The primary findings of this study were: 1) The significant increased GWI, GCW and GWW with decreased GWE were observed in the pregnant women with PE; 2) Among MyW properties, GWW was more elevated than GCW, which consequently resulting the decline in GWE; 3) There was a diverse relationship between MyW components and LV morphological as well as functional indices. Both GWI and GCW was directly linked to SVI, LAVI, sphericity index and RWT, while tissue Doppler e was inversely associated with GWW and positively with GWE. Furthermore, the prolonged Tei index was correlated with the decrease in GWI, GCW and GWE, as well as the increase in GWW.
To our knowledge, this is the first report about the characteristics of MyW indices during the pregnancy complicated by PE. In the present study, the measurements of GWI, GCW, GWW, and GWE derived from the new non-invasive way exhibited excellent feasibility and a good intra- and inter-observer variability, thus, rendering MyW a reliable tool to assess cardiac function in pregnant women. Furthermore, the new method allows us to distinguish the changes in each MyW component, therefore providing a new perspective on the myocardial biomechanics, cardio-metabolic conditions and pathophysiological changes during PE pregnancy.
Characteristics Of Myw During Pe Pregnancy
Early works reported the declined longitudinal deformation in the PE cases despite LVEF value within the normal ranges [3, 19]. The data in the current study confirmed their findings. However, LVEF and strain represent myocardial shortening but neglect the load condition. It has been proven that the increase in afterload can result in the decrease in contractile shortening and lead to misinterpreting the true systolic function [10, 20]. Instead, MyW takes into account afterload as well as myocardial deformation together and is therefore considered to be a less load-dependent parameter for evaluating cardiac performance. Using the new non-invasive method, the current study presented a significant increase in GWI, GCW and GWW in the PE pregnancies versus normal gestations. Further, among those MyW components, the increment in the median GWW values far exceeded the increment in GCW (145.38% versus 24.37%, respectively), causing the remarkable decrease in GWE.
Correlation Of Myw Measurement With Echocardiographic Indices In Pe
Despite weak association, the study demonstrated the variable relationship of MyW properties with cardiac structural and performative indices. Higher GCW and GWI were correlated with higher SVI, larger LA volume, higher sphericity index and higher RWT. GWW was positively related to LVMI and inversely to tissue Doppler e velocity. Meanwhile higher GWE was linked to LVEF and higher tissue Doppler e. Furthermore, Tei index, a time-interval index for comprehensive evaluation of diastolic and systolic function, showed a negative correlation with GCW, GWI, and GWE, and a positive correlation with GWW. Nonetheless, there was no association between MyW indices and body surface area as well as body mass index in this study cohort. Similar results have been obtained from other studies [11]. Thus, among MyW components, probably, GWI and GCW are related to myocardial contractility, GWW is related to diastolic function, and GWE is related to both systolic and diastolic function. Additionally, the variables used to calculate MyW, BP and GLS, were not included the multivariable regression analysis in this study.
How To Explain The Changes In Myw Components During Pe Pregnancy
Since arterial pressure increases during the pregnancy complicated by PE, stroke work performs in a shortening time interval, compensated by the LV raising myocardial oxidative metabolism, improving energy level to enhance the ability of the LV to pump against the elevated afterload [21]. In addition to taking into account increased cardiac loading, higher GWI and GCW reflect the changes of cardiac contraction and metabolism in PE gestation, but not detected by LVEF and GLS.
The element of GWW is the work done by the ventricle but does not generate stroke volume. It has been reported that the increase in LV end-systolic stiffness, a parameter of myocardial contractility indicating LV pumping against a given pressure, is related to the increase in arterial afterload. As such, in the present study, higher GWW may also be associated with higher wall stress of myocardium against the elevated BP in the women with PE. In addition, because metabolic substrates cannot be recycled by the myocytes during ventricular wall stretching, the energy will be converted to heat and storage in the myocardium, which is so-called internal cardiac work and partially accounts for the ventricle suction during early diastolic phase [22, 23]. And the higher ventricular mass, the higher values of GWW in the study. Therefore, the upward GWW should indicate an increase in the contractile reserve in the condition of PE. However, the findings could not be observed by the strain only for not taking into account pressure.
Finally, GWE represents work efficiency of myocardium and is calculated indirectly from the ratio of GCW and GWW. Since an unproportional increase in constructive and wasted work properties, GWE decreased significantly in the PE group, which might imply the imbalance between cardiac stroke work and myocardial energy metabolism during the PE pregnancy.
Limitation
There were some limitations in the study as follows:
Firstly, selection bias may be unavoidable in this study because it is a cross-sectional, single-center study with a limited number of participants. Secondly, BP readings derived from sphygmomanometer in the brachial artery, for measuring LV pressure non-invasively, can be imprecise. Central BP should be lower than the brachial values. However, this was also a limit in the study of Russell et al [9] and it have been considered reliable in the health subjects [10, 11]. Thirdly, owing to the software supplied by a single vendor, the calculation of MyW may not independent of vendors.