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 (TGA), which is considered the most common congenital heart lesion that presents in neonates.

Types

thumb|Subcostal [[echocardiography|echocardiographic view showing discordant ventriculoarterial connections together with the presence of parallel, rather than crossing, great arteries arising from the ventricles.]]

Transposed vessels can present with atriovenous, ventriculoarterial and/or arteriovenous discordance. The effects may range from a slight change in blood pressure to an interruption in circulation depending on the nature and degree of the misplacement, and on which specific vessels are involved.

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 two main arteries are in swapped positions; however, both terms are also commonly used, though to a slightly lesser extent, in reference to levo-TGA – in which both the arteries and the ventricles are swapped; while other defects in this category are almost never referred to by either of these terms.

Dextro-Transposition of the great arteries

Dextro-Transposition of the great arteries (also known as dextro-TGA) is a cyanotic heart defect in which the aorta arises from the right ventricle and the pulmonary artery arises from the left ventricle. This switch causes deoxygenated blood from the right heart to be pumped immediately through the aorta and circulated throughout the body and the heart itself, bypassing the lungs altogether. In this same condition, the left heart continuously pumps oxygenated blood back into the lungs through the pulmonary artery, instead of out into the body's circulation as it normally would. In effect, two separate "parallel" circulatory systems are created. It is called a cyanotic congenital heart defect (CHD) because the newborn infant turns blue (cyanotic) from the lack of oxygen.

Levo-Transposition of the great arteries

Levo-Transposition of the great arteries (also known as Levo-TGA, congenitally corrected TGA, double discordance, or ventricular inversion) is a rare, acyanotic heart defect in which the primary arteries are transposed, with the aorta anterior and to the left of the pulmonary artery, and the morphological left and right ventricles with their corresponding atrioventricular valves are also transposed. In other words, the right ventricle is on the left side of the heart and the left ventricle is on the right side of the heart. The systemic and the pulmonary circulation are connected in this condition. Complications can arise from the pressure change due to the fact that the right ventricle, which is adapted for pumping blood into the low-pressure pulmonary circulation, is being tasked with pumping blood at a much higher pressure against the high resistance of the systemic circulation, since it is now in the position of where the left ventricle is typically located.

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.

Symptoms and signs

Symptoms may appear at birth or after birth. The severity of symptoms depends on the type of TGV, and the type and size of other heart defects that may be present (ventricular septal defect, atrial septal defect, or patent ductus arteriosus). Most babies with TGA have blue skin color (cyanosis) in the first hours or days of their lives, since dextro-TGA is the more common type.

Other symptoms include:

Fast breathing (tachypnea)
Difficulty breathing (dyspnea)
Fast heart rate (tachycardia)
Poor feeding
Echocardiogram: An echocardiogram is an ultrasound of the heart that accurately assesses the heart’s structure and function, and can show the specific features of TGA, if present. This imaging modality allows for the definitive diagnosis of TGA to be made. Atrial septostomy can also be performed, usually with a cardiac catheter instead of surgery, to enlarge a natural connection between the heart's upper chambers (atria). This will allow for the oxygen-rich and oxygen-poor blood to mix, resulting in improved oxygen delivery to the baby's body.

Additional images

300px|thumb|left|Normal heart anatomy compared to d-TGA

thumb|Echocardiography of a complex transposition with a [[ventricular septal defect and pulmonary stenosis.<br />Abbreviations: LV and RV=left and right ventricle, PT=pulmonary trunk, VSD=ventricular septal defect, PS=pulmonary stenosis.]]

thumb|center|[[Echocardiogram in transposition of the great arteries. This subcostal view shows the left ventricle giving rise to a vessel that bifurcates, which is thus identified as the pulmonary artery.<br />Abbreviations: RA=right atrium, RV=right ventricle, LV=left ventricle, PT=pulmonary trunk, LPA and RPA=left and right pulmonary artery.]]