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Atrioventricular canal defect
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ATRIOVENTRICULAR CANAL DEFECT
What is atrioventricular canal defect?
Atrioventricular canal (AV canal or AVC) defect is a complex congenital (present at birth)
defect that results in a large hole in the center of the heart. This defect involves several
abnormalities of structures inside the heart:
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An atrial septal defect allows oxygen-rich (red) blood to pass from the left atrium
through the opening in the septum, and then mix with oxygen-poor (blue) blood in
the right atrium.
A ventricular septal defect allows oxygen-rich (red) blood to pass from the left
ventricle through the opening in the septum, and then mix with oxygen-poor (blue)
blood in the right ventricle.
Abnormalities of the mitral or tricuspid valves allow blood that should be
moving forward from the ventricle into either the pulmonary artery or the aorta to
instead flow backward into the atria.
Normally, oxygen-poor (blue) blood returns to the right atrium from the body, travels to the
right ventricle, then is pumped 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 out to the body through the aorta.
An atrial septal defect allows oxygen-rich (red) blood to pass from the left atrium through
the opening in the septum, and then mix with oxygen-poor (blue) blood in the right atrium.
A ventricular septal defect allows oxygen-rich (red) blood to pass from the left ventricle
through the opening in the septum, and then mix with oxygen-poor (blue) blood in the right
ventricle.
Abnormalities of the mitral or tricuspid valves allow blood that should be moving forward
from the ventricle into either the pulmonary artery or the aorta to instead flow backward
into the atria.
Atrioventricular canal occurs in two out of every 10,000 live births, equally in boys and girls.
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What causes atrioventricular canal defect?
The heart is forming during the first eight weeks of fetal development. It begins as a hollow
tube, then partitions form within the tube that eventually become the septa (or walls)
dividing the right side of the heart from the left. Atrial and ventricular septal defects occur
when the partitioning process does not occur completely, leaving openings in the atrial and
ventricular septum. The valves that separate the upper and lower heart chambers are being
formed in the latter portion of this eight-week period, and, for some reason, they do not
develop properly.
There may be genetic influences on the development of atrioventricular canal. Consider the
following statistics:
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CHD is present in half of children born with Down syndrome, and 45 percent of these
cases have AV canal; Down syndrome is caused by the presence of three #21
chromosomes in the cells of the body, rather than the usual pair (two) of
chromosomes.
Similarly, one-third of all children born with AV canal also have Down syndrome.
Fourteen percent of mothers with an AV canal defect give birth to a child with the
disease.
Some studies have investigated a possible link between the use of retinoic acid (a
medication used for the treatment of dermatologic problems such as acne and facial
wrinkles) while pregnant and the development of atrioventricular canal in the fetus.
Other chromosome abnormalities (in addition to Down syndrome) are linked to the
development of atrioventricular canal. Maternal age can have an effect on the prevalence of
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AV canal, which may be related to the increased probability of a woman giving birth to a
child with Down syndrome as she gets older.
Why is atrioventricular canal a concern?
If not treated, this heart defect can cause lung disease. When blood passes through both
the Atrio Septal Defect and Ventrical Septal Defect from the left side of the heart to the
right side, a larger volume of blood than normal must be handled by the right side of the
heart. This extra blood then passes through the pulmonary artery into the lungs, causing
higher pressure than normal in the blood vessels in the lungs.
As pressure builds up in the lungs, the flow of blood from the left side of the heart to the
right side and on to the lungs will diminish. This helps preserve the function of the lungs,
but causes yet another problem. Blood flow within the heart goes from areas where the
pressure is high to areas where the pressure is low. If the septal defects are not repaired,
and lung disease begins to occur, pressure in the right side of the heart will eventually
exceed pressure in the left. In this instance, it will be easier for oxygen-poor (blue) blood to
flow from the right side of the heart, through the ASD and VSD, into the left ventricle, and
on to the body. When this happens, the body does not receive enough oxygen in the
bloodstream to meet its needs, and children may become cyanotic, or exhibit a blue coloring
in their skin, lips and nailbeds.
Because blood is pumped at high pressure through the septal openings, the lining of the
right and left ventricles will become irritated and inflamed. Bacteria in the bloodstream can
easily infect this injured area, causing a serious illness known as bacterial endocarditis.
What are the symptoms of an atrioventricular canal defect?
