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
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Figure 1.
Diagram showing the five transverse views.
V1 Abdominal situs: fetal lie must be determined so the left
and right sidedness of structures can be assessed in order to
diagnose complex cardiac malformations accurately. The scanning
plane passes through the abdomen at the level of the
intrahepatic portion of the umbilical vein and in normal situs,
the aorta (AoD) lies to the left and the inferior vena cava (IVC)
to the right of the spine.
V2 Four chamber view: allows
assessment of morphology and symmetry. The left atrium (LA) is
characterised by the coronary sinus and the left atrial
appendage and the right ventricle (RV) by the offsetting of the
tricuspid valve with attachments to the septum and the moderator
band. Flow passes through the oval foramen (FO) from the right
atrium (RA) to fill the left ventricle (LV). There is only a
small contribution to LV filling from the left (LPV) and right
pulmonary veins (RVP) until late in gestation.
V3 and V4 Great
arterial crossover: the aorta (Ao) arises first, sweeping to the
fetal right and the pulmonary artery (PA) crosses over. The
great arteries are usually easiest to differentiate by
confirming early bifurcation into the right and left branch
pulmonary arteries (RPA, LPA), characteristic of the pulmonary
artery.
V5 The three vessel and trachea view enables a
comparison of the transverse aortic arch (Ao) and ductal arch
(or duct). They should be of similar sizes. Additional vessels
such as a persistent left superior caval vein (SVC) or aberrant
left subclavian artery may be identified at this level.
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Figure 2.
Cardiac position.
(2.1, top left) A normal cardiac axis is one where a line drawn from the
spine to the front of the fetal chest passes through the tri- cuspid valve (–). R represents the right side of the fetus in
all images. (2.2) Left axis deviation is a sign of congenital
heart disease, particularly where the outflow tracts are
involved, such as Tetralogy of Fallot (---- axis). (2.3) A left
diaphragmatic hernia usually displaces the heart to the right
and is usually easy to detect as the stomach (St) lies behind
the left atrium (LA) in the chest. (2.4) A right-sided
diaphragmatic hernia is more diffi- cult to detect as it may not
be consistently in the chest and the sonographic appearance of
liver (Li) is sometimes similar to lung. It may displace the
heart markedly to the left thus exaggerating the left axis
deviation often seen with congenital heart disease. (2.5)
Pleural effusion (Pl Eff) outlines the left lung (Lu) pushing
the heart to the right. (2.6, bottom right) Congenital cystic adenomatoid
malformation (CCAM) is characterized by bright echogenic areas
in the lung that may cause cardiac displacement.
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Figure 3. Four-chamber view.
(3.1, top left) Disproportion is an important characteristic of CHD and is
most obvious in hypoplastic left heart syndrome, where there is
mitral (MAtr) and aortic atresia. The right ventricle (RV) forms
the apex of the heart. (3.2) Coarctation of the aorta is often
suspected because of disproportion at the four chamber view. The
right atrium (RA) and ventricle (RV) are larger than left-sided
structures. (3.3) In pulmonary atresia with intact septum the
right atrium (RA) is often enlarged due to tricuspid
regurgitation, and the right ventricle (RV) is thickened and
shorter than normal due to poor trabecular development. The
tricuspid valve (TV) may be dysplastic. (3.4) Absent left
atrioventricular connection [usually mitral atresia (MAtr)]
results in severe ventricular disproportion and forms part of
hypoplastic left heart syndrome or is associated with double
outlet right ventricle. (3.5) Absent right atrioventricular
connection, usually tricuspid (TAtr) atresia, is associated with
severe ventricular disproportion (larger left ventricle, LV)
unless there is a large ventricular septal defect (VSD). (3.6,
bottom right) A
persistent left superior caval vein may be a normal variant.
When it drains to the coronary sinus (CS) it may obstruct flow
through the developing mitral valve and result in cardiac
disproportion with a smaller left than right ventricle (RV).
This is associated with an increased risk of CHD, particularly
coarctation of the aorta.
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Figure 4. Septal defects.
