Download Hypoplastic left heart syndrome

Ultrasound Obstet Gynecol 2000; 15: 271±278.
Editorial
Hypoplastic left heart syndrome
J.M. SIMPSON
INTRODUCTION
Hypoplastic left heart syndrome (HLHS) is the term used
to describe a group of congenital heart lesions characterized by severe underdevelopment of left heart structures.
Up to the early 1980s this condition was untreatable and
was uniformly fatal in early infancy. The initial reports of
Norwood and colleagues provided the impetus for active
intervention for this condition1. Advances in surgical
techniques mean that intervention is now possible for
this condition, with better results in recent years2.
Hypoplastic left heart syndrome may be diagnosed during
fetal life, thus a knowledge of this condition is highly
relevant to those involved in prenatal diagnosis. This
Editorial aims to describe the antenatal sonographic
features of HLHS and to address issues regarding prenatal
and postnatal management.
DEFINITION
Hypoplastic left heart syndrome is not a single entity but is
rather a spectrum of congenital heart malformations
characterized by severe hypoplasia of the left ventricle
and left ventricular outflow tract. In `classical' HLHS the
aortic valve is atretic, with either atresia or severe
hypoplasia of the mitral valve. In some instances, the
term has been applied to other lesions including critical
aortic stenosis with severe hypoplasia of the left ventricle,
unbalanced atrioventricular septal defects with hypoplasia
of the left ventricle and aorta, and severe coarctation of the
aorta. In this Editorial, unless stated otherwise, the term
HLHS will be applied to cases of `classical' HLHS. Where
relevant, reference will be made to the other variants of
HLHS.
SO NOGR A PH IC FEAT URES
The sonographic features of some of the more common
forms of HLHS are described below.
`Classical' hypoplastic left heart syndrome
Mitral and aortic atresia
There is no communication between the left atrium and left
ventricle. This may be due to a complete absence of the left
atrioventricular connection or an imperforate mitral valve.
Typically, the left ventricle is slit-like and there may be no
demonstrable left ventricular cavity at all (Figure 1).
Aortic atresia (mitral valve patent)
INCIDENCE
The birth incidence of HLHS has been estimated to be 0.1±
0.25/1000 livebirths3,4. These birth estimates will certainly
underestimate the incidence during fetal life, because they
do not include cases of spontaneous intrauterine death
which occur with increased frequency in fetuses with
congenital heart disease. One large study described a 5%
rate of spontaneous intrauterine death in a series of 161
cases of HLHS diagnosed prenatally5.
EDIT ORIAL
The left ventricle is echogenic, hypoplastic and globular,
contrasting with the slit-like ventricle observed in mitral
atresia (Figure 2).
Other variants of HLHS
Critical aortic stenosis with hypoplastic left ventricle
In this condition, the left ventricle typically appears
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Figure 1 Mitral and aortic atresia. The right atrium and right ventricle
are easily seen but the left ventricle is exceedingly hypoplastic with no
demonstrable cavity. RA ˆ right atrium; RV ˆ right ventricle;
LA ˆ left atrium.
echogenic and poorly contracting. The mitral valve is
patent and there is some forward flow of blood through
the stenotic aortic valve. Sequential prenatal echocardiographic studies usually demonstrate subnormal growth of
the left heart with advancing gestation so that, by term, the
left ventricle and aorta may be severely hypoplastic. In
such cases, the left heart structures may be judged
incapable of supporting the systemic arterial circulation
and management will be akin to other forms of HLHS6,7. It
is in this group of fetuses, with severe aortic stenosis, that
balloon dilation of the aortic valve has been advocated,
with the aim of promoting growth and function of the left
ventricle, thereby maximizing the possibility of a biventricular repair8,9. In one case in which prolonged survival
Figure 2 Aortic atresia (mitral valve patent). The right ventricle forms
the apex of the heart. The left ventricle is globular, echogenic and
hypoplastic. RV ˆ right ventricle; LV ˆ left ventricle.
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Figure 3 Critical aortic stenosis with hypoplastic left ventricle. The
right ventricle forms the apex of the heart. The left ventricle is
hypertrophied, globular and mildly echogenic. RV ˆ right ventricle;
LV ˆ left ventricle; RA ˆ right atrium.
was documented, prenatal echocardiographic measurements did not demonstrate any short-term improvement
in cardiac function in that fetus7. Thus the role of prenatal
intervention in such cases remains controversial (Figure 3).
