Transposition
of the Great Arteries (TGA)
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 body.
- 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
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.
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 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.
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
demands.
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 lungs.
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
birth.
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 diagnosis.
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 muscle stress.
- 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.
Specific
treatment for transposition of the great arteries
will be determined by your child's physician based
on:
- 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 following:
- 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) blood.
- 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
muscle.
- Other defects, such
as atrial or ventricular septal defects or a
patent ductus arteriosus, are commonly closed.
After
surgery, infants will return to the intensive
care unit (ICU) for a few days to be closely monitored
during recovery.
While
your child is in the ICU, special equipment will
be used to help him/her recover, and may include
the following:
- ventilator -
a machine that helps your child breathe while
he/she is under anesthesia during the operation.
A small, plastic tube is guided into the windpipe
and attached to the ventilator, which breathes
for your child while he/she is too sleepy to
breathe effectively on his/her own. After a
transposition of the great arteries, children
will benefit from remaining on the ventilator
overnight or even longer so they can rest.
- intravenous (IV) catheters
- small, plastic tubes inserted
through the skin into blood vessels to provide
IV fluids and important medicines that help
your child recover from the operation.
- arterial line -
a specialized IV line is placed in the wrist
or other area of the body where a pulse can
be felt, that measures blood pressure continuously
during surgery and while your child is in the
ICU.
- nasogastric (NG) tube
- a small, flexible tube that keeps
the stomach drained of acid and gas bubbles
that may build up during surgery.
- urinary catheter -
a small, flexible tube that allows urine to
drain out of the bladder and accurately measures
how much urine the body makes, which helps determine
how well the heart is functioning. After surgery,
the heart will be a little weaker than it was
before, and, therefore, the body may start to
hold onto fluid, causing swelling and puffiness.
Diuretics may be given to help the kidneys to
remove excess fluid from the body.
- chest tube -
a drainage tube may be inserted to keep the
chest free of blood that would otherwise accumulate
after the incision is closed. Bleeding may occur
for several hours, or even a few days after
surgery.
- heart monitor -
a machine that constantly displays a picture
of your child's heart rhythm, and monitors heart
rate, arterial blood pressure, and other values.
Your
child may need other equipment not mentioned here
to provide support while in the ICU, or afterwards.
The hospital staff will explain all of the necessary
equipment to you.
Your
child will be kept as comfortable as possible
with several different medications; some which
relieve pain, and some which relieve anxiety.
The staff will also be asking for your input as
to how best to soothe and comfort your child.
After
discharged from the ICU, your child will recuperate
on another hospital unit for a few days before
going home. You will learn how to care for your
child at home before your child is discharged.
Your child may need to take medications for a
while, and these will be explained to you. The
staff will give you written instructions regarding
medications, activity limitations, and follow-up
appointments before your child is discharged.
Infants
who spent a lot of time on a ventilator, or who
were fairly ill while in the ICU, may have trouble
feeding initially. These babies may have an oral
aversion; they might equate something placed in
the mouth, such as a pacifier or bottle, with
a less pleasant sensation such as being on the
ventilator. Some infants are just tired, and need
to build their strength up before they will be
able to learn to bottle feed. Strategies used
to help infants with nutrition include the following:
- high-calorie formula
or breast milk
Special nutritional supplements may be added
to formula or pumped breast milk that increase
the number of calories in each ounce, thereby
allowing your baby to drink less and still consume
enough calories to grow properly.
- supplemental tube
feedings
Feedings given through a small, flexible tube
that passes through the nose, down the esophagus,
and into the stomach, that can either supplement
or take the place of bottle-feedings. Infants
who can drink part of their bottle, but not
all, may be fed the remainder through the feeding
tube. Infants who are too tired to bottle-feed
at all may receive their formula or breast milk
through the feeding tube alone.
Pain
medications, such as acetaminophen or ibuprofen,
may be recommended to keep your child comfortable
at home. Your child's physician will discuss pain
control before your child is discharged from the
hospital.
If any
special treatments are to be given at home, the
nursing staff will ensure that you are able to
provide them, or a home health agency may assist
you.
You
may receive additional instructions from your
child's physicians and the hospital staff.
Many
infants who undergo TGA surgical repair will grow
and develop normally. However, after TGA repair,
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:
- 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
Prior
to the early 1990’s, TGA was generally treated
surgically with a Mustard procedure or a Senning
procedure. These procedures created a tunnel,
or baffle, in the atria to correct blood flow.
In the late 1980’s, the arterial switch
procedure was introduced. This procedure “switches”
the aorta and pulmonary artery to the proper locations.
However, the arterial switch procedure may not
be indicated in certain situations.
For
individuals whose TGA was repaired using a Mustard
or Senning procedure, complications such as heart
failure and dysrhythmias may develop in the second
or third decade of life. There is also a risk
for sudden death. Thus, these individuals should
receive regular follow-up care at a center offering
pediatric or adult congenital cardiac care throughout
the individual’s lifespan.
Consult
your child's physician regarding the specific
outlook for your child.
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