Validation of maternal cardiac output trending with impedance cardiography against transthoracic Doppler echocardiography in healthy pregnant women.

During healthy pregnancy, the maternal cardiovascular system changes to
contribute to optimal growth and development of the foetus and help to protect
the mother from risks. Major hemodynamic changes induced by pregnancy include
increase of the maternal cardiac output (CO) above non-pregnant levels. CO is a
functional parameter, reflecting the total demand placed on the cardiovascular
system. CO is defined as the volume of blood pumped into the aorta per unit
time and is calculated as the product of stroke volume (SV) and heart rate
(HR). Direct and indirect causes of maternal mortality and morbidity like
preeclampsia and haemorrhage and cardiac diseases, have been associated with
substantial changes in CO. Nowadays, monitoring maternal cardiovascular
function is limited to indirect parameters of maternal cardiovascular function
including heart rate and blood pressure. Measuring the CO could be a major help
in directing management and treatment in pregnant woman with cardiac pathology
and in pregnancy complications.

Invasive techniques such as Intermittent Bolus Pulmonary Artery
Thermodilution, continue to be the gold standard to measure CO. Since this
method requires right heart catheterization with a pulmonary artery catheter,
it is associated with a variety of complications to the participant. This
method is controversial on account of its invasiveness and with inherent risks.
A non-invasive continuous measurement could be of major value.

Transthoracic echocardiography (TTE) is a clinically established non-invasive
diagnostic method that provides assessment of cardiac structure and function.
CO can be calculated with two-dimensional pulsed wave Doppler as the product of
the cross-sectional area and and left ventricular outflow tract velocity time
integral (LVOT VTI). This method has been validated to measure CO against
invasive techniques in and outside pregnancy. However, this technique has its
limitations. TTE is dependent on the operator*s skill in acquiring images
taking correct measurements and continuous assessment is time consuming.

ICG allows continuous, non-invasive monitoring of the CO. ICG is a method that
detects changes in thoracic electrical bioimpedance between simple skin
electrodes, together with a conventional ECG. To estimate CO, it uses complex
algorithms based on assumptions regarding the thoracic dimensions and shape to
convert changes in thoracic impedance into volume changes. In theory, the
specific pattern of major physiological adaptations of the pregnant body could
influence these assumptions. Physioflow, the device we will use for ICG, was
designed to monitor performing athletes, and is thereby equipped with a high
signal stability. On that account it can be of value in woman during both
pregnancy and labour, which puts an enormous strain on the maternal
cardiovascular function. Although there have been numerous validation studies
of methods of continuous CO measurement, the majority evaluated the measurement
of the actual value of CO. Less than one-fifth of the studies addressed CO
trending. Although the accuracy of ICG for absolute CO values appears
moderately convincing, it is generally agreed to be capable of trend analysis.
However, this technique has not been validated in pregnancy.

As a result, further validation of ICG trending ability during pregnancy is
required. We aim to examine the agreement in CO trending between ICG and the
clinically established method of TTE in a cohort of healthy pregnant woman. To
induce changes in the CO during our measurements, we will submit pregnant women
to a limited exercise.

A prospective comparative study with non-invasive techniques will be performed
in order to compare CO trending by ICG with TTE. This trial will be conducted
at a tertiary care center, Erasmus University Medical Center Rotterdam. We
propose a maximum duration of the study of six months.

Burden associated with participation exists of one investigation for an
estimated time of 30 minutes. The patients will be examined with ICG and TTE in
the left lateral decubitus position in all measurements. After the baseline
measurement, participants will exercise on a home trainer until their heart
rate rises up to 70% of their maximum heart rate. When this limit is reached,
participants will exercise at this heart rate for 1 minute. Subsequently the
second measurement takes place. When the heart rate decreases to <20% of the
maximum heart rate, the last measurement will be performed. Moreover, maternal
data will be collected during participation, including the blood pressure and
measured height and weight to determine current BMI. Self-reported age, weight
prior to conception, gravidity and parity will be obtained. There is no risk
associated with participation for mother and foetus. There is no individual
benefit for participants.