Examination of the fetal heart: making a
diagnosis and avoiding pitfalls
Ultrasound Journal, May 2007, Vol. 15, No. 2, 62-67
This
article is reproduced with kind permission of the BMUS Ultrasound
publishers,
www.ingentaconnect.com/content/maney
|
Introduction
 We recommend an initial approach to examination
of the fetal heart using the five transverse views to
identify abnormality (Fig. 1) as described in this journal previously. 1
This article presents a practical approach to improving
detection at the routine anomaly scan, as well as making a
diagnosis of congenital heart disease (CHD) using additional
coronal and longitudinal views of the fetus that will aid in
cardiac diagnosis.
It also points out that some of the pitfalls in
imaging and interpretation. Sequential scans are usually
required to acquire the necessary details to prepare for postnatal
management, including surgery, and to monitor cardiac growth
and disease progression.
Prenatal diagnosis of CHD allows for planning
of delivery, optimal use of services and decisions regarding
perinatal treatment, such as prostaglandin administration.
Surgical outcome is excellent for most types of congenital
heart disease with mortality
<5%,
but fetal outcomes are often worse, usually a reflection of the associated
extracardiac malformations and aneuploidy.
Still images of the heart are sometimes difficult
to interpret and are poor substitutes for moving images, and we
intend to provide small movie clips to
accompany this article (see Figures).
|
Key Points
Views and techniques
used to make a
fetal cardiac
diagnosis
-
Five
transverse views form the basic protocol for fetal heart
screening.
-
Determining fetal left- and right-sidedness remains an essential
first step.
-
Oblique,
short axis and sagittal views help to confirm morphology
and relationships of ventricles and great arteries.
-
Colour
Doppler (differing modalities include velocity and power)
will help delineate small vessels,
particularly in the sagittal views.
-
Pulsed
Doppler of vessels provides important
physiological information when colour Doppler suggests
an abnormality.
-
Abnormal
cardiac axis and disproportion are important
indicators of CHD.
|
Cardiac Position
The first stage of assessment is to determine fetal lie, essential
to appreciate right and left sidedness of the fetus and to
interpret the sonographic images.1
Because of the relatively
horizontal position of the fetal heart in the chest, coronal views
of the fetal body produce short axis views of the heart and
longitudinal views give sagittal views of the circulation (see
Fig. 2, shown right).
A normal cardiac axis is one where a line, drawn from the
spine to the front of the fetal chest, passes through the
tricuspid valve. The position of the heart in the chest may be
altered by cardiac and extracardiac factors. Unilateral pleural
effusions may shift the position of the heart in the chest and
may be associated with Noonan or Down’s syndrome. Bilateral
pleural effusions may cause various degrees of cardiac
compression (depending on their size) resulting in a small,
centrally placed heart. When there is increased echogenicity
of the lungs it is important to track the pulmonary veins and
look for collateral vessels carefully to ascertain whether there is
an additional blood supply to the affected lung segment. This is
characteristic of a sequestered lobe and may differentiate it from a
congenital cystic adenomatoid malformation (CCAM).
Pitfalls
Left axis deviation of the heart is associated with cardiac
abnormality, 2
but may also
reflect space occupying lesions in the chest. It is more
difficult to detect cases where there is a right-sided
diaphragmatic hernia, which may not be fixed in
the chest, but may displace the heart to the left thus
exaggerating left axis deviation often seen with outflow tract
malformations such as Tetralogy of Fallot (Fig.
2.4, shown on the right).
Vascular abnormalities, such as a double aortic arch, may
lead to tracheal compression in the fetus and cause enlargement of the lungs, masquerading as extensive bilateral CCAMs, the result of a naturally occurring ‘tracheal plug’
procedure.
Situs
The first
of the
five transverse views is that
of the abdomen from which abdominal situs is assessed. This is
normal if the aorta lies to the left of the spine and the
inferior caval vein anterior and to the right. Any other
arrangement is abnormal and should be investigated further. A
wide variety of cardiac abnormalities may be associated,
particularly atrioventricular septal defect, but sometimes the
heart may be normal. A detailed assessment of these conditions
is beyond the scope of this article.
3
Next page:
Four Chambers &
Septal Defects
>
Introduction &
Cardiac Position |
Four Chambers &
Septal Defects | Great Arteries
&
Arch Abnormalities | Figures |
References & Glossary
||
heart conditions | heart sketch
Please note
that this article is copyright and may not be reproduced
without the publisher's permission. |
|
|
|
