Validation of bioimpedance estimates of cardiac output in preeclampsia

Maternal cardiac function, uterine artery hemodynamics and natriuretic peptides at 22-24 weeks of gestation and subsequent development of hypertensive disorders of pregnancy

INTRODUCTION

Maternal cardiac dysfunction as well as abnormal uterine artery (UtA) Doppler are associated with hypertensive disorders of pregnancy (HDP), but their relation is unclear. We investigated the correlation between maternal cardiac function, UtA hemodynamics and natriuretic peptides, and explored differences between women who subsequently developed HDP and those who did not.

MATERIAL AND METHODS

This was a prospective cross-sectional cohort study of 347 pregnant women at 22-24 weeks. Maternal cardiac function and systemic hemodynamics were investigated at baseline and after 90 seconds of passive leg raising using impedance cardiography. Preload reserve was defined as percent change (Δ%) in stroke volume and cardiac output from baseline to passive leg raising. UtA hemodynamics was studied using Doppler ultrasonography. UtA blood flow, resistance and pulsatility index were calculated. Fasting venous blood samples were analyzed for natriuretic peptides (pro atrial natriuretic peptide [proANP], N-terminal pro brain natriuretic peptide [Nt-proBNP] and C-type natriuretic peptide [CNP]). The course and outcome of pregnancy were recorded.

RESULTS

At baseline, ProANP correlated significantly with cardiac output (r = -0.122; P = .023) and left cardiac work index (r = -0.112; P = .037), whereas Nt-ProBNP correlated significantly with acceleration index (r = .127; P = .018) and velocity index (r = -0.111; P = .039. CNP correlated significantly with UtA blood flow (r = .118; P = .028) and resistance (r = -0.112; P = .037) but not with UtA pulsatility index (r = .034; P = .523). None of the natriuretic peptides correlated with preload reserve. At 22-24 weeks, women who subsequently developed HDP had lower UtA blood flow (552 vs 692 mL/min; P = .028), higher UtA resistance (0.28 vs .17 mmHg/mL/min; P = .004) and higher mean UtA pulsatility index (1.12 vs .84; P < .001) compared with those who did not; however, the natriuretic peptide levels were similar in the two groups. Women developing HDP had a significantly higher increase in stroke volume and cardiac output and more reduction in systemic vascular resistance following passive leg raising compared with the reference group. Left cardiac work index, acceleration index and velocity index decreased following passive leg raising in the reference group but increased in women who later developed HDP.

CONCLUSIONS

ProANP correlated with cardiac output and cardiac work, Nt-proBNP with indices of cardiac contractility, and CNP with UtA blood flow and resistance. None of these natriuretic peptides measured at 22-24 weeks of gestation reflected cardiac preload reserve or predicted development of HDP.

Agreement between preload reserve measured by impedance cardiography and echocardiography during pregnancy

Purpose

Accurate assessment of cardiac function is important during pregnancy. Echocardiography and impedance cardiography (ICG) are commonly used noninvasive methods to measure stroke volume (SV) and cardiac output (CO). The difference in stroke volume (ΔSV) or cardiac output (ΔCO) measured at baseline and after passive leg raising (PLR) is a measure of preload reserve that predicts volume responsiveness. However, the agreement between these two methods in measuring preload reserve during pregnancy is unclear. The aim of our study was to investigate the correlation and the agreement between Doppler echocardiography and ICG in assessing preload reserve in pregnant women.

Methods

In this prospective observational cross-sectional study, preload reserve was assessed by measuring the SV and CO during baseline and 90 s after PLR simultaneously by Doppler echocardiography and ICG in healthy pregnant women during the second and third trimesters. Bland–Altman analysis was used to determine the agreement between the two methods. Bias was calculated as the mean difference between two methods and precision as 1.96 SD of the difference.

Results

A total of 53 pregnant women were included. We found a statistically significant correlation between ΔSV (R = 0.56, p < 0.0001) and ΔCO (R = 0.39, p = 0.004) measured by ICG and Doppler echocardiography. The mean bias for ΔSV was 2.52 ml, with a precision of 18.19 ml. The mean bias for ΔCO was 0.21 l/min, with a precision of 1.51 l/min.

Conclusion

There was a good agreement and a statistically significant correlation between ICG and Doppler echocardiography for measuring preload reserve.

Static and Functional Hemodynamic Profiles of Women with Abnormal Uterine Artery Doppler at 22-24 Weeks of Gestation

Objective

To compare cardiac function, systemic hemodynamics and preload reserve of women with increased (cases) and normal (controls) uterine artery (UtA) pulsatility index (PI) at 22–24 weeks of gestation.

