Download Antenatal diagnosis of fetal heart malformation

The heart of the matter
Antenatal diagnosis of
fetal heart malformation
at 11 to 14 weeks gestation
The incidence of fetal cardiac malformation amongst live births (eight per 1000)
is six times greater than chromosomal abnormalities and four times that of
­neural tube defects.
Furthermore, over half of these
babies have a significant defect
which ­contributes to 20 per cent of
all ­neonatal deaths and up to 50 per
cent of all infant deaths.1 Importantly,
there is good evidence supporting the
view that prenatal detection of these
major defects improves p
­ ostnatal
Dr Simon Meagher ­outcome, particularly for lesions
such as ­transposition of the great
FRANZCOG
­arteries (TGA) and other arterial duct
­dependent l­esions. For this reason
amongst o
­ thers, there is increasing international interest in the
­prenatal detection of ­congenital heart defects (CHD).
Detection rates of fetal cardiac malformation in the mid-trimester
is variable and dependent on many factors, including o
­ perator
­expertise, patient size, fetal position and the complexity of
the s­ pecific cardiac lesion. For example, a recent population
study in Victoria revealed a detection rate for the more obvious
­abnormalities such as hypoplastic left heart and double outlet/
inlet ventricle of 84 per cent and 74 per cent respectively, whereas
detection rates in more subtle lesions such as coarctation and
­transposition were 26 per cent and 17 per cent ­respectively.2
­Identification of all these abnormalities in the first trimester is
unquestionably more difficult. The fetus at 11 to 14 weeks is
­approximately 6 to 8 cm in length. The fetal heart size at 12 weeks
measures 11 mm long and 6 mm across, therefore, ­approximately
the size of the fifth fingernail. This said, the axial and lateral
­resolution of current ultrasound systems using high frequency
­endovaginal ultrasound is 0.1 mm. Also, recently published
­detection rates in specialist centres now approximate the detection
rates at the mid-trimester and thus it is a matter of time before the
majority of CHD in Australia will become detectable at 11 to 14
weeks.
Nuchal translucency and heart defects
In the first trimester, an increased nuchal translucency (NT) is a
strong indicator of underlying congenital heart disease, far stronger
than a past history of CHD or diabetes. Of all births with CHD, 25
to 30 per cent would be expected to demonstrate an increased NT
at 11 to 14 weeks. Conversely, the incidence of CHD in fetuses
with an increased NT is five per cent. Also, the greater the NT, the
greater the chance of underlying CHD ( Table 1). Therefore, patients
with an NT of greater than 8.5 mm and normal ­chromosomes
over 60 per cent will have underlying CHD.3 Thus, in patients
with a ­normal karyotype following chorionic villus sampling or
­amniocentesis, the increased NT should be regarded as a pointer
to cardiac malformation. Indeed, once the NT reaches 3 mm, a
targeted fetal echocardiogram should be considered. Of note in the
presence of an increased NT, there is no obvious bias towards any
particular lesion or sidedness of heart defect.
Table 1.
Bands of risk for increased nuchal translucency and congenital heart
malformation.3
NT Range
Incidence of major CHD
NT in the range 2.5-2.9 mm
2.4%
(10/416)
NT in the range 3.0-3.4 mm
2.6%
(8/306)
NT in the range 3.5-4.4 mm
3.1%
(12/384)
NT in the range 4.5-6.4 mm
8.3%
(13/157)
NT in the range 6.5-8.4 mm
19%
(8/42)
NT in the range > 8.5 mm
64.3% (9/14)
Tricuspid regurgitation
Tricuspid regurgitation (TR) at 11 to 14 weeks is seen in up to 70
per cent of fetuses with Trisomy 21 and has been introduced in the
United Kingdom to the Fetal Medicine Foundation first trimester
nuchal translucency program. Like nuchal translucency, TR is also
an indicator of CHD and recent evidence suggests its association
with CHD may be independent of nuchal thickening (Figures 3a and
3b). Its assessment in the first trimester may help subselect the group
of fetuses with an increased NT and congenital heart malformation.
While TR assessment is not yet routine practice in Australia, it seems
likely that assessment of this marker in the future may help identify
fetuses with major CHD.