Severe coarctation of the aorta
Features of coarctation of the aorta in the fetus include a
marked dominance of right heart structures compared to
those of the left, affecting the great arteries and/or
ventricles coupled with relative hypoplasia of the distal
aortic arch. In these fetuses the mitral and aortic valves are
patent. The diagnosis of coarctation of the aorta is
Figure 4 Severe coarctation of the aorta. This echocardiogram was
taken at 27 weeks gestation. There is marked asymmetry of
ventricular and atrial size. The left ventricle does, however, extend to
the apex of the heart and the mitral and aortic valves were patent. By
term, the left ventricle and aorta were so hypoplastic that a Norwood
strategy was adopted postnatally. LV ˆ left ventricle; LA ˆ left
atrium; RV ˆ right ventricle; RA ˆ right atrium.
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Figure 5 Severely unbalanced atrioventricular septal defect. The right
ventricle is dominant and the left ventricle is tiny and slit like. This
fetus also had interruption of the inferior vena cava (left atrial
isomerism/visceral heterotaxy). RV ˆ right ventricle; RA ˆ right
atrium; LV ˆ left ventricle.
particularly difficult during fetal life and sequential studies
may be required to be confident of the diagnosis10±12. In
most of these cases, surgery on the aortic arch is sufficient
for a biventricular repair of the heart. In a subgroup,
however, the left ventricle, mitral valve and aorta are so
hypoplastic that the management of more classical forms
of HLHS may be adopted postnatally. This poses major
problems for counselling of parents with affected fetuses
early in pregnancy. Parents of fetuses with severe coarctation of the aorta need to be advised that if growth of left
heart structures is poor as pregnancy advances, then a
biventricular repair may be impossible and the postnatal
management will be that of HLHS (Figure 4).
Severely unbalanced atrioventricular septal defect
Some fetuses with atrioventricular septal defects demonstrate marked asymmetry in the size of the ventricles and
great arteries. If the left ventricle and aorta are severely
hypoplastic, then it may not prove possible to septate the
heart surgically into left and right ventricles, because the
left ventricle and aorta are too small for this to be a viable
option. In such cases the postnatal management will be
that of fetuses with classical HLHS. The discrepancy
between right and left heart structures has a variable
progression, making prognostication early in pregnancy
extremely difficult (Figure 5).
A S S O C I AT E D F E AT U R E S
The incidence of extracardiac and chromosomal abnormalities in fetuses with HLHS varies widely in reported
series. Unfortunately, this often reflects differences in
definitions of what constitutes HLHS. Differences in
referral population will also influence the incidence of
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Simpson
extracardiac and chromosomal abnormalities. Previous
data from this center has demonstrated a 4±5% incidence
of karyotypic abnormalities in classical HLHS, defined as
aortic atresia with an atretic or stenotic mitral valve5,13.
Others have reported a higher incidence of karyotypic
abnormalities in HLHS14±16. In critical aortic stenosis, the
incidence of karyotypic abnormalities is exceedingly low
with no such abnormalities demonstrated in two large
series from this center5,13. Fetuses with atrioventricular
septal defects or coarctation of the aorta have a much
higher incidence of karyotypic abnormalities5,13. In the
study of Natowicz et al. nine of 83 patients with HLHS
had chromosomal abnormalities including trisomy 13,
trisomy 18 and trisomy 2116. Close inspection of their
data, however, reveals that many affected fetuses had
unbalanced atrioventricular septal defects or coarctation of
the aorta, rather than classical HLHS.
Extracardiac structural malformations may coexist with
HLHS, which can adversely affect the prognosis17. The
incidence of extracardiac abnormalities described in a
postmortem series of 128 cases of classical HLHS from our
center was 3%18 which is much lower than other series15,16.
In terms of management, a detailed search for extracardiac malformations is required in all cases of HLHS,
and fetal karyotyping should be discussed. The estimation
of risk of karyotypic abnormalities will depend on the
exact form of HLHS that is identified. Hence, an accurate
cardiological diagnosis is essential. In practice, some
parents may elect to terminate the pregnancy on the basis
of the cardiac findings, regardless of associated anomalies.
