Heart | Transposition of the great arteries with intact atrial septum

The heart is made up of four important chambers (two ventricles and two atria), as well as a wall called the “atrioventricular septum” that separates the left and right sides of the heart, four important valves, and critical arteries and veins that all work together to pump blood from the heart to the lungs and to the rest of the body. Serious health risks may result from the abnormal development of any of these structures.

Essential Information

  • The septum refers to the wall that separates the left side of the heart (the left ventricle and left atrium) from the right side of the heart (the right ventricle and the right atrium). Sometimes, there is a small opening in the septum, called an atrial septal defect (ASD) or a ventricular septal defect (VSD). If there is no opening, or only a very small opening, in the septum separating the left atrium from the right atrium, this is referred to as an intact or restrictive atrial septum.
  • Transposition of the great arteries (TGA) occurs when the two main arteries leaving the heart, the aorta and the pulmonary artery, are reversed in their connections. 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. If TGA occurs in combination with an intact or restrictive atrial septum, the condition is very severe. Babies born with TGA will require urgent attention to be stabilized after they are born. They will also require surgery to correct the abnormal structure of their heart.
  • In certain cases of TGA with an intact or restrictive atrial septum, a small hole may be created in the atrial septum while the baby is still inside the womb in order to help improve baby’s stability after birth.

Overview

The heart is made up of four important chambers (two ventricles and two atria), as well as a wall called the atrioventricular septum that separates the left and right sides of the heart, four important valves, and critical arteries and veins that all work together to pump blood from the heart to the lungs and to the rest of the body. Serious health risks may result from the abnormal development of any of these structures.

Transposition of the great arteries (TGA) occurs when the two main arteries leaving the heart, the aorta and the pulmonary artery, are reversed in their connections (the aorta connects to the right side of the heart instead of the left, and the pulmonary artery connects to the left side of the heart instead of the right). When this happens, 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 more severe. Babies born with TGA will require urgent attention to be stabilized after they are born. They will also require surgery to correct the abnormal structure of their heart.

TGA is typically detected on ultrasound between 18-22 weeks’ GA. These diagnoses are then confirmed by a targeted assessment of the unborn baby’s heart structure and function, called a fetal echocardiogram. Occasionally, additional imaging in the form of a fetal cardiac MRI may be required.

 

Treatment

Because the outcomes of babies with TGA with an intact or restrictive atrial septum are poor, a procedure to create a hole, or a shunt in the atrial septum may be offered while the baby is still in the womb. This procedure is done under ultrasound-guidance using a catheter, called a stent, and a small balloon. Though emergency neonatal surgery will still be required after birth, in-utero intervention may reduce the severity of the damage to the heart and the lungs and improve the survival rates for affected babies.

Referral Information (for physicians)

Procedures are typically performed as soon as the diagnosis is confirmed to allow for maximal in-utero growth. Echocardiography will be organized at The Hospital for Sick Children (SickKids). Patients should prepare for 2-3 days admission at Mount Sinai Hospital as surgical feasibility is highly dependent on fetal position. Postoperatively, out-of-province patients will be referred back to a local centre with experience in managing these high-risk cardiac conditions for further antenatal care and delivery. Local patients will have ongoing follow-up at Mount Sinai Hospital and SickKids.