Orthostatic challenged cardiac contractility in pre-eclampsia, as measured by impedance cardiography

Abstract

Aim: To evaluate maternal cardiac contractility following orthostatic challenge in normal pregnancy (NP) and pre-eclampsia (PE) using impedance cardiography (ICG). Methods: 16 women with NP, 12 with early-onset PE (EPE) and 14 with late-onset PE (LPE) underwent a consecutive series of ICG-examinations in different positions: (a) supine 1, (b) standing, (c) sitting and (d) supine 2. Parameters of contractility, i.e. acceleration index (ACI), velocity index (VI) and heather index (HI), were evaluated. Means and SD were calculated and compared statistically using t-test.

Results: ACI values increased after position change a>b and b>c in NP, but did not change in EPE or LPE. As a result, ACI was significantly higher in NP compared to EPE and LPE during positions b and c: 1.29±0.56 vs 0.78±0.36 s-2 (p=0.01) and 1.26±0.42 vs 0.82±0.23 s-2 (p<0.01). Measurements for other contractility parameters showed similar results. Discussion: Contractility increases when moving to upright positions in NP, but not in PE. Our observations can be explained with basic cardiovascular physiology: when supine, pelvic compression of the gravid uterus provokes a decrease in venous return, which in turn induces a decrease in sytolic function. In pre-eclampsia, this does not occur, indicating changes in either venous return and/or systolic function. Expansion of studies in cardiac contractility in pre-eclampsia is needed, in order to understand much better the mechanisms of abnormal cardiac adaptation during pregnancy and the role of venous return in pre-eclampsia. Our study illustrates that impedance cardiography is useful for this type of research.