Atrioventricular Septal Defect

Overview

Atrioventricular septal defect (AVSD), also referred to as endocardial cushion defects, refers to the following three heart defects:

• Atrial septal defect (ASD) – ASD refers to a hole in the “wall” (septum) of the heart that separates the two upper chambers (atria). The hole allows blood to pass between the two chambers.
• Inlet ventricular septal defect (VSD) – VSD refers to a hole in the septum between the heart’s two lower chambers (ventricles).
• Existence of a common atrioventricular valve – In normal hearts, two valves—the mitral and tricuspid valves—help control blood flow between the heart's upper and lower chambers. In AVSD, the two valves are combined, resulting in a common atrioventricular opening (canal).

The occurrence of AVSD is much higher in children with Down syndrome than in other children. Approximately 40–50% of children with Down syndrome have congenital heart disease (CHD), most of which are AVSD.¹ 

Progression and possible complications

The two holes in the heart wall (ASD and VSD) allow blood from the left heart chambers to cross to the right heart chambers. Because blood in the right heart chambers travels to the lungs to pick up oxygen, the two holes permit increased blood flow to the lungs. Increased blood flow to the lungs can cause them to become congested. As the lungs become congested, breathing becomes more rapid. Difficult breathing and the increased load on the heart, as it works harder to pump blood to the body, will eventually lead to congestive heart failure and poor growth.

In addition, some blood from the right heart (blue because it has low oxygen content) may pass to the left side of the heart. When this occurs, blood from the left side of the heart, which goes to the body, may be less filled with oxygen and, thus, bluer in color than normal. This might be noticed as a mild bluish discoloration of the child’s lips and nail beds, a condition called cyanosis.

Treatment

In early infancy, medications are prescribed to help the baby cope with congestive heart failure. The medications that are often recommended include those that do the following:

• Improve heart function (such as digoxin).
• Reduce blood volume by increasing urine output (such as furosemide, a diuretic).
• Reduce blood flow resistance to the body, making it easier for the heart to pump (such as captopril).
• Eventually, surgery will be needed at about 6 to 9 months of age. The surgeon will close the two holes (ASD and VSD) and create two atrioventricular valves to replace the single valve.

Failure to repair the AVSD may result in irreversible damage to the lungs' blood vessels (pulmonary vascular obstructive disease). As blood vessel damage progresses, less blood flows to the lungs, resulting in cyanosis (mentioned above). Eventually, an unrepaired AVSD may lead to death, but surgical repair within the first year of life aims to prevent that outcome.

References

1. Circulation: Cardiovascular Quality and Concerns