Singleton pregnancies diagnosed with PE for the first time in the antenatal clinic were recruited for this study. PE was identified according to the criteria of the International Society for the Study of Hypertension in Pregnancy (ISSHP) in 2014. Pregnancies with medical conditions, including essential hypertension, renal or cardiovascular disorders etc., multiply pregnancy, and gestational diabetes mellitus or pregnancy-induced hypertension were ineligible. There was no difference in the age and gestational week between PE and normal pregnant women. Were considered as complications: maternal or fetal death, emergency delivery, hospitalization of more than 7 days for the newborn due to tension disorder, birth weight < 2500 g and any eclampsia. In addition, 39 age-matched, healthy, nonpregnant women were enrolled as control subjects. Informed consent was obtained from all included subjects, which was approved by the institutional review board and ethics committee of the Affiliated Hospital of Qingdao University.
Echocardiographic studies were performed in all subjects using a commercially echocardiography system (EPIQ7C, Philips Healthcare) and a broad-band S5-1 probe (1.0–5.0 MHz). Connecting the electrocardiogram, all images were obtained from the standard views in the left lateral position at the end of inspiration. The frame rate was 52–76 frames/s. Measurements were performed for three consecutive cardiac cycles and averaged.
The interventricular septum (IVS), LV posterior wall (LVPW), LV end-systolic and end-diastolic diameters (LVDd) and LA dimension were measured in parasternal long axial view of LV according to the recommendation. Relative wall thickness (RWT) was calculated following the previous description. LV mass was calculated according to a necropsy validated formula of LV mass = 0.8 × (1.04 × ((IVS + LVDd + (LVPW)3 − ( LVDd)3) + 0.6 and indexed to body surface area (BSA). LV ejection fraction was calculated by averaging measurements of end-diastolic and end-systolic volumes from apical views using the biplane Simpson's method. Diastolic parameters were measured from the apical four-chamber view using pulsed-wave Doppler at the level of the mitral orifice included early (E) and late (A) transmitral flow velocities, the ratio of early to late velocities (E/A). The average of peak early diastolic velocities at septal and lateral of mitral annular (e') assessed by pulsed-wave tissue Doppler, and the E/e' ratio to estimate LV filling pressure.
From apical views, LA volumes were calculated by the area–length method and averaged to calculate maximum (LAVmax) and minimal volumes. The LA emptying fraction (LAEF) was obtained from the relative difference between LA maximum and minimal volumes.
Analysis of the LA Strain by STE
Standard 2D images from the apical two-chamber view were recorded and the imaging data were imported into the software of TomTec special for off-line analysis of LA. The three tracing points were placed in the IVS site and LV lateral wall site of the mitral annulus and LA apex. After tracing of the endocardial LA borders, the region of interest was automatically determined, and speckles were tracked frame by frame. In cases of insufficient tracking, manual adjustments were applied to optimize tracking quality. LA deformation is a cyclic process, which can be sub-divided into three phases including reservoir, conduit and contraction phase. Different phases of LA global longitudinal strain (LAGLS) were identified from the plotted strain curve including LV systole (LA reservoir stage, LASr), LV early diastole (conduit phase, LAScd), and LV late diastole (LA contraction stage, LASct) (Fig. 1). In the study,the ventricular cycle was used and the zero reference of the strain curve was set at LV end-diastole. Then the phasic values of LA strain were calculated as follows (Fig. 2):
1. LASr = strain during reservoir phase, measured as the difference of the strain value at mitral valve opening minus ventricular end-diastole.
2. LAScd = strain during conduit phase, measured as the difference of the strain value at mitral valve opening minus the onset of atrial contraction.
3. LASct = strain during contraction phase, measured as the difference of the strain value at the onset of atrial contraction minus ventricular end-diastole.
In addition, LA compliance was estimated by the quotient of LASr and E/e'. LV global longitudinal strain was analyzed as previously described.
Interobserver and intraobserver agreement
The imaging data was analyzed by one observer in random order. To assess interobserver variability, parameters were analyzed by a second observer who was blinded to the measurement of the first observer. To test intraobserver variability, a single observer analyzed the data twice on occasions separated by an interval of 1 month.
Statistical software package used was SPSS version 23.0 (SPSS, Inc., Chicago, IL, USA). Data are expressed as mean ± standard deviation for continuous variables. Differences among continuous variables were tested using a one way analysis of variance. The chi-square test was used for comparison of data as appropriate. Pearson's coefficient was performed to determine the correlation between two variables. Multivariate regression analysis was used to eliminate the interaction among factors. The interobserver and intraobserver agreements were determined by evaluation of the intraclass correlation coefficients. P value < 0.05 was considered to indicate statistical significance. All measurements of strain were presented as its absolute value.