Atrioventricular Septal Defect or AV Canal (AVSD)

An atrioventricular septal defect (AVSD) is a heart defect in which there are holes between the chambers of the right and left sides of the heart, and the valves that control the flow of blood between these chambers may not be formed correctly.

This condition is also called atrioventricular canal (AV canal) defect or endocardial cushion defect. In AVSD, blood flows where it normally should not go. The blood may also have a lower than normal amount of oxygen, and extra blood can flow to the lungs. This extra blood being pumped into the lungs forces the heart and lungs to work hard and may lead to congestive heart failure.

Atrioventricular septal defect was previously known as “common atrioventricular canal” (CAVC) or “endocardial cushion defect” and are a relatively common family of congenital heart defects.

Antrioventricular septal defects is characterised by a deficiency of the atrioventricular septum of the heart. They account for about 5 percent of all congenital heart disease, and are most common in infants with Down syndrome. (About 15 percent to 20 percent of newborns with Down syndrome have an atrioventricular septal defects). Forty-five percent of children with Down syndrome have congenital heart disease. Of these, 35–40% have AV septal defects.

Atrioventricular septal defect (AVSD) or atrioventricular canal defect (AVCD), previously known as “common atrioventricular canal” (CAVC) or “endocardial cushion defect” (ECD), is characterized by a deficiency of the atrioventricular septum of the heart.

It is caused by an abnormal or inadequate fusion of the superior and inferior endocardial cushions with the mid portion of the atrial septum and the muscular portion of the ventricular septum.

• Atrioventricular means ‘of the atria and the ventricles’ – the four chambers of the heart.
• Septal means ‘of the septum’ – the wall between the left and right sides of the heart.
• Defect refers to a hole.

So Atrioventricular Septal Defect means there is a hole between the atria and between the ventricles.

In a normal heart there is a mitral valve between the left atrium and ventricle and a tricuspid valve between the right atrium and ventricle.

The blood on the left side of the heart is at higher pressure than the blood on the right side of the heart. This means that oxygenated blood flows from the left side of the heart, through the holes and mixes with the deoxygenated blood on the right side of the heart. The result is that there is too much blood on the right hand side of the heart. This blood then has to flow at high pressure into the pulmonary artery towards the lungs.

The one atrioventricular valve often leaks either into the left or right atrium or both. This makes the heart less efficient than normal so it has to work harder to function.

AVSDs can also be ‘partial’ or ‘intermediate’. In a partial AVSD there is only a hole between the atriums and there are two valves, although the mitral valve is deformed and often leaky. In an intermediate AVSD there is a small hole between the ventricles.

What is an atrioventricular septal or AV canal defect?

Atrioventricular septal defect (AVSD), or AV canal, is a heart defect that involves the valves between the heart’s upper and lower chambers and the walls between the chambers. Other terms used to describe this problem include endocardial cushion defect and AV canal defect.

A similar but less serious form of atrioventricular septal defect is called primum atrial septal defect or incomplete or partial atrioventricular septal defect. The cause of atrioventricular septal defect is not known. Overall it is quite rare and accounts for 4% of heart defects diagnosed in children. However, it is quite common in children with Down syndrome and occurs in about 25% of these children.

chambers are called the atria and the lower chambers are called the ventricles. The wall between the upper chambers is called the atrial septum and the wall between the lower chambers is called the ventricular septum. In the normal heart, the valve between the right atrium and right ventricle is called the tricuspid valve and the valve between the left atrium and the left ventricle is called the mitral valve. In children with AVSD, the tricuspid and mitral valves do not develop normally which then affects the growth of the atrial and ventricular septum.

Most of the time, there is one “common” valve separating the hearts upper and lower chambers (1) instead of two separate valves. In addition, there is a hole in the atrial septum (2) called an atrial septal defect and a hole in the ventricular septum (3) called a ventricular septal defect. In primum atrial septal defect, there are two separate valves between the upper and lower heart chambers but they are not entirely normal and there is an atrial septal defect.

