Hypoplastic Left Heart Syndrome
Hypoplastic Left Heart Syndrome
What is hypoplastic left heart syndrome?
Hypoplastic left heart syndrome (HLHS) is a congenital (present at birth) syndrome
that involves a combination of several abnormalities of the heart and great blood
vessels.
In the normal heart, oxygen-poor (blue) blood returns to the right atrium from the
body, travels to the right ventricle, then is pumped through the pulmonary artery
into the lungs where it receives oxygen. Oxygen-rich (red) blood returns to the left
atrium from the lungs, passes into the left ventricle, and then is pumped out to the
body through the aorta.
In hypoplastic left heart syndrome, most of the structures on the left side of the
heart are small and underdeveloped. The degree of underdevelopment differs from
child to child. The structures affected usually include the following:
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Mitral valve — The valve that controls blood flow between the left atrium and
left ventricle in the heart.
Left ventricle — The lower left-hand chamber of the heart. It receives oxygenrich (red) blood from the left atrium and pumps it into the aorta, which takes
the blood to the body. The left ventricle must be strong and muscular in order
to pump enough blood to the body to meet its requirements.
Aortic valve — The valve that regulates blood flow from the heart into the
aorta.
Aorta — The largest artery in the body and the primary blood vessel leading
from the heart to the body.
Perhaps the most critical defect in HLHS is the small, underdeveloped left ventricle.
This chamber is normally very strong and muscular so it can pump blood to the
body. When the chamber is small and poorly developed, it will not function
effectively and cannot provide enough blood flow to meet the body's needs. For this
reason, an infant with hypoplastic left heart syndrome is in a very critical situation.
Hypoplastic left heart syndrome occurs in up to four out of every 10,000 live births.
The syndrome comprises 8 percent of all cases of congenital heart disease. It is one
of the top three heart abnormalities to cause problems in the newborn. HLHS occurs
slightly more often in boys than in girls. In many children, HLHS occurs by chance,
with no clear reason evident for their development.
What causes hypoplastic left heart syndrome?
Hypoplastic left heart syndrome is the result of abnormal underdevelopment of
sections of the fetal heart during the first 8 weeks of pregnancy. Some congenital
heart defects may have a genetic link, either occurring due to a defect in a gene, a
chromosome abnormality, or environmental exposure, causing heart problems to
occur more often in certain families. In hypoplastic left heart syndrome, there may
be abnormalities of other organs.
What are the symptoms of hypoplastic left heart syndrome?
Infants with HLHS usually develop symptoms shortly after birth. The following are
the most common symptoms of hypoplastic left heart syndrome. Each child may
experience symptoms differently. Symptoms may include:
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cyanosis (blue color of the skin, lips and nailbeds)
pale skin
sweaty or clammy skin
cool skin
heavy and/or rapid breathing
fast heart rate
What are the treatments for hypoplastic left heart syndrome? Specific
treatment for hypoplastic left heart syndrome will be determined by your child's
physician based on:
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your child's age, overall health and medical history
extent of the disease
your child's tolerance for specific medications, procedures or therapies
how your child's doctor expects the disease will progress
your opinion or preference
Your child most likely will be admitted to the intensive care unit (ICU) or special care
nursery once symptoms are noted. Initially, your child may be placed on oxygen, or
a ventilator to assist his/her breathing. Intravenous (IV) medications may be given
to help the heart and lungs function more efficiently.
What is the surgical repair for hypoplastic left heart syndrome? The surgical
approach to HLHS is directed toward using the one good ventricle to do the work that
is normally done by two ventricles, and to separate the "blue" or pulmonary
circulation from the "red" or systemic circulation, as is the case in the normal heart.
Treatment consists of three stages ending with the Fontan procedure.
The Fontan procedure takes advantage of the fact that blood flows so easily through
the mature lung that it does not need the force of the right ventricle to push it
through. In fact, the great veins bringing "blue" blood back to the heart, called the
superior vena cava and inferior vena cava, can be channeled directly to the lungs
through the pulmonary artery, bypassing the right ventricle altogether. When this is
achieved, the right ventricle (in HLHS, the only ventricle) can be devoted to pumping
"red" blood to the rest of the body. In this way, "blue" blood pathways and "red"
blood pathways are separate, with "blue" blood reaching the lungs passively, where
it is oxygenated before returning to the single ventricle as "red" blood, then pumped
to the body.
The blood vessels of the lungs change over the first year of life. The Fontan
procedure depends on sufficiently easy flow through the lungs to not require the
force of a ventricle to conduct blood through the pulmonary circuit. This is not
possible in the first months of life, and two operations must precede the Fontan
procedure until the lungs are ready.
The Stage I operation (Norwood Procedure) connects the right ventricle to the
aorta so that its flow, which will eventually be "red" blood, will be delivered to the
body through branches of the aorta. This usually involves rebuilding a small aorta
and connecting it to the ventricle. To survive the newborn period, blood flow to the
immature lungs must be forceful. Blood flow to the lungs is provided through a tube
from a branch of the aorta to the pulmonary artery called the Modified BlalockTaussig Shunt.
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Usually, at between three and eight months of age, the lungs mature to the point
that blood flows more easily through, and ventricular force is no longer necessary.
The Stage II, or Bi-directional Glenn Shunt, is a direct connection between the
superior vena cava and the pulmonary artery, diverting half of the "blue" blood
directly to the lungs without the assistance of the ventricle.
Finally, with still further lung maturity, the vessels of the lungs can accommodate all
the body's "blue" blood and the Stage III, or Fontan procedure, can be done. The
Fontan procedure connects the inferior vena cava to the pulmonary artery by
creating a channel, or baffle, through the heart to direct its flow to the pulmonary
artery. Now all the "blue" blood flows passively to the lungs, and the single ventricle
pumps exclusively "red" blood to the body.
What is the long-term outlook after treatment for hypoplastic left heart
syndrome? Children with hypoplastic left heart syndrome will need follow-up care
throughout their life to make sure their heart continues to work correctly. Most will
require heart medicines. Consult your child's physician regarding the specific outlook
for your child.
Source: Children’s Hospital, Boston Cardiology Website, Accessible at:
http://www.childrenshospital.org/az/Site502/mainpageS502P0.html
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