Ductus venosus
Absence or reversal of flow in the ductus venosus (DV) at 11 to 14
weeks is an indicator of Down syndrome. Recent data, however,
also show that Doppler velocimetry of the DV can help improve
the predictive capacity of increased NT in the detection of ­major
­congenital heart defects in chromosomally normal fetuses. In
patients with a thickened NT and normal chromosomes ­following
invasive testing, the finding of an absent or reversed A-wave in
the ductus venosus is associated with a three-fold increase in the
likelihood of a major cardiac defect, whereas the finding of normal
ductal flow is associated with a halving in risk for such defects.
Therefore, in patients with normal karyotype following invasive
testing where absent ductous venosus (ADV) or reversed ductous
venosus (RDV) has been observed, a fetal echocardiogram should
be considered. There is also data emerging to suggest that an
abnormal first trimester DV blood flow is a risk factor not only for
Continued on page ?
The heart of the matter
Figure 1.
A normal four-chamber view of the heart at 12 weeks on both B-mode (left) and
colour Doppler e­ xamination (right). Normal atrial and ventricular symmetry is
observed.
Figures 3a and 3b.
Figure 2.
Normal outflow tracts at 12 weeks are demonstrated on this ­duplex image in which
B-mode is shown on the left and directional power Doppler on the right.
The ­calibre and direction of the main ­pulmonary artery (MPA), right pulmonary
artery (RPA), aorta (AO), ductus arteriosis (AD) and descending aorta (DA) are all
seen more easily with colour Doppler examination.
Doppler assessment of the right heart reveals tricuspid regurgitation (TR) which indicates the possibility of ­underlying CHD.
The heart of the matter
CHD, but an indicator of other structural anomalies and perinatal
death in fetuses with normal NT.4
Assessment of fetal heart anatomy
The fetal heart is best assessed at both transabdominal and
­transvaginal examination. There should be few reasons why a
­transvaginal examination is not offered routinely to all patients at the
11 to 14-week scan. Accepting the limitations of probe ­movement
and accepting the unpredictability of fetal position, greater cardiac
details are obtained in most patients with this approach (Figure
1). The ease of recognition of normal fetal heart anatomy at 12
versus 11 weeks is striking. A one-week increase in fetal size makes
a significant difference in cardiac anatomy resolution. For this
reason, patients are best booked after 12 weeks of gestation. The
­identification of normal cardiac structures at 12 weeks has a strong
negative predictive value which is of clinical relevance in the setting
where first trimester risk factors have been identified (see below).
The four chambers of heart and outflow tracts are identifiable in
skilled hands in up to 90 per cent of patients.
‘Improved high frequency ­vaginal
probes, increasing sensitivity of
colour Doppler technology and ever
increasing maternal body h
­ abitus,
should steer clinicians ­towards
­routine endovaginal u
­ ltrasound
­examination of the fetal heart
­during the first trimester.’
Colour Doppler examination in the first trimester is a powerful tool
in the routine assessment of fetal cardiac structure and will provide
detail of the outflow tracts in patients where views on gray scale
are limited (Figure 2). Also, colour Doppler examination has the
­potential to unveil TR or muscular septal defects, which for the
greater part are not seen on B-mode examination at this stage in
gestation (Figure 3). 4D ultrasound using spatio-temporal image
correlation (STIC) technology is emerging as a useful screening and
diagnostic tool for CHD at the mid-trimester and beyond. At this
point in time however, its application in the first trimester is limited.
However, 3D static volume acquisition of the heart using colour
(‘glass body’ render) has potential in its assessment of cardiac
function including tricuspid regurgitation and septal defects. With
respect to fetal cardiac malformation, the image sequences upon
which mid-trimester diagnoses rely are similar in the first trimester.
In transposition of the great vessels, the major arteries arise from
the heart in parallel (Figure 6 ); in Tetralogy of Fallot the aorta
­overrides the inter-ventricular septum (Figure 7); and in hypoplastic
left heart, the left ventricle is small and the right heart chambers and
right ­ventricular outflow tract are dilated (Figures 5a and 5b). The
­diagnoses of more subtle abnormalities such as right-sided aortic
arch and atrioventricular (AV) canal defects can be more difficult
(Figures 8a and 8b).