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

Complete AVSD

A complete AVSD 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 AVSD 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 AVSD

A partial or incomplete AVSD occurs when the heart has some, but not all of the defects of a complete AVSD. There is usually a hole in the atrial wall or in the ventricular wall near the center of the heart. A partial AVSD 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.

Formation of Atrioventricular Septal Defect

A normal heart during development develops a septum or partition and two valves that separate the upper atrium from the lower ventricle and also separates the heart into four chambers but with atrioventricular septal defect this does not occur because the septum has not developed properly. Hence, the primary defect being the failure of formation of the part of the heart that arises from an embryonic structure known as the endocardial cushions.

The endocardial cushions are responsible for separating the central parts of the heart near the tricuspid and mitral valves (AV valves), which separate the atria from the ventricles. The structures that develop from the endocardial cushions include the lower part of the atrial septum (wall that divides the right atrium from the left atrium) and the ventricular septum (wall that divides the right ventricle from the left ventricle) just below the tricuspid and mitral valves.

The endocardial cushions also complete the separation of the mitral and tricuspid valves by dividing the single valve between the embryonic atria and ventricles. An atrioventricular septal defect may involve failure of formation of any or all of these structures.

There are several types of AV canal defects, the most severe being the Complete AV Septal Defect, where there is only one common AV valve over a large hole between all four chambers of the heart. All four chambers mix blood and there is typically a large amount of blood going to the lungs. Both ventricles have to pump harder and pulmonary hypertension (high blood pressure in the lungs) develops over time. Heart failure and poor growth are common findings.

Classification

A variety of different classifications have been used, but the defects are usefully divided into “partial” and “complete” forms.

In the partial AVSD, there is a defect in the primum or inferior part of the atrial septum but no direct intraventricular communication (ostium primum defect).

In the complete AVSD (CAVSD), there is a large ventricular component beneath either or both the superior or inferior bridging leaflets of the AV valve. The defect involves the whole area of the junction of the upper and lower chambers of the heart, i.e. where the atria join the ventricles. There is a large hole between the lower portion of the atria and the upper or `inlet’ portion of the ventricles and this is associated with a significant abnormality of the valves separating the atria from the ventricles.

 The valves in effect become a common atrio-ventricular valve, and the severity of the defect depends largely on the supporting attachments of the valve to the ventricles and whether the valve allows dominant flow from the right atrium to right ventricle and from left atrium to left ventricle (“unbalanced” flow). The overall problems are similar to those of VSD but are more complicated.

There is an increased flow of blood to the lungs through both the ventricular and atrial components of the defect. In addition, the abnormal atrio-ventricular valve invariably leaks, so that when the ventricles contract, blood flows not only forwards to the body and the lungs, but also backwards into the atria.

The back-pressure effect on the atria causes congestion of blood in the left atrium in particular, and this in turn causes congestion in the veins draining the lungs. The effect on the baby is to worsen the heart failure that is associated with an isolated VSD and to hasten the onset of pulmonary hypertension. It should be mentioned that CAVSD is found in approximately one-third of babies who have Down syndrome, but it also occurs as an isolated abnormality.

Causes and Risk Factors

The causes of congenital heart defects, such as AVSD, among most babies are unknown. Some babies have heart defects because of changes in their genes or chromosomes. In particular, AVSD is common in babies with Down syndrome, a genetic condition that involves an extra chromosome 21 (also called trisomy 21).

Congenital heart defects are also thought to be caused by the combination of genes and other factors that might increase the risk of having a baby with a congenital heart defect, such as things the mother comes in contact with in her environment, what she eats or drinks, or certain medications she uses during pregnancy.

Diagnosis

AVSD can be diagnosed before birth during a pre-natal scan. AVSD’s are common in children with Down Syndrome. Therefore, if your child has Down’s Syndrome, his or her heart may have been examined to check for an AVSD. If your child’s heart condition is very complex the AVSD may be just one of a number of defects.

After they are born, babies with AVSD may have a bluish tint to their skin and they may be breathless and have problems feeding. Feeding problems can mean that the baby has difficulty putting on weight and babies with AVSD are also prone to chest infections.

Babies and children with AVSD will also have heart murmur. The murmur is the sound of the extra blood being pushed towards the lungs and leaking through the valve.

