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).