Atrioventricular canal defect is a combination of heart problems resulting in a defect in the center of the heart. The condition occurs when there's a hole between the heart's chambers and problems with the valves that regulate blood flow in the heart.
Sometimes called endocardial cushion defect or atrioventricular septal defect, atrioventricular canal defect is present at birth (congenital). The condition is often associated with Down syndrome.
Atrioventricular canal defect allows extra blood to flow to the lungs. The extra blood forces the heart to overwork, causing the heart muscle to enlarge.
Untreated, atrioventricular canal defect can cause heart failure and high blood pressure in the lungs. Doctors generally recommend surgery during the first year of life to close the hole in the heart and to reconstruct the valves.
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Atrioventricular canal defect can involve only the two upper chambers of the heart (partial) or all four chambers (complete). In either type, extra blood circulates in the lungs.
Complete atrioventricular canal defect
Signs and symptoms usually develop in the first several weeks of life. These signs and symptoms are generally similar to those associated with heart failure and might include:
- Difficulty breathing or rapid breathing
- Lack of appetite
- Poor weight gain
- Pale skin color
- Bluish discoloration of the lips and skin
- Excessive sweating
- Irregular or rapid heartbeat
- Swelling in the legs, ankles and feet (edema)
Partial atrioventricular canal defect
Signs and symptoms might not appear until early adulthood and might be related to complications that develop as a result of the defect. These signs and symptoms can include:
- Abnormal heartbeat (arrhythmia)
- Shortness of breath
- High blood pressure in the lungs (pulmonary hypertension)
- Heart valve problems
- Heart failure
When to see a doctor
See your doctor if you or your child develops signs or symptoms of atrioventricular canal defect.
Chambers and valves of the heart
A normal heart has two upper (receiving) and two lower (pumping) chambers. The upper chambers, the right and left atria, receive incoming blood. The lower chambers, the more muscular right and left ventricles, pump blood out of your heart. The heart valves, which keep blood flowing in the correct direction, are gates at the chamber openings (for the tricuspid and mitral valves) and exits (for the pulmonary and aortic valves).
Atrioventricular canal defect
Atrioventricular canal defect includes a hole in the wall between the heart's chambers and flaws in the heart's valves. This defect is classified by whether it's partial, involving only the upper two chambers, or complete, in which blood can travel freely among all four chambers.
Atrioventricular canal defect occurs before birth when a baby's heart is developing. Some factors, such as Down syndrome, might increase the risk of atrioventricular canal defect. But the cause is generally unknown.
The normal-functioning heart
The heart is divided into four chambers, two on the right and two on the left.
The right side of your heart moves blood into vessels that lead to the lungs. There, oxygen enriches the blood. The oxygen-rich blood flows back to your heart's left side and is pumped into a large vessel (aorta) that circulates blood to the rest of your body.
Valves control the flow of blood into and out of the chambers of your heart. These valves open to allow blood to move to the next chamber or to one of the arteries, and close to keep blood from flowing backward.
What happens in atrioventricular canal defect
In partial atrioventricular canal defect:
- There's a hole in the wall (septum) that separates the upper chambers (atria) of the heart.
- Often the valve between the upper and lower left chambers (mitral valve) also has a defect that causes it to leak (mitral valve regurgitation).
In complete atrioventricular canal defect:
- There's a large hole in the center of the heart where the walls between the atria and the lower chambers (ventricles) meet. Oxygen-rich and oxygen-poor blood mix through that hole.
- Instead of separate valves on the right and left, there's one large valve between the upper and lower chambers.
- The abnormal valve leaks blood into the ventricles.
- The heart is forced to work harder and enlarges.
Factors that might increase a baby's risk of developing atrioventricular canal defect before birth include:
- Down syndrome
- German measles (rubella) or another viral illness during a mother's early pregnancy
- Alcohol consumption during pregnancy
- Poorly controlled diabetes during pregnancy
- Smoking during pregnancy
- Certain medications taken during pregnancy — talk to your doctor before taking any drugs while you're pregnant or trying to become pregnant
- Having a parent who had a congenital heart defect
Complications of atrioventricular canal defect can include:
- Enlargement of the heart. Increased blood flow through the heart forces it to work harder than normal, causing it to enlarge.
- Pulmonary hypertension. When there is a hole (defect) that allows mixing of oxygenated (red) and deoxygenated (blue) blood, the amount of blood that goes to the lungs is increased. This results in pressure buildup in the lungs, causing high blood pressure in the lungs.
- Respiratory tract infections. Atrioventricular canal defect can cause recurrent bouts of lung infections.
- Heart failure. Untreated, atrioventricular canal defect usually results in the heart's inability to pump enough blood to meet the body's needs.
Complications later in life
Treatment greatly improves the outlook for children with atrioventricular canal defect. However, some children who have corrective surgery may still be at risk later in life of:
- Leaky heart valves
- Narrowing of the heart valves
- Abnormal heart rhythm
- Breathing difficulties associated with lung damage
Common signs and symptoms of these complications include:
- Shortness of breath
- Rapid, fluttering heartbeat
Additional surgery might be needed to correct complications of atrioventricular canal defect.
Atrioventricular canal defect generally can't be prevented.
Heredity may play a role in some heart defects. If you have a family history of heart defects or if you already have a child with a congenital heart defect, talk with a genetic counselor and a cardiologist before getting pregnant again.
Immunization with rubella vaccine has been one of the most effective preventive strategies against congenital heart defects.