In such circumstances, blood or tissue should be sent for
fetal karyotyping and a postmortem examination of the
fetus may provide additional information.
A N T E N ATA L M A N A G E M E N T
Most cases of HLHS are detected during midtrimester
ultrasound scanning of the low-risk obstetric population.
From the parents' perspective, the pregnancy will have
been thought to be proceeding normally up to this point
and the suspicion of a major cardiac abnormality at this
stage of pregnancy is immensely stressful. Urgent referral
for confirmation of the diagnosis and an explanation of the
prognosis is indicated which will usually involve a fetal
cardiologist or a pediatric cardiologist with specific
training in fetal echocardiography.
At this author's center, all parents are initially seen by
one of two consultants accompanied by a nurse counsellor
with extensive experience in pediatric cardiology. Information given during the initial consultation is accompanied by
written information about the condition. The postnatal
treatment options are explained, including surgical and
nonsurgical risks, and the uncertain long-term prognosis.
Termination of pregnancy is also discussed. In the United
Kingdom, the majority of patients opt to terminate the
pregnancy following the diagnosis of HLHS19 which is in
accord with our own departmental experience. There is
also the option of nonintervention following the delivery of
affected babies. This final option has become more
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controversial, particularly in view of the improving results
of postnatal interventions. My own view is that the wishes
of the parents should be respected in this regard.
We have found that the provision of relevant written
information to parents at the initial consultation has been
of great benefit. The retention of verbal information given
to parents, devastated by the finding of severe congenital
heart disease, is likely to be limited. Such information
should be coupled with the offer of a repeat consultation if
desired20. Some parents will also wish to discuss postnatal
management directly with the pediatric cardiac surgeon
who will be involved in their child's care. It is vital that
there is a co-ordinated team approach to management,
which will include the referring obstetrician, fetal medicine
specialist, cardiologist, cardiac surgeon and intensive care
staff.
Some parents will also consult outside sources of
information on hypoplastic left heart syndrome, including
the internet. This has occurred with sufficient frequency
that we now provide the internet addresses of relevant
sites, including a national parent support group for HLHS,
`Left Heart Matters' (www.lhm.org.uk).
P O S T N ATA L T R E AT M E N T S T R AT E G I E S
Prenatal recognition of HLHS provides an opportunity to
plan postnatal management. This means optimizing the
condition of the affected baby to undergo surgical
intervention. In the vast majority of cases of HLHS
diagnosed prenatally at our center, the parents opt for
delivery at the cardiac center to avoid the need for
postnatal transfer of the baby and, importantly, to avoid
potential separation of the parents and baby. The
advantages of this approach have been described previously21. Following delivery, a prostaglandin E infusion is
commenced to maintain ductal patency and the prenatal
diagnosis of HLHS is confirmed echocardiographically.
The circulatory physiology of the newborn infant with
HLHS is abnormal. Pulmonary venous blood returns to the
left atrium and crosses the atrial septum to the right atrium
where it mixes with systemic venous blood. All blood
leaves the heart through the right ventricle and main
pulmonary artery. By maintaining ductal patency, blood
can flow from the main pulmonary artery into the aorta,
where a proportion will pass in a retrograde manner into
the head and neck vessels, and the remainder will pass to
the descending aorta. This circulation presents a challenge
in achieving the appropriate balance between pulmonary
and systemic blood flow.
There are two surgical options. The first option is staged
palliative surgery of the type first described by Norwood
and colleagues. The second is that the infant undergoes
heart transplantation. The details of both management
strategies are described below.
Norwood Protocol
The first Norwood operation was performed in the United
States in the early 1980s1. The Norwood approach to
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Figure 6 Diagramatic representation of the first stage Norwood
operation, Surgery involves (a) reconstruction of the aortic arch, (b)
insertion of a systemic to pulmonary artery shunt and (c) atrial
septectomy to prevent obstruction of pulmonary venous return and
allow mixing of oxygenated and deoxygenated blood. RA ˆ right
atrium; RV ˆ right ventricle; LA ˆ left atrium. Diagram reproduced
from Left Heart Matters website (www.lhm.org.uk), with permission
management of the hypoplastic left heart syndrome is a
staged surgical palliation. The first stage, which is usually
performed in the first week of life, consists of reconstruction of the aortic arch, using the main pulmonary artery as
a single outlet from the right ventricle of the heart (Figure
6). As part of this surgery the branch pulmonary arteries
are disconnected from the main pulmonary artery. Therefore, to maintain adequate pulmonary blood flow, a
systemic to pulmonary artery shunt is inserted. Pulmonary
venous flow returns to the right atrium by crossing the
atrial septum from left to right. There is the potential for
restriction of blood flow at the level of the atrial septum
so an atrial septectomy is routinely performed. This
permits mixing of pulmonary venous and systemic venous
blood.
