Truncus arteriosus is a rare birth defect that occurs when the two main arteries of the heart don’t form correctly during fetal development. Patients with this condition have one large, wide blood vessel where two separate ones should be located. This abnormality changes the way that blood moves through the heart and lungs and throughout the rest of the body.

Early in development, a fetus has one common trunk within the heart—a wider-than-normal blood vessel carrying blood flow away from the heart. As the fetus grows, the trunk normally branches off to form two arteries, a pulmonary artery and an aorta, which serve different purposes. Oxygen-poor blood (low in oxygen) in the heart travels through the pulmonary artery to the lungs so that it may become oxygenated (oxygen-rich). Oxygen-rich blood leaves the heart through the aorta to reach the rest of the body.

Babies born with truncus arteriosus still have one wide blood vessel instead of a separate aorta and pulmonary artery. Some blood that moves through this common trunk travels to the lungs, and some travels to the rest of the body. Because a mix of oxygen-rich and oxygen-poor blood passes through the common trunk, the blood that leaves the heart isn’t fully oxygenated. As a result, babies with this condition may have bluish skin, difficulty breathing, and other signs that their bodies are not receiving enough oxygen.

Truncus arteriosus is a rare condition. About 250 babies are born in the United States each year with this birth defect. Fewer than 1% of all congenital (present at birth) heart defects are truncus arteriosus.

Babies born with truncus arteriosus usually experience heart failure within the first few weeks of life. However, when the condition is surgically corrected during infancy, more than 80% of patients live to adulthood. Most patients do quite well, especially with improving surgical techniques and more options for aortic and pulmonic valve repairs and replacements. As they grow, most patients require additional surgical and/or catheterization procedures related to their heart valves. Follow-up cardiology care is lifelong for these patients.

Truncus arteriosus is a congenital heart defect that prevents the heart from sending enough oxygen-rich blood throughout the body. This occurs because blood vessels within a fetus’s heart did not develop normally during pregnancy. The condition causes heart failure, and, without treatment, babies may die within the first year of life.

When a baby is born with a healthy heart, it can provide enough oxygen-rich blood to the body. Oxygen-poor blood from the body enters the heart’s right atrium (the upper right chamber) and then travels to the right ventricle (the lower right chamber). The blood moves through the pulmonary valve and into the main pulmonary artery, bringing the oxygen-poor blood to the lungs. In the lungs, the blood becomes oxygenated. It then enters the heart’s left atrium (the upper left chamber), moves to the left ventricle (the lower left chamber), and passes through the aortic valve to the aorta, the blood vessel through which oxygen-rich blood travels throughout the body.

A baby born with truncus arteriosus has one large blood vessel, known as the common trunk, instead of a main pulmonary artery and an aorta. The baby also has one truncal valve instead of a pulmonary valve and an aortic valve, both of which may leak. Babies with truncus arteriosus also have a ventricular septal defect (VSD), a hole in the wall that separates the heart’s two ventricles, allowing blood to pass between the heart’s lower chambers.

In a baby with the condition, oxygen-poor blood enters the heart’s right atrium and moves to the right ventricle. Because of a VSD, oxygen-poor blood from the right ventricle is able to mix with oxygen-rich blood from the left ventricle. This mixed blood then passes through the truncal valve and into the common trunk.

From there, some of the mixed blood flows to the lungs, picking up oxygen and traveling to the left atrium and left ventricle. This blood again mixes with blood from the right ventricle because of the hole between these chambers, then passes back through the common trunk. The heart muscle works harder than usual because it is pumping more blood than it should to the lungs, which can lead to heart failure.

Some of the mixed blood that enters the common trunk travels out of the heart to the rest of the body. However, the blood isn’t adequately oxygenated to provide the body’s organs, structures, and cells with enough oxygen to function well.

It’s important to note that some patients have different subtypes of truncus arteriosus, with slightly different blood vessel configurations.

Doctors aren’t sure why some babies are born with truncus arteriosus, although a genetic or chromosomal abnormality may be responsible.

A strong association exists between truncus arteriosus and DiGeorge syndrome, which is also known as 22q11.2 deletion syndrome.

