 Atrioventricular Canal Defect
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Normal heart
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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:
- 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. See About the Heart and Blood Vessels for more information on how the heart normally works.
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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.
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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.
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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.
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Atrioventricular canal occurs in two out of every 10,000 live births, equally in boys and girls.
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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
- sweating
- pale skin
- cool skin
- rapid breathing
- heavy breathing
- rapid heart rate
- congested breathing
- disinterest in feeding, or tiring while feeding
- poor weight gain
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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.
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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:
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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 experiences will also help with the diagnosis.
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- Chest X-ray — A diagnostic test that uses invisible electromagnetic energy beams to produce images of internal tissues, bones and organs onto film. With an ASD, the heart may be enlarged because the right atrium and ventricle have to handle larger amounts of blood flow than normal. Also, there may be changes that take place in the lungs due to extra blood flow that can be seen on an X-ray.
- 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 opening and determine how large the opening is, as well as how much blood is passing through it.
- Cardiac Catheterization — A 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 in the pulmonary artery and aorta. Contrast dye is injected to more clearly visualize the structures inside the heart. If the echocardiogram has provided enough information, this procedure is often not needed to evaluate ASD.
- Cardiac Magnetic Resonance Imaging (MRI) — A non-invasive test that uses three-dimensional imaging technology produced by magnets to accurately determine blood flow and functioning of the heart as it is working.
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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
- extent of the disease
- your child's tolerance for specific medications, procedures or therapies
- how your child's doctor expects the disease may progress
- your opinion or preference
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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:
- 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:
- 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.
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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.
Consult your child's physician regarding the specific outlook for your child.
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Complementing the Cardiovascular Program of Children's Hospital Boston is the nation's most intensive clinical and basic research program focused on pediatric heart disease. Children's is a world leader in opening new avenues of "translational research," bringing laboratory advances to the bedside and doctor's office as quickly as possible. All senior medical staff members of the Cardiovascular Program participate in clinical research activities.
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Contact Children's Hospital Boston Cardiovascular Program physicians for a second opinion.
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