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Atrioventricular Canal Defects

09/07/2023 Conditions

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Overview

Atrioventricular (AV) canal defects are congenital heart defects, meaning they are present at birth. The condition occurs when the heart doesn’t form correctly during fetal development. It is often associated with Down syndrome. It can be associated with other heart abnormalities as well.

Normally, the right and left sides of the heart are separated by walls, known as a septum. An atrioventricular canal defect is a hole between these walls. These holes allow blood from each side of the heart (oxygen-rich and oxygen-poor) to mix together.

In addition, the tricuspid valve (right side of the heart) and mitral valve (left side of the heart) that control the flow of blood between the upper and lower chambers of the heart often are not formed correctly, causing them to leak. In many cases instead of two valves there is only a single common valve leading from the upper chambers into the bottom chambers of the heart (known as a common AV valve).  As a result of these defects, excess blood flows to the lungs, causing the heart and lungs to work harder than normal. Untreated, an infant with an AV canal defect may have rapid breathing and difficulty growing. Surgery is typically performed during infancy to correct the defects.

Other names used for these defects include: AV canal defect, AVC defect, atrioventricular septal defect (AVSD) and endocardial cushion defect.

Two Types of Atrioventricular Canal Defects

Atrioventricular canal defects may be “complete” or “partial,” depending on the structural abnormalities.  

  • A complete atrioventricular canal defect is the most severe form of this condition. Babies with this condition have a large hole in the center of the heart, resulting in mixing of blood between the upper and lower chambers of the heart. Additionally, instead of having two separate valves leading from the upper chambers to the lower chambers, one on the left side and one on the right, the baby has one large common valve that may not function correctly. 

Complete atrioventricular canal defects can be balanced or unbalanced. A balanced atrioventricular canal defect means that the single, large valve in the middle of the heart opens equally into both pumping chambers. Unbalanced atrioventricular canal defect means that the single, large valve in the middle of the heart opens preferentially into one of the pumping chambers. In this situation, one of the pumping chambers may be too small to pump blood effectively.

Complete atrioventricular canal defects can be associated with other heart defects that may complicate the care of the baby.

  • A partial (or incomplete) atrioventricular canal defect is a hole in the wall between either the upper or lower chambers of the heart (typically the upper chambers). One of the heart valves, usually the left-sided valve, may also be malformed, preventing it from functioning normally.

How does an atrioventricular canal defect affect my baby?

The hole in the wall between the two sides of the heart allows the blood from each side to mix together (oxygen-rich and oxygen-poor). Too much blood gets pumped to the lungs, causing the lungs to become congested. The lung congestion can cause the babies to tire out while feeding, breathe fast, or have poor weight gain. If the defect is left untreated for too long, the vessels in the lungs can be damaged irreversibly.

Surgery is typically performed within the first year of life to repair the defect. For newborns with a complete atrioventricular canal defect, surgery within the first 3-6 months may be necessary.  

Cause and Risk Factors

Atrioventricular canal defects are rare. The condition is estimated to affect 1 out of every 2,000 to 5,000 babies.

The cause is typically unknown. The condition occurs in the first eight weeks of fetal development as the heart is forming. The tissues that form the septum don’t completely grow together, leaving a hole in the wall. The heart valves also don’t form properly.

Factors that may increase the risk of an AV canal defect include:

  • German measles (rubella) in the mother early in pregnancy
  • Alcohol or tobacco use during pregnancy
  • Uncontrolled diabetes in the mother during pregnancy
  • Certain medications taken during pregnancy
  • Having a parent who had a congenital heart defect
  • Having a genetic abnormality such as Down syndrome (trisomy 21)

Testing and Diagnosis

An atrioventricular canal defect may be detected during a routine prenatal ultrasound. Additional testing, including fetal echocardiography, is typically needed to confirm the diagnosis and learn more about the defect.

In other cases, atrioventricular canal defect may not be diagnosed until after the baby is born. The doctor may detect a heart murmur, an abnormal sound caused by blood flow problems in the heart. Other symptoms may include difficulty breathing, fatigue, poor feeding and weight gain, pale or bluish skin, sweating, an irregular heartbeat, and swelling (edema).

In mild cases of partial atrioventricular canal defect, symptoms might not appear until early adulthood when complications occur.

Testing may include a chest x-ray, an electrocardiogram (EKG), and echocardiogram of the baby’s heart.

Specialized Evaluation and Prenatal Care

If the defect is suspected or diagnosed during pregnancy, prompt referral to a fetal cardiac center is important for further evaluation and to ensure proper delivery and treatment planning.