If your child has the partial or intermediate form of AVSD there may not be any symptoms early in life, other than a heart murmur.

When a heart murmur is heard the tests used can be:

• pulse, blood pressure, temperature, and number of breaths a baby takes a minute
• listening with a stethoscope for changes in the heart sounds
• an oxygen saturation monitor to see how much oxygen is getting into the blood
• a chest x-ray to see the size and position of the heart
• an ECG (electrocardiogram) to check the electrical activity
• an ultrasound scan (echocardiogram) to see how the blood moves through the heart
• checks for chemical balance in blood and urine
• a catheter or Magnetic Resonance Imaging test may be needed

AVSD may be diagnosed during pregnancy or soon after the baby is born.

During Pregnancy

During pregnancy, there are screening tests (also called prenatal tests) to check for birth defects and other conditions. AVSD may be diagnosed during pregnancy with an ultrasound test (which creates pictures of the baby using sound waves), but whether or not the defect can be seen with the ultrasound test depends on the size or type (partial or complete) of the AVSD.

The healthcare provider can request a fetal echocardiogram to confirm the diagnosis if AVSD is suspected. A fetal echocardiogram is an ultrasound of the baby’s heart which shows more detail than the routine prenatal ultrasound test. The fetal echocardiogram can show problems with the structure of the heart and how well the heart is working.

After the Baby is Born

During a physical exam of an infant, a complete AVSD may be suspected. Using a stethoscope, a doctor will often hear a heart murmur (an abnormal “whooshing” sound caused by blood flowing through the abnormal hole). However, not all heart murmurs are present at birth. Babies with a complete AVSD usually do show signs of problems within the first few weeks after birth.

When symptoms do occur, they may include

• Breathing problems
• Pounding heart
• Weak pulse
• Ashen or bluish skin color
• Poor feeding, slow weight gain
• Tiring easily
• Swelling of the legs or belly

For partial AVSDs, if the holes between the chambers of the heart are not large, the signs and symptoms may not occur in the newborn or infancy periods. In these cases, people with a partial AVSD might not be diagnosed for years.

Symptoms which might indicate that a child’s complete AVSD or partial AVSD is getting worse include

• Arrhythmia, an abnormal heart rhythm. An arrhythmia can cause the heart to beat too fast, too slow, or erratically. When the heart does not beat properly, it can’t pump blood effectively.
• Congestive heart failure, when the heart cannot pump enough blood and oxygen to meet the needs of the body.
• Pulmonary hypertension, a type of high blood pressure that affects the arteries in the lungs and the right side of the heart.

The healthcare provider can request one or more tests to confirm the diagnosis of AVSD. The most common test is an echocardiogram. This is an ultrasound of the heart that can show problems with the structure of the heart, like holes between the chambers of the right and left side of the heart, and any irregular blood flow. An electrocardiogram (EKG), which measures the electrical activity of the heart, chest x-rays, and other medical tests may also be used to make the diagnosis. Because many babies with Down syndrome have an AVSD, all infants with Down syndrome should have an echocardiogram to look for an AVSD or other heart defects.

Symptoms

Symptoms include difficulty breathing (dyspnea) and bluish discoloration on skin and lips (cyanosis). A newborn baby will show signs of heart failure such as edema, fatigue, wheezing, sweating and irregular heartbeat.

Symptoms of babies with congestive heart failure usually develop gradually over the first 1-2 months of life are:

• breathe fast and hard,
• often sweat and / or tire out while feeding, and
• grow slowly or sometimes even lose weight.

A small number of infants with a complete atrioventricular septal defect will not develop congestive heart failure. This occurs because in some cases, the muscle cells that line the small arteries to the lungs get bigger and constrict to try to protect the lungs from the extra flow and high pressure caused by the atrioventricular septal defect. This is known as increased pulmonary vascular resistance (PVR) or pulmonary vascular disease and this condition is more common in infants with Down syndrome.

The increase in pulmonary vascular resistance is very effective in preventing the signs and symptoms of congestive heart failure by minimizing the amount of left-to-right shunt, and may even cause blood with low oxygen to go from the right ventricle to the left ventricle and out to the body without picking up oxygen. This causes cyanosis, which is a bluish discoloration of the skin, fingernails and mouth and it may also cause the murmur to be softer.

