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 should carry red (oxygenated) blood from the heart to the body, and the pulmonary artery should carry 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 pulmonary and aortic valves.
A part of the wall between the left and right ventricles is missing (VSD) so that this single blood vessel is able to receive blue blood from the right side of the heart, and red blood from the left side of the heart.
In 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.
Link to animation of a normal heart :
http://www.childrens-heart-fed.com/__data/assets/file/0015/23622/normal.swf
Link to animation of Truncus Arteriosus :
http://www.childrens-heart-fed.com/__data/assets/file/0004/23647/truncus.swf
There may be other differences that affect how your child is treated – the VSD may be missing, the valve may not work well, and may leak or be narrowed.
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 he or she 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
- a catheter or Magnetic resonance Imaging test may be needed
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 irreparably 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.
The usual procedure is to place 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.
