Septal Defect, Atrioventricular / Atrioventricular Canal Defect
Atrioventricular canal defect is a combination of several abnormalities in the heart present at birth (congenital). This defect includes a hole between the chambers of the heart and problems with the valves that regulate blood flow in the heart. Atrioventricular canal defect may also be called endocardial cushion defect or atrioventricular septal defect.
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. Both types allow extra blood to circulate to the lungs, causing the heart to enlarge.
Atrioventricular canal defect is often associated with Down syndrome. Infants with atrioventricular canal defect may have trouble breathing, and they may not grow normally. If left untreated, atrioventricular canal defect may cause congestive heart failure and high blood pressure in the lungs. To correct this defect, doctors often recommend surgery during the first year of life to close the hole and reconstruct the valves.
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 close to keep blood from flowing backward.
A hole in the wall
In partial atrioventricular canal defect, a hole exists in the wall (septum) that separates the upper chambers (atria), and the mitral valve between the upper and lower left chambers does not close completely (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. Often, this valve doesn't 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.
Risk Factor :
Although the exact cause of atrioventricular canal defect is unknown, several factors may increase the risk of your baby being born with this condition.
Children born with Down syndrome, a genetic condition resulting from an extra 21st chromosome, are at increased risk of congenital heart defects. Forty-five percent of children with Down syndrome have congenital heart disease. Of these, 20 percent to 25 percent have atrioventricular canal defect.
Other factors that may increase the risk of congenital heart defects include :
- A mother who had German measles (rubella) or another viral illness during early pregnancy
- A parent who had a congenital heart defect
- Excessive alcohol consumption during pregnancy
- A mother who has diabetes
- Taking some types of medications during pregnancy
When to seek medical advice :
Contact your doctor if your baby 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
- Shortness of breath
- Easily tiring
- A persistent cough or wheezing with white or pink blood-tinged phlegm
- Swelling of the legs, ankles or feet
- Swelling of the abdomen
- 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, years or even decades, depending on the extent of the defect. But, anytime the signs or symptoms above start to appear, seek medical care.
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 congestive heart failure, including :
- Fatigue and weakness
- Persistent cough or wheezing with white or pink blood-tinged phlegm
- Swelling (edema) in the legs, ankles and feet
- Swelling of the abdomen (ascites)
- Sudden weight gain from fluid retention
- Decreased alertness
- Irregular or rapid heartbeat
Partial atrioventricular canal defect
Signs and symptoms of a partial atrioventricular canal defect may not appear until later in life, often in the 20s and 30s. When they do become noticeable, signs and symptoms are usually related to complications that develop as a result of the defect, such as abnormal heart rhythm (arrhythmia), congestive heart failure and high blood pressure in the lungs (pulmonary hypertension).
If your baby has a partial atrioventricular canal defect, his or her doctor may not detect anything wrong right away. However, if your baby has a complete atrioventricular canal defect, signs and symptoms usually become noticeable within the first few weeks of life.
Your baby's doctor may suspect a heart defect such as atrioventricular canal defect if your baby is having trouble breathing or having difficulty feeding and gaining weight. Your doctor may also suspect a heart defect if he or she hears a heart murmur — an abnormal whooshing sound caused by turbulent blood flow.
Doctors typically use an echocardiogram to diagnose atrioventricular canal defect. This test uses high-pitched sound waves that bounce off the heart to produce moving images that the doctor can view on a video screen. In a baby with atrioventricular canal defect, the echocardiogram reveals a hole in the wall between the heart chambers and abnormal valves. Because this test can track blood flow, it also shows blood moving through the hole from the left side to the right side of the heart, allowing oxygen-rich and oxygen-poor blood to mix.
In some cases, doctors may use cardiac catheterization to diagnose atrioventricular canal defect. During this procedure, the doctor inserts a thin flexible tube (catheter) into an artery or vein in the groin and advances it up to the heart. A dye is injected through the catheter to make the heart structures visible on X-ray pictures. The catheter also allows the doctor to measure pressure in the chambers of the heart and in the blood vessels.
Potential complications of atrioventricular canal defect include :
- Pneumonia. If your baby has an untreated atrioventricular canal defect, he or she may have recurrent bouts of pneumonia — a serious lung infection.
- Enlargement of the heart (cardiomegaly). Increased blood flow through the heart forces it to work harder than normal, causing it to enlarge.
- Congestive heart failure. If left untreated, atrioventricular canal defect will result in congestive 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.
Complications later in life
People who have surgery to correct atrioventricular canal defect sometimes have 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, fever and a rapid, fluttering heartbeat, among others.
Surgery is necessary to correct atrioventricular canal defect. During the procedure, a surgeon closes the hole in the septum with one or two patches. The patches remain in the heart permanently, becoming part of the septum as the heart's lining grows over it.
For a partial atrioventricular canal defect, the surgery also involves repair of the mitral valve so it will close tightly. If repair isn't possible, the valve may need to be replaced instead.
If your baby has complete atrioventricular canal defect, the surgery also includes separation of the single valve into two valves, one on the left side and one on the right side of the repaired septum. If reconstruction of the single valve into two valves isn't possible, heart valve replacement may be necessary.
After corrective surgery, your child will need lifelong follow-up care with a heart doctor (cardiologist) who specializes in congenital heart disease.
Your child will also need to take antibiotics before dental procedures and other surgical procedures to prevent infection (endocarditis).
Many people who have corrective surgery for atrioventricular canal defect don't need additional surgery. However, some complications, such as heart valve leaks, may require treatment.
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, before future pregnancies talk with a genetic counselor and a cardiologist experienced in congenital heart defects.