Transposition Of The Great Arteries (TGA)
When the aorta and the pulmonary artery are connected to the heart in reverse of their normal positions, the condition is termed as transposition of the great arteries (TGA).
- The reversed positions of the pulmonary artery and the aorta results in the reversal of the flow of oxygenated and deoxygenated blood; the oxygen-rich blood reaching the lungs instead of getting circulated to the body.
- Severe blue coloration of the infant’s skin (cyanosis) and breathing difficulty are the usual symptoms which are present at birth.
- The typical symptoms present at birth point to this condition; ECG, x-ray and echocardiography help in confirming the diagnosis.
- Surgical intervention within days of birth is necessary.
The deoxygenated blood returning to the heart normally gets emptied into the right atrium and then into the right ventricle from where it gets pumped out to the lungs via the pulmonary artery for oxygenation. When transposition of the great arteries is present, the oxygen-poor blood reaches the right ventricle as usual, but from there it gets pumped into the aorta instead of into the pulmonary artery going to the lungs. The aorta which normally supplies oxygenated blood to the other parts of the body thus receives deoxygenated blood instead. In the meantime, the oxygenated blood from the lungs returns via the pulmonary vein to the left atrium and into the left ventricle as usual. But, from the left ventricle it gets pumped back into the lungs again through the pulmonary artery, forming a closed loop between the heart and the lungs.
When infants are born with transposition of the great arteries (TGA), they may survive for a few days because of the existence of an opening between the left and right atria, called foramen ovale which allows the mixing up of the oxygenated and deoxygenated blood inside the heart. A blood vessel called ductus arteriosus, which connects the pulmonary artery to the aorta in the fetus, also allows some amount of mixing, as long as it remains patent. Often, in infants with transposition of the great arteries, a septal defect is present in the wall between the ventricles too. The limited oxygen supply which is made available to the body through the mixed blood may be sufficient for the infant to survive in the first few days after birth.
Symptoms such as bluish discoloration the body called cyanosis, and breathing difficulty, are usually present right from the time of birth. A physical examination of the infant, followed by x-ray, ECG, and an echocardiography, confirms the presence of transposition of the great arteries (TGA). Surgical correction as early as possible is necessary to save the life of the infant. Until the surgery can take place, a drug called alprostadil is given to keep the fetal circulatory pathways open. A minimally invasive procedure called balloon septostomy too may be performed for shunting the blood till surgery is performed. During surgery, the aorta is attached to the left ventricle and the pulmonary artery is connected to the right ventricle. The coronary arteries are reattached to the aorta after its repositioning.
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Yasser Elnahas
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