Transposition of great arteries (TGA)
A simple illustration of TGA
The normal heart has 4 chambers, 2 on the right side and 2 on the left side. The right sided chambers contain oxygen poor or blue blood and the left sided chambers contain oxygen rich or red blood. The right and left sides of the heart are separated by a wall. ‘Blue’ blood from the right pumping chamber is pumped into the lungs through a vessel called the pulmonary artery. ‘Red’ blood from the left pumping chamber is pumped into the body through a vessel called the aorta.
In transposition of great arteries the two blood tubes are swapped across; the aorta arises from the right side and the pulmonary artery arises from the left side. This means that the blue blood from the right side circulates in the body resulting in a 'blue baby' and the red blood from the left side circulates in the lungs.
This condition is present right from the time the heart is formed at 6-8 weeks of pregnancy and can be detected during the ultrasound scan that is performed in early pregnancy. After birth the baby is noted to be blue as the oxygen levels in the blood are very low. If left untreated most of the babies with this condition will die within the first month of life and 95% will die within the first year of life.
Sometimes these babies need urgent treatment after birth and a life-saving balloon procedure called balloon atrial septostomy may need to be performed. This is done in order to improve the oxygen levels in the blood. This however is only a temporary procedure and the only definitive treatment is open heart surgery. This has to be carried out within the first few weeks of life and is called an Arterial Switch Operation. It involves swapping the blood vessels over so that they are connected to the correct side of the heart.
The heart after the Arterial Switch operation
Although the operation carries a risk there is a success rate of around 90% in a good children’s cardiac unit. The long term results of this procedure are very good and these patients go on to lead a near-normal life.
If the child does not get prompt, timely treatment the risks of the operation increase. Also, there is a point in time beyond which the arterial switch operation cannot be performed. In this case, a less ideal operation called the Atrial Switch Operation will need to be carried out.
In summary, transposition of great arteries is a serious birth defect of the heart that needs early detection and timely treatment. Although the operation does carry some risk, the long-term outcome is generally very good and we expect most patients to lead a 'normal' life.