Transposition of the great vessels pathophysiology


 * Associate Editor(s)-In-Chief: Priyamvada Singh, M.B.B.S. [mailto:psingh@perfuse.org]; ; Keri Shafer, M.D. [mailto:kshafer@bidmc.harvard.edu]; Assistant Editor(s)-In-Chief: Kristin Feeney, B.S. [mailto:kfeeney@perfuse.org]

Pathophysiology
Fetal Ciculation→Oxygen-rich blood from placenta(drains to)→Umbilical vein (drains to)→Right atrium (drains to) →Fossa ovalis(drains to)→Left ventricle (drains to)→The pulmonary artery(drains to)→Ductus arteriosus(drains to)→Descending aorta

The fetus circulation in-utero is different compared to the extra-uterine circulation. The fetus tolerates a D-TGA well in-utero due to this difference in circulation. The high resistance in the pulmonary circulation compared to the placenta, allows the blood to flow to the descending aorta rather than to the lung. Due to this the fetus gets blood with a higher oxygen tension.

Pathophysiology in Dextro-TGA in extra-uterine life-


 * In normal cardiac anatomy, the aorta is positioned posterior and to the right of the main pulmonary artery. Aorta being positioned anterior and slightly rightward of the pulmonary artery. These changes cause the aorta to arise from the right ventricle and the pulmonary artery from the left ventricle (ventriculoarterial discordance).
 * In Uncorrected D-TGA the systemic and pulmonary circulations are parallel circuits which means that the deoxygenated systemic venous blood comes to the right ventricle and inplace of going to the lungs, drains back to the systemic circulation via the aorta. Similarly, oxygenated pulmonary venous blood is recirculated to the lungs via the pulmonary artery.
 * This parallel circulation is incompatible to life.
 * For a child with dextro-TGA to survive, a communication between the two parallel circuits is necessary.
 * Various connections that allow mixing in these patients are: patent foramen ovale, ventricular septal defect, atrial septal defect,patent ductus arteriosus or the bronchopulmonary collateral circulation.
 * Ventricular septal defect (VSD) occurs (in about 50%) of patients with D-TGA. Patients with a VSD may have other cardiac anomalies like pulmonary stenosis or atresia, overriding of atrioventricular valve, and coarctation of aorta.
 * Left ventricular outflow tract obstruction is common in D-TGA and is present in up to 25 percent of patients.