2.3. Application of 2D-Speckle-Tracking-Echocardiography
(fetalHQ®)
The post-processing speckle-tracking, a semiautomated state-of-the-art
technique, uses conventional grayscale B-mode frame-by-frame-analysis.
As already described elsewhere, this pattern-recognizing method tracks
the movement of the speckles representing the movements of the
endocardium. They are generated by the interaction of the ultrasound
with the endocardial border and show a unique spatial pattern for each
region of the endomyocardial interface. Endomyocardial speckles follow
tissue motion in all dimensions and their image-processing
algorithm-based detection allows the quantitative analysis of velocities
and deformations (strain, strain rate) of the myocardium during the
cardiac cycle [14].
After measurement of global dimensions at end-diastole (ED) (Figure 1a,
Video-Clip S1), for 2D-STE analysis, the raw cine-loop clips of the
4-CVs were loaded into the semiautomated border recognition program
fetalHQ®. Anatomic M-mode (AMM) was used to place a line across the
lateral right ventricle wall at the level of tricuspid annulus
perpendicularly to the area of interest to define a single cardiac cycle
by identifying end-systole (ES) and ED (Figure 1b). The clearest cardiac
cycle with best endocardial visualization was selected by determining
the first ED and the subsequent ED by marking the nadir on the AMM
signal, and finally, the ES (first frame before opening the
atrioventricular valve) by marking the peak on the AMM signal (Figure
1c). Once the most optimized cardiac cycle is selected, the systolic
endocardial border of each ventricle was automatically tracked
algorithm-based by the software in the previously defined end-systole
frame along this cardiac cycle by manual identification of three
landmarks (three-point-analysis): the septal and the lateral
atrioventricular valve annulus as well as the apex, where the
consideration of the moderator band required special attention. For the
option of more in-depth analyses of the base (1-8), the middle (9-16)
and the apex (17-24), both ventricles were divided into 24 segments
automatically (cardiac mapping). It was ensured that the course of the
generated line of the endocardial border from the right and left
ventricles could be tracked from the beginning at the insertion of the
atrioventricular valve either on the lateral or septal wall passing the
apex and ending at the valve insertion on the opposite wall (Figure 1d
and e). If fine tuning was necessary to ensure that the endocardium was
adequately traced, end-systolic and -diastolic endocardial tracking were
adjusted manually by each operator independently.
Finally, automatically calculated global and segmental parameters for
fetal cardiac morphometry and function depicted graphically with
superimposed AMM were obtained (Figure 1f). For a better evaluation of
the quite complex tool fetalHQ®, the following parameters were selected
and compared for both ventricles: For fetal cardiac morphometry
(ventricular size and shape) ED and SI, for fetal cardiac function
(ventricular contractility) endoGLS and FS. For simplicity, segments 1,
9, and 17 were selected for the three sections with their 24 segments
(base, middle, apex).