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 Table of Contents  
Year : 2019  |  Volume : 17  |  Issue : 4  |  Page : 385-392

Reference values for left ventricular strain using 2-dimensional speckle tracking in primary school-aged healthy Egyptian children

1 Department of Cardiology, Al-Azhar University, Cairo, Egypt
2 Pediatrics, Al-Azhar University, Cairo, Egypt

Date of Submission01-Sep-2019
Date of Decision12-Nov-2019
Date of Acceptance09-Dec-2019
Date of Web Publication14-Feb-2020

Correspondence Address:
Layla A Mohamed
Alnargis 8, Villa 64, Fifth Settlement, Cairo 11835
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/AZMJ.AZMJ_115_19

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Background The aim was to set normal values of two-dimensional speckle-tracking echocardiography (2D-STE)-derived left ventricular strain is a prerequisite for its routine clinical application in children. The aim of this study was to establish our values of LV systolic strain using 2D-STE in a large cohort of primary school-aged healthy Egyptian children.
Participants and methods All studied cases underwent complete physical examination, including anthropometric, heart rate, and blood pressure measurements. Transthoracic echocardiography was acquired in 420 healthy participants, including routine echocardiography study, and tissue Doppler imaging and 2D-STE were performed. Global longitudinal strain (GLS), global circumferential strain (GCS), and global radial strain (GRS) values were determined. Multiple linear regression was performed to define the strongest predictors for GLS, GCS, and GRS.
Results A total of 420 children were included, with a mean age of 9.39±1.98 years. GCS values were −33.97±8.86% at the mitral valve and −33.88±8.59% at papillary muscle (PM). GLS values were −21.6±2.59% in apical four-chamber, −21.96±2.34% in apical two-chamber, and −22.17 ±2.58% in apical three-chamber views, whereas the GRS values were 46.34±10.05 at mitral valve and 46.37±9.97 at PM. Further analysis showed that the age was the strongest predictor of GRS and GCS (B=−2.018 and 2.47, respectively, and P<0.001 for both), whereas DBP was the strongest predictor of GLS (R2=0.048, P<0.001).
Conclusion This is the first Egyptian report that defines normal reference values for myocardial strain in longitudinal, circumferential, and radial directions assessed using 2DSTE imaging in a large pediatric cohort. There is a need to use age-specific reference values for the adequate interpretation of 2DSTE measurement.

Keywords: 2-dimensional speckle tracking echo, healthy children, normal strain value, reference value

How to cite this article:
Habib SA, Ahmad GM, Mohamed LA, Mohamed RA. Reference values for left ventricular strain using 2-dimensional speckle tracking in primary school-aged healthy Egyptian children. Al-Azhar Assiut Med J 2019;17:385-92

How to cite this URL:
Habib SA, Ahmad GM, Mohamed LA, Mohamed RA. Reference values for left ventricular strain using 2-dimensional speckle tracking in primary school-aged healthy Egyptian children. Al-Azhar Assiut Med J [serial online] 2019 [cited 2020 Jul 16];17:385-92. Available from: http://www.azmj.eg.net/text.asp?2019/17/4/385/278391

  Introduction Top

One important parameter in determinant diagnosis, prognosis, and follow-up of cardiopulmonary diseases in children is assessment of left ventricular (LV) systolic function. However, conventional parameters have important limitations [1],[2]. LV motion is not as simple as contraction and relaxation. Based on the orientation of the complex myofibers arrangement of the LV, which run in a longitudinal, radial, and circumferential directions, various types of deformation can be assessed [3],[4].

2D-STE is a relatively reproducible technique that is independent of the angle of insonation and enables quantification of both global and regional myocardial systolic and diastolic functions in various relevant condition [5]. It is used recently to evaluate and quantitatively measure LV strain parameters in pediatric age group. However, application of LV strain by using 2D speckle tracking for the assessment of LV function in children with different clinical scenarios requires a knowledge of normal range values [6].

  Aim Top

We aimed to establish reference values of LV systolic strain using 2D speckle tracking echocardiography in a large cohort of primary school-aged healthy Egyptian children.

  Participants and methods Top

Study population

We included 420 Egyptian children in a single-center study, who were recruited for echocardiographic evaluation. All consecutive children aged from 6 to 12 years were referred from both Pediatric and Cardiology Outpatient Clinics at Al-Zahraa University Hospital (Cairo, Egypt). Patients with structural heart disease, arrhythmia, hypertension, and/or chronic or recent acute illness were excluded.

Informed oral consent had been obtained from each participant’s parent, and the study was approved by Al-Azhar University-Faculty of Medicine for Girls ethical committee.

A complete physical examination was performed, including anthropometric, heart rate, and blood pressure (BP) measurements. Height was measured bare foot to the nearest 0.1 cm using a portable Stadiometer. Weight was measured in light clothing to the nearest 0.1 kg using a digital Heine portable scale. Body surface area and BMI were calculated as well. The 5th, 85th, and 95th percentiles were used according to the international statistics standards. The mean values of BP were measured and corrected for age and sex in the form of centile bands and compared with US National Childhood Blood Pressure standards. The BP percentiles were determined accordingly [7].