At Texas Children’s Fetal Center, we arrange for you to visit for a comprehensive assessment by a team of specialists experienced in the diagnosis and treatment of congenital heart defects, including maternal-fetal medicine physicians (high-risk OB/GYNs), fetal cardiologists, fetal imaging experts, geneticists and pediatric cardiologists.

Additional testing may include:

Our specialists will then meet with you about the results, discuss treatment recommendations, and answer any questions your family has, to help you make the most informed decisions regarding your baby’s care and treatment.

During pregnancy, mother and baby will be closely monitored for early detection of complications, including fetal non-immune hydrops which can develop if there is severe leaking of the heart valves, an abnormal heart beat, or if the pumping chambers of the heart become weak.

Delivery

For the best possible outcomes, delivery should take place at a center with the highest quality congenital heart program, ensuring the expertise and resources required to treat babies with these complex defects, including an advanced neonatal intensive care unit (NICU) or cardiac intensive care unit (CICU) if needed.

Delivery and postnatal care should be carefully planned and coordinated. Our Fetal Center team works closely with Texas Children’s Heart Center, seamlessly transitioning your baby’s care at delivery to this national leader in pediatric cardiology and heart surgery. Here, the pediatric specialists treating your child have been an integral part of their care team since before birth.

Following delivery at Texas Children’s Pavilion for Women, newborns with atrioventricular canal defect and no other associated heart defects receive a complete initial assessment by a newborn medicine specialist and cardiologist in the NICU. The baby will be watched closely to make sure he/she is feeding well and breathing normally prior to being discharged from the hospital. Babies that go home will have routine check-ups with a pediatric cardiologist to monitor the infant before surgery is performed.

Babies with the unbalanced form of complete atrioventricular septal defect, other associated heart defects or medical conditions, or that require assistance with breathing or feeding may remain in the hospital for a longer period of time. In some cases, these babies may need to remain hospitalized until heart surgery is performed.

Surgery After Birth

Surgery is required after birth to repair the atrioventricular canal defect. Surgery is typically recommended within the first year of life. In some cases, the condition may be managed with medications until the baby is big enough for surgery.

A permanent patch will be sewn over the holes between the upper and lower chambers of the heart. As the child grows, heart tissue will grow and cover the patch. For babies with complete atrioventricular canal defect, the large single valve will be reconstructed to form two separate valves.  Malformed valves will be repaired or replaced.

Children born with an atrioventricular canal defect require lifelong follow-up care by a cardiologist experienced in congenital heart conditions, to monitor for any complications.

At Texas Children’s Heart Center, our pediatric cardiologists will follow your child through adolescence, seamlessly transitioning their care at adulthood to a cardiologist who specializes in the treatment of adults with congenital heart defects.  

Your baby’s postnatal care team may include:

Why Texas Children’s Fetal Center?

  • A single location for expert maternal, fetal and pediatric care. Texas Children’s Hospital offers mothers and babies the specialized care required for the diagnosis and treatment of congenital heart conditions all in one location, for highly coordinated care and treatment planning.
  • A skilled, experienced team with proven outcomes. We have a dedicated team of maternal-fetal medicine specialists, fetal imaging experts, fetal and pediatric cardiologists, congenital heart surgeons, neonatologists and others who work in concert to care for you and your baby every step of the way, using proven protocols we’ve developed over the years. With their combined expertise and unified approach, this team offers the best possible care for pregnancies involving atrioventricular canal defects.
  • We care for your child’s cardiac needs at every stage of life, from fetus to adulthood. Our comprehensive approach starts with your first prenatal visit and continues through delivery, postnatal care, childhood and adulthood, thanks to one of the nation’s leading teams of fetal, pediatric and adult congenital heart specialists.

Texas Children’s – #1 in the Nation for Pediatric Cardiology and Heart Surgery

Our Fetal Cardiology Program is a collaboration between Texas Children’s Fetal Center and Texas Children’s Heart Center, ranked #1 in the nation for pediatric cardiology and heart surgery by U.S. News & World Report for consecutive years, with outcomes among the best in the country.

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Research and Clinical Trials

Texas Children’s, together with our partner institution Baylor College of Medicine, constantly strives to seek new and better treatments for babies with congenital heart defects.

For more information, please contact the Cardiovascular Clinical Research Core at 832-826-2064 or email sandrea@texaschildrens.org.

Learn more about our fetal cardiology research.

For more information or to schedule an appointment,

call Texas Children’s Fetal Center at 832-822-2229 or 1-877-FetalRx (338-2579) toll-free.

Our phones are answered 24/7. Immediate appointments are often available.