While infants with a complete atrioventricular septal defect and elevated pulmonary vascular resistance often grow better and appear healthier those with low pulmonary vascular resistance and congestive heart failure, the occurrence of increased pulmonary vascular resistance is an indication to proceed quickly with surgical correction of the defect.

What are the effects of this defect on my child’s health?

Atrioventricular septal defect is a serious heart problem that usually causes heart-related symptoms. Unlike some heart defects, the problem does not resolve with time and most children must undergo heart surgery. The good news is that this surgery is usually very successful and most children do very well.

There are some patients with primum atrial septal defect who do not require surgery because the valves have little or no leakage and the atrial septal defect is small. The effects from AVSD are caused by the holes in the heart walls and leakage from the abnormal valve. The holes allow blood in the heart’s left side (oxygenated or red blood that has returned from the lungs) to leak back to the heart’s right side.

This results in a large amount of blood that the right side of heart must pump again to the lungs. The heart has to work much harder than normal to pump enough blood out to the body because so much of it returns instead to the heart’s right side.

The workload is further increased by leakage of the heart valve. As a result of the extra workload, most babies with AVSD develop signs of congestive heart failure such as rapid breathing, feeding problems, slow weight gain, low energy, and cold, clammy sweating. These symptoms usually appear between 4 and 8 weeks of age but can occur earlier in some infants. Another possible health effect of AVSD is pulmonary artery hypertension. This problem develops more slowly and is caused by the extra pulmonary blood flow.

The pulmonary arteries that take blood from the heart’s right side to the lungs are not well suited to the increased pressure caused by the extra blood flow. Over time, if the problem is not corrected, the pulmonary arteries become thick and stiff which makes the heart have to work even harder.

This is a very serious problem with no effective treatment. For unknown reasons, children with Down syndrome are very prone to this problem so heart surgery is often done when the child is 4-6 months old.

Exercise recommendations: Exercise recommendations are best made by a patient’s doctor so that all relevant factors can be included in the decision. In general, exercise restrictions for patients with repaired atrioventricular septal defects are not necessary and children can participate in competitive and vigorous athletic activities. Children with Down syndrome have an increased incidence of a spine abnormality that necessitates some restrictions in activity.

Some of these problems can occur after surgery or later in life:

• It is common for the valves to leak a little. If this becomes severe, they may need to be repaired or even replaced with artificial valves.
• If an artificial valve is inserted then the child will need to take an anticoagulant medicine to stop blood clots forming.
• The electrical system of the heart is sometimes damaged during surgery. This can cause a slow heartbeat, called heart block. This may need to be corrected by giving the child a pacemaker.
• Some patients go on to develop sub-aortic stenosis, a blockage below the aortic valve, which may need to be repaired using open heart surgery.

Treatment

Treatment is surgical and involves closure of the atrial and ventricular septal defects and restoration of a competent left AV valve as far as is possible. Open surgical procedures require a heart-lung machine and are done with a median sternotomy. Surgical mortality for uncomplicated ostium primum defects in experienced centers is 2%; for uncomplicated cases of complete atrioventricular canal, 4% or less. Certain complications such as tetralogy of Fallot or highly unbalanced flow across the common AV valve can increase risk significantly.

All AVSDs, both partial and complete types, usually require surgery. During surgery, any holes in the chambers are closed using patches. If the mitral valve does not close completely, it is repaired or replaced. For a complete AVSD, the common valve is separated into two distinct valves – one on the right side and one on the left side.

The age at which surgery is done depends on the child’s health and the specific structure of the AVSD. If possible, surgery should be done before there is permanent damage to the lungs from too much blood being pumped to the lungs. Medication may be used to treat congestive heart failure, but it is only a short term measure until the infant is strong enough for surgery.

Infants who have surgical repairs for AVSD are not cured; they might have lifelong complications. The most common of these complications is a leaky mitral valve. This is when the mitral valve does not close all the way so that it allows blood to flow backwards through the valve. A leaky mitral valve can cause the heart to work harder to get enough blood to the rest of the body; a leaky mitral valve might have to be surgically repaired.

