Truncus Arteriosus

Overview

When a baby develops, a single large blood vessel emerges from the heart, dividing into two large arteries: the pulmonary artery and the aorta.

• The pulmonary artery carries blood from the lower right chamber of the heart (right ventricle) to the lungs, where it picks up oxygen.
• The aorta carries oxygen-rich blood from the heart's lower left chamber (left ventricle) to the rest of the body.

In truncus arteriosus, the large single blood vessel doesn't separate like it should, leaving one large artery that becomes the aorta, with the pulmonary artery arising from the aorta without connection to the heart. It's associated with a ventricular septal defect (VSD), which allows blood to flow from both pumping chambers to the single blood vessel.

According to the Centers for Disease Control and Prevention (CDC), there are about 250 cases of truncus arteriosus each year in the U.S., occurring either by itself or as part of certain genetic disorders¹ such as DiGeorge syndrome, which is a chromosomal disorder that results in several poorly developed body systems, including heart defects, poor immune system function, a cleft palate, and low calcium levels in the blood.

Progression and complications

The hole (VSD) allows blood from both the right and left sides of the heart to exit together to the single artery. This leads to the mixing of poorly oxygenated blood from the right ventricle to mix with well-oxygenated blood on the left side, resulting in lower oxygen levels than normal. In addition, the defect leads to excessive blood flow to the lungs, which eventually can lead to damage to the blood vessels of the lungs and damage to the blood vessels of the lungs, resulting in trouble breathing and increased stress on the heart.

If left untreated, truncus arteriosus will lead initially to symptoms that include rapid breathing, poor feeding, and failure to gain weight and grow properly. Within months, the bluish discoloration of the skin will increase, and damage to the lungs' blood vessels will result in less blood flow to the lungs—a situation that eventually will cause death. However, with surgical treatment, children born with truncus arteriosus can lead practically normal lives.

Treatment

Surgical repair of truncus arteriosus is recommended in the first two weeks of the baby’s life. In the procedure, the surgeon separates the blood vessels going to the lungs (pulmonary arteries) from the truncus arteriosus and connects them to the right ventricle using several types of materials, such as a donated blood vessel (homograft) or a Contegra conduit. In addition, the hole in the heart (VSD) is closed so that only blood from the left ventricle pumps into the truncus arteriosus, which serves as the aorta, carrying blood from the left ventricle to the body.

The pulmonary arteries may be too narrow to carry adequate amounts of blood to the lungs from the right ventricle for two reasons:

• They may start small.
• The surgical repair may require that they be stretched to connect them to the right ventricle.

These two factors may result in the narrowing of the pulmonary arteries (branch pulmonary artery stenosis). Repeated surgery or widening of the pulmonary arteries in the hospital’s cardiac catheterization laboratory may be needed to relieve this. Repeat surgery may also be needed to replace the homograft since it stays fixed in size and doesn’t grow with the child. As the child grows closer to final adult size, a manmade valve may be placed in the tube or homograft that connects the right ventricle to the lung arteries.

References

1. Centers of Disease Control and Prevention (CDC)