Facts about Atrioventricular Septal Defect (AVSD)
An atrioventricular septal defect (AVSD) is a birth defect of the heart in which there are holes between chambers of the heart, and the valves that control the flow of blood between these chambers may not be formed correctly. This means that blood flows where it normally should not be able to, and extra blood flows to the lungs. This defect is also known as atrioventricular canal (AV canal) defect or endocardial cushion defect.
There are two general types of AVSD that can occur, depending on which structures are not formed correctly:
- Complete AVSD
This occurs when there is a large opening in the center of the heart where the wall from the top of the heart (atrial septum) and the wall from the bottom of the heart (ventricular septum) would normally meet. This means there is a hole in both the atrial septum and the ventricular septum. Also, instead of blood flowing from the atria to the ventricles through a tricuspid valve on the right side of the heart and a mitral valve on the left side of the heart, there is one common valve in the middle of the heart. This valve has abnormal leaflets or flaps and often does not close tightly. These defects occur because during development, the walls between the chambers (septa) did not grow all the way into the middle of the heart, and the early common valve failed to separate into two distinct valves (tricuspid and mitral valves). A complete AVSD allows blood to flow between all four chambers through the central opening.
- Partial or Incomplete AVSD
This occurs when not all the defects of a complete AVSD occurred. There is usually a hole in the wall between the atria or a hole in the wall between the ventricles near the middle of the heart, but there are usually two valves between the atria and ventricles (not a common valve). However, with a partial AVSD, one of the valves (usually the mitral valve) does not close completely and allows blood to leak backward.
In a baby without a congenital heart defect, the right side of the heart pumps oxygen-poor blood from the heart to the lungs. The left side of the heart pumps oxygen-rich blood to the rest of the body.
In babies with a partial or complete AVSD, blood is able to cross from the left side of the heart back to the right side through the holes between the chambers of the heart. This results in blood of different oxygen levels mixing. It also increases the amount of blood that is pumped to the lungs. This extra blood being pumped into the lungs forces the heart and lungs to work hard and may lead to problems in the lungs. If not repaired, the AVSD may increase the risk for other problems, including congestive heart failure.
CDC estimates that each year about 2,000 babies in the United States are born with AVSD. In other words, about 1 out of every 2,120 babies born in the United States each year is born with some type of AVSD.1
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 (trisomy 21). Congenital heart defects are also thought to be caused by the combination of genes and other risk factors such as things the mother comes in contact with in her environment, or what the mother eats or drinks, or certain medications she uses during pregnancy.
AVSD may be diagnosed during pregnancy or soon after the baby is born.
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), but whether or not the defect can be seen with the ultrasound test depends on the size of the AVSD and if it’s a partial or complete AVSD. If the health care provider suspects that a baby may have an AVSD, the health care provider can request a fetal echocardiogram to confirm the diagnosis. 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 the heart is working with this defect.
After the Baby is Born
A complete AVSD is usually suspected after a physical exam of the infant. Using a stethoscope, a doctor will often hear a heart murmur (an abnormal “whooshing” sound caused by blood flowing through the abnormal hole). However, it is not uncommon for a heart murmur to be absent right at birth. Babies with a complete AVSD usually show signs of problems within the first few weeks after birth. Symptoms may include:
- Problems breathing
- Pounding heart
- Weak pulse
- Ashen or bluish skin color
- Poor feeding, poor weight gain
- Tiring easily
- Swollen legs or abdomen
However, for partial AVSDs, if the holes between the chambers of the heart are not particularly big, the signs and symptoms may not occur in the newborn or infancy periods. In these cases, people with a partial AVSD may not be diagnosed for years. Symptoms that may occur in people with partial AVSD include
- Arrhythmia, which is a problem with how the heart beats; in a person with an arrhythmia, the heart can beat too fast, too slow, or irregularly
- Congestive heart failure, which is when the heart cannot pump enough blood and oxygen to meet the needs of the body
- High blood pressure in the lungs
The health care 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 in the walls between the chambers, 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.
All AVSDs, both partial and complete types, usually require surgery. During surgery, any holes in the septa will be closed using patches. If the mitral valve does not close completely, it will be 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.
The age at which surgery is done depends on how sick the child is and the specific structure of the AVSD. If possible, surgery should be done before there is permanent damage 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 conditions is a leaky mitral valve. This is when the mitral valve doesn’t close all the way and allows blood to flow backwards through the valve. A leaky mitral valve can make the heart work harder to get enough blood to the rest of the body and 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 their progress, avoid complications, and check for other health conditions that might develop as they get older. With proper treatment, most babies with AVSD grow up to lead healthy, productive lives.
- Parker SE, Mai CT, Canfield MA, et al. for the National Birth Defects Prevention Network. Updated national birth prevalence estimates for selected birth defects in the United States, 2004-2006. Birth Defects Res A Clin Mol Teratol 2010;88:1008-1016.
Mitral Valve: The mitral valve is the valve that controls the flow of blood from the left atrium to the left ventricle.
Tricuspid Valve: The tricuspid valve is the valve that controls blood flow from the right atrium to the right ventricle.
Congestive Heart Failure: Congestive heart failure is when the heart cannot pump enough oxygen-rich blood to meet the needs of the body.
Genes: A gene is a part of DNA (the genetic instructions in all living things). People inherit one copy of each gene from their mother and one copy from their father. The genes that a person inherits from his or her parents can determine many things, like what a person will look like and whether the person might have certain diseases.
- Centers for Disease Control and Prevention
National Center on Birth Defects and Developmental Disabilities
Division of Birth Defects and Developmental Disabilities
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Atlanta, GA 30333
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