The second stage of the Norwood protocol involves
surgical anastamosis of the superior vena cava to the
Figure 7 Second stage Norwood operation. Venous blood flowing
through the superior vena cava is redirected to the pulmonary arteries
and the systemic to pulmonary artery shunt is taken down. Diagram
reproduced from Left Heart Matters website (www.lhm.org.uk), with
permission
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Editorial
Figure 8 Completion of Fontan circulation. Blood flow through the
superior and inferior vena cava is directed to the pulmonary
circulation. The right ventricle pumps oxygenated blood though the
reconstructed aorta. Diagram reproduced from Left Heart Matters
website (www.lhm.org.uk), with permission
pulmonary arteries (Figure 7). This is typically performed
at 6±12 months of age by a hemi-Fontan or bidirectional
Glenn operation. The third stage of palliation consists of
redirecting flow from the inferior vena cava to the
pulmonary arteries and is usually performed beyond the
age of two years (Figure 8). This final `Fontan' circulation
leaves systemic venous blood passing directly to the
pulmonary arteries under passive venous pressure.
Oxygenated systemic arterial blood is pumped around
the body through a reconstructed aortic arch by the right
ventricle.
One of the main concerns of parents whose fetus is
found to have HLHS is the risk of interventions and the
long-term prognosis. The procedural risk with the first
stage Norwood operation continues to be much higher
than the later stages. Operative survival has ranged from
46 to 76% in a number of reports from centers in the
United Kingdom and the United States2,22±25. The review
of 212 cases of patients undergoing stage 1 Norwood
surgery at the Children's Hospital in Boston demonstrated
that survival improved with increased experience of
intervention for HLHS2. This is likely to reflect improved
surgical technique and perioperative care. The second and
third stages of the Norwood protocol have a much lower
mortality than the first stage, typically around 5% or
less2,22,24,25. The long-term prognosis of the final Fontan
circulation is essentially unknown. Data from children
with a Fontan circulation following management of a
variety of different forms of congenital heart disease has
demonstrated decreasing functional status with time which
seems to reflect the Fontan circulation per se rather than
any specific operative complication26. Given that the
Norwood strategy was only devised in the 1980s, many
aspects of the long-term prognosis remain unknown.
As well as concerns about the mortality of HLHS, there
have been legitimate concerns about the morbidity of
treatment. In 1995, Rogers et al. reported major developmental abnormalities in seven of 11 survivors of surgery
for HLHS27. A later report by a different group
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demonstrated more encouraging results with one of 12
children meeting criteria for significant mental retardation28. In the cohort of 26 survivors of HLHS surgery at
the author's center, three have significant neurological
impairment24.
There are a number of possible causes of neurological
impairment in HLHS. Post-mortem data has indicated that
congenital brain anomalies may coexist with HLHS29.
Some patients have been found to have cerebral ischemic
changes or infarcts preoperatively28,30. Improved preoperative condition is one major benefit of prenatal
diagnosis of HLHS, which may help to reduce neurological
morbidity31. In cases where a diagnosis is not made
prenatally, many of these babies present with circulatory
collapse which may adversely affect the neurological
outcome. Operative factors may also impact on neurological outcome. The study of Kern et al. suggested a
relationship between a prolonged circulatory arrest time
during surgery and poor intellectual function28. Thus,
improvements in surgical technique have the potential to
reduce neurological morbidity.
Heart transplantation
Neonatal heart transplantation is an alternative to staged
surgical palliation for the treatment of HLHS. This has the
attraction that the circulatory physiology is more normal
than the Norwood approach. Various centers have
produced encouraging results for this approach with 1year survival of 70±84% in infants who undergo
surgery32±34. A better functional status has also been
reported in survivors of heart transplantation vs. the
Norwood approach35. Although this approach appears
attractive, it is severely limited by the shortage of suitable
donors. There are also longer term problems including
rejection of the transplanted heart, accelerated atherosclerosis and side-effects of immunosuppressive drugs such
as infection and lymphoproliferative disease. This technique does, however, present an alternative to the Norwood
strategy where there is donor availability.
