Transposition of the great arteries is a condition where the attachments of the aorta and the pulmonary trunk to the heart are swapped (“transposed”). This means the right ventricle pumps blood into the aorta and the left ventricle pumps blood into the pulmonary vessels. In this scenario are two separate circulations that don’t mix: one travelling through the systemic system and right side of the heart and the other traveling through the pulmonary system and left side of the heart.
The condition can also be associated with:
- Ventricular septal defect
- Coarctation of the aorta
- Pulmonary stenosis
During pregnancy there is normal development of the fetus. The gas and nutrient exchange happens in the placenta, therefore it is not necessary for blood to flow to the lungs. After birth the condition is immediately life threatening as there is no connection between the systemic circulation and the pulmonary circulation. The baby will be cyanosed.
Immediate survival depends on a shunt between the systemic circulation and pulmonary circulation that allows blood flowing through the body an opportunity to get oxygenated in the lungs. This shunt can occur across a patent ductus arteriosus, atrial septal defect or ventricular septal defect.
The defect is often diagnosed during pregnancy with antenatal ultrasound scans. Close monitoring is necessary during the pregnancy and arrangements should be made so that the woman gives birth in a hospital capable of managing the condition after birth.
Where the defect was not detected during pregnancy it will present with cyanosis at or within a few days of birth. A patent ductus arteriosus or ventricular septal defect can initially compensate by allowing blood to mix between the systemic circulation and the lungs, however within a few weeks of life they will develop respiratory distress, tachycardia, poor feeding, poor weight gain and sweating.
Where there is a ventricular septal defect, this will allow some mixing of blood between the two systems and provide some time for definitive treatment.
A prostaglandin infusion can be used to maintain the ductus arteriosus. This allow blood from the aorta to flow to the pulmonary arteries for oxygenation.
Balloon septostomy involves inserting a catheter into the foramen ovale via the umbilicus, and inflating a balloon to create a large atrial septal defect. This allows blood returning from the lungs (on the left side) to flow to the right side of the heart and out through the aorta to the body.
Open heart surgery is the definitive management. A cardiopulmonary bypass machine is used to perform an “arterial switch” procedure within a few days of birth. If present, a VSD or ASD can be corrected at the same time.
Last updated July 2019