Atrioventricular Septal Defect

Definition

Atrioventricular (AV) septal defects comprise a range of malformations characterized by varying degrees of incomplete development of the inferior portion of the atrial septum, the inferior portion of the ventricular septum, and the AV valves.

These anomalies have also been called endocardial cushion defects and AV septal defects.

Description

The basic defect is a deficiency of the AV septum which separates the left ventricular inlet from the right atrium. It causes anomalies that range in severity from a small ostium primum atrial septal defect to a complete AV septum, which also involves defects in the interventricular septum and the mitral and tricuspid valves.

The atrial septum forms during the embryonic development of the heart. Defects may develop at a number of locations in the wall.

Most commonly the defect involves the foramen ovale, an oval-shaped hole in the wall that is present in all children during the fetal period but closes spontaneously soon after birth. If the foramen ovale is larger than it should be or if the flap of tissue that usually closes it is displaced or deficient, the hole may remain after birth.

Perhaps 25 percent or more of atrial septal defects diagnosed incidentally, because a murmur is heard, or through echocardiography done during infancy, will close spontaneously.

When the child reaches 2 or 3 years of age, most atrial defects that are producing clinical signs (enlarged right heart, substantially increased pulmonary blood flow), although not necessarily symptoms, should be repaired.

An atrioventricular septal defect (canal defect) is usually quite complex, and can be partial or complete.

The complete defect, which is more comon, involves the portion of the heart where that atrial septum (the wall vertically dividing the heart's upper chambers) meets the ventricular septum (separating the heart's lower chambers), as well as the valves - mitral and tricuspid - that divide these chambers horizontally.

Partial defects involve only the lower portion of the atrial septum (called ostium primum atrial septal defect and usually associated with a mitral valve defect) or, rarely, may involve only the ventricular septum, with or without a mitral valve abnormality.

The effect of the complete canal defect is a large hole spanning both the upper and lower parts of the septum and the presence, in place of two discrete mitral and tricuspid valves, of one large valve that spans both sides of the defect.

The defect is compounded by the fact that this rudimentary valve does not always close properly, so that some of the blood flows back, or regurgitates, into one of the upper chambers.

These effects result in an excessive amount of blood flowing to the lungs (a large left-to-right shunt) early in life, which produces severe symptoms of congestion and pulmonary hypertension.

Infants with this congenital defect are often emaciated because of the hard work required to breathe and consequent inability to take adequate nourishment.

Causes and Risk Factors

Atrial septal defect is often associated with Down syndrome. Approximately 25 percent of children born with this syndrome have the defect, while approximately 50 percent of children with the defect have Down syndrome.

The evidence suggests that one or more genes responsible for heart development may be found on chromosome 21. Several candidate genes are being currently investigated.

On the other hand, ASD can occur in children with no other genetic abnormality.

Symptoms

In most patients with atrial septal defects, symptoms are rare during childhood. While children with large atrial left-to-right shunts are often thin, neither respiratory symptoms nor severe growth failure is common. If anything, there may be a heart murmur, but it may not be evident until the child's second year. In itself, the murmur is not a problem, but it should be monitored periodically.

Diagnosis

The diagnosis of ASD is often made incidentally in the course of a routine physical examination of a child. In other situations, the child will be demonstrating symptoms of heart failure.

In all cases, the definitive diagnosis is made by means of a cardiac catheterization in which the defect is demonstrated.

Treatment

Traditional surgical repair for an atrial septum defect, involving a dacron patch, is both safe and effective. A newer clamshell-like double-umbrella device that can be implanted under local anesthesia via a catheter procedure also shows promise.

Surgical intervention for atrioventricular septal defect is usually required within the first few months of life, regardless of the presence of Down syndrome, because medical management is rarely able to prevent severe congestive heart failure. Without surgery, there is usually irreversible damage to the walls of the pulmonary blood vessels.

Questions to Ask Your Doctor

Where is the defect located?

Is it partial or complete?

Why is this a problem?

Will the condition worsen?

Is surgical intervention indicated?

How will this be performed?