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Atrioventricular Canal Defect (AVCD)


Atrioventricular canal defects (AVCDs) are congenital heart defects in which a hole is present in the wall between the two sides of the heart. They make up 3% to 5% of congenital heart disease cases. AVCDs occur in 0.24 to 0.31 out of 1000 live births.

An atrioventricular canal defect (AVCD) is a congenital heart defect (this means it’s present at birth) that affects the wall between the two sides of the heart. A hole is present between the heart's chambers.

Sometimes it is small enough to affect only the top part of the heart (the atria), which is called a partial AVCD. In a partial ACVD, the two valves between the top part of the heart (the atrium) and the bottom part of the heart (the ventricles) do not function properly.

A complete AVCD affects all four chambers of the heart. The hole is in the middle of the four chambers, and the blood mixes throughout the heart. Only one valve is present in a complete AVCD, and this is in the center of the heart where the defect in the wall is.

Atrioventricular canal defects are also called atrioventricular septal defects or endocardial cushion defects.

How does a healthy heart work?

The blood circulates through the body in this pattern:

  1. Blood from the body comes into the right atria through one of the two chambers at the top of the heart
  2. From here, it goes through the mitral/bicuspid valve
  3. Into the right ventricle, which is one of the two chambers at the bottom of the heart
  4. Into the pulmonary artery, which is the artery that supplies blood to the lungs
  5. Into the lungs where it picks up oxygen
  6. Into the pulmonary veins that lead back into the heart from the lungs
  7. Into the left atria, which is the other chamber at the top of the heart
  8. Through the tricuspid valve
  9. Into the left ventricle, which is the other chamber at the bottom of the heart
  10. Out into the rest of the body
  11. Back into the right atria to begin the cycle all over again

In a healthy heart, the four chambers and valves work together to pump blood through the lungs and body. The right side of the heart pumps blood only to the lungs and the left side pumps blood only to the body. As a result, the oxygen-rich blood from the lungs and the oxygen-depleted blood from the body never mix.

The valves close after each heartbeat to prevent the blood from flowing back into the previous heart chamber while the heart is between beats.

How does an AVCD change the heart's function?

There are two types of atrioventricular canal defects: partial and complete.

In a partial AVCD, a hole is present in the wall between the atria, which are the two top chambers of the heart. Blood can shunt from the left side to the right side of the heart, which puts extra strain on the right side and increases the pressure in the lungs. This causes increased workload for the heart and increased pressure in the lungs.

Sometimes the mitral valve (the valve between the right atria and the right ventricle) can be affected and blood can flow back into the atria from the ventricle. This condition is called mitral valve regurgitation or insufficiency.

In a complete AVCD, the hole is in the middle of the wall between all four chambers. Blood flows between all of the chambers, mixing oxygen rich-blood from the lungs with oxygen-depleted blood from the body. The blood is not going to the proper places to receive oxygen or provide oxygen to the body. The heart must work harder to provide adequate blood and oxygen to the lungs and body.

In a complete AVCD, there is only one valve in the middle of the heart instead of two separate mitral and tricuspid valves.

Causes and risk factors

Although the exact cause of an AVCD is not always known, atrioventricular canal defects often appear in children with chromosomal abnormalities, especially Down syndrome. They can be present in children without these conditions, but this is much less common.

Atrioventricular canal defects are often seen in children whose mothers had certain health conditions before or during pregnancy, including:

  • Drinking alcohol during pregnancy
  • Smoking during pregnancy
  • Taking certain medications during pregnancy
  • Diabetes before pregnancy
  • Gestational diabetes mellitus (diabetes that develops during pregnancy)
  • German measles (rubella) during the first few months of pregnancy
  • Obesity
  • Having a close relative (especially a parent) with a CHD

Symptoms

The symptoms someone experiences will depend on whether they have a partial or complete AVCD and what size the defect is.

Symptoms of a partial AVCD may not appear until later in life and may include:

  • Arrhythmia (abnormal heart rhythm)
  • Shortness of breath
  • Pulmonary hypertension (high blood pressure in the blood vessels in the lungs)
  • Problems with the heart valves
  • Heart failure

Complete AVCD symptoms usually develop in the first few weeks after birth. Infants usually develop rapid breathing and have difficulty gaining weight when they have a complete AVCD. Other symptoms include:

  • Wheezing
  • Fatigue
  • Lethargy
  • Lack of appetite and difficulty eating
  • Pale skin
  • Bluish discoloration of the lips and skin
  • Excessive sweating, especially during feeding
  • Fast or irregular heartbeat
  • Swelling in the legs, ankles, and feet
  • Working hard to breath
  • Enlarged liver
  • Enlarged heart

Diagnose

Doctors can use an echocardiography to diagnose AVCDs early.

A chest x-ray can check for an enlarged right side of the heart or larger blood vessels that lead to the lungs.

An electrocardiogram (EKG or ECG) can show any electrical disturbances in the heart caused by the malformed anatomy.

A cardiac MRI can help a doctor visualize the heart structure and function to point out any abnormalities.

Complications

Even after successful surgery, some patients may have complications such as:

  • Shortness of breath
  • Endocarditis (infection in the heart)
  • Enlarged heart
  • Pulmonary hypertension (high blood pressure in the lungs)
  • Frequent lung or respiratory infections
  • Heart failure

Talk to your doctor if you have been diagnosed with an AVCD and you are pregnant or plan to become pregnant. You may be considered a high-risk pregnancy.

Treatments and outlook

Doctors may initially prescribe medications to decrease the heart's workload, reduce blood pressure, or make it easier for the heart to beat.

Surgery is usually necessary to correct the defect. An infant with a complete AVCD will generally need surgery before six months of age. A surgeon may want to perform a cardiac catheterization to identify the defective anatomy before the surgery. During the surgery the surgeon will place a patch over the hole and repair the valves or turn the one valve into two.

10% to 20% of children will need additional surgeries, usually to repair a leaking valve or patch.

An estimated 3% of children with an AVCD will die, about 90% will survive for ten years.

Key take-aways

An atrioventricular canal defect is a hole in the wall between the two sides of the heart. Depending on whether it is a partial or complete AVCD, the mitral valve may not work well or there may only be one valve in the middle of the heart where the heart wall should be.

Oxygenated and deoxygenated blood can mix in the heart, which increases the heart's workload and exerts more pressure on the lungs.

Symptoms of congestive heart failure and pulmonary hypertension will typically result.

The treatment for these conditions is surgery and life-long cardiology follow-up.

Sources:

American Heart Association. (2021). Complete Atrioventricular Canal Defect. Complete Atrioventricular Canal defect (CAVC) | American Heart Association

Mayo Clinic. (2021). Atrioventricular Canal Defect. Atrioventricular canal defect - Symptoms and causes - Mayo Clinic

Umapathi, Krishna Kishore; Agasthi, Pradyumna. (2021). Atrioventricular Canal Defects. Atrioventricular Canal Defects - StatPearls - NCBI Bookshelf (nih.gov)

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