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Atrioventricular canal defect

Atrioventricular canal defect is a combination of several abnormalities in the heart present at birth (congenital abnormalities). This defect, which is sometimes called endocardial cushion defect or atrioventricular septal defect, occurs when there's a hole between the chambers of the heart and problems with the valves that regulate blood flow in the heart.

Atrioventricular canal defect allows extra blood to circulate to the lungs. Ensuing problems overwork the heart and cause it to enlarge.

Atrioventricular canal defect is often associated with Down syndrome. If left untreated, atrioventricular canal defect may cause heart failure and high blood pressure in the lungs. To fix this defect, doctors often recommend surgery during the first year of life to close the hole and reconstruct the valves.

Symptoms Causes Risk factors Complications Prevention

There are two common types of atrioventricular canal defect — partial and complete. The partial form involves only the two upper chambers of the heart. The complete form allows blood to travel freely among all four chambers of the heart. In either type, extra blood circulates in the lungs.

Complete atrioventricular canal defect

Signs and symptoms of complete atrioventricular canal defect usually develop in the first several weeks of life. They include:

  • Difficulty breathing (dyspnea)
  • Lack of appetite
  • Poor weight gain
  • Bluish discoloration of the lips and skin (cyanosis)

If your baby has complete atrioventricular canal defect, he or she may also develop signs and symptoms of heart failure, including:

  • Fatigue
  • Wheezing
  • Swelling (edema) in the legs, ankles and feet
  • Sudden weight gain from fluid retention
  • Excessive sweating
  • Decreased alertness
  • Irregular or rapid heartbeat

Partial atrioventricular canal defect

Signs and symptoms of a partial atrioventricular canal defect may not appear until early adulthood. When they do become noticeable, signs and symptoms may be related to complications that develop as a result of the defect, and may include:

  • Abnormal heartbeat (arrhythmia)
  • Heart valve problems
  • Heart failure
  • High blood pressure in the lungs (pulmonary hypertension)

When to see a doctor

Contact your doctor if you or your child develops any of the following signs or symptoms. These could be indications of heart failure or another complication of atrioventricular canal defect:

  • Poor appetite
  • Failure to gain weight, in infants and children
  • Shortness of breath
  • Easily tiring
  • Swelling of the legs, ankles or feet
  • Bluish discoloration of the skin

Some babies with the partial form of atrioventricular canal defect may not have any signs or symptoms for weeks, months or even years, depending on the severity of the defect. But, anytime the signs or symptoms above start to appear, seek medical care.

Atrioventricular canal defect occurs during fetal growth when your baby's heart is developing. While some factors, such as Down syndrome, may increase the risk of atrioventricular canal defect, in most cases the cause is unknown.

The normal-functioning heart

Your heart is divided into four chambers, two on the right and two on the left. In performing its basic job — pumping blood throughout your body — your heart uses its left and right sides for different tasks. The right side moves blood into vessels that lead to your lungs. In your lungs, oxygen enriches your blood, which circulates to your heart's left side. The left side of your heart pumps blood into a large vessel called the aorta, which 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 they close to keep blood from flowing backward.

What happens in atrioventricular canal defect

In partial atrioventricular canal defect, a hole exists in the wall (septum) that separates the upper chambers (atria) of the heart. Also, the mitral valve between the upper and lower left chambers often has a defect called a cleft 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 upper chambers (atria) and lower chambers (ventricles) meet. Instead of two separate valves — one on the right (tricuspid) and one on the left (mitral) — one large common valve exists between the upper and lower chambers. And, this valve may not close tightly.

Oxygen-rich and oxygen-poor blood mix through the hole in the septum, and the abnormal valves leak blood into the heart's lower chambers (ventricles). These problems make the heart work harder, causing it to enlarge.

Although the exact cause of atrioventricular canal defect is unknown, several factors may increase the risk of a congenital heart defect, such as:

  • Down syndrome in the baby. Down syndrome is a genetic condition resulting from an extra 21st chromosome.
  • German measles (rubella) or another viral illness during early pregnancy.
  • Having a parent who had a congenital heart defect.
  • Drinking alcohol during pregnancy.
  • Poorly controlled diabetes during pregnancy.
  • Taking some types of medications during pregnancy. Check with your doctor before taking any drugs while you're pregnant and even when you're trying to get pregnant.

Treating an atrioventricular canal defect helps your child avoid potential complications, such as:

  • Enlargement of the heart. Increased blood flow through the heart forces it to work harder than normal, causing it to enlarge.
  • Heart failure. Untreated, atrioventricular canal defect will usually result in heart failure — a condition in which the heart is unable to pump enough blood to meet the body's needs.
  • High blood pressure in the lungs (pulmonary hypertension). When the heart's left ventricle weakens and can't pump out enough blood, the increase in pressure backs up through the pulmonary veins to the arteries in the lungs, causing high blood pressure in the lungs.
  • Pneumonia. If your baby has an untreated atrioventricular canal defect, he or she may have recurrent bouts of pneumonia — a serious lung infection.

Complications later in life

Although treatment greatly improves the outlook for children with atrioventricular canal defect, some who have corrective surgery may still be at risk of the following associated conditions later in life:

  • Leaky heart valves (regurgitation)
  • Narrowing of the heart valves (stenosis)
  • Heart rhythm abnormalities (arrhythmias)
  • Breathing difficulties associated with damage to the lungs (pulmonary vascular disease)

Common signs and symptoms of these complications include shortness of breath, fatigue and a rapid, fluttering heartbeat, among others. In some cases, such as a leaky heart valve, a second surgery may be needed.

In most cases, atrioventricular canal defect can't be prevented. 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.

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