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Transposition of the Great Arteries
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Transposition of the Great Arteries
What is transposition of the great arteries?
Transposition of the great arteries (TGA) is a congenital (present at birth) heart
defect that occurs when the large vessels that take blood away from the heart to the
lungs, or to the body, are improperly connected.
Normally:
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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, then is pumped through the aorta out to the body.
In transposition of the great arteries, the aorta is connected to the right
ventricle, and the pulmonary artery is connected to the left ventricle -- the exact
opposite of a normal heart's anatomy:
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Oxygen-poor (blue) blood returns to the right atrium from the body,
passes through the right atrium and ventricle, then goes into the
misconnected aorta back to the body.
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Oxygen-rich (red) blood returns to the left atrium from the lungs, passes
through the left atrium and ventricle, then goes into the pulmonary artery
and back to the lungs.
Two separate circuits are formed -- one that circulates oxygen-poor (blue) blood
from the body back to the body, and another that recirculates oxygen-rich (red)
blood from the lungs back to the lungs.
Other heart defects are often associated with TGA, and actually may be necessary in
order for an infant with transposition of the great arteries to live. Openings in the
wall separating the left and right sides of the heart, called atrial septal defect or
ventricular septal defect, will allow blood from one side to mix with blood from
another, creating "purple" blood with an oxygen level somewhere between that of
the oxygen-poor (blue) and the oxygen-rich (red) blood.
A patent ductus arteriosus (another type of congenital heart defect) will allow mixing
of oxygen-poor (blue) and oxygen-rich (red) blood through the connection between
the aorta and pulmonary artery. The "purple" blood that results from this mixing is
beneficial, providing small, if not normal, amounts of oxygen to the body.
What causes transposition of the great arteries?
The heart is forming during the first eight weeks of fetal development. The problem
occurs in the middle of these weeks, allowing the aorta and pulmonary artery to be
attached to the incorrect chamber.
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. Most of the time this heart
defect occurs sporadically (by chance), with no clear reason for its development.
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Why is transposition of the great arteries a concern?
Babies with TGA have two separate circuits -- one that circulates oxygen-poor (blue)
blood from the body back to the body, and another that recirculates oxygen-rich
(red) blood from the lungs back to the lungs. Without an additional heart defect that
allows mixing of oxygen-poor (blue) and oxygen-rich (red) blood, such as an atrial or
ventricular septal defect, infants with TGA will have oxygen-poor (blue) blood
circulating through the body, a situation that is critical. Even with an additional
defect present that allows mixing, babies with transposition of the great arteries may
not have enough oxygen in the bloodstream to meet the body's demands.
Even when a significant amount of mixing of oxygen-poor (blue) and oxygen-rich
(red) blood occurs, other problems may be present. The left ventricle, which in TGA
is connected to the pulmonary artery, is usually the stronger of the two ventricles
since it normally has to generate a lot of force to pump blood to the body. The right
ventricle, connected to the aorta in TGA, is considered the weaker of the two
ventricles and may not be able to pump blood efficiently to the body. As a result, it
will enlarge under the strain.
What are the symptoms of transposition of the great arteries?
The obvious indication of TGA is a newborn who becomes cyanotic (blue) in the
transitional first day of life, when the maternal source of oxygen (from the placenta)
is removed. Cyanosis is noted in the first hours of life in about half the infants with
TGA, and within the first days of life in 90 percent of them. The degree of cyanosis is
related to the presence of other defects that allow blood to mix, including a patent
ductus arteriosus -- a fetal connection between the aorta and the pulmonary artery
present in the newborn, which usually closes in the first few days after birth.
Symptoms may include:
--rapid breathing
--labored breathing
--rapid heart rate
--cool, clammy skin
What are the treatments for transposition of the great arteries?
Specific treatment for transposition of the great arteries 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 to 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.
Other important aspects of initial treatment include the following:

A cardiac catheterization procedure can be used as a diagnostic procedure, as
well as an initial treatment procedure for some heart defects. A cardiac
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o
catheterization procedure will usually be performed to evaluate the defect(s)
and the amount of blood that is mixing.
As part of the cardiac catheterization, a procedure called a balloon atrial
septostomy may be performed to improve mixing of oxygen-rich (red) and
oxygen-poor (blue) blood.
o A special catheter with a balloon in the tip is used to create an opening
in the atrial septum (wall between the left and right atria).
o The catheter is guided through the foramen ovale (a small opening
present in the atrial septum that closes shortly after birth) and into the
left atrium.
o The balloon is inflated.
o The catheter is quickly pulled back through the hole, into the right
atrium, enlarging the hole, allowing blood to mix between the atria.
An intravenous medication called prostaglandin E1 is given to keep the ductus
arteriosus from closing.
Within the first 1 to 2 weeks of age, transposition of the great arteries is surgically
repaired. The procedure that accomplishes this is called a "switch," which roughly
describes the surgical process.
The surgical correction of TGA is carried out through an incision in the middle of the
chest. The breast bone is split in the middle and 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. The aorta and pulmonary arteries are disconnected
and reconnected to their proper ventricles. The coronary arteries must be transferred
to the newly positioned aorta as well, or "blue" blood will supply the muscle of the
heart. Associated holes between the chambers of the heart are closed. The heart is
then restarted as the heart-lung machine is withdrawn.
What is the long-term outlook after TGA surgical repair?
Many infants who undergo TGA surgical repair will grow and develop normally. After
TGA repair, however, your infant will need to be followed periodically by a pediatric
cardiologist who will make assessments to check for any heart-related problems,
which can include the following:
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fast, slow or irregular heart rhythms
leaky heart valves
narrowing of one or both of the great arteries at the switch connection site(s)
narrowing of the coronary arteries at their switch connection site
Source: Children’s Hospital, Boston Cardiology Website, Accessible at:
http://www.childrenshospital.org/az/Site511/printerfriendlypageS511P0.html
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