This figure shows paired images of four chamber views taken in
the transverse fetal plane (top) and short axis view of the heart
from the coronal fetal plane (sax, bottom) to illustrate
characteristics of septal defects.
(4A) The perimembranous
ventricular
septal defect (PM VSD) is associated with lack of offset of the
mitral (MV) and tricuspid valves (TV), and can be imaged in the
transverse plane between the TV and aorta (Ao). The short axis
view (sax), below, confirms that the MV is normal, thus excluding an atrioventricular septal defect.
(4B) The atrioventricular septal
defect is also characterized with lack of offset of the
atrioventricular valves, but there is no mitral or tricuspid
valves, but a common atrioventricular junction and valve. There
is a moderate atrial (A) and ventricular component (V) in this
example. The short axis view (sax), below, confirms that the valve is
the common
valve of an atrioventricular septal defect.
(4C) The
muscular
ventricular
septal defect (Musc VSD) is associated with normal off-set of the mitral and tricuspid valves (TV) and has muscular
margins. The short axis view (sax), below, confirms that there is no straddle
of TV or MV supporting chordae.
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Figure 5. Great arteries.
(5.1, top left) This is an oblique view (note ribs) showing parallel
relationship of the aorta (Ao) and pulmonary arteries (PA)
arising from the right (RV) and left ventricles (LV),
respectively. (5.2) In Tetralogy of Fallot, there is an aorta (Ao)
overriding the interventricular septum (IVS) and a smaller
pulmonary artery (not shown). (5.3) In a common arterial trunk there
is a solitary outlet from the heart (Trunk) from which the
pulmonary artery arises (PA). Colour Doppler confirms there is
prograde flow into the PA. Double outlet right ventricle (DORV)
is not a diagnosis, but describes the ventriculo-arterial
connections. (5.4) In DORV, both great arteries arise predomi- nantly
from the right ventricle (RV) and may be normally related as in
this case with the aorta (Ao) arising centrally, and an anterior
pulmonary artery (PA). In this example there is severe aortic stenosis and hypoplasia.
(5.5) In aortic atresia the aortic valve (Ao)
is thickened and doming with no forward flow. (5.6, bottom
right) Pulmonary atresia
may be membranous as in this case where the pulmonary valve (PV)
is clearly seen with post-stenotic pulmonary dilatation or shows
long segment muscular atresia.
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Figure 6. Three-vessel and trachea view.
(6.1, top left) The three vessel view may show only one transverse arch,
as in this example of simple transposition of the great arteries
we see only the transverse aortic arch (Ao Arch) running to the
left of the trachea (Tr) and the right superior vena caval vein
(RSVC). (6.2) This image illustrates two normal variants a
right-sided aortic arch (RAoA) and a left superior caval vein (LSVC).
The arterial duct (DA) is left sided surrounding the trachea (Tr).
(6.3) This case shows a right-sided aortic arch (RAoA) and
left-sided arterial duct (DA) surrounding the trachea (Tr). The
insert shows the aberrant left subclavian artery (LSA) arising
from the duct of Kommerell, running behind the trachea. (6.4) A
double aortic arch may be difficult to diagnose in the fetus
because of the large arterial duct. This case shows bifurcation
of the ascending aorta (Ao) around the trachea. In this case
there was a left-sided arterial duct (not shown in this plane)
and a persistent left (LSVC), as well as right (RSVC) superior
caval vein. This vascular arrangement is likely to have caused
tracheal (Tr) compression resulting in bilateral hyperechogenic
lungs (Lu) and ascites (Asc). (6.5, 6.6, bottom right) In cases of complex
duct-dependent malformations colour Doppler of transverse (main
image) and sagittal views (inserts) of the arch will show
reversal of flow in the superior (aortic, AoA) or inferior (ductal,
DA) arches, where there is left- or right-sided outflow tract
obstruction, respectively.
Next page:
References & Glossary
>
Introduction
&
Cardiac Position |
Four Chambers &
Septal Defects | Great Arteries
&
Arch Abnormalities | Figures |
References & Glossary
||
heart conditions | heart sketch
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