Abstract:

Objective

To assess the application value of two-dimensional speckle tracking imaging（2D-STI） in the evaluation of fetal left atrial strain in three phases， and to explore the correlation between the three phases of left atrial strain and gestational age， and whether the technique has angular dependence on the apex orientation in fetal heart examination.

Methods

A total of 180 normal singleton fetuses in the second and third trimesters who underwent fetal echocardiography at the Department of Diagnostic Ultrasound ＆ Echocardiography，Sir Run Run Shaw Hospital， Zhejiang University College of Medicine from November 2021 to January 2022 were selected. A total of 611 fetal four-chamber view video clips with different apex angles were obtained. 2D-STI analysis was used to obtain the peak storage strain （LASr_ED）， peak pipeline strain （LAScd_ED）， and peak systolic strain （LASct_ED） of the left atrium. 2D-STI could not identify the onset of atrial contraction in 11 fetuses （32 dynamic images）， and could not distinguish the atrial contraction phase from the conduit phase. Linear regression analysis was used to analyze the relationship between gestational age and 2D-STI parameters in patients in whom the three phases of left atrial strain with the apex orientation of 10：30 to 1：30 in the four-chamber view could be well tracked and identified. A total of 579 dynamic images with good tracking and recognition of the three phases of left atrial strain were selected， including 126 during 18-24 gestational weeks，190 during 25-28， 150 during 29-32， and 113 during 33-36. The patients were divided into four groups according to the apex orientation： group 1（apex orientation： 10：30-1：30）， group 2 （1：30-4：30）， group 3 （4：30-7：30）， and group 4 （7：30-10：30）. The F test and LSD-t test were used to compare the left atrial strain parameters between different groups of normal fetuses in the same gestational weeks.

Results

2D-STI could successfully track and identify the three temporal variations of the left atrium in 94.76% （579/611） of fetuses. LASr_ED and LASct_ED decreased with the increase of gestational age（r=-0.32， P＜0.001； r=-0.35， P＜0.001）， while LAScd_ED increased with the increase of gestational age （r=0.15，P＜0.05）. There was no statistical difference in the three strain parameters of the left atrium in different apex orientations among the four groups at 18-24 gestational weeks and 25-28 gestational weeks （all P＞0.05）. There were significant differences in LASr_ED among the four groups at 29-32 gestational weeks （F=2.759， P=0.044）.There were significant differences in LASr_ED and LAScd_ED among the four groups at 33-36 gestational weeks（F=2.919， P=0.037； F=4.234， P=0.007）. Pairwise comparisons were then made among the four groups. There were no significant differences in LASr_ED， LAScd_ED， and LASct_ED between group 1 and group 3 during the same gestational weeks （all P＞0.05）， and in LASr_ED， LAScd_ED， and LASct_ED between group 2 and group 4 during the same gestational weeks （all P＞0.05）.

Conclusion

LASr_ED and LASct_ED of normal fetuses in the second and third trimesters are weakly negatively correlated with gestational age. There is a very weakly positive correlation between LAScd_ED and gestational age in normal fetuses in the second and third trimesters. 2D-STI has no apex angle dependence in the practical application of fetal left atrial strain in the second trimester， but has certain apical angle dependence in the third trimester. Choosing axial or transverse four-chamber heart view as the unified image acquisition standard can help obtain fetal left atrial strain parameters more accurately， and provides a basis for quantitative assessment and continuous monitoring of fetal cardiac function.

Key words: Echocardiography, Fetus, Atrial function, Two-dimensional speckle tracking