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Truncus Arteriosus

Definition :
Truncus arteriosus is a rare heart defect present at birth (congenital), in which one single great vessel (truncus) leads out of the heart, instead of a pulmonary artery and an aorta, and there’s a large hole between the bottom two chambers of the heart.

As a result of truncus arteriosus, oxygen-rich and oxygen-poor blood mix within the heart and are pumped both to the lungs and to the rest of the body. Due to excessive blood flow in the heart and lungs, truncus arteriosus can cause congestive heart failure, breathing difficulties and high blood pressure in the lungs. If left untreated, truncus arteriosus can lead to irreversible high blood pressure in the lungs.

Babies born with truncus arteriosus require surgery during the first several months of life to close the hole and repair the arteries. As part of the surgery, a tube, called a conduit, is placed in the heart to restore normal blood flow from the heart to the lungs. This conduit usually must be replaced as your child grows.

Corrective heart surgery has led to a tremendous improvement in the outlook for most babies born with truncus arteriosus. However, even after surgery, close follow-up is important for babies born with truncus arteriosus.

Causes :
Truncus arteriosus occurs during fetal growth when your baby's heart is developing. Although some factors — such as rubella or other viral illnesses during early pregnancy, diabetes, or Down syndrome — may increase the risk of this condition, in most cases the cause is unknown.

Your heart has four chambers. Normally, the pulmonary artery is attached to the lower right chamber (right ventricle). The

pulmonary artery carries oxygen-poor blood from your heart to be enriched with oxygen in your lungs. From your lungs, the oxygen-rich blood goes to your heart’s upper left chamber (left atrium), through the mitral valve into the lower left chamber (left ventricle). The aorta is normally attached to the left ventricle. It carries oxygen-rich blood out of your heart back to your body. Valves control the flow of blood into and out of the chambers of your heart. These valves open to allow blood to move to the next chamber or to one of the arteries and close to keep blood from flowing backward.

In babies who have truncus arteriosus, instead of the aorta and the pulmonary artery leading from the heart separately, they are merged into one great vessel (truncus). A large hole in the wall (septum) between the two lower chambers of the heart (ventricles) results in one large single chamber instead of two separate ones. In this chamber, oxygen-rich and oxygen-poor blood mix and are pumped both to the lungs and to the rest of the body. The valve separating the truncus from the ventricles often is abnormal and may allow blood pumped out of the heart to leak back in.

Risk Factor :
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 21st chromosome, also are at increased risk of having truncus arteriosus and other congenital heart defects.

When to seek medical advice :
Seek medical help if you notice that your baby has the following problems :

  • Shortness of breath
  • Lack of appetite
  • Poor weight gain
  • Lethargy
  • Excessive sleepiness
  • Blue color of the skin
Symptoms :
Signs and symptoms of truncus arteriosus usually develop in the first several weeks or months of life. They include :
  • Blue color of the skin (cyanosis)
  • Lack of appetite
  • Poor weight gain
  • Difficulty breathing

If your baby has truncus arteriosus, he or she may also develop signs and symptoms of congestive heart failure, including :

  • Fatigue and weakness
  • Persistent cough or wheezing with white or pink blood-tinged phlegm
  • Swelling (edema) in the legs, ankles and feet
  • Swelling of the abdomen (ascites)
  • Sudden weight gain from fluid retention
  • Decreased alertness
  • Irregular or rapid heartbeat

Diagnosis :
Signs and symptoms of truncus arteriosus usually appear during the first weeks or months of life. Your baby's doctor may suspect a heart defect, such as truncus arteriosus, if your baby is having trouble breathing or having difficulty feeding and gaining weight. Your doctor may also suspect a heart defect if he or she hears a heart murmur — an abnormal whooshing sound caused by turbulent blood flow.

Doctors typically use an echocardiogram to diagnose truncus arteriosus. In this test, high-pitched sound waves bounce off the heart to produce moving images that can be viewed on a video screen. In a baby with truncus arteriosus, the echocardiogram reveals a single great vessel (truncus) leading from the heart, a hole in the wall between the heart's lower chambers (ventricular septal defect) and, in some cases, abnormalities in the valve between the truncus and the ventricles (truncal valve).

Because an echocardiogram can track blood flow, in babies with truncus arteriosus it shows blood moving through the hole in the septum, allowing oxygen-rich and oxygen-poor blood to mix. It also reveals the amount of blood flowing into the lungs, which can help determine your baby's risk of high blood pressure in the lungs (pulmonary hypertension).

Complications :
Potential complications of untreated truncus arteriosus include :

  • Congestive heart failure. Truncus arteriosus results in congestive heart failure — a condition in which the heart can't pump enough blood to meet the body's needs.
  • Enlargement of the heart (cardiomegaly). The increased blood flow through the heart produced by truncus arteriosus forces it to work harder than normal, causing the heart to enlarge.
  • 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.
  • Eisenmenger's syndrome. Over time, permanent damage develops due to high blood pressure in the lungs (pulmonary hypertension). In this condition, called Eisenmenger's syndrome, much of the blood flow through the ventricular septal defect goes from the right ventricle to the left ventricle and bypasses the lungs entirely.

Untreated truncus arteriosus is often fatal within the first year of life, usually due to complications associated with severe congestive heart failure.

Complications later in life
People who have surgery to correct truncus arteriosus sometimes have the following associated conditions later in life :

  • Progressive pulmonary hypertension
  • Narrowing of the heart valves (stenosis)
  • Leaky heart valves (regurgitation)
  • Heart rhythm disturbances (arrhythmias)
  • Conduit problems requiring surgery

Common signs and symptoms of these complications include shortness of breath, dizziness, fatigue and a rapid, fluttering heartbeat, among others.

All infants with truncus arteriosus require surgery to correct the defect. Most undergo surgery within the first two months of life.

During the procedure, your baby's surgeon will close the ventricular septal defect, often with a patch. He or she will separate the pulmonary arteries from the single great vessel and connect them to the right ventricle by implanting a tube (conduit) with a valve between them. This allows for normal blood flow from the heart to the lungs. If the truncus valve is abnormal, the surgeon will also repair or replace it, as needed, during the procedure.

After surgery
After corrective surgery, your baby will need lifelong follow-up care with a heart doctor (cardiologist) who specializes in congenital heart disease, 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 addition, over time the conduit may become narrowed or leak and require replacement.

In most cases, truncus arteriosus cannot be prevented. If you have a family history of heart defects or if you already have a child with a congenital heart defect, before you and your partner decide to have a child, consider talking with a genetic counselor and a cardiologist experienced in congenital heart defects.

Please be aware that this information is provided to supplement the care provided by your physician. It is neither intended nor implied to be a substitute for professional medical advice. CALL YOUR HEALTHCARE PROVIDER IMMEDIATELY IF YOU THINK YOU MAY HAVE A MEDICAL EMERGENCY. Always seek the advice of your physician or other qualified health provider prior to starting any new treatment or with any questions you may have regarding a medical condition.
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