Transposition of the Great Arteries (TGA)
What is transposition of the great arteries?
Transposition of the great arteries is a congenital
(present at birth) heart defect. Due to abnormal development
of the fetal heart during the first 8 weeks of pregnancy, the
large vessels that take blood away from the heart to the
lungs, or to the body, are improperly connected.
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
receives oxygen. Oxygen-rich (red) blood returns to the left
atrium from the lungs, passes into the left ventricle, and
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.
- 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
- 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 lungs back to the lungs, and
another that recirculates oxygen-rich (red) blood from the
body back to the body.
Other heart defects are often associated with TGA, and they
actually may be necessary in order for an infant with
transposition of the great arteries to live. An opening in the
atrial or ventricular septum will allow blood from one side to
mix with blood from another, creating "purple" blood with an
oxygen level somewhere in-between that of the oxygen-poor
(blue) and the oxygen-rich (red) blood. Patent ductus
arteriosus (another type of congenital heart defect) will also
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 at least smaller amounts of oxygen to
the body, if not a normal amount of oxygen.
Because of the low amount of oxygen provided to the body,
TGA is a heart problem that is labeled "blue-baby syndrome."
Transposition of the great arteries is the second most
common congenital heart defect that causes problems in early
infancy. TGA occurs in 5 to 7 percent of all congenital heart
defects. Sixty to 70 percent of the infants born with the
defect are boys.
What causes transposition of the great arteries?The
heart is forming during the first 8 weeks of fetal
development. The problem occurs in the middle of these weeks,
allowing the aorta and pulmonary artery to be attached to the
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.
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 lungs back
to the lungs, and another that recirculates oxygen-rich (red)
blood from the body back to the body. 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
fatal. Even with an additional defect present that allows
mixing, babies with transposition of the great arteries will
not have enough oxygen in the bloodstream to meet the body's
Even when a good bit of mixing of oxygen-poor (blue) and
oxygen-rich (red) blood can occur, other problems are present.
The left ventricle, which in TGA is connected to the pulmonary
artery, is 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
the weaker of the two ventricles. Because the right ventricle
is weaker, it may not be able to pump blood efficiently to the
body, and it will enlarge under the strain of the job. The
left ventricle may pump blood into the lungs more vigorously
than needed, leading to strain in the blood vessels in the
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 of 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
The following are the other most common symptoms of TGA.
However, each child may experience symptoms differently.
Symptoms may include:
- rapid breathing
- labored breathing
- rapid heart rate
- cool, clammy skin
The symptoms of TGA may resemble other medical conditions
or heart problems. Always consult your child's physician for a
How is transposition of the great arteries
diagnosed?A pediatric cardiologist and/or a neonatologist
may be involved in your child's care. A pediatric cardiologist
specializes in the diagnosis and medical management of
congenital heart defects, as well as heart problems that may
develop later in childhood. A neonatologist specializes in
illnesses affecting newborns, both premature and full-term.
Cyanosis is the major indication that there is a problem
with your newborn. Your child's physician may have also heard
a heart murmur during a physical examination. A heart murmur
is simply a noise caused by the turbulence of blood flowing
through the openings that allow the blood to mix.
Other diagnostic tests are needed to help with the
diagnosis, and may include the following:
- chest x-ray - a diagnostic test which uses
invisible electromagnetic energy beams to produce images of
internal tissues, bones, and organs onto film.
- electrocardiogram (ECG or EKG) - a test that
records the electrical activity of the heart, shows abnormal
rhythms (arrhythmias or dysrhythmias), and detects heart
- echocardiogram (echo) - a procedure that
evaluates the structure and function of the heart by using
sound waves recorded on an electronic sensor that produce a
moving picture of the heart and heart valves.
- cardiac catheterization - a cardiac
catheterization is an invasive procedure that gives very
detailed information about the structures inside the heart.
Under sedation, a small, thin, flexible tube (catheter) is
inserted into a blood vessel in the groin, and guided to the
inside of the heart. Blood pressure and oxygen measurements
are taken in the four chambers of the heart, as well as the
pulmonary artery and aorta. Contrast dye is also injected to
more clearly visualize the structures inside the heart.
Treatment for transposition of the great
arteries:Specific treatment for transposition of the
great arteries will be determined by your child's physician
- your child's age, overall health, and medical history
- extent of the disease
- your child's tolerance for specific medications,
procedures, or therapies
- expectations for the course of the disease
- your opinion or preference
Your child will most likely be admitted to the intensive
care unit (ICU) or special care nursery once symptoms are
noted. Initially, your child may be placed on oxygen, and
possibly even on 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
- A cardiac catheterization procedure can be used as a
diagnostic procedure, as well as initial treatment procedure
for some heart defects. A cardiac 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)
- 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).
- 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.
- The balloon is inflated.
- 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 operation is performed under general anesthesia, and
involves the following:
- The aorta is moved from the right ventricle to its
normal position over the left ventricle.
- The pulmonary artery is moved from the left ventricle to
its normal position over the right ventricle.
- The coronary arteries are moved so they will originate
from the aorta and take oxygen-rich (red) blood to the heart
- Other defects, such as atrial or ventricular septal
defects or a patent ductus arteriosus, are commonly closed.