5. Discussion:
The deformation imaging using speckle tracking echocardiography is used as tool of assessment of the LV function in the diagnosis and management of several cardiopulmonary diseases in children. The ASE and EACVI guidelines consider STE derived GLS as feasible and reproducible for routine clinical use.
The normal reference range of values for 2DSTE-derived LV LS in pediatric and adult population has been described by many authors. The reference range of values for 2DSTE and 3DSTE derived LV LS, in neonatal age has been reported in few studies and that with limited enrollment. (13) This study establishes reference ranges of values of LV global LS in a cohort of 102 normal full-term neonates.
This is a retrospective study, and we enrolled all neonates with transthoracic echocardiograms during the period of study. These were all routine 2-d echocardiographic studies and some of them did not have all the three apical views in particular the 2-chamber view which is sometimes technically demanding. Therefore, we had to drop many studies from inclusion. We performed the M-Mode analysis to get FS and EF and also the EF by bi-plan Simpson’s method to make sure that all the enrolled population have normal function by conventional methods, so that our 2DSTE analysis would truly indicate a dependable reference for normal neonates.
Our study revealed fractional shortening that ranges between 27 and 42 % (mean 34± 3) which is correlated well with several studies performed in neonates. Similarly, Biplane Simpson method-derived ejection fraction was ranging between 55 and 73% (mean 61± 3).
The volume-based measurements of left ventricular function are different from direct measurement of myocardial motion by myocardial deformation (strain) using speckle tracking echocardiography. Our study revealed myocardial global longitudinal strain in normal healthy neonates ranging from -13.5 to -22.9 % (mean -19.9- ± 1.2), (Table 3). These values are correlated well with the values presented by Jashari et al, in their meta-analysis for normal ranges of left ventricular strain in children and neonates when they found normal values between –12.9 and 26.5% (mean -20.5%).(9,14)
Most of the studies reported longitudinal strain, an extremely sensitive sign of deteriorating LV systolic function especially in neonates with aortic valve stenosis, aortic coarctation or hypertrophic obstructive cardiomyopathy. Therefore, establishing normal values and routine performance of myocardial longitudinal strain is crucial on those patients to predict the early signs of myocardial dysfunction.(9, 15)
Our study shows that 2D-STE analysis is feasible in neonatal period. We observed a positive correlation between Biplane Simpson method-derived ejection fraction and myocardial strain-derived ejection fraction in healthy neonates (Table 3). This may suggest potential advantage of using myocardial strain-derived EF over the volumetric-based EF which is load dependent as well as geometry-dependent compared to myocardial strain.
Performing GLS for the left ventricle necessitate assessment of LV myocardial strain in all the three views for the LV; 4-ch, 3-ch and 2 chambers views which is felt by some practitioners to be time consuming process. Despite all the advantages of the technique for performing LV myocardial strain assessment, we modeled to evaluate whether apical 4-chambers view alone could be a reasonable reflector for the LV global longitudinal strain. We observed a statistically significant correlation between 4-ch longitudinal strain and the cumulative GLS for the left ventricle, (Table 3)
Moreover, 4ch 2DSTE derived EF was significantly correlated with GLS-derived EF as well as the EF calculated by biplane Simpson method. These observations of the 2DSTE apical 4-chambers values may suggest the usefulness of 4 chamber view alone to be a good reflector for the GLS instead of performing all the three views for the left ventricle (in patients with missing 3 chamber or 2 chamber apical views). This would make it possible to get the quantification of LV longitudinal strain from the apical 4 chamber view alone and then to follow that very patient with the same parameters to detect any change in myocardial function. It is easy to perform, and post-processing time has decreased with the newer automated systems.