What causes atrioventricular canal?
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:
- Congenital heart disease (CHD) is present in half of children born with Down syndrome, and close to half 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 #21 chromosomes.
- Similarly, about one-third of all children born with AV canal defect also have Down syndrome.
- About 15 percent of mothers with an AV canal defect give birth to a child with the disease.
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.
Why is atrioventricular canal a concern?
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 and 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 normals. 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 patients become cyanotic, or exhibit a blue coloring in their skin, lips, and nail beds.
Because blood is pumped at high pressure through the septal openings, the right ventricle 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.
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:
- 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, after years blood within the heart will "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, nail beds, and skin. The symptoms of AVC may resemble other medical conditions or heart problems. Always consult your child's physician for a diagnosis.