Two-dimensional transthoracic echocardiography

All participants underwent a detailed TTE examination in the left lateral position according to the recommendations of the American Society of Echocardiography [8]. Every examination was performed at rest, without using sedation. Images were obtained with a 2.5-MHz (M3S) matrix transducer using a commercially available system, the Vivid E9 echocardiographic scanner (GE Ultrasound, Horten, Norway). Complete 2D, Doppler, and color Doppler were performed in all accessible windows including parasternal long-axis; parasternal short-axis (basal, mid, and great vessels); apical four-chamber, two-chamber, five-chamber, and three-chamber; subcostal; and suprasternal views with ECG physiosignal displayed with all detected echo-Doppler study with Loop recording of two to three cycles. All images were stored digitally for further off-line analysis at EchoPAC GE version 201 (Chicago, Illinois, United States).

Routine echocardiographic parameters

Quantifications of cardiac chamber size, ventricular mass, and systolic and diastolic LV function were done in accordance with the recommendations for chamber quantification of the American Society of Echocardiography [8].

2-Dimensional speckle tracking echocardiography

Two-dimensional multiframe B-mode (grayscale) images were obtained in the apical four-chamber, apical two-chamber, apical long axis and parasternal mid cavity short-axis view [at the level of the papillary muscle (PM)], and parasternal basal short-axis view [at the level of the mitral valve (MV)]. A sector scan angle of 30–60 was chosen, and frame rates of 70–90 Hz were used. Cine loops format was used to store data for later off-line analysis. The timing of aortic valve opening and closure with respect to peak systolic strain were manually obtained, using single-gated pulsed-wave Doppler images of the LVOT.

Using the Automated Function Imaging software (AFI, Chicago, Illinosis, USA), longitudinal strain was studied, whereas radial and circumferential strain were evaluated manually. The software automatically divided the cross-sectional images into six segments, which were named and identified according to the statement of the Cardiac Imaging Committee of the Council on Clinical Cardiology of the American Heart Association. Strain curves of the three consecutive cardiac cycles and values of the manual timing were imported into a custom-made software package for further analysis. Strain values are dimensionless and are expressed as percentages. Negative strain values reflect shortening, whereas positive strain values reflect lengthening or thickening [9].

All offline measurements with Echo PAC were performed by a single observer. [Figure 1] and [Figure 2] show an illustration of two-dimensional strain imaging.
Figure 1 Global longitudinal peak systolic strain (LAX=−19.4%, A4C=−22.8%, A2C=−24.7% and average=−22.3%).

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Figure 2 Global circumferential strain at the level of papillary muscle (−31.7%).

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Statistical analysis

The sample size calculation technique used in this research was the simple random technique with the following Slovin’s formula [10]: n=N/1+Ne2, where N is the total population children from 6 to 12 years old (12 500 000 and e is the margin of error allowed in selecting the sample (0.05), so n=400 children were required (total children population was identified via Egyptian ministry of education newsletter 2018).

Results were analyzed using the Statistical Package for the Social Sciences Software (SPSS version 25.0; IBM corp., Armonk, New York, USA). Continuous variables were expressed as the mean±SD whereas categorical variables were expressed as frequencies and percent. After normality confirmation by central limit theory and homogeneity confirmation by Levene’s test, we performed unpaired Student’s t-test for comparison between two independent groups. Univariate analysis for multiple independent group comparisons was performed using one-way analysis of variance test with post-hoc Bonferroni correction. The associations between variables were assessed by Pearson’s r correlation analysis. P less than or equal to 0.05 was accepted as statistically significant with confidence interval (CI) greater than 95% and P less than or equal to 0.001 was considered highly significant.

  Results Top

We studied 420 Egyptian children aged between 6 and 12 years, with normal echocardiographic findings. There were 210 (50%) male and 210 (50%) female, and the mean age of studied group was 9.39±1.98 years, which ranged between 6 and 12 years. We found that 36 (8.57%) children were underweight, 19 (4.52%) were overweight and 10 (2.38%) were obese, whereas the rest of them 355 (84.52%) had average weight and BMI. Moreover, we found that 71 (16.9%) children were short and 14 (3.33%) were tall, whereas 335 (79.76%) had average height.

