Causes

Tricuspid atresia occurs during fetal heart development. Some genetic factors, such as Down syndrome, might increase your baby's risk of congenital heart defects such as tricuspid atresia, but the cause of congenital heart disease is usually unknown.

How the heart works

Your heart is divided into four chambers — the right atrium and right ventricle and left atrium and left ventricle. The right side of the heart moves blood to the lungs, where it picks up oxygen before it circulates to your heart's left side. The left side pumps blood into a large vessel called the aorta, which circulates the oxygen-rich blood to the rest of your body.

Valves control the flow of blood into and out of your heart. These valves open to allow blood to move to the next chamber or one of the arteries, and they close to keep blood from flowing backward.

When things go wrong

In tricuspid atresia, the right side of the heart can't pump enough blood to the lungs because the tricuspid valve is missing. A sheet of tissue blocks the flow of blood from the right atrium to the right ventricle. As a result, the right ventricle is usually small and underdeveloped (hypoplastic).

Blood instead flows from the right atrium to the left atrium through a hole in the wall between them (septum). This hole is either a heart defect (atrial septal defect) or an enlarged natural opening that's supposed to close soon after birth (patent foramen ovale).

After the blood flows to the left atrium, it enters the left ventricle and then is pumped to the aorta. To get to the lungs, blood flows through a vessel that connects the aorta to the pulmonary artery (ductus arteriosus). All hearts have a ductus arteriosus while the baby is in the uterus, but shortly after birth, the ductus closes.

A baby with tricuspid atresia might need medication to keep the ductus from closing after birth. A procedure or surgery to create an opening between the atria or to provide a connection from the aorta to the pulmonary artery might be needed.

Many babies born with tricuspid atresia have a hole between the ventricles (ventricular septal defect). In these cases, some blood can flow through the hole between the left ventricle and the right ventricle, and then blood is pumped to the lungs through the pulmonary artery.

However, the valve between the right ventricle and the pulmonary artery (pulmonary valve) might be narrowed, which can reduce blood flow to the lungs. If the pulmonary valve isn't narrowed and if the ventricular septal defect is large, too much blood can flow to the lungs, which can lead to heart failure.

Some babies have other heart defects as well.