Atrioventricular Canal Defect – Causes, Complications, and Prevention.

Overview

Atrioventricular canal defect (AVCD) or atrioventricular septal defect (AVSD) 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.

Types of atrioventricular canal defect

There are two general types of AVCD that can occur, depending on which structures are not formed correctly:

Complete AVCD

A complete AVCD occurs when there is a large hole in the center of the heart which allows blood to flow between all four chambers of the heart. This hole occurs where the septa (walls) separating the two top chambers (atria) and two bottom chambers (ventricles) normally meet. There is also one common atrioventricular valve in the center of the heart instead of two separate valves – the tricuspid valve on the right side of the heart and the mitral valve on the left side of the heart. This common valve often has leaflets (flaps) that may not be formed correctly or do not close tightly. A complete AVCD arises during pregnancy when the common valve fails to separate into the two distinct valves (tricuspid and mitral valves) and when the septa (walls) that split the upper and lower chambers of the heart do not grow all the way to meet in the center of the heart.

Partial or Incomplete AVCD

A partial or incomplete AVCD occurs when the heart has some, but not all of the defects of a complete AVCD. There is usually a hole in the atrial wall or in the ventricular wall near the center of the heart. A partial AVCD usually has both mitral and tricuspid valves, but one of the valves (usually mitral) may not close completely, allowing blood to leak backward from the left ventricle into the left atrium.

Causes

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.

Risk factors of atrioventricular canal defect

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

What are the signs and symptoms?

The size of the openings will affect the type and severity of symptoms, as well as the age at which they first occur. The larger the openings, the more serious the condition.

If your baby has complete AVSD, the signs and symptoms usually become clear in the first few weeks of life. Symptoms vary for each child, but commonly include:

• Difficult or congested breathing
• Poor appetite or poor weight gain
• Lack of interest or unusual tiredness during feeding
• Cyanosis: A blue tone to the skin, lips, or nails
• Pale, cool or sweaty skin
• A heartbeat that is too fast

Complete AVSD may lead to congestive heart failure. If your baby develops congestive heart failure, the signs and symptoms may include:

• Fatigue, weakness, and lack of alertness
• Sudden weight gain or swelling of the legs, ankles, feet or belly
• A heartbeat that is irregular or too fast
• Coughing or wheezing that doesn’t go away, sometimes with white or pink phlegm that has blood in it

If your child has partial AVSD, signs and symptoms may not become clear for weeks, months, or even years. Some people with partial AVSD don’t show signs until they are adults in their 20s or 30s, whey they may develop conditions such as abnormal heart rhythm, congestive heart failure and high blood pressure in the lungs.

Your baby’s doctor may also suspect partial AVSD if he or she hears a heart murmur — an abnormal whooshing noise, heard through a stethoscope exam, which may indicate a problem with blood flow. Most heart murmurs are called “innocent heart murmurs.” Children with innocent heart murmurs do not have a heart defect and do not experience heart problems. However, if a heart murmur is present along with other symptoms, your doctor may want to investigate further by ordering other tests.

Complications of AVCD or AVSD

AVSD may have trouble breathing and they may not grow normally. Left untreated, the potential complications of AVSD also include:

• Pneumonia: Untreated AVSD may lead to repeated problems with this lung infection.
• Enlargement of the heart (cardiomegaly): Increased blood flow through the heart forces it to work harder, which causes it to grow larger.
• Congestive heart failure: Left untreated, AVSD causes congestive heart failure, a condition in which the heart cannot pump enough blood to meet the body’s needs.
• High blood pressure in the lungs (pulmonary hypertension): When the heart weakens and can’t pump enough blood, this increases blood pressure in the heart and lungs. High blood pressure in the blood vessels in the lungs can cause lung damage.
• Bacterial endocarditis: A serious infection of the lining of the heart.

How is an atrioventricular canal defect diagnosed?

Front view cross section of heart showing atria on top and ventricles on bottom. Mitral and tricuspid valves are rebuilt. Patch is in ASD and another patch in VSD.

During a physical exam, the healthcare provider checks for signs of a heart problem such as a heart murmur. This is an extra noise caused when blood doesn’t flow smoothly through the heart. If a heart problem is suspected, your child may be referred to a pediatric cardiologist. This is a doctor with special training to diagnose and treat heart problems in children. To check for an AV canal defect, the following tests may be done:

• Chest X-ray. X-rays are used to take a picture of the heart and lungs.
• Electrocardiogram (ECG). The test records the electrical activity of the heart.
• Echocardiogram (echo). Sound waves (ultrasound) are used to create a picture of the heart and look for structural defects.
• Cardiac catheterization: a thin tube is inserted into the heart through a vein and/or artery in either the leg or through the umbilicus (“belly button”).
• Pulse oximetry: a noninvasive way to monitor the oxygen content of the blood.
• Cardiac MRI. This test gives 3-D images of the heart. It can show any defects.

How is an atrioventricular canal defect treated?

Treatment will depend on your child’s symptoms, age, and general health. It will also depend on how severe the condition is. All children with an AVCD will need to have surgery to fix it. They may also need other treatments.

Medicine

Many children will need medicine to help their heart and lungs work better, such as:

• This medicine helps the heart pump better.
• This medicine helps the kidneys remove extra fluid from the body.
• ACE (angiotensin-converting enzyme) inhibitors. These medicines make it easier for the heart to pump blood to the body.

Nutrition

Babies may become tired when feeding. This may stop them from eating enough to gain weight. Your child may need:

• High-calorie formula or breastmilk. Your child may need special nutritional supplements added to his or her formula or pumped breastmilk.
• Supplemental tube feedings. Your child may need to be fed through a tube. This small, flexible tube passes through the nose, down into the esophagus, and into the stomach. Your child may have tube feedings in addition to or instead of formula or breastmilk.

Infection control

Children with heart problems are at risk for infections of the lining of the heart and heart valves (bacterial endocarditis). Make sure that you tell all of your child’s healthcare providers that your child has an AV canal defect. Your child may need to take antibiotics before medical tests or procedures to prevent infections.

Surgery

Your child will need surgery to repair the septal openings and heart valves. This is done to stop his or her lungs from becoming damaged further. Your child’s heart doctor will decide when the best time for surgery is. After the surgery, your child’s heart doctor may give him or her antibiotics. This is to prevent infections after he or she leaves the hospital.

Most children have surgery by the age of 6 months. Children with Down syndrome may develop lung problems earlier, and may need to have surgery at a younger age.

Support Care

Babies with AVSD may have slower growth and harder time eating. A high calorie diet may be recommended. These babies also have a higher risk of severe infections. Respiratory or lung infections will be treated very carefully.

Some will need to have activity limits as they get older. This is more common if valves can not be fully repaired and blood flow is still mixed.

Long Term Care

Your baby will be watched throughout their life. Problems can happen as they get older. Watching them on a regular basis will let their doctor treat problems as they come up. This may involve:

• A yearly exam with a heart specialist
• Regular tests of heart function
• Changes to treatment plan

Prevention of atrioventricular canal defect

There is no way to prevent AVCD since the cause is unknown. 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.