Pediatric Atrioventricular (AV) Canal Defect

An atrioventricular (AV) canal defect is a complicated heart defect, involving a large hole in the center of the heart, and oftentimes, defects in the valves that control blood flow through the heart. It is also known as an atrioventricular septal defect or an endocardial cushion defect.

Normally, the right side of the heart collects unoxygenated (blue) blood from the body in a thin-walled chamber called the right atrium. The blood then goes through a valve (which keeps blood flowing in one direction) into one of the main pumping chambers, called the right ventricle. Similarly, when oxygenated (red) blood returns from the lungs to the heart, it collects in the left atrium and goes through a valve into the other main pumping chamber, the left ventricle. The left ventricle pumps the oxygenated blood to the body. There is a wall between the two atria, called the atrial septum, and between the two ventricles, called the ventricular septum. The two valves that separate the two atria from the two ventricles are adjacent to each other.

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There is an area in the middle of the heart where the atrial septum, the two valves, and the ventricular septum come together. In children with an AV canal defect, that area is not formed properly, and the linings and valves may be affected. This causes blood flow to be compromised and inefficient, overworking the heart.

Most commonly, an atrioventricular canal defect is “complete,” with a large portion of the atrial and ventricular walls missing. In addition, the two valves that are adjacent to each other may merge, leaving one opening between all four chambers. It is possible to have an "incomplete" or “partial” defect, where only some of the area is properly formed and some is not.

The causes of heart conditions such as AV canal defect among most babies are unknown. Some babies have heart defects because of changes in their genes or chromosomes. A combination of environmental exposures and genetic factors are likely responsible, but little is known about the specific cause. A large number of patients with Down syndrome have AV Canal defects, although a number of children without Down syndrom will develop an AV Canal defect.

An AV canal defect may be diagnosed during pregnancy with a fetal echocardiogram, which is a specialized ultrasound of the fetal heart. The affiliated physicians in the Fetal Cardiology Program at The Fetal Center will confirm a diagnosis and prepare a delivery plan for both mom and baby. A multidisciplinary team of specialists will also develop the baby's immediate care plan following delivery.

If an AV canal defect is not diagnosed in utero, and suspicion of a heart defect occurs after the baby is born, a pediatrician will refer the patient to a pediatric cardiologist or neonatologist to determine the diagnosis.

Atrioventricular canal defect symptoms usually appear several weeks after birth. Infants may work harder to breathe and may fail to gain weight due to an overworked heart and excessive blood flow to their lungs. Excess sweating, pale or bluish skin, and the decreased ability to feed may also signal problems.

Doctors may observe the child’s troubled breathing and use a stethoscope to hear a heart murmur, often caused by the excess blood flow to the lungs. The following tests may be ordered to find more details:

• An echocardiogram (ECHO) uses sound waves (ultrasound) to produce images on a screen of the heart and blood vessels in action. These reveal whether the heart is pumping properly.
• An electrocardiogram (EKG or ECG), a painless exam, checks the heart’s electrical action to reveal damage or abnormal heartbeats, suggesting problems with the heart.
• Chest X-rays create images of the heart and lungs to reveal heart enlargement or excess blood flow to the lungs.
• A cardiac MRI (magnetic resonance imaging) uses radio waves, magnets and a computer to form three-dimensional images of the heart, which can reveal structural abnormalities.
• Cardiac catheterization involves a thin, long tube that is inserted into a blood vessel and guided into an artery or vein in the heart. Dye sometimes is injected to highlight the organ’s structure.

Surgery is needed for atrioventricular canal defect treatment and usually is performed at 3-8 months of age, with the timing depending on the severity of the child’s symptoms. An untreated AV canal defect can induce heart failure and high blood pressure in the lungs.

Atrioventricular canal defect surgery involves an up and down (vertical) incision in the middle of the chest. It is necessary to place the child on the heart-lung machine to provide blood flow to the rest of the body while the surgical team repairs the heart itself. During surgery, a patch is placed to separate the two atria and two ventricles from each other. This same patch also divides the two valves.

What Are the Long-Term Effects?

Most children do very well after surgery for AV canal defects. However, it is recognized that the surgery is complex and a small percentage of children after atrioventricular canal defect surgery will have problems, usually with the left-sided valve (the valve between the left atrium and left ventricle). Despite the repair, the valve is not truly normal and is prone to leaking. Approximately 10% of children who have a repair of an AV canal can expect to need further surgery at some time in their lives, usually to further repair the left-sided heart valve.

What Follow-Up Care Is Needed?

Patients who have an AV canal repaired will follow up with the surgeon about 2 weeks after discharge and will see their pediatric cardiologist 3-4 weeks after discharge. Activity is limited for 6-8 weeks after surgery due to the sternal bone healing, but after that time, there are little, if any, restrictions placed.

Lifelong follow up with a pediatric cardiologist is needed. Checkups generally are needed yearly. Also, antibiotics may be prescribed before dental surgery or other operations to decrease the risk of endocarditis, a bacterial infection of the heart’s lining. This is particularly true if the child’s original valve has been replaced with a mechanical valve, or the child has remaining heart defects after the original surgery.

Later in life, should a female patient hope to get pregnant, she should be evaluated by a cardiologist beforehand.

At Children’s Heart Institute at Children’s Memorial Hermann Hospital, patients with congenital or acquired heart disorders receive hands-on specialized care 24/7 from a team of affiliated physicians and specialty-trained nurses who aim to deliver the best possible outcomes.

Children’s Memorial Hermann Hospital was named one of the top children's hospitals nationally in Cardiology & Heart Surgery by U.S. News & World Report. In addition, Children’s Heart Institute is among the top congenital heart surgery programs in North America for patient care and outcomes, according to the Fall 2019 Society of Thoracic Surgeons (STS) Congenital Heart Surgery Database Report of 118 STS participating programs.

In collaboration with various subspecialties, the affiliated team provides comprehensive care for newborns, children and adolescents, with the ability to transition into adult congenital cardiac care. Team members have the experience and skills necessary to offer innovative treatment methods and specialized services, including, but not limited to:

• Biventricular repairs and biventricular conversions
• Congenital heart optimization
• Full repairs for complex congenital heart defects in newborns
• Hybrid catheterization and surgical procedures
• Minimally invasive transcatheter pulmonary valve (TPV) therapy
• Minimally invasive repairs
• Treatment for adult congenital heart disease
• Valve repairs and preservation

With the Level IV Neonatal Intensive Care Unit (NICU) and a dedicated Children’s Heart Institute Intensive Care Unit at Children’s Memorial Hermann Hospital, critical heart patients have access to quality, specialized care. By utilizing state-of-the-art techniques, the team at Children’s Heart Institute strives to offer patients with the most complex problems the greatest opportunity for a normal life.

If you have any questions, use the online tool below to help us connect with you. To refer a patient or schedule an appointment, please contact our clinic using the information below.

• Pediatric Cardiology Clinic
  The University of Texas Health Science Center Professional Building
  6410 Fannin, Suite 370
  Houston, TX 77030
  Phone: (713) 486-6755 (Appointment Line)
   
• Pediatric and Congenital Heart Surgery Clinic
  The University of Texas Health Science Center Professional Building
  6410 Fannin, Suite 370
  Houston, TX 77030
  Phone: (713) 500-5746
  CMHH-Heart@memorialhermann.org

The Children’s Heart Institute is a collaboration between the affiliated physicians at McGovern Medical School at UTHealth Houston and Children’s Memorial Hermann Hospital. Typically, patients are seen on an outpatient basis at a UT Physicians clinic with all inpatient procedures performed at Children’s Memorial Hermann Hospital.