A child or adult with an AVSD will need regular follow-up visits with a cardiologist (a heart doctor) to monitor his or her progress, avoid complications, and check for other health conditions that might develop as the child gets older. With proper treatment, most babies with AVSD grow up to lead healthy, productive lives.

Infants born with AVSD are generally in sufficient health to not require immediate corrective surgery. If surgery is not required immediately after birth, the newborn will be closely monitored for the next several months, and the operation held-off until the first signs of lung distress or heart failure.

This gives the infant time to grow, increasing the size of, and thereby the ease of operation on, the heart, as well as the ease of recovery. Infants will generally require surgery within three to six months, however, they may be able to go up to two years before the operation becomes necessary, depending on the severity of the defect.

Once an AVSD is diagnosed the child will be carefully monitored to see when they need surgery. If the heart is not able to operate properly then parents may be told that their child is in ‘heart failure’. Symptoms of heart failure include the lungs and other organs becoming heavy or ‘wet’ with fluid. A careful check will be kept on the child’s weight as any increase can be due to fluid retention. To help get rid of the extra fluid the child may need special medicines called diuretics.

A complete AVSD causes pulmonary hypertension (high pressure of blood in the lung arteries), and an operation will need to be performed before the lungs are damaged. This operation is open heart surgery, which means that the heart will need to be stopped and opened to repair it. A heart bypass machine will take over the job that the heart normally does.

The aim of the operation is to make the circulation of blood through the heart and lungs normal. A patch is put over the holes between the atria and ventricles. The single atrioventricular valve is then divided to make two effective valves. If a child has other heart defects, the kind of surgery needed will depend on how the heart can best be modified to cope with all the problems he or she has.

For most children this surgery is low risk, but it can depend on how well your child is otherwise. The doctors will discuss risks with you in detail before asking you to consent to the operation. The length of time in hospital will usually be only 10 to 12 days, of which one or two will be spent in the intensive care and high dependency unit. Of course this depends on how well your child is before and after the surgery, and whether any complications arise.

If the surgery is straightforward, and your child does not have other health problems, he or she should be completely well shortly after surgery. There will be a scar down the middle of the chest, and there may be small scars where drain tubes were used. These fade very rapidly in most children, but they will not go altogether. Smaller scars on the hands and neck usually fade away to nothing.

How is the problem treated?

As described previously, surgery is almost always needed for children with AVSD. If possible, the surgery is delayed until the child is about 4 to 6 months of age to allow the child to grow. Before surgery, the goals of treatment are to control symptoms of congestive heart failure and to ensure adequate weight gain.

Giving the child heart medicines such as digoxin (Lanoxin), and furosemide (Lasix) may do this. Sometimes a medicine that maintains potassium levels called spironolactone (Aldactone) is used. Medicines that lower blood pressure like captopril are also sometimes used to decrease the work of the heart. To promote weight gain, richer formula or breast milk supplements are helpful since infants with congestive heart failure need more calories than other babies.

 If the baby is still unable to gain weight, surgery may be done earlier. Open-heart surgery is the mainstay of treatment for children with AVSD. The repair involves placement of one or two patches to divide the common valve into right and left sides and close the holes. This is performed after beginning heart/lung bypass to support the circulation during the repair itself.

Stitches are also placed in the valve to decrease valve leakage. The results for surgical repair are very good and 95% of patients do well without significant complications. Complications include abnormal heart rhythm and residual valve leakage.

Complications

When there are holes in the septum that divide the four chambers of the heart the oxygen-rich blood and oxygen-poor blood mix this creates more stress on the heart to pump blood to where oxygen is needed. As a result, you get enlargement of the heart, heart failure (being unable to adequately supply body with needed oxygen, pulmonary hypertension, and pneumonia.

The development of pulmonary hypertension is very serious. And this because the left ventricle is weakened due to its overuse. When this happens, the pressure backs up into the pulmonary veins and the lungs. This type of damage is irreversible which is why immediate treatment is recommended after diagnosis.

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