Truncus arteriosus

Overview

Truncus arteriosus (TRUNG-kus ahr-teer-e-O-sus) is a rare, life-threatening heart condition present at birth. That means it's a congenital heart defect. Learning that your baby has a serious heart condition can be difficult. But truncus arteriosus can be treated with surgery. This treatment is often successful, especially when done soon after birth.

In a typical heart, there are two separate blood vessels that leave the heart. One is the aorta. It carries blood to the body. The other is the pulmonary artery. It carries blood to the lungs.

With truncus arteriosus, only one large blood vessel leaves the heart instead of two. This lets oxygen-poor and oxygen-rich blood mix. Because of this, the body may not get enough oxygen. Too much blood also may go to the lungs. The heart must work harder because blood does not flow the way it should.

Other names for this condition are common arterial trunk or persistent truncus arteriosus. Surgery repairs the heart structure and fixes blood flow.

A baby with truncus arteriosus also usually has a hole between the two lower heart chambers, called the ventricles. The hole is called a ventricular septal defect.

Other terms you may hear that sound like truncus arteriosus but are not the same thing are:

• Ductus arteriosus. This is the term for a blood vessel found in a developing baby, also called a fetus, that connects parts of the pulmonary artery to the aorta. If this blood vessel fails to close properly after birth, the resulting congenital heart defect is called patent ductus arteriosus. That differs from truncus arteriosus because it occurs in a different place in the heart.
• Conus arteriosus. This is the name for part of the developing heart between the truncus arteriosus and the right ventricle.

Truncus arteriosus does not look exactly the same in every baby. Researchers have grouped these different types of truncus arteriosus by the branching of the blood vessels that carry blood to the lungs, called the pulmonary arteries.

One of the most common groupings is the Collet and Edwards classification.

• Type 1. The pulmonary arteries come off of the single truncus arteriosus first as a single blood vessel before dividing into a right and left pulmonary artery.
• Type 2. The right and left pulmonary arteries come off separately but close to each other on the back wall of the truncus arteriosus.
• Type 3. The right and left pulmonary arteries come off farther away from each other on opposite sides of the truncus arteriosus.

In the past, this grouping included a type 4. But that's now considered a different condition called pulmonary atresia. Your care team can explain the type of truncus arteriosus your child has and the different ways it is corrected.

Causes

Truncus arteriosus happens as your baby's heart forms during pregnancy. There's often no clear cause. Genetics and environmental factors may play a role.

How the heart works

To understand more about truncus arteriosus, it may be helpful to know how the heart typically works.

The typical heart has four chambers. They are:

• The right upper chamber, also called the right atrium. This heart chamber receives oxygen-poor blood from the body.
• The right lower chamber, also called the right ventricle. This heart chamber pumps blood into the lungs through a large vessel called the pulmonary artery. The blood flows through the pulmonary artery into smaller vessels in the lungs where it picks up oxygen.
• The left upper chamber, also called the left atrium. This heart chamber receives oxygen-rich blood from the lungs through vessels called pulmonary veins.
• The left lower chamber, also called the left ventricle. This chamber pumps the oxygen-rich blood to the body through the body's largest blood vessel, called the aorta.

A baby's heart before birth

The way an unborn baby's heart forms during pregnancy is complex. At some point, there is a single large blood vessel leading out of the heart. The vessel is called the truncus arteriosus. It usually splits in two as the unborn baby grows in the womb. One part becomes the lower end of the body's main artery, called the aorta. The other part becomes the lower part of the pulmonary artery.

But in some babies, the truncus arteriosus never splits. The wall separating the two ventricles doesn't close all the way. This results in a large hole between these heart chambers, called a ventricular septal defect.

Babies with truncus arteriosus also often have an issue with the heart valve that controls blood flow from the ventricles to the single vessel. Often, this valve does not form in the typical way. It may not close all the way when the heart relaxes. Blood can move the wrong way, going back into the heart. This is called truncal valve regurgitation. The valve also may not open completely when the heart pumps, making it harder for blood to leave the heart. This is called truncal valve stenosis.

