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Heart | Transposition of the great arteries with intact atrial septum

The heart is made up of four chambers (two ventricles and two atria, separated by a wall called the septum) and four valves. The foramen ovale is an opening in the septum connecting the right and left atria. The right side of the heart pumps blood to the lungs and the left side pumps blood to the brain and body. Serious health risks may result from the abnormal development of any of these structures.

Essential Information

  • Transposition of the great arteries (TGA) occurs when the connections of the two main arteries leaving the heart, the aorta and pulmonary artery, are reversed.
  • Oxygen-rich blood from the lungs may not reach the rest of the body, and oxygen-poor blood may not reach the lungs.
  • If TGA occurs in combination with an intact or restrictive atrial septum, the condition is severe.
  • If TGA occurs in combination with an intact or restrictive atrial septum, a procedure may be offered to the fetus before birth.

Overview

Transposition of the great arteries (TGA) occurs when the connections of the two main arteries leaving the heart, the aorta and pulmonary artery, are reversed. In this case, oxygen-rich blood from the lungs may not reach the rest of the body, and oxygen-poor blood may not reach the lungs.  

The foramen ovale is a hole in the inter-atrial septum which normally exists and allows oxygenated blood to shunt from the right to left atria. Sometimes the atrial septum can be either “intact” or “restrictive”. In TGA, the patency of this hole is very important after birth to help get oxygen rich blood to the fetal body and brain.

If TGA occurs in combination with an intact or restrictive atrial septum, the condition is severe. Such babies can have very low oxygen levels at birth and may be critically ill.  Babies born with TGA will require urgent stabilization and surgery to correct the abnormal structure of their heart.

Fetal Therapy

As the outcome of babies with TGA with an intact or restrictive atrial septum is poor, a procedure to either create an opening (septoplasty) or to place a stent in the atrial septum may be offered in-utero. This procedure is done under ultrasound-guidance using a fine needle, catheter, and small balloon. Though emergency surgery will still be required after birth, fetal intervention may reduce the severity of the damage to the heart and lungs and may improve the stability and minimize immediate complications after birth for affected babies.

Referral Information (for physicians)

Fetal echocardiography will be organized at the Hospital for Sick Children (SickKids). Procedures are done in the Fetal Medicine Unit at Mount Sinai Hospital. Post-operatively, out-of-province patients will be referred back to their local center for ongoing antenatal care and delivery. Local patients will have ongoing follow-up at Mount Sinai and SickKids hospitals. 

Please refer patients via the Fetal Cardiac Program at SickKids.