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What is an 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.

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 AV 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.


What are the causes?

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's syndrome have AV Canal defects, although a number of children without Down's will develop an AV Canal defect.

How is it diagnosed?

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.

Symptoms for an AV canal defect 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.

How is it treated?

Surgery for an AV canal defect is needed 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.

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 AV canal 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 percent 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.

Why choose the Children’s Heart Program?

As part of the Children’s Heart Program at Children’s Memorial Hermann Hospital, the affiliated cardiologists and affiliated cardiovascular surgeons collaborate as a multidisciplinary team to treat babies prior to birth, infants, children and young adults with congenital and acquired heart disorders.  The team of affiliated physicians, nurses and coordinators work together with you to determine the best treatment plan for your child.  Your child’s referring physician is also kept fully informed of your child’s treatment plan. 

At Children’s Memorial Hermann Hospital, the affiliated cardiologists and affiliated cardiovascular surgeons understand the unique challenges, circumstances and intricacies of caring for young patients with heart conditions. In addition to the team’s medical expertise, Children’s Memorial Hermann Hospital provides families with patient-centered care, keeping families fully involved as part of the child’s treatment team as well as offering resources to meet the needs of your entire family.

Contacts

Pediatric Cardiology Clinic
The University of Texas Health Science Center Professional Building
6410 Fannin, Suite 370
Houston, TX 77030

Phone: (832) 325-6516

Pediatric Cardiovascular Surgery Clinic
The University of Texas Health Science Center Professional Building
6410 Fannin, Suite 950
Houston, TX 77030

Clinic Phone: 832-325-7234

Nurse Line: 713-500-7324

Note: This page is meant to be a helpful, informative introduction on the subject of AV canal defects in children. The information may not be applicable to all cases, especially if there are additional defects. It is not meant to replace the opinion of a personal physician.

03/2016 – This page was updated and approved by an affiliated pediatric physician at the Children’s Heart Program.