Transposition of the great vessels
Transposition of the great vessels (TGV) is a group of congenital heart defects involving an abnormal spatial arrangement of any of the great vessels: superior and/or inferior venae cavae, pulmonary artery, pulmonary veins, and aorta. Congenital heart diseases involving only the primary arteries (pulmonary artery and aorta) belong to a sub-group called transposition of the great arteries.
Although “transposed” literally means “swapped”, many types of TGV involve vessels that are in abnormal positions, while not actually being swapped with each other. The terms TGV and TGA are most commonly used in reference to dextro-TGA – in which the arteries are in swapped positions; however, both terms are also commonly used, though to a slightly lesser extent, in reference to
Dextro-Transposition of the great arteries
In dextro-Transposition of the great arteries (dextro-TGA) deoxygenated blood from the right heart is pumped immediately through the aorta and circulated to the body and the heart itself, bypassing the lungs altogether, while the left heart pumps oxygenated blood continuously back into the lungs through the pulmonary artery. In effect, two separate “circular” (parallel) circulatory systems are created. It is called a cyanotic congenital heart defect (CHD) because the newborn infant turns blue from lack of oxygen.
Levo-Transposition of the great arteries
Levo-Transposition of the great arteries is an
Simple and complex TGV
In many cases, TGV is accompanied by other heart defects, the most common type being intracardiac shunts such as atrial septal defect including patent foramen ovale, ventricular septal defect, and patent ductus arteriosus. Stenosis, or other defects, of valves and/or vessels may also be present.
When no other heart defects are present it is called ‘simple’ TGV; when other defects are present it is called ‘complex’ TGV.
Preexisting diabetes mellitus of a pregnant mother is a risk factor that has been described for the fetus having TGV.
On chest X-ray, transposition of the great vessels typically shows a cardio-mediastinal silhouette appearing as an “egg on a string“, wherein in which the enlarged heart represents an egg on its side and the narrowed, atrophic thymus of the superior mediastinum represents the string.
For newborns with transposition, prostaglandins can be given to keep the ductus arteriosus open which allows mixing of the otherwise isolated pulmonary and systemic circuits. Thus oxygenated blood that recirculates back to the lungs can mix with blood that circulates throughout the body. The arterial switch operation is the definitive treatment for dextro-transposition. Rarely the arterial switch is not feasible due to particular coronary artery anatomy and an atrial switch operation is preferred.