Impedance cardiography: a straightforward and reliable tool to evaluate differences of cardiac reflex response between normal pregnancy and pre-eclampsia.

Abstract

Introduction: Reflex responses of cardiac cycle time intervals (CCTI) can be measured by echocardiography, and are reported to differ between uneventful pregnancy (UP) and pre-eclampsia(PE). It is unknown whether impedance cardiography (ICG) is a useful method to measure CCTI during pregnancy. Objectives: ICG measurements of CCTI before and after orthostatic challenge are evaluated in UP and in the clinical phase of PE. Methods: Examinations were performed twice in 16 UP (30–36 weeks), and once in 30 early PE (EPE, <34 weeks) and in 32 late PE (LPE, 34 weeks). A 3rd generation ICG device using a 4 electrode arrangement (NICCOMO, Medis, Germany) was used to measure CCTI in supine position and after moving to upright position. The pre-ejection period (PEP) is the time-interval between ventricular depolarisation and start of aortic flow. The left ventricular ejection time (LVET) is the time-interval between opening and closing of the aortic valve. Diastolic time (DT) is heart period duration – (PEP+LVET). Orthostatic-induced changes from supine to upright position (cardiac reflex response or CRR) were evaluated using One-sample Wilcoxon Signed Rank Tests. All CRRs in EPE and LPE were compared to UP using Mann-Whitney U tests. Data are represented as medians (interquartile ranges). Results: Maternal age was comparable between all groups [29 (26–32) years; p0.47]. Gestational age was comparable between both early [31 (28–32) vs 31 (27–33) weeks] and late [37 (36–39) vs 38 (36–39) weeks] third trimester UP and PE [p0.38]. Pre-gestational BMI was higher in EPE compared to UP [26 (24–32) vs 23 (21–24); p<0.01]. This was not true for LPE [25 (23–28); p=0.06]. Birth weight percentiles were lower in both EPE and LPE compared to UP [UP: 44 (38–78), EPE: 18 (5–28), LPE: 31 (18–59); p<0.05], and also lower in EPE compared to LPE [p=0.03]. CRRs within each group are shown in Table 1. The CRRs of PEP were significantly different between UP and both EPE and LPE [p⩽0.01], due to orthostatic-induced increase in PE but not in UP. Conclusion: Our study confirms that orthostasis does not change PEP in UP but induces a significant increase of PEP in PE. The increased reflex-induced duration of isovolumetric contraction time can be explained by a decreased left ventricular performance in the clinical phase of PE as compared to UP. ICG turns out to be a straightforward and useful method to evaluate these hemodynamic features.