Newborns with truncus arteriosus have bluish skin and may begin to experience heart failure symptoms, including:

• Bluish skin
• Shortness of breath
• Rapid breathing
• A pounding heartbeat
• Weak pulse
• Poor feeding habits
• Sweating
• Extreme sleepiness or lethargy
• Heart murmur
• Enlarged liver

Certain genetic or chromosomal abnormalities may increase the risk of truncus arteriosus, including:

• DiGeorge syndrome (22q11.2 deletion syndrome)
• Duplication of chromosome arm 8q
• Mutation of the NKX2.6 gene
• Mutation of the GATA6 genes

Most commonly, congenital heart anomalies such as truncus arteriosus may be detected during pregnancy via a routine ultrasound in the second trimester. When doctors suspect a heart abnormality, including truncus arteriosus, they may order a fetal echocardiogram, an ultrasound exam that shows the structure and function of a fetus's heart. A fetal echocardiogram can be used to diagnose truncus arteriosus starting at 18 weeks of pregnancy.

Occasionally, truncus arteriosus is diagnosed during the first few days of a newborn’s life by the newborn’s medical history, physical exam, and diagnostic tests.

When a newborn has bluish skin and signs of heart failure, doctors will want to know if the baby was diagnosed with any genetic or chromosomal abnormalities, including DiGeorge syndrome, or if there is a family history of the condition.

During a physical exam, doctors will note the baby’s bluish skin, watch for labored breathing, observe whether the baby is lethargic, and feel the abdomen for an enlarged liver. The doctor will listen to the baby’s heart with a stethoscope to see if there is a murmur or other abnormal sounds that could indicate truncus arteriosus.

Doctors may offer the following diagnostic tests to check for truncus arteriosus:

• Pulse oximetry. Doctors use this screening test to see if a baby’s blood-oxygen levels are normal or low. They briefly attach a device to the baby’s hand or foot to measure the amount of oxygen in the blood. Patients with truncus arteriosus typically have low blood-oxygen levels.
• Chest X-ray. Images of the chest may show an enlarged heart (the heart muscle becomes overworked from pumping more blood than usual)
• Genetic testing. A blood sample may be used to look for 22q11.2 or other genetic mutations.
• Echocardiogram (or “echo”). This ultrasound exam of the heart uses a transducer (or wand) to pick up sound waves from the chest and torso to create images of the heart. When a patient has truncus arteriosus, the echocardiogram shows the presence of a common trunk rather than a main pulmonary artery and an aorta. The images also confirm that the patient has a VSD and a single truncal valve—and that blood flows through the heart in an abnormal pattern.
• Electrocardiogram (ECG or EKG). During this test, doctors stick sensors to a patient’s chest and torso to measure the heart’s electrical activity. When a patient has truncus arteriosus, the test results may show that the heart muscle surrounding the lower ventricles is enlarged because the heart is working harder than it should.

Doctors surgically correct truncus arteriosus within the first few months of a baby’s life. A newborn may need medication (diuretics, digoxin, and ACE inhibitors) to manage the symptoms of heart failure before of surgery.

When a baby is ready for surgery, often around 1 or 2 months of age, doctors perform several procedures:

• Doctors use a patch to close the hole in the heart wall (the ventricular septal defect and, in some cases, an atrial septal defect).
• If the truncal valve is leaky, doctors repair it.
• Doctors create two blood vessels—a main pulmonary artery and an aorta—so blood can travel through the heart on its intended route.

o Doctors usually designate the common trunk as the aorta and the truncal valve as the aortic valve. They route this blood vessel so that oxygen-rich blood from the left ventricle passes through it to the rest of the body.

o Doctors use an artificial blood vessel (a conduit) and an artificial valve to serve as the pulmonary artery and pulmonary valve. They route this new blood vessel so that oxygen-poor blood travels from the right ventricle into the lungs, where the blood becomes oxygenated.

Truncus arteriosus is a life-threatening condition. More than 70% of babies born with this birth defect who do not undergo surgery will die in the first year of life.

The surgical correction of truncus arteriosus helps many patients lead normal lives. After surgery, more than 80% of patients live to age 20 or older.

Patients will need to have their heart monitored by a cardiologist regularly for the rest of their lives. Most patients will need follow-up surgery as they get older. In many cases, it’s related to the conduit used as a pulmonary artery, which cannot grow as the patient ages, and the need for heart valve replacements. Other times, a leaky valve needs to be repaired or replaced. By age 10, 75% of patients require another procedure to keep the heart functioning well.

In adulthood, some patients who have undergone surgery for truncus arteriosus may experience arrhythmias (heart-rhythm problems), pulmonary hypertension (high blood pressure in the lungs), or other complications. Some patients need to restrict their physical activity.

This article was medically reviewed by Dina Ferdman, MD, a Yale Medicine pediatric cardiologist who cares for children with congenital heart disease.