Materials and Methods

A prospective cross-sectional study of 620 pregnant women. UtA blood flow velocities were measured using Doppler ultrasonography, and PI was calculated. Mean UtA PI ≥ 1.16 (90th percentile) was considered abnormal. Maternal hemodynamics was investigated at baseline and during passive leg raising (PLR) using impedance cardiography (ICG). Preload reserve was defined as percent increase in stroke volume (SV) 90 seconds after passive leg raising compared to baseline.

Results

Mean UtA PI was 1.49 among cases (n = 63) and 0.76 among controls (n = 557) (p < 0.0001). Eighteen (28.6%) cases and 53 (9.5%) controls developed pregnancy complications (p <0.0001). The mean arterial pressure and systemic vascular resistance were 83 mmHg and 1098.89±293.87 dyne s/cm⁵ among cases and 79 mmHg and 1023.95±213.83 dyne s/cm⁵ among controls (p = 0.007 and p = 0.012, respectively). Heart rate, SV and cardiac output were not different between the groups. Both cases and controls responded with a small (4–5%) increase in SV in response to PLR, but the cardiac output remained unchanged. The preload reserve was not significantly different between two groups.

Conclusion

Pregnant women with abnormal UtA PI had higher blood pressure and systemic vascular resistance, but similar functional hemodynamic profile at 22–24 weeks compared to controls. Further studies are needed to clarify whether functional hemodynamic assessment using ICG can be useful in predicting pregnancy complications.

Bioimpedance cardiography in pregnancy: A longitudinal cohort study on hemodynamic pattern and outcome

Background

Pregnancy associated cardiovascular pathologies have a significant impact on outcome for mother and child. Bioimpedance cardiography may provide additional outcome-relevant information early in pregnancy and may also be used as a predictive instrument for pregnancy-associated diseases.

Methods

We performed a prospective longitudinal cohort trial in an outpatient setting and included 242 pregnant women. Cardiac output and concomitant hemodynamic data were recorded from 11^th–13^th week of gestation every 5^th week as well as at two occasions post partum employing bioimpedance cardiography.

Results

Cardiac output increased during pregnancy and peaked early in the third trimester. A higher heart rate and a decreased systemic vascular resistance were accountable for the observed changes. Women who had a pregnancy-associated disease during a previous pregnancy or developed hypertension or preeclampsia had a significantly increased cardiac output early in pregnancy. Furthermore, an effect of cardiac output on birthweight was found in healthy pregnancies and could be confirmed with multiple linear regression analysis.

Conclusions

Cardiovascular adaptation during pregnancy is characterized by distinct pattern described herein. These may be altered in women at risk for preeclampsia or reduced birthweigth. The assessment of cardiac parameters by bioimpedance cardiography could be performed at low costs without additional risks.

Maternal functional hemodynamics in the second half of pregnancy: a longitudinal study

Objective

Cardiovascular response to passive leg raising (PLR) is useful in assessing preload reserve, but it has not been studied longitudinally during pregnancy. We aimed to investigate gestational age associated serial changes in maternal functional hemodynamics and establish longitudinal reference ranges for the second half of pregnancy.

Materials and Methods

This was a prospective longitudinal study on 98 healthy pregnant women who were examined 3–5 times during 20–40 weeks of gestation (a total of 441 observations). Maternal cardiac function and systemic hemodynamics were assessed at baseline and 90 seconds after PLR using impedance cardiography (ICG). The main outcome measures were gestational age specific changes in ICG-derived variables of maternal cardiovascular function and functional hemodynamic response to PLR.

Results

Hemodynamic response to PLR varied during pregnancy. PLR led to an insignificant increase in stroke volume during 20⁺⁰ to 31⁺⁶ weeks, but later in gestation the stroke volume was slightly lower at PLR compared to baseline. PLR caused no significant change in cardiac output between 20⁺⁰ and 23⁺⁶ weeks and a significant decrease after 24⁺⁰ weeks. A decrease in heart rate, mean arterial pressure, and cardiac contractility was observed during PLR throughout the second half of pregnancy. Systemic vascular resistance was reduced by PLR up to 32⁺⁰ weeks, but increased slightly thereafter.

Conclusion

Healthy pregnant women appear to have limited preload reserve and reduced cardiac contractility, especially in the third trimester, which makes them vulnerable to fluid overload and cardiac failure.

Effect of passive leg raising on systemic hemodynamics of pregnant women: a dynamic assessment of maternal cardiovascular function at 22-24 weeks of gestation

Objective

To investigate functional hemodynamic response to passive leg raising in healthy pregnant women and compare it with non-pregnant controls.

