Truncus arteriosus

Definition

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.

Symptoms

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

Causes

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.

If your baby has truncus arteriosus, one very large vessel leads out of the heart, instead of two separate vessels, and there's a hole in the wall between the ventricles (ventricle septal defect). The oxygen-rich blood (red) and the oxygen-poor blood (blue) mix together, resulting in blood with an insufficient oxygen supply (purple) for the body.

Risk factors

While the exact cause of truncus arteriosus is unknown, several factors may increase the risk of a baby being born with this condition. These include:

• A mother who had rubella (German measles) or another viral illness during early pregnancy
• A parent who had a congenital heart defect
• Excessive alcohol consumption during pregnancy
• A mother who has diabetes
• Taking some types of medications during pregnancy

Children born with Down syndrome, a genetic condition resulting from an extra copy of chromosome 21, also are at increased risk of having truncus arteriosus and other congenital heart defects.

Complications

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.

Preparing for your appointment

When you contact your baby's doctor about your concerns, he or she may ask you to schedule an appointment or immediately refer you to a heart specialist for children (pediatric cardiologist). This will depend on the severity of the signs and symptoms you have described over the phone.

Because there's often a lot of ground to cover, it's a good idea to be well prepared for your appointment. Here's some information to help you get ready for your appointment and to know what to expect from your doctor.

What you can do
Preparing a list of questions will help you make the most of your time together with your baby's doctors:

• What kinds of tests will my child undergo?
• What are the options for treatment? What are the possible complications of treatment?
• What is the long-term outlook for my child?
• What impact would a heart defect or the subsequent treatment have on another condition my baby has?
• Are there any brochures or other printed material that I can take home with me? What Web sites do you recommend visiting?

In addition to the questions that you've prepared to ask your baby's doctor, don't hesitate to ask questions during your appointment at any time that you don't understand something.

What to expect from your doctor
Your child's doctor will likely ask you the following questions:

• Does your baby ever appear blue?
• How long are feeding times, or how much does your baby drink?
• How often and how long is your baby sleeping?
• How does your baby respond to touch?
• Have you noticed changes in any of these behaviors?

When your baby was born, your baby's height, weight and head circumference were recorded, and these measurements are taken at all regularly scheduled appointments with your child's doctor. He or she will repeat these measurements during a special appointment and determine if there has been any delay in growth.

Your baby's doctor will also listen to your baby's lungs to assess his or her breathing and the possibility of fluid in the lungs. The doctor will listen to your baby's heart to determine if there are irregular heartbeats (arrhythmia) or an abnormal whooshing sound caused by turbulent blood flow (heart murmur).

For babies with truncus arteriosus, much of their medical care is provided by a pediatric cardiologist along with a pediatric cardiac surgeon and often a whole team of specialized staff.

Tests and diagnosis

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:

Echocardiogram
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.

X-ray
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.

Treatments and drugs

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
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.

Coping and support

Caring for a baby with a serious heart problem, such as truncus arteriosus, can be challenging. Here are some strategies that may help make it easier:

• Seek support. Ask for help from family members and friends. Contact nonprofit organizations, such as the American Heart Association or Mended Hearts, for information about support groups in your area.
• Record your baby's health history. Write down your baby's diagnosis, medications, surgery and other procedures, the dates they were performed, your pediatric cardiologist's name and phone number, and any other important information about your baby's care. It's also very helpful to include a copy of the operative report from your child's surgeon in your records. This information will help you recall the care your child has received, and it will be useful for doctors unfamiliar with your child who need to review his or her health history.
• Talk about your concerns. You may worry about the risks of vigorous activity, even after your child has had corrective surgery. Talk with the cardiologist about which activities are safe for your child. If some are off-limits, encourage your child in other pursuits rather than focusing on what he or she can't do. If other issues about your child's health concern you, discuss them with your child's doctor or pediatric cardiologist.

Prevention

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.