Transposition of the Great Arteries

How does it happen?

Transposition of the great arteries, TGA, occurs during the development of the conotruncal septum around week 5 of development, pictured above (Cameron, 2015). This structure fails to properly spiral where the aorta gets situated behind the pulmonary artery. Because of this, the aorta can be situated either to the right or left of the pulmonary artery in a more linear orientation.  This theory was proposed in 1981 by Maria de la Cruz by studying chick embryo heart development. Another theory for why this condition occurs is that the upper anterior portion of the right ventricle, subpulmonary conus, gets either resorbed or is underdeveloped. This theory was put forth by Goor and Edwards in 1973. There is some recent genetic evidence showing that a missense mutation in the gene MED13L is found to be correlated to TGA.

How is it diagnosed?

This condition is not easily seen via ultrasound of the developing fetus and often requires further testing after some indications are found during an exam. Some of these indications include cyanosis, tachypnea, and murmurs. TGA is usually caught with in the first 30 days following birth. Interestingly, there is a form of transposition of the great arteries, L-TGA, that can be left undetected till later in life when the patient begins to have symptoms of heart failure. The best way to visualize this condition is with echocardiograms in which the aorta and pulmonary artery can be seen.

Treatment

The most common treatment for TGA is an arterial switch in which the aorta and pulmonary artery are switched just above their respective valves thus restoring the proper blood flow. Another procedure that can be performed is known as the Rastelli procedure. This is for patients that have TGA, narrowing of the pulmonary artery, and a large enough VSD. During this procedure, the VSD is repaired and done in such a manner that allows for only the left ventricle to flow into the aorta. A device is then implanted shuttling blood from the right ventricle to the pulmonary artery.

Citations

Cameron, D. Surgery for congenital diseases of the aorta. J. Thorac. Cardiovasc. Surg. 149, S14–S17 (2015).

Napoli, C., Schiano, C., & Soricelli, A. (2019). Increasing evidence of pathogenic role of the Mediator (MED) complex in the development of cardiovascular diseases. Biochimie, 165, 1–8. https://doi.org/10.1016/j.biochi.2019.06.014