Truncus arteriosus

Truncus arteriosus (TRUNG-kus ahr-teer-e-O-sus) is a heart defect that creates severe circulatory problems. If your baby has truncus arteriosus, one large vessel leads out of the heart, instead of two separate vessels — one leading out of each of the lower chambers of the heart. Also, the two lower chambers are missing a portion of the wall dividing them. As a result of truncus arteriosus, 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.

If left untreated, truncus arteriosus usually leads to death within the first or second year of life. Surgery to repair the heart and blood vessels is usually successful, especially if the repair occurs before your baby is 2 months old.

Truncus arteriosus, one of the least common heart defects, is also known as persistent truncus arteriosus.

Truncus arteriosus occurs during fetal growth when your baby’s heart is developing and is, therefore, present at birth (congenital). In most cases the cause is unknown. An overview of typical heart structure and function is helpful in understanding the defects of truncus arteriosus.

The heart
Your heart has four pumping chambers that circulate your blood. The “doors” of the chambers (valves) control the flow of blood, opening and closing to ensure that blood flows in a single direction.

The heart’s four chambers are:

  • The right atrium, the upper right chamber, receives oxygen-poor blood from your body and delivers it into the right ventricle.
  • The right ventricle, the lower right chamber, pumps the blood through a large vessel called the pulmonary artery and into the lungs, where the blood is resupplied with oxygen.
  • The left atrium, the upper left chamber, receives the oxygen-rich blood from the lungs and delivers it into the left ventricle.
  • The left ventricle, the lower left chamber, pumps the oxygen-rich blood through a large vessel called the aorta and on to the rest of the body.

Normal heart development
The formation of the heart in a fetus is a complex process. At a certain point, all fetuses have a single large vessel (truncus arteriosus) exiting the heart. During normal development of the heart, however, 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.

Also during this process, the ventricles develop into two chambers separated by a wall (septum).

Truncus arteriosus in newborns
In babies born with truncus arteriosus, the single large vessel never finished dividing into two separate vessels. And the wall separating the two ventricles never closed completely, resulting in a large hole between the two chambers (ventricular septal defect).

Truncus arteriosus in a newborn is also called persistent truncus arteriosus, because an early stage of heart development persisted until birth.

In addition to the primary defects of truncus arteriosus, 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.

Signs and symptoms of truncus arteriosus usually develop in the first few weeks of life. They include:

  • Blue coloring of the skin (cyanosis)
  • Poor feeding
  • Poor responsiveness
  • Delayed growth or growth failure
  • Excessive sleepiness
  • Shortness of breath (dyspnea)
  • Rapid breathing (tachypnea)
  • Irregular heartbeats (arrhythmia)
  • Excessive sweating (diaphoresis)

When to see a doctor
Seek medical treatment if you notice that your baby has any of the following problems:

  • Blue coloring of the skin (cyanosis)
  • Poor feeding
  • Poor responsiveness
  • Poor weight gain
  • Excessive sleepiness
  • Excessive sweating

Some signs of truncus arteriosus may indicate a problem that needs urgent care. If your baby experiences any of the following signs and symptoms and you can’t see your baby’s doctor immediately, seek emergency medical care:

  • Rapid, shallow or labored breathing
  • Worsening of blue coloring of the skin
  • Loss of consciousness

The abnormal heart structures of truncus arteriosus result in severe problems with blood circulation. Because the ventricles aren’t separated and all blood exits from a single vessel, the oxygen-rich blood and the oxygen-poor blood mix together — resulting in blood that doesn’t carry enough oxygen. The mixed blood flows from the single large vessel to the lungs, the arteries of the heart and the rest of the body.

