Atrioventricular canal defect (AV canal) is a congenital (present at birth) heart defect. Other terms used to describe this defect are endocardial cushion defect and atrioventricular septal defect (AVSD). 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 complex heart problem that involves several abnormalities of structures inside the heart, including the following:
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 (the wall) between the two atria, 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 (the wall) between the two ventricles, 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. This results in leakage of the mitral or tricuspid valves, known as regurgitation or insufficiency.
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 they too do not develop properly.
There may be genetic influences on the development of atrioventricular canal. Consider the following statistics:
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 volume of blood is also under high pressure, since the pressure in the left ventricle is high. This blood then passes through the pulmonary artery into the lungs, causing higher volume than normal higher pressure than normal in the blood vessels in the lungs.
The lungs are able to cope with this extra volume of blood at high pressure for a while. The child will be breathing at a faster rate than normal since the lungs have a lot of extra blood at high pressure compared to normal. After a while, however, the blood vessels in the lungs become damaged by this extra volume of blood at high pressure. The blood vessels in the lungs get thicker. Those changes are reversible at first. With time, these changes in the lungs become irreversible, resulting in irreversible damage to the lungs themselves.
As the arteries in the lungs get thicker, the flow of blood from the left side of the heart to the right side and on to the lungs will diminish. 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 side of the heart, and on to the body. When this happens, the body does not receive enough oxygen in the bloodstream to meet its needs, and children 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 right and left ventricles will remain thick. Bacteria in the bloodstream can occasionally infect the abnormal valves in the heart (the abnormal mitral and tricuspid valves associated with AV canal defects), 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:
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. Diagnostic testing for congenital heart disease varies by the child's age, clinical condition, and institutional preferences. Some tests that may be recommended include the following:
Specific treatment for atrioventricular canal will be determined by your child's physician based on:
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:
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.
At surgery, the ventricular septal defect is often closed with a synthetic patch made from a polyester-like material known as Dacron. The atrial septal defect is often closed with a pericardial patch made from the membrane that covers the outside surface of the heart. The valve repair technique consists of converting the abnormal three-leaflet mitral valve into a two-leaflet mitral valve. This is accomplished by suturing the cleft (the cut in the valve leaflets) to recreate a two-leaflet (two-cusp) mitral valve. The tricuspid valve may also be repaired, depending on the surgeon's preference.
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 or 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 or her recover, and may include the following:
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 of which relieve pain, and some of which relieve anxiety. The staff will also be asking for your input as to how best to soothe and comfort your child.
After discharge 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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