Pulmonary atresia is a congenital heart defect (the
baby is born with it) in which the pulmonary valve does not develop normally or
remains blocked after birth. ("Atresia" means absent and pulmonary refers to the lungs.)
The structure of the heart
The heart has four chambers—the right atrium and the
left atrium (plural: atria) on top and the right and left ventricles (pumping
chambers) on the bottom. The heart is divided by a solid wall called the septum
into two sides: the right side sends blood to the lungs to get oxygen, while the
left side of the heart moves oxygen-rich blood to the rest of the body through
the aorta (the main artery in the heart).
There are also four valves in the heart, which open and close to allow blood to move through the chambers: (figure to right shows
the inside of the heart).
- The tricuspid valve, located on the right side of the heart
between the right ventricle and the right atrium;
- The pulmonary valve, located on the right side of the heart
between the right ventricle and the pulmonary artery (the blood vessel that
carries blood to the lungs);
- The mitral valve, located between the left ventricle and the left
atrium;
- The aortic valve, located on the left side of the heart, between
the aorta and the left ventricle
The pulmonary valve has three flaps (also called
leaflets or cusps) that normally open to let blood flow forward from the right
ventricle into the pulmonary artery. The leaflets also close to prevent blood
from flowing backward into the heart.
In some babies with pulmonary atresia, the right
ventricle of the heart, the pulmonary artery, and the tricuspid valve may be
underdeveloped. Some infants may also have a ventricular septal defect, or
opening in the wall (septum) between the right and left ventricles. This opening
allows oxygen-rich blood to mix with oxygen-poor blood.
If there is no pulmonary valve or if it is blocked,
blood cannot flow through the pulmonary artery to reach the lungs, where it
receives oxygen. Instead, oxygen-poor (blue) blood is pumped throughout the
body. The lips, fingers, and toes of the infant may appear blue because of a
lack of oxygen in the blood. This condition is known as cyanosis.
The fetal heart has an opening (the foramen ovale)
between the pulmonary artery and the aorta. It usually closes after birth, but
sometimes remains open in newborns who have pulmonary atresia. The foramen ovale
allows oxygen-poor blood to pass from the right atrium to the left atrium of the
heart, where it flows through the left ventricle to the aorta.