Complications

Truncus arteriosus causes severe changes in how blood flows through the lungs, heart and rest of the body.

Complications of truncus arteriosus in babies include:

• Breathing trouble. Extra fluid and blood in the lungs can make it difficult to breathe.
• High blood pressure in the lungs, also called pulmonary hypertension. This condition causes the blood vessels in the lungs to become stiff and narrow. It becomes hard for the heart to pump blood into the lungs.
• Enlargement of the heart. Pulmonary hypertension and increased blood flow strain the heart. The heart must work harder to pump blood. This causes the heart muscle to grow larger. The enlarged heart weakens over time.
• Heart failure. In this condition, the heart cannot supply the body with enough blood. Too little oxygen and too much strain on the heart can lead to heart failure.

Even when surgery successfully treats truncus arteriosus, some complications can happen later in life, such as:

• Pulmonary hypertension that gets worse.
• Backward flow of blood through a heart valve, called regurgitation.
• Irregular heartbeats, called arrhythmias.

Common symptoms of these complications include:

• Dizziness.
• Feeling very fast, fluttering heartbeats.
• Feeling very tired.
• Shortness of breath when exercising.
• Swelling of the belly, legs or feet.

Truncus arteriosus in adults

Rarely, some people born with truncus arteriosus live beyond infancy without heart surgery. They may live with this congenital heart disease into adulthood. But adults with the condition will almost certainly have heart failure and develop a complication from pulmonary hypertension called Eisenmenger syndrome. This syndrome is caused by lung damage that doesn't go away.

Diagnosis

Truncus arteriosus is usually diagnosed soon after a child is born. The baby may look blue or gray and have trouble breathing.

When a baby is born, a healthcare professional listens to the baby's lungs to check breathing. If a baby has truncus arteriosus, the healthcare professional may hear fluid in the lungs during this exam. The health professional also listens to the baby's heart to check for irregular heartbeats or a whooshing sound, called a murmur.

Tests

Tests to diagnose truncus arteriosus include:

• Pulse oximetry. A sensor placed on the baby's fingertip records the amount of oxygen in the blood. Too little oxygen may be a sign of a heart or lung condition.
• Chest X-ray. This test shows the condition of the heart and lungs. It can show the size of the heart. A chest X-ray also can tell whether the lungs have extra fluid.
• Echocardiogram. An echocardiogram uses sound waves to create pictures of the beating heart. This is the main test to diagnose truncus arteriosus. It shows blood flow through the heart and heart valves. In a baby with truncus arteriosus, the test shows one single large vessel leading from the heart. There's typically a hole in the wall between the ventricles.

Survival rates

Truncus arteriosus treatment greatly improves survival for babies with truncus arteriosus. After treatment and release from the hospital, almost 80% of these babies are alive after 30 years, according to research.

Truncus arteriosus is not a condition that gets better on its own. Without treatment, a baby's lifespan may be very short. Babies who aren't treated live an average of five weeks. About 15% of babies who do not have surgery for the condition survive to age 1. After that time, these children tend to get complications from the condition.

Coping and support

Caring for a baby with a serious heart condition, such as truncus arteriosus, can be challenging. Here are some strategies that might be helpful.

• Seek support. Ask for help from family members and friends. Connecting with others in support groups may help manage stress. Contact nonprofit organizations, such as the American Heart Association.
• Keep track of your baby's health history. Include details about any diagnoses, medicines, surgeries and other procedures. Note the dates for surgeries and procedures. Include medicine dosages. Write down healthcare professionals' names and phone numbers. If possible, get a copy of medical reports. This information helps you remember who provided care. It's also helpful to healthcare professionals who are not familiar with your child's health history.
• Talk about your concerns. You might worry about the risks of strenuous activity, especially after heart repair surgery. Ask your child's heart doctor, called a pediatric cardiologist, which activities are safe for your child.