in developing countries. Similarly, if we utilize Z-score standards from developed countries for obtaining Z-score value in neonates of our country, it could lead to false results and poor decision-making.[4],[32]

There are no authentic data which say that neonatal cardiac dimensions vary between developed and developing countries, but we know, there are differences seen in other body parameters between developing and developed counties.[4] Therefore, separate charts and graphs are required in developing countries based on their studies. Multiple studies for calculating Z scores and scatter plots of various cardiac structures have been done.[4],[20],[33] The most recently published articles in this area[10],[28],[29],[30],[32] reveal that only a few of the studies in this area of research have come from developing countries. However, a comparison of the parameters of our study with a western study[26] has shown that majority of the values are lower compared to the western standards, thus it emphasizes the need for such a Z score in a developing country [Table 4].
Table 4: Comparison of the present study's measurements with previously published Western nomograms for a new-born (selected parameters)

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A similar study was conducted by Trivedi et al. between 2014 and 2016. It shows that the relationship between Haycock's BSA and the dependent variables is the best predictor of normal progression with age with high sensitivity.[1] Another study was conducted by Gokhroo et al. in which the data of various commonly evaluated cardiovascular structures using echocardiography in Indian children were studied and found that the relationship between Haycock's BSA and the dependent variable is the most sensitive predictor of normal progression with age.[4] With respect to study on Z-score of the pediatric population in our country, it is considered one of the largest studies. The graphs from this study can be used to acquire the Z-score of the respective echocardiographic parameter. We hypothesize that the small number of participants and new-borns up to 24 h only might have resulted in low R2 values in our study, and hence, no strong relationship between BSA and dependent variables is found in the present study.


This study was limited to participants chosen from the single hospital-based sample and 100 subjects were included in the study. Neonates included in our study belong to lower socioeconomic strata. The effects of less variability in age group, and hence, body weight and BSA may have resulted in low R2 values. Furthermore, only neonates up to 24 h of life were included in the study, and hence, a large-scale population-based study with a larger age group range would help overcome some of these limitations.

  Conclusions Top

The Z-score graphs and the reference range of various assessed parameters obtained from our study could be useful as compared to western charts for the use in developing countries in planning the appropriate cardiac intervention and surgery in the neonatal population.

Furthermore, we found that there is no strong correlation between BSA and our chosen parameters in new-borns this study has tried to derive Z-scores graphs for various two-dimensional echo and M-mode parameters in Indian new-borns up to 24 h after birth and we have graphs for various echocardiographic parameters in Indian new-borns up to 24 h after birth. However, large-scale studies with variety of age groups will be needed before they can become clinically applicable.

Ethics clearance

This study was approved by the Instituational Ethics Committee (IEC) on 29th august 2019.

Financial support and sponsorship


Conflicts of interest

There are no conflicts of interest.

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  [Table 1], [Table 2], [Table 3], [Table 4]


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