Truncus arteriosus (TA) is a rare congenital cardiovascular anomaly. Normally, there are two separate vessels coming out of the heart. In babies with truncus arteriosus  only one large blood vessel leads out of the heart. In addition, the two lower chambers of the heart are missing a portion of the wall that divides them. Consequently, oxygen-poor blood that should go to the lungs and oxygen-rich blood that should go to the rest of the body are mixed together, causing severe circulatory problems.

The disorder can be fatal if left untreated . Generally, surgery is successful and is done within two months of the child’s birth.

Symptoms

Truncus arteriosus symptoms which are obvious in the first few weeks of life, include:

  • Excessive sleepiness
  • Blue coloring of the skin
  • Poor feeding
  • Poor growth
  • Breathing problems
  • Irregular heartbeats
  • Excessive sweating

Causes

In most cases the cause of  truncus arteriosus is unknown and occurs during fetal growth when the baby's heart is developing. 

The heart has four pumping chambers that circulate the blood. The "doors" of the chambers (valves) control the flow of blood, opening and closing to ensure that blood flows in a single direction. They are the  right atrium, the right ventricle, the left atrium and the left ventricle.

A complex process occurs during the formation of the fetal heart. At a certain point, all fetuses have one large vessel exiting the heart. During normal development of the heart this very large single vessel divides into two parts. One part becomes the lower portion of the aorta, which is attached to the left ventricle. The other part becomes the lower portion of the pulmonary artery, which is attached to the right ventricle. During this process, the ventricles develop into two chambers separated by a wall (septum).

In babies born with truncus arteriosus, the single large vessel did not finish dividing into two separate vessels. And the wall separating the two ventricles did not close completely. This leaves a large hole between the two chambers.

In addition,  the valve controlling blood flow from the ventricles to the singe large vessel (truncal valve) is often defective, allowing blood to flow backward into the heart.

Risk Factors

The exact cause of truncus arteriosus is unknown, but several factors may increase the risk of a baby being born with a heart condition, including:

  • Viral illness during pregnancy.
  • Poorly controlled diabetes during pregnancy.
  • Certain medications taken during pregnancy.
  • Certain chromosomal disorders.
  • Smoking during pregnancy.

Complications

If the baby has truncus arteriosus, the abnormal circulation of blood usually results in:

  • Respiratory problems.
  • High blood pressure in the lungs (pulmonary hypertension).
  • Enlargement of the heart (cardiomegaly).
  • Heart failure.

Even with successful surgical repair of the heart during infancy, other complications associated with truncus arteriosus may occur later in life:

  • Progressive pulmonary hypertension
  • Leaky heart valves (regurgitation)
  • Heart rhythm disturbances (arrhythmias)

Prevention

In most cases, congenital heart defects, such as truncus arteriosus, can not be prevented.

If you are thinking about becoming pregnant, there are several steps you can take to help ensure a healthy baby, including:

  • Getting vaccinated before getting pregnant.
  • Avoiding dangerous medications.
  • Taking folic acid.
  • Controlling diabetes.