Most congenital heart defects, including tricuspid atresia, result from changes that occur early as the baby's heart is developing before birth. The exact cause is usually unknown.
How the heart works
To understand more about tricuspid atresia, it may be helpful to know how the heart typically works.
The heart is divided into four chambers, two on the right and two on the left.
- The right upper chamber is called the right atrium.
- The right lower chamber is called the right ventricle.
- The left upper chamber is called the left atrium.
- The left lower chamber is called the left ventricle. The left ventricle is the heart's main pumping chamber.
To pump blood throughout the body, the heart uses its left and right sides for different tasks.
- The right side of the heart moves blood to the lungs through the lung arteries. These are the pulmonary arteries.
- In the lungs, blood picks up oxygen and then returns to the heart's left side through the pulmonary veins.
- The left side of the heart pumps the blood through the body's main artery, called the aorta. The blood then flows out to the rest of the body.
Valves control the flow of blood into and out of the heart. The heart valves open to allow blood to move to the next chamber or to one of the arteries. The heart valves close to keep blood from flowing backward.
What happens in tricuspid atresia
In tricuspid atresia, the tricuspid valve is missing. A sheet of tissue blocks the flow of blood between the right heart chambers. There's no way for blood to move from the right upper chamber to the right lower chamber. The right side of the heart is no longer able to pump blood to the lungs.
Instead, blood flows from the heart's right upper chamber directly to the left upper chamber through a hole in the wall between them. The hole is either a congenital heart defect called an atrial septal defect or a natural opening called the foramen ovale. When the foramen ovale doesn't close after birth, it's called a patent foramen ovale.
How blood flows after that depends on whether there are other heart structure problems. In some babies with tricuspid atresia, blood moves from the left lower heart chamber into the body's main artery, the aorta. Then it goes to the lungs through a temporary connection called the ductus arteriosus. This connection typically closes after birth.
Many babies born with tricuspid atresia also have a hole between the lower heart chambers. This hole is called a ventricular septal defect or VSD. If this occurs, some blood can flow through the hole directly to the main lung artery. The amount of blood going to the lungs depends on the size of the VSD and whether the pulmonary valve is narrowed. If the VSD is large, too much blood can move to the lungs. This can cause heart failure.