Levo-Transposition of the great arteries

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levo-Transposition of the great arteries (l-Transposition of the great arteries, levo-TGA, or l-TGA), also commonly referred to as congenitally corrected transposition of the great arteries (CC-TGA), is an acyanotic congenital heart defect (CHD) in which the primary arteries (the aorta and the pulmonary artery) are transposed, with the aorta anterior and to the left of the pulmonary artery; and the morphological left and right ventricles are also transposed.

Use of the term "corrected" has been disputed by many due to the frequent occurrence of other abnormalities and or acquired disorders in l-TGA patients.

In segmental analysis, this condition is described as atrioventricular discordance (ventricular inversion) with ventriculoarterial discordance.

l-TGA is often referred to simply as transposition of the great arteries (TGA); however, TGA is a more general term which may also refer to dextro-transposition of the great arteries (d-TGA).

Another term commonly used to refer to both l-TGA and d-TGA is transposition of the great vessels (TGV), although this term can have an even broader meaning than TGA.

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Overview

In a normal heart, oxygen-depleted ("blue") blood is pumped from the right atrium into the right ventricle, then through the pulmonary artery to the lungs where it is oxygenated. The oxygen-rich ("red") blood then returns, via the pulmonary veins, to the left atrium from which it is pumped into the left ventricle, then through the aorta to the rest of the body, including the heart muscle itself.

With l-TGA, blue blood is pumped from the right atrium into the morphological left ventricle (which lies on the right side of the heart), then through the pulmonary artery to the lungs. The red blood then returns, via the pulmonary veins, to the left atrium from which it is pumped into the morphological right ventricle, then through the aorta.

Variations and similar defects

Simple and complex l-TGA

l-TGA is often accompanied by other heart defects, the most common type being intracardiac shunts such as atrial septal defect (ASD) including patent foramen ovale (PFO), ventricular septal defect (VSD), and patent ductus arteriosus (PDA). Stenosis of valves or vessels may also be present.

When no other heart defects are present it is called 'simple' l-TGA; when other defects are present it is called 'complex' l-TGA.

Symptoms

Simple l-TGA does not immediately produce any visually identifiable symptoms, but since each ventricle is intended to handle different blood pressures, the right ventricle may eventually hypertrophy due to increased pressure and produce symptoms such as dyspnea or fatigue.

Complex l-TGA may produce immediate or more quickly-developed symptoms, depending on the nature, degree and number of accompanying defect(s). If a right-to-left or bidirectional shunt is present, the list of symptoms may include mild cyanosis.

Diagnosis

l-TGA can sometimes be diagnosed in utero with an ultrasound after 18 weeks gestation. However, many cases of simple l-TGA are "accidentally" diagnosed in adulthood, during diagnosis or treatment of other conditions.

Treatment and Prognosis

Simple l-TGA has a very good prognosis, with many individuals being asymptomatic and not requiring surgical correction.

In a number of cases, the (technically challenging) "double switch operation" has been successfully performed to restore the normal blood flow through the ventricles.

• Royal Children's Hospital, Melbourne

• Mayo Clinic, Arizona - Florida - Minnesota, USA