Journal of Cardiovascular Echography

ORIGINAL ARTICLE
Year
: 2015  |  Volume : 25  |  Issue : 3  |  Page : 67--71

Normal range of left ventricular strain, dimensions and ejection fraction using three-dimensional speckle-tracking echocardiography in neonates


Ziad Bulbul, Ziad Issa, Ghassan Siblini, Nasser Moiduddin, Giovanni Di Salvo 
 King Faisal Specialist Hospital and Research Centre, Riyadh, Saudi Arabia

Correspondence Address:
Ziad Bulbul
King Faisal Specialist Hospital and Research Centre, Heart Center MBC-16, P. O. Box: 3354, Riyadh 11211
Saudi Arabia

Abstract

Aims: Three-dimensional speckle-tracking echocardiography (3D-STE) is a promising new technique to evaluate left ventricular (LV) mechanics. The feasibility and normal values of LV strain using 3D-STE have recently been established in adults and children. Unfortunately, no data are available in neonates. The aims of this study were to evaluate the feasibility and establish normal values of 3D LV volumes, ejection fraction (EF), and the 4 normal strains in healthy neonates. Materials and Methods: Of 50 consecutive newborns who were delivered at our hospital or returned to their first newborn follow-up within the first 3 weeks of life, 38 babies underwent full echocardiographic evaluation, including the acquisition of at least 3 full volume data sets from the apical window, while naturally sleeping. Data sets were analyzed offline. Global LV longitudinal, circumferential, and radial strain, as well as 3D LV volumes and EF, were measured using 3D-STE. Results: Of the 50 newborns, 2 patients were excluded because of significant intra-cardiac shunts, and in another 10 subjects, parents did not give consent. At least one data set was adequate for analysis in all the remaining subjects. Mean indexed LV diastolic, systolic volumes, and EF were 24.7 ± 3.6 ml/m 2 , 9.2 ± 1.3 ml/m 2 , and 63% ± 3.7%, respectively. Normal global longitudinal, circumferential, radial, and tangential 4D strain were −20.9% ± 2.8%, −32.4% ± 3.1%, 44.3% ± 3.4%, and −39.7% ± 3.4%, respectively. Conclusions: 3D-STE is feasible in newborns without the needed for sedation. Reference values of normal, regional, and global LV 4D strain and volumes were obtained.



How to cite this article:
Bulbul Z, Issa Z, Siblini G, Moiduddin N, Di Salvo G. Normal range of left ventricular strain, dimensions and ejection fraction using three-dimensional speckle-tracking echocardiography in neonates.J Cardiovasc Echography 2015;25:67-71


How to cite this URL:
Bulbul Z, Issa Z, Siblini G, Moiduddin N, Di Salvo G. Normal range of left ventricular strain, dimensions and ejection fraction using three-dimensional speckle-tracking echocardiography in neonates. J Cardiovasc Echography [serial online] 2015 [cited 2020 Sep 23 ];25:67-71
Available from: http://www.jcecho.org/text.asp?2015/25/3/67/166074


Full Text

 INTRODUCTION



Assessment of left ventricular (LV) function is the most common and clinically relevant task in the congenital echocardiography laboratory. Historically, those measurements have been estimated using M-mode (MM) and two-dimensional (2D) echocardiography, [1],[2],[3] with several limitations. [4],[5],[6],[7],[8]

Strain echocardiography, on the other hand, permits the quantification of LV global and regional function, which provides new insights in different experimental and clinical scenarios. [9],[10],[11],[12] Recently, LV strain derived from 3D speckle-tracking echocardiography (3D-STE) has been validated against cardiac magnetic resonance imaging in children and adults. [13] This new technique has the potential to better evaluate the LV function in neonates with congenital heart disease and to be of help in the surgical decision-making. However, to the best of our knowledge, there are no data on 3D-STE in full-term neonates to assess LV mechanics.

In this study, we sought to establish the feasibility of the acquisition and analysis of 3D data sets, and to establish using 3D-STE, normal values for LV volumes, and ejection fraction (EF) as well as the 3D global strain (GS) parameters in a group of healthy neonates.

 MATERIALS AND METHODS



Fifty consecutive normal full-term neonates were recruited prospectively. All the subjects were born in our institution and were either awaiting the discharge of their mothers or presenting for their first newborn baby regular checkup.

The inclusion criteria were:

No history of congenital orAcquired heart disease, andCompletely normal results on 2D and Doppler echocardiography, with no structural defects and with normal chamber size and systolic function.