Materials and Methods

This was a prospective cross-sectional study with a case-control design. A total of 108 healthy pregnant women at 22–24 weeks of gestation and 54 non-pregnant women were included. Cardiac function and systemic hemodynamics were studied at baseline and 90 seconds after passive leg raising using non-invasive impedance cardiography.

Main outcome measures

Trends and magnitudes of changes in impedance cardiography derived parameters of cardiac function and systemic hemodynamics caused by passive leg raising, and preload responsiveness defined as >10% increase in stroke volume or cardiac output after passive leg raising compared to baseline.

Results

The hemodynamic parameters in both pregnant and non-pregnant women changed significantly during passive leg raising compared to baseline, but the magnitude and trend of change was similar in both groups. The stroke volume increased both in pregnant (p = 0.042) and non-pregnant (p = 0.018) women, whereas the blood pressure and systemic vascular resistance decreased (p<0.001) following passive leg raising in both groups. Only 14.8% of pregnant women and 18.5% of non-pregnant women were preload responsive and the difference between groups was not significant (p = 0.705).

Conclusion

Static measures of cardiovascular status are different between healthy pregnant and non-pregnant women, but the physiological response to passive leg raising is similar and not modified by pregnancy at 22–24 weeks of gestation. Whether physiological response to passive leg raising is different in earlier and later stages of pregnancy merit further investigation.

Noninvasive cardiac monitoring in pregnancy: impedance cardiography versus echocardiography

OBJECTIVE

The objective of this study was to report thoracic impedance cardiography (ICG) measurements and compare them with echocardiography (echo) measurements throughout pregnancy and in varied maternal positions.

METHOD

A prospective cohort study involving 28 healthy parturients was performed using ICG and echo at three time points and in two maternal positions. Pearson's correlations, Bland-Altman plots and paired t-tests were used for statistical analysis.

RESULT

Significant agreements between many but not all ICG and echo contractility, flow and resistance measurements were demonstrated. Differences in stroke volume (SV) due to maternal position were also detected by ICG in the antepartum (AP) period. Significant trends were observed by ICG for cardiac output and thoracic fluid content (TFC; P<0.025) with advancing pregnancy stages.

CONCLUSION

ICG and echo demonstrate significant correlations in some but not all measurements of cardiac function. ICG has the ability to detect small changes in SV associated with maternal position change. ICG measurements reflected maximal cardiac contractility in the a AP period yet reflected a decrease in contractility and an increase in TFC in the postpartum period.

Impedance cardiography facilitates differentiation of severe and superimposed preeclampsia from other hypertensive disorders

OBJECTIVE

To determine if hemodynamic profiling using noninvasive impedance cardiography (ICG) reliably identifies the patient with severe (SPRE) or superimposed (SuPRE) preeclampsia.

METHODS

Late gestation hypertensive pregnant patients underwent immediate ICG evaluation. Findings were compared between patients subsequently achieving or not achieving American College of Obstetricians and Gynecologists criteria for SPRE or SuPRE.

RESULTS

Patients with severe disease were more likely to have depressed cardiac function and higher systolic blood pressure, mean arterial blood pressure, systemic vascular resistance, and thoracic fluid content compared to nonsevere hypertensive disease.

CONCLUSION

ICG hemodynamic profiling of late gestation hypertensive patients can rapidly and reliably identify those with SPRE or SuPRE.

Measure of hemodynamic patterns by thoracic electrical bioimpedance in normal pregnancy and in preeclampsia

OBJECTIVE

To compare the differences in the hemodynamics between normal pregnancy and preeclampsia, using thoracic electrical bioimpedance.

STUDY DESIGN

We compared heart rate, end-diastolic volume, systolic volume, cardiac output, ejection fraction and peripheral vascular resistances in 18 healthy pregnant women with 15 with preeclamptic women at the following intervals: third trimester, 48 h post-partum, 2 and 6 months post-partum. We took the measurements by thoracic electrical bioimpedance. Statistical analysis was performed by means of Wilcoxon rank-sum test and p < 0.05 was considered statistically significant.

RESULTS

The heart rate was lower in the preeclampsia group during the third trimester and the systolic volume was also lower at 48 h post-partum; this implies a lower cardiac output in women with preeclampsia during pregnancy and in the immediate puerperium. The systemic vascular resistances were higher in preeclampsia in the third trimester and at 48 h post-partum. At 2 and 6 months post-partum, the hemodynamic situation had equalized in both groups.

CONCLUSIONS

Preeclampsia is a situation of low cardiac output and high peripheral resistances compared with a normal pregnancy.