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.