About Truncus Arteriosus

What it is

Truncus arteriosus (common truncus) occurs when a single common blood vessel comes from the heart, instead of the usual two vessels. A baby with this condition may need surgery or other procedures soon after birth. Therefore, this defect is considered a critical congenital heart defect (critical CHD).

Truncus arteriosus happens when the blood vessel from the heart in the developing baby fails to separate completely during development. This leaves a connection between the aorta and pulmonary artery. There are several different types of truncus, depending on how the arteries remain connected. There is also usually a hole between the bottom two chambers of the heart (ventricles) called a ventricular septal defect (VSD).

As blood flows to the lungs and the rest of the body, oxygen-poor blood and oxygen-rich blood are mixed together. As a result, too much blood goes to the lungs. This causes the heart to work harder to pump blood to the rest of the body.

Instead of having an aortic valve and a pulmonary valve, babies with this condition have a single common valve (truncal valve). This truncal valve controls blood flow out of the heart and is often abnormal. For example, the valve can be thickened and narrowed, which can block the blood as it leaves the heart. It can also leak, causing blood that leaves the heart to leak back into the heart across the valve.

Occurrence

Truncus arteriosus occurs in 1 out of every 15,984 live births. It can occur by itself or as part of certain genetic disorders. There are about 230 cases of truncus arteriosus per year in the United States^[1].

Signs and symptoms

Infants with truncus arteriosus usually are in distress in the first few days of life. This is because of the high amount of blood going to the lungs which makes the heart work harder. Infants with truncus arteriosus can have a bluish looking skin color, called cyanosis, because their blood doesn't carry enough oxygen. Infants with truncus arteriosus or other conditions causing cyanosis can have symptoms such as:

• Problems breathing
• Fast heart rate
• Weak pulse
• Ashen or bluish skin color
• Poor feeding
• Extreme sleepiness

Risk factors

The causes of truncus arteriosus among most babies are unknown. Some babies have heart defects because of changes in their genes or chromosomes. A combination of genes and other risk factors may increase the risk for truncus arteriosus. These factors can include things in a mother's environment, what she eats or drinks, or the medicines she uses.

Testing and diagnosis

Truncus arteriosus may be diagnosed during pregnancy or soon after the baby is born.

During pregnancy

During pregnancy, screening tests (prenatal tests) check for birth defects and other conditions. An ultrasound, a tool that creates pictures of the baby, may detect truncus arteriosus. If a healthcare provider suspects truncus arteriosus, they can request a fetal echocardiogram to confirm the diagnosis. A fetal echocardiogram is a more detailed ultrasound of the baby's heart. This test can show problems with the structure of the heart. The test can show a single large vessel coming from the heart, and how the heart is working with this defect.

After the baby is born

If a healthcare provider suspects a baby might have truncus arteriosus, they can request an echocardiogram to confirm the diagnosis. An echocardiogram is an ultrasound of the heart. This test can show problems with the structure of the heart. It can show the single large vessel coming from the heart or misshapen truncal valve. It can also show how the heart is working (or not) with this defect. This defect could be the blood leaking back into the heart or the blood moving through a hole between the ventricles.

Truncus arteriosus can also be detected with newborn pulse oximetry screening. Newborn screening using pulse oximetry can identify some infants with truncus arteriosus before they show any symptoms.

Treatments

Medicines

Some babies and children will need medicines to help:

• Strengthen the heart muscle
• Lower their blood pressure
• Help the body get rid of extra fluid

Nutrition

Some babies with truncus arteriosus become tired while feeding and do not eat enough to gain weight. To make sure babies have a healthy weight gain, a special high-calorie formula might be prescribed. Some babies become extremely tired while feeding and might need to be fed through a feeding tube.

Surgery

Surgery is needed to repair the heart and blood vessels. This is usually done in the first few months of life. Options for repair depend on how sick the child is and the specific structure of the defect. The surgery's goal is to create a separate flow of oxygen-poor blood to the lungs and oxygen-rich blood to the body. Usually, surgery to repair this defect involves the following steps:

1. Close the hole between the bottom chambers of the heart (ventricular septal defect) usually with a patch.
2. Use the original single blood vessel to create a new aorta. This will carry oxygen-rich blood from the left ventricle out to the body.
3. Use an artificial tube (conduit) with an artificial valve to connect the right ventricle to the arteries going to the lungs. This will carry oxygen-poor blood to the lungs.

What to expect long-term

Most babies with truncus arteriosus survive the surgical repair, but may need more surgery or other procedures as they get older. For example, the artificial tube doesn’t grow, so it will need to be replaced as the child grows. There also may be blockages to blood flow which may need to be relieved, or problems with the truncal valve.

A person born with truncus arteriosus will need regular follow-up visits with a cardiologist (a heart doctor). These visits will help monitor their progress and avoid complications or other health problems.