The size of the septal openings will affect the type of symptoms noted, the severity of
symptoms, and the age at which they first occur. The larger the openings, the greater the
amount of blood that passes through from the left side of the heart to the right and
overloads the right heart and the lungs.
Symptoms occur in infancy. The following are the most common symptoms of AVC.
However, each child may experience symptoms differently. Symptoms may include:
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fatigue
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sweating
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pale skin
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cool skin
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rapid breathing
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heavy breathing
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rapid heart rate
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congested breathing
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disinterest in feeding, or tiring while feeding
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poor weight gain
As the pressure in the lungs rises, blood within the heart will eventually "shunt" through the
septal openings from right heart to the left. This allows oxygen-poor (blue) blood to reach
the body, and cyanosis will be noted. Cyanosis gives a blue color to the lips, nailbeds and
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skin. The symptoms of AVC may resemble other medical conditions or heart problems.
Always consult your child's physician for a diagnosis.
What are the treatments for atrioventricular canal defect?Specific treatment for
atrioventricular canal defect will be determined by your child's physician based on:
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your child's age, overall health and medical history
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extent of the disease
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your child's tolerance for specific medications, procedures or therapies
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how your child's doctor expects the disease may progress
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your opinion or preference
AV canal defect is treated by surgical repair of the defects. However, medical support (i.e.,
medications) may be necessary until the operation is performed. Treatment may include:
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Medical Management — Many children will eventually need to take medications to
help the heart and lungs work better, due to strain from the extra blood passing
through the septal defects. Medications that may be prescribed include the following:
o Digoxin - helps strengthen the heart muscle, enabling it to pump more
efficiently
o Diuretics - the body's water balance can be affected when the heart is not
working as well as it could. These medications help the kidneys remove
excess fluid from the body.
o ACE (angiotensin-converting enzyme) inhibitors - dilates the blood vessels,
making it easier for the heart to pump blood forward into the body
Adequate Nutrition — Infants may become tired when feeding, and may not be
able to eat enough to gain weight. Options that can be used to ensure your baby will
have adequate nutrition include:
Infection control - children with certain heart defects are at risk for developing an
infection of the inner surfaces of the heart known as bacterial endocarditis. A
common procedure that puts your child at risk for this infection is a routine dental
check-up and teeth cleaning. Other procedures may also increase the risk of the
heart infection occurring. However, giving children with heart defects an antibiotic by
mouth before these procedures can help prevent bacterial endocarditis. It is
important that you inform all medical personnel that your child has a an
atrioventricular canal defect so they may determine if the antibiotics are necessary
before a procedure.
Surgical repair - the surgical correction of CAVC 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, usually through the right atrium. The
hole in the wall between the right and left ventricles, or VSD is closed by sewing to it
a patch of Dacron cloth or a patch of thin leather-like material called pericardium.
The affected tricuspid and mitral valves are reconstructed and supported by the
rebuilt septum.
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Finally, the Atrial Septal Defect is closed with a patch of pericardium. The heart is then
closed and restarted as the heart-lung machine is withdrawn.
The operative methods used to repair atrioventricular canal defect have improved
greatly in the past decade, and the operation has a high likelihood of success.
Advancements in cardiovascular surgical repair include minimally invasive cardiac
surgery.
Most children undergo surgery by the age of 6 months. Children with Down syndrome
may develop lung problems earlier than other children, and may need to have surgical
repair at an earlier age. The atrial and ventricular septal defects often are closed with a
pericardial patch made from the membrane that covers the outside surface of the heart,
or a patch made from synthetic material. The valve repair technique will differ according
to the abnormality and the surgeon's preferences.
What is the long-term outlook after Atrio Ventricular canal defect surgical
repair?
Many children who have had an Atrio Ventricular canal defect repair will live healthy
lives. Activity levels, appetite and growth will eventually return to normal in most
children. Your child's cardiologist may recommend that antibiotics be given to prevent
bacterial endocarditis for a specific time period after discharge from the hospital.
Some children will still have some degree of mitral or tricuspid valve abnormality after
AV canal repair surgery. This may require another operation in the future to repair the
leaky valve(s).
Children with Down syndrome will benefit from special programs that enhance their
mental and physical development. Your child's physician can assist you in locating such
programs in your community.
Source: Children’s Hospital, Boston Cardiology Website, Accessible at:
http://www.childrenshospital.org/az/Site521/mainpageS521P0.html
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