Truncus Arteriosus

Truncus arteriosus is typically accompanied by another heart abnormality known as a ventricular septal defect. This is a hole in the wall (septa) separating the heart’s two lower chambers, or ventricles. This opening allows a mix of oxygenated blood from the left ventricle and oxygen-depleted blood from the right ventricle. These abnormalities have three consequences.

• The volume of blood flowing to the lungs is increased.
• The amount of blood coursing to the body may be decreased.
• The body’s blood supply carries less oxygen than normal.  

In truncus arteriosus, there is only a single (sometimes malformed) truncal valve instead of the two normal valves: aortic and pulmonary. This abnormal valve inhibits blood from leaving the heart and allows blood that has already left the heart to leak back inside.

This combination of structural abnormalities can lead to a number of serious problems, including:

• Respiratory problems
• High blood pressure in the lungs (“pulmonary hypertension”)
• Enlargement of the heart
• Weakening of the heart
• Heart failure 
• Decreased blood flow to body organs

Symptoms of Truncus Arteriosus

Within the first week of life, infants with truncus arteriosus often begin to show respiratory problems and occasionally cyanosis (blue lips, skin and extremities). Babies may also have irritability, excessive sleep, weak pulse, rapid breathing and poor ability to feed.

Patients with truncus arteriosus sometimes have additional health problems not directly related to the heart. A small deletion on the long arm of chromosome 22 can lead to abnormally low calcium levels in the blood. There may also be an increased risk of infection caused by a low number of certain white blood cells, called T-cells. This 22q11.2 deletion is sometimes referred to as DiGeorge syndrome.

Diagnosis of Truncus Arteriosus

Truncus arteriosus can be diagnosed during pregnancy by a routine prenatal ultrasound or fetal echocardiogram. A fetal echocardiogram not only provides an accurate and detailed picture of the structures of the heart, it also allows the doctor to see how the heart functions.

After birth, a heart murmur may alert doctors to a potential problem. However, because not all heart murmurs are serious, additional diagnostic testing through chest x-ray, EKG and echocardiogram are required. Many states (including Indiana) require testing (pulse oximeter screening) of all newborn babies for low oxygen levels before discharge from the newborn nursery. Failing this test sometimes leads to a diagnosis of truncus arteriosus.