1 Introduction:
With advancement in technology, echocardiographic evaluation of cardiac
function is rapidly changing, and newer promising techniques are being
identified. The traditional tools for assessment of left ventricular
function are fractional shortening (FS) and ejection fraction (EF).
Fractional shortening (FS) includes assessment of maximum dimensional
changes of the left ventricular cavity in diastole and systole in
relation to the end diastolic dimension. Normal values for FS in infants
and pediatrics has been established and are typically between 28-46%(1, 2)
Ejection fraction, on the other hand, is calculated via assessing
volumetric changes of the left ventricular cavity between diastole and
systole in relation to end diastolic volume.
Both modalities (FS and EF) encounter several challenges related to
assumption of left ventricular geometry. Both are pressure dependent,
and they are not accurate in estimating LV function in case of
myocardial regional dyskinesia and in case of paradoxical motion of the
interventricular septum. Moreover, FS and EF mainly assess
circumferential fiber shortening and did not consider the longitudinal
motion of the LV.
Myocardial strain is a relatively new echocardiographic tool using
speckle tracking echocardiography (STE). It has been successfully used
in adult population to evaluate the regional and global systolic
function of the left ventricle. This technique consists of
frame-by-frame tracking of the ultrasound signals of the myocardial
speckles. Strain is a dimensionless parameter representing the
deformation of an object, in relation to its original shape. It is
expressed as percent change from the original dimension.
\(Strain\ (s)=\frac{L1-L0}{L0}\)
Where S is the longitudinal strain, L1 is the length at a given point of
time, and L0 is the baseline length.
Adapting this ultrasound tool in pediatrics and particularly in neonates
faces many problems including small heart size and fast heart rate.
Nevertheless, some studies have been performed in pediatrics and showed
relatively good reproducibility and feasibility. This is mainly due to
the fact that the investigation could be adjusted at higher frame rate
and the independency of the STE from the angle of incidence in contrast
to tissue Doppler derived signals which have shown to be angle
dependent. (3)
Another advantage of STE is the ability to assess longitudinal motion of
the left ventricle, in contrast to fractional shortening and ejection
fraction which assess only the circumferential fiber shortening and
radial thickening. This is particularly important, as some cardiac
lesions are known to affect longitudinal motion of the left ventricle
before it progress to global systolic dysfunction (4,
5) Therefore, it is important to establish a diagnostic tool to assess
longitudinal function of the LV to detect early signs of functional
impairment. The utility of STE in assessing the left ventricular
longitudinal motion was studied in adult and pediatric population,
however, only few studies with small patient number have documented the
utility of speckle tracking echocardiography in assessment of myocardial
longitudinal strain in neonates. (6, 7, 8) The aim of
our study is to evaluate 2-DTE longitudinal strain of the left ventricle
in neonates, to establish the reference values for our population and to
compare the global longitudinal strain-derived EF to the commonly used
tools for assessment of left ventricular systolic function (FS and EF).