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Tetralogy of Fallot
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Tetralogy of Fallot
Tetralogy of Fallot (TOF or "TET") is a complex condition involving several associated
congenital (present at birth) heart defects that occur due to abnormal development of the
fetal heart. These problems include the following:
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Ventricular Septal Defect (VSD) - A hole in the ventricular septum, or
dividing muscular wall between the two lower pumping chambers of the heart
known as the right and left ventricles.
Pulmonary (or right ventricular outflow tract) Obstruction - A muscular
obstruction in the right ventricle, just below the pulmonary valve, that
decreases the normal flow of blood. The pulmonary valve also may be small,
and the pulmonary arteries in the lungs can be affected.
Overriding Aorta - An aorta that is shifted toward the right side of the heart
so that it sits over the ventricular septal defect.
"Tetralogy" refers to four heart problems. The fourth problem is that the right
ventricle becomes enlarged as it tries to pump blood past the obstruction into the
pulmonary artery. This is known as "hypertrophy."
Normally, 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 picks up oxygen. Oxygen-rich (red) blood returns to the left atrium
from the lungs, passes into the left ventricle, then is pumped through the aorta out
to the body.
In Tetralogy of Fallot, blood flow within the heart varies and is largely dependent on
how severe the obstruction from the right ventricle to the lungs is. Tetralogy of Fallot
encompasses a family, or spectrum of diseases, from nearly no obstruction to severe
obstruction or, in some cases, atresia of the pulmonary valve.
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With mild right ventricle obstruction, the pressure in the right ventricle can be
slightly higher than the left. Some of the oxygen-poor (blue) blood in the
right ventricle will pass through the VSD to the left ventricle, mix with the
oxygen-rich (red) blood there, and then flow into the aorta. The rest of the
oxygen-poor (blue) blood will go its normal route to the lungs. These children
may have slightly lower oxygen levels than usual, but may not appear blue.
Oxygen, or saturation levels, can be checked with a skin sensor ("sat" probe),
and normally are 99 percent.
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With more serious obstruction in the right ventricle, it is harder for oxygenpoor (blue) blood to flow into the pulmonary artery, so more of it passes
through the VSD into the left ventricle, mixing with oxygen-rich (red) blood,
and then moving out to the body. These children will have lower than normal
oxygen levels in the bloodstream, and may appear blue, especially whenever
the pressure in the right ventricle is very high and large amounts of oxygenpoor (blue) blood pass through the VSD to the left side of the heart. These
children can have skin blood saturations as low as 80 percent, and sometimes
even lower.
Tetralogy of Fallot occurs in about two out of every 10,000 live births. It makes
up about 8 percent of all cases of congenital heart disease. Tetralogy of Fallot
occurs equally in boys and in girls.
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What causes Tetralogy of Fallot?
Tetralogy of Fallot occurs due to improper development of the heart in the first eight
weeks of fetal growth.
Most of the time, this heart defect occurs sporadically (by chance), with no clear
reason evident for its development. 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.
One genetic link that has been associated with Tetralogy of Fallot is a deletion, or
tiny missing piece, of chromosone 22q11. This is present in a minority of patients but
is thought to be more common in those with a severe form of Tetralogy of Fallot,
with pulmonary atresia. The condition is known as the 22q11 deletion, and blood
tests are available to detect it.
Environmental exposures, such as maternal abuse of alcohol during pregnancy
leading to fetal alcohol syndrome (FAS), are linked to Tetralogy of Fallot. Mothers
who take medications to control seizures and mothers with phenylketonuria (PKU)
also are more likely to have a baby with Tetralogy of Fallot.
Why is Tetralogy of Fallot a concern?
The amount of oxygen-poor (blue) blood that passes through the VSD to the left side
of the heart varies. If the right ventricle obstruction is severe, or if the pressure in
the lungs is high, a large amount of oxygen-poor (blue) blood passes through the
VSD, mixes with the oxygen-rich (red) blood in the left ventricle, and is pumped to
the body. The more blood that goes through the VSD, the less blood that goes
through the pulmonary artery to the lungs, and the less oxygen-rich (red) blood that
returns to the right side of the heart. Soon, nearly all the blood in the left ventricle is
oxygen-poor (blue). This is an emergency situation, as the body will not have
enough oxygen to meet its needs.
Some situations, such as crying, increase the pressure in the lungs temporarily, and
increasing blueness might be noted as a baby with Tetralogy of Fallot cries. In other
situations, the pathway from the right ventricle to the pulmonary artery becomes
tighter, preventing much blood from passing that way, and allowing oxygen-poor
(blue) blood to flow through the VSD into the left heart circulation. Both of these
situations are nicknamed "TET spells." Sometimes, steps can be taken to lessen the
pressure or the obstruction, allowing more blood to flow into the lungs and less
through the VSD. These steps, however, are not always effective.
What are the symptoms of Tetralogy of Fallot?
The following are the most common symptoms of tetralogy of Fallot. Each child may
experience symptoms differently. Symptoms may include:
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Because large amounts of oxygen-poor (blue) blood can flow to the body
under certain circumstances, one of the indications of Tetralogy of Fallot is
cyanosis (blue color of the skin, lips and nailbeds) that occurs with such
activities as crying or feeding, and quickly becomes more obvious.
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Some babies do not have noticeable cyanosis (blue color of the skin, lips and
nailbeds), but instead may be very irritable or lethargic due to a decreasing
amount of oxygen available in the bloodstream.
Some children become pale or ashen in color, and may have cool, clammy
skin.
Any of these can be symptoms of Tetralogy of Fallot. The symptoms of
Tetralogy of Fallot may resemble other medical conditions or heart problems.
Always consult your child's physician for a diagnosis.
What are the treatments for Tetralogy of Fallot? Specific treatment for
Tetralogy of Fallot 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 condition
your child's tolerance for specific medications, procedures or therapies
how your child's doctor expects the condition may progress \
your opinion or preference
The surgical correction of TOF is typically carried out through an incision in the
middle of the chest. The incision is continued through the breastbone, or sternum,
which is spread apart to expose the heart. A heart-lung machine is used to do the
work of the heart while the heart is cooled, stopped, emptied and opened, through
the right atrium or ventricle. The hole in the wall between the right and left
ventricles, or VSD, is closed with a patch of Dacron cloth or a patch of thin leatherlike material called pericardium. The muscle bundles and the narrowed pulmonary
valve blocking the right ventricle are divided, and the passage out of the right
ventricle toward the lungs is widened, usually by applying a patch to this area. The
heart is then closed and begins pumping as the heart-lung machine is withdrawn.
There are many variations of this surgery, each of which is tailored for the specific
needs of a particular child's anatomy.
What is the long-term outlook after Tetralogy of Fallot surgical repair?
Most children who have had a Tetralogy of Fallot surgical repair will live healthy lives.
Activity levels, appetite and growth will eventually return to normal in most children.
Your child's cardiologist will recommend that antibiotics be given to prevent bacterial
endocarditis after discharge from the hospital.
Source: Children’s Hospital, Boston Cardiology Website, Accessible at:
http://www.childrenshospital.org/az/Site515/mainpageS515P0.html
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