In the normal heart, two arteries emerge from the heart: 

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

In truncus arteriosus, a single blood vessel emerges from the heart and then branches into a pulmonary artery and an aorta. This single vessel, called the truncus arteriosus, emerges from both ventricles – specifically from the hole in the wall between the two ventricles, called the ventricular septal defect (VSD). 

Truncus arteriosus occurs in 1 percent of children with heart diseases.

Symptoms and Progression of Truncus Arteriosus

The presence of the hole between the heart’s two pumping chambers and the fact that only one artery comes out of the heart together cause poorly oxygenated blood (blue in color) returning from the body to mix with the well-oxygenated blood (pink in color) that is returning from the lungs. When the mixed blood is pumped to the body, the child’s skin coloration turns bluish. This bluish discoloration is called cyanosis. 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 heart failure, in which the heart is unable to pump enough blood to the body.  

If not treated, truncus arteriosus will lead initially to heart failure. Symptoms of heart failure include rapid breathing, poor feeding, and failure to gain weight and grow properly. Within months, the bluish discoloration of the skin will increase. Damage to the blood vessels of the lungs 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 of Truncus Arteriosus

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 (the pulmonary artery) from the truncus arteriosus and connects them to the right ventricle using a donated blood vessel (homograft). In addition, the hole in the heart (ventricular septal defect) 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 be small to start with, and 
• The surgical repair may require that they be stretched in order to connect them to the right ventricle. 

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