Truncus Arteriosus (or Common Arterial Trunk)

What is Truncus Arteriosus?

When a baby’s heart is developing in the womb, one large blood vessel, the truncus arteriosus, should divide to become the two main arteries: the aorta, and the pulmonary artery.  

The aorta carries red (oxygenated) blood from the heart to the body, and the pulmonary artery carries blue (deoxygenated) blood to the lungs.

If the aorta and pulmonary artery do not divide, the child is born with a persistent truncus arteriosus or common arterial trunk. This one big artery has one large valve instead of there being two arteries with pulmonary and aortic valves.

A part of the wall between the left and right ventricles is missing (Ventricular Septal Defect). This means that the truncus arteriosus is able to receive blue blood from the right side of the heart, and red blood from the left side of the heart.  

The truncus arteriosus divides into the aorta and the pulmonary arteries, which carry this mixture of blood to the lungs and to the body. There are 3 possible types:

• Type 1 - the pulmonary artery branches off just above the valve.
• Type 2 - the pulmonary arteries to the lungs branch separately but close together directly off the truncus.
• Type 3 - the pulmonary arteries branch separately and are further apart.

There may be other differences that affect how your child is treated – e.g. the VSD may be missing or the valve may not work well.

The result of truncus arteriosus is usually that too much blood is going to the lungs and too little red (oxygenated) blood is reaching the body.

Diagnosis

Truncus Arteriosus can sometimes be seen on a scan during pregnancy.

After birth your baby may have been diagnosed because a heart murmur was heard. The child becomes increasingly blue (cyanosed), because of the blue blood going being pumped to the body instead of the lungs.  

Because of the high pressure they will develop congestive heart failure as blood flow to the lungs increases, be breathless, difficult to feed and ‘fail to thrive’.

When a heart defect is suspected the tests used can be:

• Pulse, blood pressure, temperature, and number of breaths a baby takes a minute;
• Listening with a stethoscope for changes in the heart sounds;
• An oxygen saturation monitor to see how much oxygen is getting into the blood;  
• A chest x-ray to see the size and position of the heart;
• An ECG (electrocardiogram) to check the electrical activity;
• An ultrasound scan (echocardiogram) to see how the blood moves through the heart;
• Checks for chemical balance in blood and urine; and
• A catheter or Magnetic resonance Imaging test may be needed.

Treatment

The aim of the treatment is to separate the circulation of the blood so that blue blood goes to the lungs, and red to the body.

Surgery

Surgery will be needed before the increased pressure damages the lungs (pulmonary vascular disease).  This will be open heart surgery.  The heart will need to be stopped and opened to repair it.  This means that a machine will have to take over the job that the heart and lungs normally do – the heart bypass machine.  

Surgery may involve placing a donor lung artery from the right ventricle to the branch lung arteries, and a plastic patch is usually used to close the hole (VSD). There is no risk of rejecting the donor lung artery, since it is not living blood vessel.

The truncus will now act as the aorta, carrying red blood from the left ventricle to the body. Surgeries will need to be repeated as your child grows.

The more complicated types of truncus arteriosus may be treated with a Fontan operation.

How the child is affected

Most babies are well, active, and gaining weight a few days after surgery. They will have a scar down the middle of the chest, and there may be small scars where drain tubes were used.  These fade very rapidly in most children, but they will not go altogether.  Smaller scars on the hands and neck usually fade away to nothing.

It is not uncommon for a child to pick up an infection, such as a chest infection or infected wound, while undergoing treatment.

After the surgery, your child will be monitored regularly by a cardiologist. Some of these problems can occur after surgery or later in life:

• The truncal valve may need replacement with an artificial valve.  If this happens the child will need to take an anticoagulant medicine to stop blood clots forming.  The anticoagulant effect has to be monitored frequently using a blood test – see Warfarin fact sheet.
• Because the flow of blood is slower than it should be in the conduit, there may be a danger of blood clotting – if this is thought to be a problem in your child’s case, your child may need to take anticoagulants (aspirin or warfarin).
• The electrical system of the heart is sometimes damaged, causing a very fast heart beat – a Supraventricular Tachycardia, or SVT – to occur.  This may be improved with medicine or ablation.

Unfortunately, because the conduit that has been put in doesn’t grow with the child, further surgery will be needed as he or she gets bigger.