Atrioventricular
Canal (AV Canal or AVC)
Atrioventricular
canal defect (AV canal) is a congenital (present
at birth) heart defect. As the fetus is growing,
something occurs to affect heart development during
the first eight weeks of pregnancy, and certain
areas of the heart do not form properly. AV canal
is a heart problem that involves several abnormalities
of structures inside the heart, including the
following:
- atrial septal defect
- an opening in the atrial septum,
or
dividing wall between the two upper chambers
of the heart known as the right and left atria.
- ventricular septal
defect - an opening in the ventricular
septum, or dividing wall between the two lower
chambers of the heart known as the right and
left ventricles.
- improperly formed
mitral and/or tricuspid valves -
the valves that separate the upper heart chambers
(atria) from the lower heart chambers (ventricles)
are improperly formed.
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, and 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 defects occur in about 5 percent of all
congenital heart disease cases and are more common
in infants with Down syndrome.
The
heart is forming during the first eight weeks
of fetal development. It begins as a hollow tube,
then partitions within the tube develop 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, either.
There
may be genetic influences on the development of
atrioventricular canal. Consider the following
statistics:
- 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 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.
If not
treated, this heart defect can cause lung disease.
When blood passes through both the ASD and VSD
from the left side of the heart to the right side,
then 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.
The
larger the volume of blood that goes to the lungs,
the higher the pressure. The lungs are able to
cope with this extra pressure for a while, depending
on exactly how high the pressure is. After a while,
however, the blood vessels in the lungs become
damaged by the extra pressure.
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.
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:
- fatigue
- sweating
- pale skin
- cool skin
- rapid breathing
- heavy breathing
- rapid heart rate
- congested breathing
- disinterest in feeding,
or tiring while feeding
- 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 skin. The symptoms
of AVC may resemble other medical conditions or
heart problems. Always consult your child's physician
for a diagnosis.
Your
child's pediatrician may have heard a heart murmur
during a physical examination, and referred your
child to a pediatric cardiologist for a diagnosis.
A heart murmur is simply a noise caused by the
turbulence of blood flowing through the opening
from the left side of the heart to the right.
Symptoms your child exhibits will also help with
the diagnosis.
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. The cardiologist will perform a
physical examination, listening to the heart and
lungs, and make other observations that help in
the diagnosis. The location within the chest that
the murmur is heard best, as well as the loudness
and quality of the murmur (harsh, blowing, etc.)
will give the cardiologist an initial idea of
which heart problem your child may have. However,
other 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. An echo can show the pattern of
blood flow through the septal openings, and
determine how large the openings are, as well
as how much blood is passing through them.
- 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. Cardiac catheterization
is recommended prior to AV canal repair if pulmonary
hypertension (high blood pressure in the vessels
of the lungs) is suspected or if other information
is desired.
Specific
treatment for atrioventricular canal 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
AV canal
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:
- 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:
- digoxin -
helps strengthen the heart muscle, enabling
it to pump more efficiently.
- 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.
- 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:
- 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, 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 may receive
their formula or breast milk through the
feeding tube alone.
- 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 goal is to repair the septal openings and
repair the valves before the lungs become damaged
from too much blood flow and pressure. Your
child's cardiologist will recommend when the
repair should be performed based on results
from the echocardiogram and cardiac catheterization.
The operative methods
used to repair atrioventricular canal have
improved greatly in the past decade, and the
operation has a high likelihood of success.
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 operation is performed
under general anesthesia.
The atrial and ventricular
septal defects are often 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.
Children
will spend time in the intensive care unit (ICU)
after an AV canal repair. During the first several
hours after surgery, your child will be very drowsy
from the anesthesia that was used during the operation,
and from medications given to relax him/her and
to help with pain. To help your child rest, these
medications might be continued overnight or longer.
As time goes by, your child will become more alert.
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
truncus repair, 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 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 fluids 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 at home, 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.
Most
infants and older children feel fairly comfortable
when they go home. Pain medications, such as acetaminophen
or ibuprofen, may be recommended to keep your
child comfortable. Your child's physician will
discuss pain control before your child is discharged
from the hospital.
Often,
infants who fed poorly prior to surgery have more
energy after the recuperation period, and begin
to eat better and gain weight faster. However,
high-calorie formulas may be needed for several
weeks or months after surgery to help your child
catch up growth-wise. Tube feedings may also be
helpful until your child is able to feed better.
After
surgery, older children usually have a fair tolerance
for activity. Your child may become tired easily,
and sleep more right after surgery, but, within
a few weeks, your child may be fully recovered.
You
may receive additional instructions from your
child's physicians and the hospital staff.
Many
children who have had an AV 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.
Consult
your child's physician regarding the specific
outlook for your child.
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