D-Transposition of the great arteries (TGA) with subaortal ventricular septal defect (VSD)

Transposition of the great arteries (TGA) is a pediatric cardiac congenital defect arising from an embryological discordance between the aorta and pulmonary trunk. During cardiac development, the conotruncal septum spirals toward the aortic sac thus dividing the truncus arteriosus into the pulmonary and aortic channels. These channels then become the pulmonary arteries and aorta, respectively. TGA occurs when the conotruncal septum fails to follow its spiral course and instead forms in a linear orientation. Consequently, the aorta arises from the right ventricle and the pulmonary trunk arises from the left ventricle. The most common form of TGA is referred to as dextro-TGA (D-TGA) which is characterized by the right ventricle being positioned to the right of the left ventricle and the aorta arising anterior and rightward to the pulmonary artery thus forming two parallel circuits. In the systemic circuit, deoxygenated blood returns to the right atrium pass through the tricuspid valve and is then forced back into systemic circulation by contraction of the right ventricle and passage into the aberrantly developed aorta. The second circuit is a pulmonary circuit in which oxygenated blood from the pulmonary veins drains into the left atrium, passes through the mitral valve, and is then forced back into the lungs via contraction of the left ventricle and through the pulmonary arteries. Patients typically present with cyanosis during the first 30 days of life. Complete parallel circuits are incompatible with life and thus require a patent ductus arteriosus and ventriculoseptal defect that allows mixing of oxygen-rich and oxygen-poor blood.