Transposition of great arteries: Transposition of great arteries (TGA) is a birth defect of the heart in which aorta originates from the right ventricle (instead of the normal left ventricle) and pulmonary artery arises from the left ventricle (instead of the normal right ventricle). This results in deoxygenated blood from the right ventricle reaching the body instead of the lungs. Hence these babies are blue at birth (cyanotic congenital heart disease).

How is transposition of great arteries recognised? 

TGA is recognized when there is bluish discoloration of the baby on the very first day of life. Several countries have started screening newborn babies for oxygen saturation using small bedside probes known as pulse oximeters. Detection of a low oxygen saturation in blood alerts us of the possibility of TGA or some other similar disorder. Early detection makes early treatment feasible. TGA is confirmed by ultrasound study of the heart (echocardiography).

What is the importance of early recognition of TGA?

TGA is one of the birth defects of the heart in early surgery is needed. The best period to surgically correct TGA is within first two weeks of life. If delayed further full correction may not be feasible. Moreover if the oxygen saturation in blood is very low, the baby may need an emergency procedure to tide over the crisis known as balloon atrial septostomy. In this procedure done in the cardiac catheterization laboratory, a hole is created in the partition between the two upper chambers of the heart. This allows mixing of blood between the two chambers and enhances delivery of blood to the lungs for oxygenation. Better oxygenation reduces the bluish discolouration and improves the delivery of oxygenated blood to the brain and other vital organs.

What are the types of surgeries done for TGA?

The best surgery for TGA is arterial switch operation. The aorta is connected back to the left ventricle and pulmonary artery back to the right ventricle. Though this is the best option, it is useful only if done very early in life. If delayed, only an atrial switch operation can be done. In atrial switch operation, the aorta and pulmonary artery are not disturbed, but the inflow connections to the left and right ventricles are reversed at the atrial level (upper chambers of the heart). The net result is that deoxygenated blood is diverted to the lungs and oxygenated blood to the aorta, which is what is required. (In TGA before surgery it is the other way round). Something like a double negative becoming a positive!