Only three children had high systolic blood pressure (SBP) and diastolic blood pressure (DBP) (despite having average weight and BMI) and only one had low SBP.Participants’ characteristics are shown in [Table 1].
Table 1 Baseline clinical characteristics of the whole study population

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Conventional echocardiographic data are shown in [Table 2].
Table 2 The mean values of conventional echocardiographic parameters

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2DSTE longitudinal, circumferential, and radial strain parameter findings of global longitudinal peak systolic strain [Global longitudinal strain (GLS)] are shown in [Table 3]. We observed higher negative values of 2DSTE longitudinal strain in apical segment compared with mid and basal segments in all examined views. On the contrary, regarding the circumferential and radial strain, we found a subtle difference in strain measures between the different examined segments ([Table 4] and [Table 5]).
Table 3 Mean values of global longitudinal peak systolic strain of different left ventricular segments

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Table 4 Mean values of left ventricular radial peak systolic strain

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Table 5 The mean values of circumferential peak systolic strain

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We performed multiple linear regression with enter model to know the strongest predictors of GLS, global radial strain, and global circumferential strain (GCS). We included age, BMI, heart rate, SBP, and DBP as independent variables, and we found that age was the strongest predictor of global radial strain and GCS (B=−2.018 and 2.47, respectively, and P<0.001 for both), whereas DBP was the strongest predictor of 2D-GLS (R2=0.048, P<0.001) ([Figure 3] and [Figure 4]).
Figure 3 Global radial strain at the level of papillary muscle (49.2%).

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Figure 4 Simple scatter with Fit Line of global radial strain by age.

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  Discussion Top

LV deformation in different directions assessed by 2D-STE was proved to be able to detect early subtle changes and specifically could pick up the subclinical dysfunction in various cardiac dysfunction in children.

Many literature studies have reported that longitudinal strain is a very sensitive parameter of subendocardial diseases. In addition, evaluation of circumferential and radial strain are also important in the assessment of compensation pattern of LV function [11].

However, lack of a normal range of values and associated variation hinder their use in every day clinical evaluation.

Up to our knowledge, this is the first study done in Egypt to set a reference range for deformation values in healthy Egyptian children.

In this paper, we thought to provide comprehensive reference values of various LV strain parameters in healthy Egyptian children between 6 and 12 years old using a General Electeric (GE, Chicago, Illinois, United States) echocardiography platform.

Left ventricular longitudinal strain

We found that the mean value of GLS was −22.5±2.56%. The values of longitudinal peak systolic strain in apical four-chamber, two-chamber, and three-chamber views were −21.25±2.59, −21.96±2.34, and −22.17±2.58%, respectively.

These values are comparable, with normal values obtained in healthy children using GE ultrasound system, where the mean value of LV LS was reported to be −21.5, −21.2, and −22.1% for apical four-chamber, two-chamber, and three-chamber views, respectively [3].

In a systematic review and meta-analysis conducted by Levy et al [12] in 2016, who reviewed 43 data set found that the mean value of LV GLS was −22.9 and −19.8% in children aged from 2 to 9 years and 10 to 13 years, respectively, using the same GE vendor.

Jashari et al. [13] also reviewed many previously published studies and included 28 data set of 1192 children and found the mean value of LV GLS was −20.5%, which was also comparable to our study result, despite using a different vendor.

Left ventricular circumferential strain

Regards LVCS, we found that the mean values of GCS in children were −33.88±8.59% at the PM level and −33.97±8.86% at the level of MV.Previously, Marcus et al. [9] reported that the mean values of LVCS at PM level were −23.4±1.7 and −23.5±1.8% for the age range 5–9 years and 10–14 years, respectively. However, at the MV level, they were −20.9±2 and −21.5±1.7% for the same age group mentioned previously.

Koopman et al. [14] also studied CS in children of different age group and found that the mean values of LVCS were −25.8±3.5 and −24.2±3.5% at the PM level and the level of MV, respectively, but with consideration to the use of different Vendor (Phillips iE33 ultrasound system, Bothell Everett Highway Bothell, WA, United States).

Left ventricular radial strain

Considering another aspect of LV deformation which is radial strain which represent myofiber thickening during systole, we found that LVRS was 46.37±9.97 and 46.52±9.52% at the PM and MV levels, respectively.

Radial strain was also studied before. Marcus et al. [9] reported the mean values of LVRS were 54.9±5.5 and 58±5.4% at PM level for the children aged 5–9 and 10–14 years, respectively, whereas at the MV level, the values were 52.3±4.5 and 54.9± 5.4% for the previously mentioned age group.

In another study done by Klitsie et al. [15], LVRS for the age group 5–9 years was identified to be 55±11.2% and for the age group 10–14 years was 23.1±2.7% using the same GE vendor.

Discrepancy of radial and circumferential strain values between our study and the previously published articles despite using the same echocardiographic vendor could be explained by difference in sample size and different racial background.

  Conclusion Top

In this study, we were able to establish reference values for LV strain in healthy school-aged Egyptian children using a widely available, cost-effective reproducible tool 2DSTE, which can help in the assessment of LV function in various pathological conditions. However, further research to study the influence of physiological variables such as age and sex on LV strain is recommended.

Financial support and sponsorship


Conflicts of interest

There are no conflicts of interest.

  References Top

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  [Figure 1], [Figure 2], [Figure 3], [Figure 4]

  [Table 1], [Table 2], [Table 3], [Table 4], [Table 5]


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