1. Introduction
The knowledge of fetal cardiac function assessment as well as fetal
echocardiography itself has advanced dramatically in recent decades
[1–5]. With its different modalities, fetal echocardiography has
become indispensable for cardiac function assessment [3,6]. With the
implementation of fetal echocardiography in clinical routine, two foci
arose: the detection of structural congenital cardiac defects (CHD) and
subsequently the assessment of fetal cardiac morphometry and function
[2,7–10]. Fetal echocardiography is crucial for indirect evaluation
of fetal ventricular size and functional parameters since the fetal
heart cannot be measured directly in utero [11]. A functional
cardiac assessment provides early detection of subclinical cardiac
dysfunction and detects intrauterine functional cardiac changes and
might help to improve and predict perinatal outcomes, including
prediction of subsequent cardiovascular risk based on fetal programming
[8,12,13]. To record complex fetal myocardial function with its
morphometry, encompassing longitudinal, radial, and circumferential
deformation (strain), two-dimensional (2D) speckle-tracking
echocardiography (STE) provides unique information of cardiac function
using myocardial deformation imaging by tracking the endocardial border
[2,10,14–16]. Thus, STE allows both, the evaluation and
quantification of global and regional, more precisely, segmental
biventricular morphometry and function [2,5,6,16–18]. Its variety
of quantifiable parameters for comprehensive analysis enables the
simultaneous measurements of ventricular as well as atrial size, shape
and contractility within a few minutes [14,16,18–24].
The end-diastolic diameter (ED) or the sphericity index (SI)
characterizes parameters for fetal cardiac morphometry (ventricular size
and shape), and endocardial global longitudinal strain (EndoGLS) or
transverse fractional shortening (FS) for fetal cardiac function
(ventricular contractility) [2].
Measurement of the ED (syn. 24-segment transverse widths/segment length)
of all 24 segments allows determination of the width and change in size
of the ventricles and objective assessment of right-to-left
disproportion, which is often associated with cardiovascular
malformations [21,23].
The SI (syn. 24-segment SI) is calculated by the ratio between the
end-diastolic mid-basal apical length divided by each of 24 transverse
lengths (SI = end-diastolic length/end-diastolic transverse length),
enables assessment of the ventricular shape and is useful to detect
abnormal cardiac function resulting from remodeling of the ventricles.
[21,22].
The endoGLS, a commonly used deformation parameter [10,14,17], is
calculated as the difference in the length of the endocardium from the
base of the lateral wall across the apex to the base of the septal wall
at end-diastole and end-systole (endoGLS = [(end-systolic endocardial
length – end-diastolic endocardial length)/end-diastolic endocardial
length] x 100) [19]. In the small fetal heart, measurement of
longitudinal global strain appears to be the most accurate and sensitive
parameter to visualize pathologies [25], even though others state
that the diagnostic and prognostic value of fetal endoGLS has remained
uncertain [10]. Because global strain parameters, such as the
endoGLS, are less sensitive to local noise and their measurement is more
practical, it is considered to be more robust compared to the segmental
ones [25,26]. There is still limited data available on the normal
ranges of endoGLS during pregnancy [2]. A significant correlation
between the endoGLS and the gestational age (GA) is controversially
debated in the current literature. Both, an increase and a decrease in
endoGLS as well as constant values have been reported previously with
advancing GA [2,3,10,14,19,25,27–29]. These conflicting data
regarding normal reference ranges and changes of endoGLS complicate the
interpretation of current results [14]. Both, abnormal increase and
decrease of endoGLS values may indicate cardiac dysfunction, depending
on the pathophysiology [12].
The FS (syn. 24-segment transverse FS) is calculated as the difference
in the transverse length of each of the 24 segments at end-diastole and
end-systole (FS = [(end-diastolic length – end-systolic
length)/end-diastolic length] x 100) provides a comprehensive method
for assessing ventricular contractility [19–21].
2D-STE has become widely used to assess fetal cardiac function to detect
cardiac dysfunction in numerous pathological intrauterine conditions by
estimating early fetal cardiac adaptive changes in several pregnancy
related complications, including CHD like coarctation of the aorta,
aortic or pulmonal stenosis or hypoplastic left ventricle
[19–23,30–34], fetal growth restriction (FGR) [17,35],
gestational diabetes [36–39], twin-to-twin transfusion syndrome
(TTTS) [40,41], pre-eclampsia [42], intrahepatic cholestasis of
pregnancy (ICP) [43], fetal non-compaction cardiomyopathy (NCCM)
[44,45] or autoimmune diseases [13].
Ultrasound examination is highly examiner-dependent – especially in
complex cardiac anatomy – and acquisition and quantification of fetal
cardiac functional parameters with accurate prenatal diagnosis by fetal
echocardiography depends on the skill and experience of the operator
[25,46,47]. The applicability of speckle-tracking is limited when
imaging conditions are suboptimal [40]. Therefore, extensive
training and education of future experts is of enormous significance
[48–51]. Applications based on artificial intelligence (AI), on
whose algorithms prenatal diagnostics will rely on increasingly, are
transforming the way clinicians use ultrasound [50,52–65].
Recently, we demonstrated the benefit of an automated tool for less
experienced operators to assess another cardiac functional parameter,
the right ventricular modified myocardial performance index (RV-Mod-MPI)
in normal pregnancies [47].
The purpose of this study was to demonstrate the feasibility of whether
less experienced operators can handle and might benefit from an
automated tool of 2D-STE for offline analysis of diverse parameters for
cardiac function in the clinical routine.