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Atrioventricular Canal Defect
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Children’s heart conditions can’t be prevented, but a lot can be done to improve and often completely repair their hearts at any age. Thanks to advanced technology and the pediatric heart experts at the Nemours Cardiac Center (based at Nemours/Alfred I. duPont Hospital for Children), most children born with a heart problem — even newborns only hours or days old — can be quickly diagnosed and treated right when it matters the most. At the Cardiac Center, we specialize in early detection and repair of congenital heart defects (also often called, “congenital heart disease”).
If your child’s been diagnosed with an atrioventricular canal defect, we’re here to ease your concerns, answer your questions, and give your child the best possible chance for a healthy future.
Atrioventricular canal defect (also known as “complete atrioventricular canal defect,” “complete atrioventricular septal defect” or a “common atrioventricular valve”) is a:
- lack of separation of the atria (the top two chambers of the heart) and the ventricles (the heart’s two lower chambers that receive blood from the atria) into separate right and left chambers
- lack of separation between the mitral and tricuspid valves (The mitral valve is the valve between the left atrium and the left ventricle. Consisting of two flaps, or “cusps,” it prevents blood from flowing back into the atrium from the ventricle. The tricuspid valve is the heart valve that controls blood flow from the right atrium into the right ventricle.)
The lack of separation of these two valves results in a single or “common” atrioventricular valve. The lack of separation of the atria results in a hole between the upper chambers of the heart (called an “atrial septal defect”), and the lack of separation of the ventricles results in a hole between the lower chambers of the heart (called a “ventricular septal defect”). Atrioventricular canal defects are also sometimes called “endocardial cushion defects,” because in the developing heart it’s the endocardial cushions that usually create the separation between the various chambers and valves.
In children with atrioventricular canal defect, the single atrioventricular may not close properly, resulting in leakage of that valve (called “atrioventricular valve regurgitation”). The atrioventricular valve and the ventricles also may be “unbalanced” — meaning, they’re not evenly divided between the left and the right.
Effects of an Atrioventricular Canal Defect
The lack of separation between the two sides of the heart in atrioventricular canal defects results in blood moving from the left side of the heart (which pumps blood out to the body) into the right side of the heart (where it’s pumped to the lungs).
This causes too much blood flow to the lungs and two main problems:
- The excess blood has to be pumped again by the heart to make it out to the body, which forces the heart to work harder than it should.
- The blood vessels in the lungs respond to the excess blood flow by tightening, which — if left untreated — may cause high blood pressure in the lungs (this is called “pulmonary hypertension”). The amount of blood moving from the left ventricle to the right ventricle and then to the lungs is determined by the size of the holes between the left and right side (the atrial septal defect and ventricular septal defect). A larger hole will allow more blood flow and will cause symptoms sooner, and the size of the ventricular septal defect is most important.
Types of Atrioventricular Canal or Atrioventricular Septal Defects
Because of this, atrioventricular canal defects are divided into categories, depending on the presence and size of the hole between the lower chambers of the heart (the ventricular septal defect, or “VSD”):
- Partial AV canal (primum ASD). When there’s no VSD (or when the VSD closes by itself), it’s called a “partial AV canal defect.” In these cases there’s a hole between the upper chambers of the heart. There’s also an abnormal atrioventricular valve. But without the hole between the lower chambers, the surgical repair is simpler and the long-term outcomes are better.
- Transitional AV canal. When the VSD is small and limits the amount of blood able to move across it (called “restrictive”) the defect is called a “transitional AV canal defect.” Because the small VSD limits the amount of blood flow between the ventricles (and, therefore, the extra work that the ventricle must do), children with transitional AV canals may take longer to develop symptoms.
- Complete AV canal. When the VSD is large and doesn’t restrict blood flow then the atrioventricular canal is called a “complete AV canal defect.” In these cases, symptoms usually develop early (within the first few months after birth).
How Does the Heart Normally Work?
When your child has a congenital heart defect, there’s usually something wrong with the structure of the heart. In order to understand your child’s condition, it can help to know how the heart should work normally.
Learn More About Normal Cardiac Anatomy »
Nemours’ experts at KidsHealth.org also offer these helpful resources to help both you and your child understand how the heart works:
Our Nemours Cardiac Center team can diagnose atrioventricular canal in utero (in the womb) during a fetal echocardiogram (“echo”). Or the defect may be diagnosed after birth due to either a murmur or signs of heart failure.
The murmur results from blood moving through the atrial septal defect (ASD) and ventricular septal defect (VSD), and sometimes from atrioventricular valve regurgitation. The movement of blood across the ASD and VSD and the leakage of the valve cause the heart to have to pump extra amounts of blood. This may cause the heart to become enlarged, or may lead to signs that the heart is struggling, including poor growth, rapid breathing and rapid heart rate. We can confirm the diagnosis with an echocardiogram (or “echo”) — a completely safe and painless test that uses ultrasound (sound waves) to build a series of pictures of the heart.
A baby with complete atrioventricular canal defect will need to have surgery within the first two to six months after birth.
Usually, the operation involves:
- carefully separating the single atrioventricular valve into two valves, including repairing the valve to correct any leakage
- sewing a patch (or patches) over the atrial septal defect (ASD) and ventricular septal defect (VSD)
Surgery may be delayed longer in children with either a transitional or partial AV canal. But all children will need surgery to repair the defect.
In children with an “unbalanced” atrioventricular canal, one of the ventricles may not be large enough to support this type of repair and the child may require a series of procedures, over time, called “single ventricle palliation.”
Following surgery, the blood flows normally through the heart, and the excessive amount of blood being pumped by the ventricles is reduced. Most children won’t need additional operations or have any activity limitations. But, as children grow, the abnormal atrioventricular valve may not grow appropriately — and, over time, this may cause either leakage or obstruction (“stenosis”) of either the left or right side of the valve. The most common reason for another operation, this happens in about 10–20 percent of children after repair of a complete atrioventricular septal defect.
Also, because of the abnormal structure of the heart, children with partial atrioventricular septal defect are at risk for developing left ventricular outflow tract obstruction or subvalvar aortic stenosis in the years following surgery. For these reasons, after repair, we routinely monitor children with atrioventricular canal defects using an echocardiogram to monitor valve function and growth.
If your child has atrioventricular canal defect, know that at the Nemours Cardiac Center we’re here to give your child the very best, most comprehensive and compassionate care. Our goal is to guide your family, from start to finish, through your child’s heart defect journey — and to help your child live the healthiest, most fulfilling life possible.
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