Reference Range for Tissue Motion Tracking of Mitral Annulus Displacement in Chinese Han Singleton Pregnancies

During normal pregnancy, the cardiovascular system of pregnant women will undergo significant adaptive changes in response to the growth of the uterus, fetus and placenta. Cardiac output and plasma volume will increase by 40% to 50% compared with non-pregnancy. The heart rate continues to increase, while the blood pressure decreases in the first and second trimesters and increases in the third trimester. The heart structure of pregnant women also remodels during pregnancy and the inner diameter of the cardiac cavity and myocardial mass increase. The above changes usually return to pre-pregnancy levels within 3-6 months after delivery. Pregnancy can change hemodynamics and cardiac structure, thereby causing corresponding changes in maternal cardiac function. Adaptive changes in maternal cardiac function can be reflected through an accurate and rapid evaluation. Changes in maternal cardiac function can be continuously observed and analyzed during pregnancy and after delivery to uncover the changing law of maternal cardiac function.

In addition, the incidence of cardiovascular disease in pregnancy is 1-4% worldwide, and about 15% of maternal deaths are caused by complications related to cardiovascular diseases during pregnancy. In China, the proportion of maternal deaths caused by cardiovascular diseases during pregnancy is increasing yearly and cardiovascular diseases during pregnancy have become the primary cause of death for critically ill pregnant women. Previous studies have shown that common complications during pregnancy, such as gestational hypertension and diabetes, can also alter maternal heart function. Therefore, early detection of changes in left ventricular systolic function of pregnant women during pregnancy and after childbirth, timely treatment and early evaluation of treatment efficacy can greatly reduce their mortality.

The Simpson's biplane method is currently used to measure left ventricular ejection fraction for clinical evaluation of left ventricular systolic function, which is especially available for patients without left ventricular geometric deformation. However, left ventricular ejection fraction cannot be sensitive to early changes in cardiac function. In recent years, two-dimensional longitudinal strain has been included for evaluating left ventricular systolic function. Myocardial longitudinal motion is responsible for maintaining 70% of normal cardiac function. Researchers believe that this method can sensitively detect early changes in left ventricular systolic function. However, the above two methods have high requirements on the quality of ultrasound images, which can clearly display the endocardium and epicardium based on good sound-transmitting conditions and good image quality. However, the image quality of pregnant women is often poor, so there is a decline in the detection accuracy.

Previous studies have shown that TMAD is independent of image quality and can effectively evaluate left ventricular systolic function and is an effective supplement to left ventricular ejection fraction and the overall longitudinal strain of the left ventricle. TMAD is a new technique for quantitative analysis of mitral annulus motion parameters. Three observation points are set on the septal side, lateral side and apex of the mitral annulus in the apical four-chamber view. The movement of the mitral annulus relative to the apex will be detected to obtain the lateral displacement of the mitral annulus septum (TMAD sep), the lateral displacement of the mitral annulus (TMAD lat), the mean displacement (TMADmid), and the mean displacement rate (TMADmidpt%). The left ventricular longitudinal systolic function will be then evaluated. TMAD only requires image acquisition from three sites and has low requirements on the quality of ultrasound images. Therefore, this measurement is simple, accurate and highly repeatable.

However, the TMAD reference value of normal healthy adults cannot be directly applied to pregnant women due to the hemodynamic changes during pregnancy. It is still necessary to establish the reference value of TMAD in pregnant women and explore its changes with gestational age, so as to provide simple, fast, accurate ultrasound parameters that do not depend on image quality for the evaluation of cardiac function during pregnancy.

The purpose of this study is to establish the reference range of TMAD parameters in Chinese Han singleton pregnancies in different pregnancy periods and early postpartum period and to explore the influencing factors of TMAD in singleton pregnancies.