To quantify the right atrial strain of normal fetuses in the second and third trimester of pregancy by using two-dimensional speckle tracking echocardiography (2D-STE) to evaluate the normal fetal right atrial function, and to analyze the possible influencing factors of fetal right atrial strain and its correlation with left atrial strain.

A total of 261 normal second- and third-trimester fetuses who underwent fetal echocardiography at Sir Run Run Shaw Hospital, Zhejiang University College of Medicine from November 2021 to March 2022 were selected. The standard four-chamber views were collected. 2D-STE offline analysis software was used to measure the global longitudinal strain of the fetal atrium, and the strain curves and parameters were obtained. The acquisition of fetal left and right atrial strain curves and parameters was analyzed. The correlation between fetal right atrial strain, heart rate, and gestational age, as well as the relationship between the display rate of strain and gestational age, heart rate, and frame rate, was analyzed. The comparison and correlation between right and left atrial strain was analyzed.

Right atrial strain curves were successfully obtained in 244 (93%, 244/261) of the 261 fetuses included. Among them, 131 (54%,131/244) fetuses had detectable right atrial reservoir strain (RASr), conduit strain (RAScd), and contraction strain (RASct), and the ratio of conduit strain to reservoir strain (RAratio) was calculated. In 113 cases (46%, 113/244) fetuses, only RASr, but not RAScd and RASct, could be identified. RASr and RASct had a weak negative correlation with gestational age (r=-0.205, P=0.001; r=-0.235, P=0.007), and RAratio had a weak positive correlation with gestational age (r=0.178, P=0.042). The fetal heart rate in the RASct group was lower than that in the non-RASCT group [(146.34±8.83) beats/min vs (149.67±7.49) beats/min, P<0.05]. The three-phase strain values of the right atrium were higher than those of the left atrium (P<0.05 for all). RASr was positively correlated with left atrial reservoir strain (LASr) (r=0.581, P<0.001), RAScd was positively correlated with left atrial conduit strain (LAScd) (r=0.258, P=0.004), and RASct was positively correlated with left atrial contraction strain (LASct) (r=0.413, P<0.001).

2D-STE has good feasibility and repeatability in assessing right atrial function in normal fetuses. The function of the right atrium in normal fetuses is similar to that of the left atrium, with three phasic strains. Right atrial strain has a weak negative correlation with gestational age.