Levo-Transposition of the great arteries

Congenitally corrected transposition of the great arteries (CC-TGA)
Diagram of the heart showing the position of the great arteries in CC-TGA
Synonyms	L-transposition of the great arteries
Specialty	Cardiac surgery, Medical genetics
Symptoms	Cyanosis, heart murmur, exercise intolerance, shortness of breath, fatigue, arrhythmias
Complications	Heart failure, arrhythmias, valve problems, right heart dysfunction, risk of sudden cardiac death
Usual onset	Present at birth, symptoms often present in infancy or early childhood
Duration	Lifelong, requires ongoing monitoring and management
Causes	The condition is caused by abnormal development of the heart during fetal life, where the atria are in the correct position, but the ventricles and arteries are transposed
Risk factors	Genetic factors, family history of congenital heart defects, other congenital conditions
Diagnosis	Echocardiogram, MRI, CT scans, cardiac catheterization for detailed imaging of the heart's structure
Differential diagnosis	Simple transposition of the great arteries, pulmonary atresia, other congenital heart defects
Prevention	No known preventive measures, prenatal screening may help identify the condition
Treatment	Surgical correction (often arterial switch operation) or medical management for symptom control
Medication	Medications for heart failure, arrhythmias, or other cardiac issues may be prescribed
Prognosis	Variable; with surgery and management, many individuals live into adulthood with a normal life expectancy, though complications can arise over time
Frequency	Rare; exact prevalence is unknown but estimated at 1 in 35,000 to 1 in 50,000 live births
Deaths	Risk of sudden cardiac death without surgical intervention, but mortality rates have improved with early diagnosis and treatment

Levo-Transposition of the great arteries is an acyanotic congenital heart defect 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; the morphological left and right ventricles with their corresponding atrioventricular valves 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).

Signs and 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.

Pathogenesis

In a normal heart, oxygen-depleted ("deoxygenated") 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 ("oxygenated") 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, deoxygenated 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 oxygenated 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

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.

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

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.