Exclusion criteria were:

Structural congenital or acquired heart disease,abnormal cardiac rhythms, and Hypertension and/or other acute or chronic illnesses.

All echocardiography studies were performed by an experienced cardiac sonographer using IE 33 platform scanner (Philips Medical Systems, Andover, MA). Matrix-array transducer (S8) was used for the routine MM, 2D, and Doppler study, and a dedicated 3D full sampling transducer (X7) was used for the 3D full volume data sets acquisition. Studies were performed with the babies asleep or quite suckling on a bottle of formula; attention was made to acquire the data sets during the resting phase of the periodic breathing or shallow breathing to minimize heart translation and the effect of breathing. Several full volume data sets were acquired from the apical and subcostal transducer position.

The echocardiograms were transferred to Xcelera R3.3 Cardiology PACS system (Philips Medical Systems, Andover, MA) and were analyzed offline. The routine echo study was reported in a separate session than that of the 3D analysis. The same experienced observer, analyzed and reported the 3D study, blinded to the finding of the routine examination. Adequate 3D data sets (without stitching artifacts and containing the whole of the LV) were analyzed using 4D LV analysis software V3.1, (TomTec Imaging Systems).

The software allows a semi-automated detection of the LV border following the identification of the mitral valve annulus and LV apex by the operator [Figure 1]. Subsequently, the system will automatically extract three orthogonal planes of the LV. One plane passes through the outflow tract and the aortic valve. The others resemble the two and four chamber views of the LV, used in the biplane method of LV volumetric measurement. In addition, following manual adjustments of the endocardial surface was performed as necessary to include the papillary muscles within the LV cavity; the 3D endocardial surface is automatically tracked using 3D speckle-tracking technology throughout the cardiac cycle. The software eventually provides longitudinal, circumferential, radial, and tangential time curves, from which peak GS and averaged peak strain at the basal, mid-ventricular, and apical levels are determined [Figure 2].{Figure 1}{Figure 2}

Principal tangential strain in 4D LV analysis describes the shortening of a surface element along the main contraction direction. It is, thus, a measure of regional myocardial contraction ability, and may represent the vector summation in longitudinal and circumferential direction, and the resulting direction of the contraction of the muscle fibers that are aligned tangentially to the myocardial surface. [13]

In addition to track the endocardial border, the software allowed the tracking and tracing the epicardial border as well. In this way, the system calculated the volume of the endocardial cavity and estimated myocardial mass. As a result, the volume of the LV all through the cardiac cycle was measured and the myocardial mass was calculated.

To assess intraobserver variability, the same observer (Z.B.) measured the 3D strain analysis of 10 randomly selected newborns twice at an interval of 2 months to avoid recall bias. To assess interobserver variability, 3D strain measurements were performed by a second observer (G.S.), who was blinded to the results of the first observer (Z.B.).

Statistical analysis

All demographic, conventional, echocardiographic and 3D strain data are presented as numbers or percentages (mean ± standard deviation). Linear correlation analysis was performed to assess the relationship between 3D strain variables (global longitudinal strain [GLS], global circumferential strain [GCS], global circumferential strain [GRS], global transverse strain [GTS], and Twist and Torsion) and age, heart rate, weight, height, and 3D derived LV volumes, LV EF, LV stroke volume (SV), and LV mass indexed for body surface area (BSA). Multiple linear regression analysis was performed to determine the additional effect of anthropometrics (age, heart rate, weight, and height) and conventional echocardiographic parameters on the 3D-studied strain variables. The anthropometric and echocardiographic parameters were considered as potential dependent variables, and all variables were simultaneously entered in the regression. P < 0.05 was considered as statistically significant. Statistical analyses were performed using SPSS for Windows version 16.0 (SPSS, Inc., Chicago, IL).

Intraobserver and interobserver agreements were calculated using the coefficient of variation (i.e., the percentage absolute difference between the measurements divided by their mean value).