Long-term issues concerning postnatal interventions
In a thought-provoking Editorial in this journal 5 years
ago, Charles Kleinman described a number of cardiological
procedures including the Mustard procedure for transposition of the great arteries, and the Fontan operation, where
initial enthusiasm was subsequently tempered by the
identification of long-term complications36. That Editorial
also summarized the ongoing debate about the `optimal'
surgical approach for HLHS. Whatever surgical approach
is taken to the management of HLHS postnatally, the
interventions are palliative rather than curative. This is a
crucial point that must be adequately addressed during
discussions with parents both prenatally and postnatally.
For fetal and pediatric cardiologists, one of the major
challenges is to impart to parents some understanding of
the long-term impact of complex congenital heart disease
on the child and family. This is often done in the context of
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relatively little medium to long-term morbidity data
compared to the amount of data on short-term mortality
and surgical technique.
It is to be hoped that the large surgical series will be
followed by an equally rigorous assessment of the nonsurgical mortality and morbidity of children with HLHS.
R E S U LT S O F S C R E E N I N G F O R H L H S
A recent United Kingdom national study recorded the
antenatal detection rates of congenital heart lesions
requiring intervention in infancy19. Two-thirds of cases
of HLHS were actually detected prenatally during the
study period (1993±1995). This was the highest detection
rate of any cardiac lesion. Cardiac defects which primarily
involved the outflow tracts and were compatible with a
normal four chamber view were detected much less
frequently, for example only 3% of cases of transposition
of the great arteries. Despite the high overall national
detection rate of HLHS, there was a large regional
variation. The detection rates of HLHS elsewhere do not
appear as high as those recorded in the United Kingdom37,38. The differences in detection rates between
different countries and regions may be explained, in part,
by variations in the uptake of midtrimester anomaly
scanning. The training, experience and supervision of
those who are performing such scans will also influence
detection rates. The quality of ultrasound equipment, the
time permitted for sonographic evaluation and the ease
with which an expert opinion can be arranged will also be
important.
When HLHS presents postnatally for the first time,
parents increasingly ask whether the lesion `should' have
been detected prenatally on routine obstetric ultrasound
scans. This is a thorny issue with potentially major
medicolegal implications. It is important that parents
understand that midtrimester anomaly scans are a form
of screening that has a number of purposes including
assessment of fetal size, identification of major structural
anomalies and a variety of `markers' of chromosomal
abnormalities. Thus, examination of the heart is only one
component of the assessment of the fetus and an
expectation of detection of all major congenital cardiac
abnormalities at primary centers is unrealistic. Even at a
tertiary fetal cardiology center, we do not offer a 100%
guarantee that all forms of congenital heart disease have
been excluded.
Our understanding of the progression of congenital
heart disease has increased in recent years. In aortic
stenosis, for example, it is well documented that the rate of
growth of the left ventricle and aorta is frequently
subnormal7. Thus, an affected fetus with a normal sized
left ventricle at 20 weeks gestational age may have a
severely hypoplastic left ventricle by term and thus will
ultimately demonstrate appearances which fall within the
spectrum of HLHS. Also, for fetuses with severe coarctation of the aorta and unbalanced atrioventricular septal
defects the asymmetry between left and right heart
structures may become more marked with advancing
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gestational age10±12. This means that the appearances of
the heart when studied at 20 weeks gestation may be
considerably different from the appearance at term.
D OE S PR E N ATA L D I A G N OSI S OF HL HS
AFFECT OUTCOME?
The question of whether prenatal diagnosis of HLHS
affects the postnatal outcome is controversial. Some
studies have compared the early surgical mortality of
fetuses who presented prenatally with those who presented
postnatally39. The study of Kumar et al.39 compared the
early surgical outcome of 27 babies with HLHS diagnosed
prenatally with 47 babies in whom the diagnosis was made
postnatally. There was no significant difference in operative mortality, but the preoperative condition of the
prenatally diagnosed group was better than those diagnosed postnatally. Others have demonstrated a lower
surgical mortality in babies diagnosed prenatally31. In the
study of Tworetzky et al.31 nine of 10 infants diagnosed
prenatally survived first stage Norwood surgery compared
with 12 out of 23 infants diagnosed postnatally.
