During the first eight weeks of a pregnancy, the fetal heart develops. An atrioventricular canal defect, also known as AV canal defect, occurs at birth when there is an error in the heart’s normal development, resulting in a large hole in the center of the heart. Your doctor may refer to the defect by other names, including endocardial cushion defect or atrioventricular septal defect (AVSD).
An AV canal defect is not a single defect, but rather a group of abnormalities affecting the major structures of the heart—the atria, the ventricles, the septa and the valves. The heart’s upper chambers are known as atria, and the lower chambers are called ventricles. The heart also has a wall (septum) that divides this muscular, fist-sized organ into right and left halves, creating the heart’s four chambers: the left atrium, the right atrium, the left ventricle and the right ventricle.
The heart also has four valves that open and close as blood pushes through the chambers and into the body. The two atrioventricular valves are the mitral valve and the tricuspid valve. These valves are located between the atria and the ventricles.
An AV canal defect can consist of the following structural problems within the heart:
- An atrial septal defect is an opening in the wall between the left and right atria. This opening permits oxygen-rich blood to move from the left atrium into the right atrium, where it mixes with oxygen-poor blood within the right atrium.
- Similarly, a ventricular septal defect is a hole in the dividing wall between the two lower chambers of the heart, the left and right ventricles. As blood moves through this opening, the oxygenated blood of the left ventricle mixes with the deoxygenated blood in the right ventricle.
- The valve that separates the upper chamber and the lower chamber on the left side—the mitral valve—is abnormally formed. This defect in the mitral valve often disrupts the normal flow of blood, frequently allowing it to flow backwards into the atrium.
- There are different varieties of AV canal defect, with varying sizes of septal defects and varying degrees of valve involvement.
There may be a genetic component to this condition, but science has yet to determine the exact cause. This type of defect is frequently seen in children with Down syndrome.
Untreated AV canal defects can cause serious damage to the heart and lungs. Because of the hole in the heart, blood flow is not properly regulated. Shunting of blood from left to right in the AV canal allows too much blood to flow into the lungs. This increased volume makes the heart work harder than normal and can eventually enlarge the heart muscle. Without treatment, the increased volume of blood flowing into the lungs may also cause congestive heart failure.
Increased blood flow to the lungs and large shunts at the ventricular level, can lead to elevated pressure in the lungs—a condition called pulmonary hypertension. Over time, this increased pressure begins to cause changes to the pulmonary blood vessels, making them thicker and more muscular. These changes can often correct themselves if the heart is repaired early. Left unattended, this can lead to irreversible damage to the lungs.
In children who develop increased pressure in the lungs, some blood starts to mix from the right side of the heart (the oxygen-poor side) into the left side (the oxygen-rich side). One consequence of this mix is that the body receives blood that is lower than normal in oxygen, which can result in a blue discoloration of the skin. The medical term for this is “cyanosis.”
Symptoms of Atrioventricular Canal Defect
The size of the hole in the septal wall and the degree and severity of the valve involvement can influence symptoms of AV canal defects, which may include:
- Disinterest in feeding or tiring while feeding
- Sweating with feedings or minimal activity
- Rapid or heavy breathing
- Poor weight gain
- Cool skin
- Rapid heart rate
- Pale or bluish skin
Diagnosis of Atrioventricular Canal Defect
Another clue that can suggest an AV canal defect (or other cardiac abnormality) is a heart murmur—a noise produced by the blood flow through the heart. Not all heart murmurs are problematic, and many can be normal in children. Doctors may perform other tests to determine the nature of a heart murmur.
Your physician may suggest non-invasive tests such as a chest x-ray or an electrocardiogram (EKG). An EKG is a quick, painless measure of the electrical activity of the heart. It offers useful information about the condition of the heart.
Another non-invasive diagnostic tool is an echocardiogram. This ultrasound test uses sound waves to create a picture showing the major structures of the heart, as well as the pumping action of the heart. An echocardiogram also provides valuable information about:
- Heart size and function
- The size of the septal openings (if present)
- The volume of blood passing through the chambers of the heart
- The functioning of the cardiac valve
Cardiac catheterization can also diagnose an AV canal defect. During this test, a catheter (a thin tube) is inserted into a blood vessel in the groin. From there, doctors carefully maneuver it through the chambers of the heart, the arteries and veins. The test allows your physician to gain additional information about the pressure and oxygen levels in the various parts of the heart, as well as structural information about the chambers, valves and septa. It is rarely used as the primary diagnostic test in patients with AV canal because the echocardiogram is an easier, non-invasive method. Cardiac catheterization is useful when there are concerns about pulmonary hypertension.
AV canal defects can be surgically repaired at Riley at IU Health. This surgery targets the septal openings and valves and has a high success rate. Individual circumstances determine the right timing for surgery.
Prior to surgery, AV canal defects are managed through combinations of various medications including Digoxin, diuretics and ACE inhibitors. Each of these drugs target different areas.
- Digoxin targets the heart muscle and helps it pump more effectively.
- Diuretics help maintain the appropriate balance of water in the body, which can be disturbed when the heart does not function normally or when there are large shunts between the chambers.
- ACE inhibitors lower blood pressure, making it easier for the heart to pump blood throughout the body.
When the heart does not function efficiently, infants may tire while eating. This limits their ability to gain weight properly. Your doctor may suggest adding fortified nutritional supplements to milk or formula to boost weight gain. A nasogastric feeding tube can also be helpful in addressing weight gain issues in certain children. This tube is inserted in the nose and guided down the esophagus and into the stomach to administer the baby’s feedings.
Your cardiologist can determine which treatment is best for your child, as well as the timing of treatment. The age and health of the child, the seriousness of the defect, the child’s medical history, and other factors are all taken into consideration when choosing the best treatment.
Key Points to Remember
Key Points to Remember
- An AV canal defect is a group of abnormalities affecting the major structures of the heart—the atria, ventricles, septa and valves.
- Without treatment, AV canal defect disrupts the normal flow of blood through the heart and can eventually lead to more serious damage to the heart and lungs.
- Labored breathing, cyanosis, abnormal fatigue, rapid heartbeat and poor weight gain may be symptoms of AV canal defect.
- AV canal defect, though serious, is treatable.
Support Services & Resources
Support Services & Resources
These resources can be helpful for parents and caregivers whose children are diagnosed with congenital heart defects.
Riley at IU Health offers a broad range of supportive services to make life better for families who choose us for their children's care.
This not-for-profit organization provides information and support to adults living with congenital heart disease.
This U.S. government website includes resources to educate parents and caregivers of children with congenital heart disease. It also shares information for the growing population of adults who are living with congenital heart disease.
As part of the National Institutes of Health, the National Heart, Lung and Blood Institute advances research and understanding of heart, lung and blood diseases and shares easy-to-digest information about congenital heart defects.
In addition to our primary hospital location at the Academic Health Center in Indianapolis, IN, we have convenient locations to better serve our communities throughout the state.