 RESULTS



Of the 50 healthy full-term newborns, 10 were excluded because their parents refused to give consent for this study. Two babies had more than mild shunting lesions (atrial septal defect type II and a large patent ductus arteriosus); both were not included in our data analysis. Thus, the final study group consisted of 38 healthy newborns (mean age was 3.7 ± 4.7 days, range: 1-15 days, and gestational age of 38.1 ± 1.1 weeks). Mean weight and BSA were 3.1 ± 0.5 kg and 0.19 ± 0.02 m 2 , respectively. Full demographic data are presented in [Table 1].{Table 1}

Conventional echocardiographic parameters and 3D LV global myocardial strain variables of the studied subjects are presented in [Table 2].{Table 2}

Linear regression analysis was performed to assess the relationship among 3D strain variables, age, weight, LV volumes, LV mass LV SV, and LV EF. GLS was not significantly correlated with any of the included variables. GCS was significantly correlated with age (r = −0.41, P = 0.01), SV (r = −0.55, P = 0.0003), LV mass index (r = −0.36, P = 0.027), and EF (r = 0.90, P < 0.0001). GRS was significantly correlated with age (r = 0.43, P < 0.0001) and EF (r = 0.79, P < 0.0001), while GTS was significantly correlated only with EF (r = −0.61, P = 0.0002).

Multiple linear regression analyses among the anthropometric and standard echocardiographic parameters were performed to determine the independent effect of these parameters on the 3D GS variables. Only age was significantly associated with GLS (P = 0.046, r = −0.20), while GCS (P < 0.0001, r = −0.90), GRS (P < 0.0001, r = 0.79), and GTS (P = 0.003, r = −0.61) were significantly associated only with EF.

Intraobserver and interobserver variability

The coefficient of variation was very good for GLS (intraobserver 0.09% and interobserver 1%) and GCS (intraobserver 2.5% and interobserver 2.8%), but poor for GRS and GTS (intraobserver 10% and interobserver 15%).

 DISCUSSION



Our data show that 3D-STE analysis is feasible on the consecutive healthy newborns, and we presented reference data for this population.

The most recent ASE\EACVI guidelines consider STE-derived GLS as reproducible and feasible for clinical use offering incremental prognostic data over LV EF in a variety of cardiac conditions. [14],[15] Thus, GLS may become a sensitive tool to assess LV mechanics and function in newborns with various congenital heart diseases. Unfortunately, only few data are available in the pediatric and newborn population on STE-derived strain variables and 3D-STE data are available only for preterm ones [Table 3]. [16],[17],[18],[19],[20] Our values for GLS are within the range of previous studies. However, differences in GLS values across different studies also reflect the use of different machines, software, and different algorithms.{Table 3}

In agreement with the previous studies, GLS is a very reproducible parameter and this could facilitate its routine clinical application.

Conflicting data exist regarding the influence of age on GSs. In our study, only a very weak association (r = −0.20) between age and GLS was demonstrated. While at multivariate analysis, GCS, GTS, and GRS were significantly associated only with 3D LV EF. This finding is consistent with the previous observations that LV size and mass continue to grow from birth to puberty but that LV systolic function, as shown by LV EF and now by strain variables, is relatively consistent from infancy. In this regard, the use of normative values for 3D-derived GLS will be greatly facilitated by its substantial independence of anthropometric, echocardiographic, and demographic factors that constitute confounding effects in other techniques.

Reproducibility

The determination of reproducibility of 3D LV strain and torsion measurements is also important when applying this new technology to daily clinical practice. Inter and intraobserver variability of 3D GLS and GCS was very good, suggesting these parameters are ready for the clinical use. On the other hand, reproducibility of GTS, GRS twist, and torsion is still high, underscoring the need for more technical advancement before is ready for clinical practice.

Limitations

Optimal image acquisition with good image quality is an important aspect to STE analysis. There is a learning curve for operators new to the technique to optimize imaging for the entire endocardial wall throughout the cardiac cycle and provide reproducible point selection for tracing. Fundamental limitations of ultrasound, such as reverberation, shadowing, dropouts, chamber foreshortening, and movement artifacts, can limit feasibility. In children and newborns, most of these limitations are overcome because of the usual, very good image quality as confirmed by our findings and previous studies on infants or children with over 90% feasibility.

The relatively low frame rate of RT3DE imaging compared with a high heart rate could potentially lead during the analysis to underestimating strain values. Because of this limitation, strain rate and LV twisting and untwisting velocities cannot be examined. [13]

Our radial strain values are significantly lower than in other studies, this may be due to different algorithms and formulas, which are proprietary and hidden from end users, and probably because in previous studies, radial strain calculations were derived from the endocardium. The ethnic group we studied is limited to the Saudi Arabian population. It should be noted that the published literature has suggested that there is variability in LV volume, mass, and function among certain ethnic groups.

 CONCLUSIONS



3D GLS analysis using the new 3D-STE is feasible and reproducible in the newborns. Further investigation is warranted for potential clinical application of this new technology in a pediatric population.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

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