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

  • Respiratory problems. The abnormal distribution of blood results in too much blood flowing into the lungs. Excessive fluid in the lungs makes it difficult for your baby to breathe.
  • High blood pressure in the lungs (pulmonary hypertension). Increased blood flow to the lungs causes the lungs’ blood vessels to narrow, increasing blood pressure and making it increasingly difficult for your baby’s heart to pump blood into the lungs.
  • Enlargement of the heart (cardiomegaly). Pulmonary hypertension and the increased blood flow through the heart force your baby’s heart to work harder than normal, causing it to enlarge. The enlarged heart gradually weakens.
  • Heart failure. The increased workload and poor oxygen supply also result in weakening of your baby’s heart. These factors can contribute to heart failure, the inability of the heart to supply the body with enough blood.

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

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

Common signs and symptoms of these complications include shortness of breath, dizziness, fatigue and a sensation of rapid, fluttering heartbeats (palpitations).

Truncus arteriosus in adults
In rare cases, a person with truncus arteriosus can survive infancy without surgical repair of the heart and live into adulthood. However, people with this condition will almost certainly develop heart failure and Eisenmenger syndrome. This syndrome is caused by permanent lung damage from pulmonary hypertension that results in much of the blood flow bypassing the lungs entirely. A heart-lung transplant is usually the only treatment option.

In order for the pediatric cardiologist to check the condition of your baby’s heart and make a diagnosis, he or she will order one or more tests:

An echocardiogram shows the structure and function of your baby’s heart. With this test, a technician spreads gel on your baby’s chest and then presses a device called a transducer against the skin over his or her heart. The transducer emits high-pitched sound waves and records the sound wave echoes as they reflect off internal structures. A computer converts the echoes into moving images on a monitor.

In a baby with truncus arteriosus, the echocardiogram reveals the single large vessel leading from the heart, a hole in the wall between the left and right ventricles, and sometimes an abnormality in the valve between the large vessel and the ventricles.

Because an echocardiogram shows the flow of blood, it may also reveal blood moving back and forth between the two ventricles and the amount of blood flowing to your baby’s lungs. The amount of blood can indicate the risk of high blood pressure in the lungs.

An X-ray exam uses electromagnetic radiation to produce still images of internal organs and structures. A chest X-ray of your baby can show the size of the heart, abnormalities in the lungs and excess fluid in the lungs.

Surgery can often repair the heart of an infant with truncus arteriosus. Sometimes multiple procedures or surgeries will be necessary. Before your baby undergoes surgery, he or she may receive extra feedings to ensure proper nutrition and medications to improve heart and lung function.

Medications that may be prescribed prior to surgery may include:

  • Digoxin (Lanoxin). This drug, also referred to as digitalis, increases the strength of heart muscle contractions.
  • Diuretics. Often called water pills, diuretics increase the frequency and volume of urination, preventing fluid from collecting in the body — a common effect of heart failure.

Surgical procedures
Most infants with truncus arteriosus undergo surgery within the first two months of life. The exact procedure will depend on your baby’s condition. Most commonly your baby’s surgeon will:

  • Close the hole between the two ventricles, often with a patch
  • Separate the upper portion of the pulmonary artery from the single large vessel
  • Implant a tube (conduit) and valve to connect the right ventricle with the upper portion of the pulmonary artery — creating a new, complete pulmonary artery
  • Reconstruct the single large vessel and aorta to create a new, complete aorta
  • Implant a new valve separating the left ventricle and aorta if necessary

After corrective surgery, your child will need lifelong follow-up care with a cardiologist to monitor his or her heart health. The cardiologist may recommend that your child limit physical activity. Your child will need to take antibiotics before dental procedures and other surgical procedures to prevent infections.

Because the conduit does not grow with your child, follow-up surgery to replace the conduit is usually necessary as he or she gets older.

In most cases, truncus arteriosus can’t be prevented. If you have a family history of heart defects or if you already have a child with a congenital heart defect, you and your partner may consider talking with a genetic counselor and a cardiologist experienced in congenital heart defects before you make a decision about becoming pregnant.

It’s best not to drink alcohol during pregnancy. If you’re concerned because you drank alcohol before you knew you were pregnant or you think you need help to stop drinking, talk with your health care provider.

If you’re a woman with diabetes, talk to your doctor about pregnancy risks associated with diabetes and how best to manage the disease during your pregnancy.