Conclusion
Improved high frequency vaginal probes, increasing ­sensitivity of
colour Doppler technology and ever increasing maternal body
­habitus, should steer clinicians towards routine endovaginal
ultrasound examination of the fetal heart during the first trimester.
Patient acceptance of a vaginal scan is predictably high once the
benefits of the examination are explained. While the learning curve
in first trimester fetal heart diagnosis may be steep, current evidence
­suggests that a diagnosis may be reached in over 90 per cent of
cases.
The first trimester provides a unique opportunity in that there are
several markers at this time which lead to the diagnosis of CHD.
One in every three cases of major CHD present with an increased
NT and Doppler velocimetry of the ductus venosus. The tricuspid
valve can help improve the predictive capacity of increased NT in
the detection of major congenital heart defects in both euploid and
aneuploid fetuses.
While first trimester detection rates of CHD in specialist centres
now approximate second trimester detection rates, it may take time
before this translates into routine practice in low-risk populations.
While climbing this learning curve, caution needs to be exercised in
the first instance, with a low threshold to seeking a second opinion,
or at least considering a repeat examination of the fetal heart later
in pregnancy.
While resolution of ultrasound increases and the understanding of
cardiac diagnosis improves, it seems unlikely however, that the 11
to 14-week scan will completely replace the mid-trimester cardiac
assessment in the near future. This is not to say we should not strive
to reach a diagnosis at earlier stages in pregnancy, particularly
since there is a captive population who are having a routine scan
performed for other reasons, namely NT assessment.
The heart of the matter
Figures 4a and 4b.
These figures demonstrate normal and reversed ductus venosus (RDV) waveform at 12 weeks gestation. The ­presence of a reverse A-wave raises the possibility of CHD.
Figure 5a.
Hypoplastic left heart at 12 weeks. On the four-chamber view, a dilated right
atrium (RA) and dilated right ventricle (RV) are seen. The left atrium is small
and the left ventricle hypoplastic.
Figure 5b.
Hypoplastic left heart at 12 weeks. The right ventricular outflow tract view
­demonstrates a dilated main pulmonary artery (MPA) and dilated right pulmonary
artery (RPA). Ductus Arteriosis (DA).
The heart of the matter
Figure 6.
Figure 7.
Figure 8a.
Figure 8b.
Transposition of the great vessels at 12 weeks. Both the aorta (AO) and pulmonary
artery (PA) arise from the heart in parallel.
Right-sided aortic arch at 12 weeks. The three-vessel tracheal view reveals the
transverse aortic arch (TAo) ­diverging from the main pulmonary artery (PA) and
to the right of the trachea.
Tetralogy of Fallot at 12 weeks. The dilated aorta is seen sitting astride the
­interventricular septum.
Cardiac exstrophy at eight weeks.
The heart of the matter
Figure 9.
Atrioventricular (AV) canal defect at 12 weeks. There is a common AV valve, absent
septum primum and ventricular septal defect.
Figure 10.
Hypoplastic right heart at 12 weeks. RV=right ventricle, LV =left ventricle,
PE=pericardial effusion.
References
1.
Yagel S, Cohen SM and Achiron R. Examination of the fetal heart by five
short-axis views: a proposed screening method for comprehensive
cardiac evaluation. Ultrasound Obstet Gynecol 2001; 17:367-369.
2. Chew C, Halliday JL, Riley MM and Penny DJ. Population-based study
of antenatal detection of congenital heart disease by ultrasound
examination. Ultrasound Obstet Gynecol 2007; 29:619-624.
3. Ghi T, Huggon IC, Zosmer N and Nicolaides KH. Incidence of major
structural cardiac defects associated with increased nuchal translucency
but normal karyotype. Ultrasound Obstet Gynecol 2002; 18:610-614.
4. Oh C, Harman C, Baschat AA. Abnormal first-trimester ductus venosus
blood flow: a risk factor for adverse outcome in fetuses with normal
nuchal translucency. Ultrasound Obstet Gynecol 2007; 30:192-196.