Truncus arteriosus (TRUNG-kus ahr-teer-e-O-sus) is a rare heart defect that's present at birth (congenital). If you or your baby has truncus arteriosus, it means that one large blood vessel leads out of the heart. Normally, there are two separate vessels coming out of the heart.
In addition, there is usually a hole — known as a ventricular septal defect — between the two lower chambers of the heart. 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. This creates severe circulatory problems.
If left untreated, truncus arteriosus can be fatal. Surgery to repair truncus arteriosus is generally successful, especially if the repair occurs before your baby is one month old.
Signs and symptoms of truncus arteriosus often develop in the first few days of life. They include:
- Blue coloring of the skin (cyanosis)
- Poor feeding
- Pounding heart
- Excessive sleepiness
- Poor growth
- Shortness of breath (dyspnea)
- Rapid breathing (tachypnea)
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
- Excessive sleepiness
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
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 the typical heart structure and function is helpful in understanding the defects of truncus arteriosus.
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 fetal heart is a complex process. At a certain point, all babies 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 single blood vessel arising from the heart, and a large hole between the two chambers (ventricular septal defect).
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.
While the exact cause of congenital heart defects, such as truncus arteriosus, is unknown, several factors may increase the risk of a baby being born with a heart condition. These include:
- Viral illness during pregnancy. If a woman contracts rubella (German measles) or another viral illness during early pregnancy, the risk of congenital heart defects in her baby is increased.
- Poorly controlled diabetes during pregnancy. Diabetes that isn't well-managed can increase the risk of birth defects, including heart defects.
- Certain medications taken during pregnancy. Many medications aren't recommended for use during pregnancy because of potential risks to the fetus.
- Certain chromosomal disorders. Children with DiGeorge's syndrome or velocardiofacial syndrome have an increased risk of truncus arteriosus. These conditions are caused by an extra or defective chromosome.
- Smoking during pregnancy. Continuing to smoke while pregnant increases the risk that the baby will be born with a heart defect.
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 in the lungs 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
- Leaky heart valves (regurgitation)
- Heart rhythm disturbances (arrhythmias)
- Problems related to prior operation
Common signs and symptoms of these complications include shortness of breath when exercising, dizziness, fatigue, abdominal swelling, swelling in the legs and feet, 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 pulmonary hypertension (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.
In most cases, congenital heart defects, such as 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.
If you're thinking about becoming pregnant, there are several steps you can take to help ensure a healthy baby, including:
- Getting vaccinated before getting pregnant. Certain viruses, such as rubella (German measles), can be very harmful during pregnancy, so it's important to make sure your immunizations are up to date before you get pregnant.
- Avoiding dangerous medications. Check with your doctor before taking any medications if you're pregnant or thinking about becoming pregnant. Many drugs aren't recommended for use during pregnancy.
- Taking folic acid. One of the few steps you can take to help prevent birth defects, including spinal cord, brain and possibly heart defects, is to take 400 micrograms of folic acid daily.
- Controlling diabetes. 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.