Patient education: Atrioventricular canal defects (The Basics)

What is an atrioventricular canal defect? — 

An atrioventricular, or "AV," canal defect is a problem in the heart that some babies are born with.

The heart is divided into 4 sections, called "chambers" (figure 1). The upper chambers are the right atrium and the left atrium, also called the "atria." The lower chambers are the right ventricle and the left ventricle. The atria connect to the ventricles through the "AV valves." Normally, there are 2 AV valves: the tricuspid valve is on the right, and the mitral valve is on the left.

When a child has an AV canal defect, the walls that separate the right and left sides of the heart are not fully formed. There are also problems with the AV valves. These things change how blood flows through the heart and make the heart work harder than normal.

There are different types of AV canal defects. Some are severe and can cause serious, long-lasting problems. Others are more minor and can often be repaired without long-term effects. Types of AV canal defects include:

●Complete defect – This is the most severe form. It means that there is a large hole in the wall separating the right and left sides of the heart (figure 2). Also, instead of 2 separate AV valves, there is a single AV valve that usually does not close properly.

●Partial defect – This is the least severe form. It means that there is a hole in the wall between the right and left upper chambers of the heart. There are 2 separate AV valves, but the left-sided valve (called the "mitral valve") is abnormal and does not close properly.

●Transitional defect – This is similar to a partial AV canal defect. But in addition to the hole in the wall between the upper chambers of the heart, there is also a hole in the wall between the right and left lower chambers.

AV canal defects are common in children with Down syndrome. But they can also happen in children without Down syndrome.

AV canal defects need to be repaired with surgery.

What are the symptoms of an AV canal defect? — 

Babies with a complete AV canal defect usually start having symptoms at 1 to 2 months of age. Symptoms happen when the heart cannot pump as well as it should. They can include:

●Breathing very fast

●Having trouble feeding

●Not growing as fast as normal

●Sweating

●Skin that looks pale, blue, or gray

In some cases, a partial AV canal defect does not cause symptoms until later in childhood or even adulthood. A person might learn that they have it after seeing a doctor for symptoms like:

●Getting short of breath after exercise

●Heart rhythm problems, for example, feeling like the heart is racing or skipping beats

If an AV canal defect is not treated, it can lead to serious problems with the heart and lungs.

Should my child see a doctor or nurse? — 

See a doctor or nurse if your baby or child:

●Seems to lose interest in feeding, or gets tired easily with feeds

●Does not gain weight or grow as quickly as other children

●Has fast or heavy breathing

●Feels like their heart is racing or beating abnormally

●Gets very tired or short of breath when they exercise

Is there a test for an AV canal defect? — 

Yes. Doctors can find it before or after a baby is born. This can be done with different imaging tests.

Tests include:

●Ultrasound during pregnancy – This uses sound waves to create pictures of the fetus. It can show if there are problems with the heart.

●"Fetal echocardiogram" – This is also done before birth. It is usually done to get a closer look at the heart if an ultrasound shows a possible problem. It gives detailed pictures of the different parts of the heart, and lets the doctor see how blood flows.

●"Echocardiogram" – This looks at the heart after the baby is born. It can confirm the type of defect and where it is. It is recommended for all babies with Down syndrome. It might also be done if a baby or child starts having symptoms that could be related to a heart problem, even if no problem was found during pregnancy.

In some cases, other tests might be done, too. These can include:

●Chest X-ray

●Electrocardiogram, or "ECG" – This measures electrical activity in the heart.

●Genetic testing – If tests find an AV canal defect before birth, doctors might suggest testing for Down syndrome. That's because this type of heart defect is common in babies born with Down syndrome.

How are AV canal defects treated? — 

They are treated with surgery. The goals of surgery are to:

●Patch the hole(s) in the heart

●Fix the valves if needed, so blood flows in the right direction

The timing for surgery depends on the type of defect:

●Babies with a complete AV canal defect usually have surgery before 6 months of age.

●Partial and transitional AV defects are usually fixed between 18 months and 3 years of age. This can also happen later if a defect is found when a child is older.

Some children can have long-term problems, even after surgery. This depends on how severe their AV canal defect is.

Your child will need to see their heart doctor regularly. The doctor will do an exam and tests at each visit. They will check for any new problems with the heartbeat or blood flow. They will also give advice about physical activity. Most children who have no symptoms after surgery can exercise normally, but this depends on the child and the exact type of defect they had.

More on this topic

Patient education: Atrial septal defects in children (The Basics)
Patient education: Ventricular septal defects in children (The Basics)
Patient education: Testing for Down syndrome during pregnancy (The Basics)
Patient education: Down syndrome (The Basics)