One of the difficulties in interpretation of such data is
that often no account is taken of babies in whom no
diagnosis is made prenatally and who do not survive to
reach a tertiary center, or who are in such poor condition
that they do not undergo surgery. In order to obtain such
data, a detailed registry of deaths within a defined
geographical region would have to be available. Such
data was produced from the north-east region of England
between 1985 and 1990. Twenty-six cases of HLHS were
documented during the study period, of which four (15%)
were first diagnosed at autopsy4. Thus, surgical series of
cases of HLHS diagnosed postnatally represent a selected
group of patients which hinders relevant comparison with
cases of HLHS diagnosed prenatally. With the trend
towards early postnatal discharge of babies from hospital,
it is possible that an increasing number of babies with
severe congenital heart disease will present at home rather
than in a hospital environment, with the potential for a
higher rate of `out of hospital deaths'. In the study of
Kumar et al. almost a quarter of the postnatally diagnosed
cases of HLHS had been discharged from hospital before
presentation39. These infants appeared to have the worst
metabolic status on admission to hospital. Whilst this did
not appear to reduce short-term survival, the effect on
long-term neurological development is unknown. In a
regional, population-based study in the United Kingdom
94 of 120 babies with left heart obstructive lesions were
discharged from hospital prior to presentation40. Thus,
prenatal diagnosis of such conditions may prevent inappropriate neonatal discharge of affected babies and
subsequent collapse at home.
RECURRENCE RISKS OF HLHS
The quoted recurrence of HLHS varies from series to
series. Nora and Nora suggested a recurrence risk of 2% if
a previous child had been affected, based on combined data
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Simpson
from Europe and North America between 1966 and 1975.
Similar recurrence risks were suggested for coarctation of
the aorta and aortic stenosis41. Allan et al. described
recurrence of aortic valve atresia in four of 110 cases (3.6%)
and recurrence of coarctation of the aorta in four of 61 cases
(6.5%) ascertained by fetal echocardiography42.
The recurrence risks for congenital heart disease are
different if either parent has had congenital heart disease. If
the mother has aortic stenosis, then a recurrence risk of
13±18% has been suggested compared to 3% if the father
is affected. For coarctation of the aorta a recurrence risk of
4% has been documented if the mother is affected and 2%
if the father is affected41.
Regardless of exact recurrence risk of these conditions,
which may fall into the spectrum of HLHS, there is an
increased chance of recurrence above the background
population risk. Thus, families who have had an affected
child should be offered detailed fetal echocardiography in
subsequent pregnancies. For parents, the prospect of a
recurrence of congenital heart disease, including HLHS,
provokes immense anxiety43. Our strong impression is that
parents value early reassurance of normality in subsequent
pregnancies. At this author's unit, a tertiary fetal cardiology center, transabdominal fetal echocardiography is
offered at 13±14 weeks gestational age to check the
main structure of the fetal heart. Echocardiography is
repeated on at least one further occasion, later in
pregnancy, to exclude more subtle abnormalities and to
document the growth of left heart structures.
S U M M A RY
Hypoplastic left heart syndrome may be accurately diagnosed during fetal life. Prenatal diagnosis provides the
opportunity for parents to make an informed choice about
their options, including surgery, nonintervention postnatally
or termination of pregnancy. Short to medium term survival
continues to improve for a condition that was previously
invariably lethal. There continues to be a significant
mortality and morbidity associated with hypoplastic left
heart syndrome, and the long-term prognosis is unknown.
Knowledge of the condition prior to birth means that babies
who are to undergo surgery present in optimal condition for
such interventions. Parents who have had an affected fetus
or child should be offered detailed fetal echocardiography to
exclude a recurrence in subsequent pregnancies.
ACKNOWLEDGEMENTS
I am grateful to the organization `Left Heart Matters' for
permission to use diagrams from their online handbook of
hypoplastic left heart syndrome (www.lhm.org.uk).
Department of Fetal Cardiology
15th Floor, Guy's Tower
Guy's Hospital
St. Thomas' Street
London SE1 9RT
UK
Ultrasound in Obstetrics and Gynecology
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