Atrioventricular septal defect (AVSD)

What is an atrioventricular septal defect?

Atrioventricular septal defect (AVSD) refers to any abnormal development of the endocardial cushions. These cushions control the separation of the parts of the heart near the tricuspid and mitral valves. It is also referred to as an atrioventricular canal defect or an AV canal defect.

AVSD in children involves the lungs overfilling with blood, potentially causing leakage. AVSD is common, accounting for about 5% of all types of congenital heart disease. AVSD is the most common heart diagnosis in children with Down syndrome and can also occur with other genetic syndromes or in isolation. It can also occur with other types of congenital heart disease like coarctation of the aorta or tetralogy of Fallot.

In AVSD, the atria and ventricles have not separated into their own chambers and the mitral and tricuspid valves have also not separated. As a result, there is a large hole between the two atria and the two ventricles, and one single atrioventricular valve instead of separate mitral and tricuspid valves.

AVSD is usually divided into three types:

• complete
• partial
• transitional

A complete AVSD, which is the most severe type, involves defects in all the parts of the heart controlled by the endocardial cushions. This means there are holes in the atrial septum and the ventricular septum, which results in an undivided AV valve.

Signs and symptoms of AVSD

Depending on the type of AVSD, the already oxygenated blood may be recirculated to the lungs, which is inefficient. The left ventricle also tends to have to work harder, which increases pressure to the lungs. This can cause the lungs to overfill with blood, potentially causing it to leak into the air around the lungs. This is called pulmonary edema and can lead to congestive heart failure.

How is AVSD diagnosed?

AVSD is usually identified through a heart murmur. Diagnosis is confirmed by doing an echocardiogram, and possibly a chest X-ray or electrocardiogram. Children with AVSD are often diagnosed within a week or two of birth.

How is AVSD treated?

AVSD is initially treated with medications to help heart function and reduce pulmonary edema. Nutritional support is often needed as children with congestive heart failure require more calories to gain weight and grow.

Rarely, children with AVSD require pulmonary artery banding to help reduce blood flow to the lungs.

Once children with AVSD are old enough, they undergo corrective surgery. Surgery can use patches to close the holes in the atrial septum or the ventricular septum and reconstruct the atrioventricular valve. Timing of surgery is usually in the first few months of life for complete AVSD but is often a little later for partial and transitional AVSD.

What is the long-term outlook for children with AVSD?

The outlook is very good following surgery. A leaky mitral valve is a rare complication that may require re-operation.