Atrioventricular septal defect (AVSD), also referred to as endocardial cushion defects, consists of three defects in the heart:

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

The occurrence of AVSD is much higher in children with Down syndrome than other children. Forty percent of all children with Down syndrome have congenital heart disease; of those, 40 percent have AVSD. 

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 an increased amount of blood to 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, as well as 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 (which is blue in color 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.

Treatments

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

• Improve heart function (such as digoxin);
• Reduce blood volume by increasing urine output (diuretics, such as furosemide); and 
• Reduce the resistance of blood flow to the body, making it easier for the heart to pump (such as captopril).  

Eventually (at about 6 to 9 months of age) surgery will be needed. 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 blood vessels of the lungs (pulmonary vascular obstructive disease). As blood vessel damage progresses, less blood flows to the lungs, resulting in bluish discoloration of the child’s skin. Eventually, an unrepaired AVSD may lead to death. Surgical repair within the first year of life aims to prevent that outcome.