Development of the cardiac autonomic nervous system in utero

Improvements in surgery and intensive care strategies result in a survival of
more than 90% of children with congenital heart disease (CHD) into adulthood
nowadays. With these higher survival rates, comorbidity becomes more apparent.
The most common comorbidity in CHD is arrhythmia, a major cause of
hospitalization and use of medication. Although frequently occurring, the
origin of these rhythm disturbances is still unclear.
It has been shown that the cardiac autonomic nervous system (cANS) affects the
arrhythmogynesis. In adults with various non-congenital heart diseases an
altered cANS, expressed by decreased heart rate variability, has been found.
Also, fetuses with CHD have a different cANS compared with healthy fetuses.
These findings led to the hypothesis that maldevelopment of the cANS could play
a role in arrhythmias. However, until now little is known about the normal
development of cANS in utero.

The ANS can be subdivided into two branches: the sympathetic and
parasympathetic branch. Sympathetic stimulation increases heart rate, force of
contraction and conduction velocity, mainly through norepinephrine.
Parasympathetic stimulation with acetylcholine results in the opposite effect.
Under normal conditions these branches are balanced. The developmental pathway
of the cANS branches is a complex process under influence of genes, cells and
their interactions. Following the anatomical findings in mice embryos, cANS
development starts after 10 weeks of gestation. The establishment of
innervation occurs at different moments in development, as it is known that
signs of the sympathetic innervations are observed later in pregnancy then
those of the parasympathetic branch. Yet, the exact timeline of innervation in
utero remains unclear.

A non-invasive tool to assess the human cANS in vivo is the analysis of heart
rate variability (HRV), a variation in the interval between consecutive
heartbeats, since alterations in HRV reflects autonomic tone. HRV-analysis is
widely used in adult cardiology, but still not common in fetal
echocardiography. Most fetal data are derived from cardiotocography (CTG)
registrations, yet CTG does not have the temporal accuracy to assess
beat-to-beat variability. Fetal magnetocardiography (MCG) and
electrocardiography (ECG) are also used in research setting, where the former
is not suitable for daily clinical use and the latter not reliable due to
signal loss. The new ultrasonographic technique color Tissue Doppler Imaging
(cTDI) could provide HRV-analysis more accurately and is an easy, non-invasive
tool for daily use in fetal medicine. Fetal HRV-analysis with cTDI has never
been studied before.

The assessment of the normal development of the cANS may help to understand the
pathophysiology of arrhythmias. Since many features are unclear, we will first
conduct a pilot study.

The primary aim of this pilot study is to gain insight in the normal
development of the cANS in utero with HRV-analysis, in order to calculate
sample size required for future research.

We will conduct a observational pilot study of 16 pregnant women. We will
invite the participants from 10 weeks of gestation onwards, since mice show a
present cANS from that point. Subjects will be assigned for a specific week of
gestation to have the first examination in order of admission. The first
participant will have the first ultrasound examination at 10 weeks of
gestation, the second participant at 11 weeks of gestation, the third
participant at 12 weeks of gestation and so on, and then the ninth participant
again at 10 weeks of gestation, and so on. This examination will be repeated
every 8 weeks until the estimated due date, which is maximal 4 investigations
during the pregnancy. All ultrasound examinations are conducted by an
experienced ultrasonographer (F.Zwanenburg, primary investigator) at Leiden
University Medical Center (LUMC), under supervision of M.C. Haak, consultant in
fetal medicine.

Ultrasound is a safe and non-invasive technique, which means that participators
are not exposed to additional risks in their pregnancy. However, imaging
examinations always carries the risk of unexpected findings, which have to be
communicated to the women. The women are examined in a tertiary care level, so
immediate counseling of a fetal medicine expert is available. Therefore, the
following steps will be executed immediately if an unexpected finding occurs:
1. The primary investigator will communicate the finding to the participator
2. The primary investigator will contact the supervisor of the day (which is a
fetal medicine expert) to evaluate the finding
3. The supervisor of the day will have a conversation with the participator in
which the finding and (if necessary) following procedures will be explained
4. The current obstetric health care provider of the participator
(midwife/gynaecologist) will be informed
The burden to participate is extra time and travel expenses, but with a maximum
of four ultrasound examinations this is mild. Participators do not have benefit
of the study.