L-transposition of the great arteries or congenitally corrected transposition of the great arteries

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-In-Chief: Priyamvada Singh, M.B.B.S. [2]; Cafer Zorkun, M.D., Ph.D. [3]; Keri Shafer, M.D. [4]; Assistant Editor(s)-In-Chief: Kristin Feeney, B.S. [5]

• levo-Transposition of the great arteries, also commonly referred to as congenitally corrected transposition of the great arteries
• It is an acyanotic heart defect 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; 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.
• The letter L in the terms l-TGA or L-TGA refers to the a leftward or Levo aorta, versus the normal dextro or rightward aorta.

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-In-Chief: Priyamvada Singh, M.B.B.S. [2]; Cafer Zorkun, M.D., Ph.D. [3]; Keri Shafer, M.D. [4]; Assistant Editor(s)-In-Chief: Kristin Feeney, B.S. [5]

Levo-transposition of the great arteries can be classified into simple and complex based on the other types of defect associated with them.

• Simple l-TGA
  • No other associated cardiac defects are present.
• Complex l-TGA
  • l-TGA is often accompanied by other heart defects, the most common type being intracardiac shunt such as atrial septal defect including patent foramen ovale, ventricular septal defect, and patent ductus arteriosus. Stenosis of heart valves or blood vessels may also be present.

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-In-Chief: Priyamvada Singh, M.B.B.S. [2]; Cafer Zorkun, M.D., Ph.D. [3]; Keri Shafer, M.D. [4]; Assistant Editor(s)-In-Chief: Kristin Feeney, B.S. [5]

In Levo-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 ejected into the aorta.

Levo-transposition of the great arteries is a defect in which atrial and ventricular morphologies are discordant, and also the morphology of each ventricle is discordant with the great artery that comes from it. In other words this anomaly is a “double discordance” with both atrioventricular and ventriculoarterial discordance, which essentially “corrects” the physiologic abnormality. The atria are in normal position and received appropriate venous return, but the atria are connected to the opposite ventricle (RA to the LV and LA to the RV). In addition the ventricles are inversely connected to the wrong great artery.

• Levo-transposition of the great arteries is a defect in which atrial and ventricular morphologies are discordant, and also the morphology of each ventricle is discordant with the great artery that comes from it.
• This anomaly is a “double discordance” with both atrioventricular and ventriculoarterial discordance, which essentially “corrects” the physiologic abnormality.
• The atria are in normal position and received appropriate venous return, but the atria are connected to the opposite ventricle RA to the LV and LA to the RV.
• The ventricles are inversely connected to the wrong great artery.

• 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 ejected into the aorta.

• Ventricular septal defect
• Pulmonary stenosis
• Left A-V valve regurgitation (tricuspid or systemic)
• Complete heart block

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-In-Chief: Priyamvada Singh, M.B.B.S. [2]; Cafer Zorkun, M.D., Ph.D. [3]; Keri Shafer, M.D. [4]; Assistant Editor(s)-In-Chief: Kristin Feeney, B.S. [5]

The cause of most congenital heart defects is unknown.

The cause of most congenital heart defects is unknown. Factors in the mother that may increase the risk of this condition include:

• Age over 40
• Alcoholism
• Diabetes
• Prenatal nutrition
• Rubella or other viral illness during pregnancy
• Generally, TGA is not known to be associated with any specific single gene defect, but some studies have shown possible genetic association in some cases of TGA, involving deletions of chromosome 22q11.

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-In-Chief: Priyamvada Singh, M.B.B.S. [2]; Cafer Zorkun, M.D., Ph.D. [3]; Keri Shafer, M.D. [4]; Assistant Editor(s)-In-Chief: Kristin Feeney, B.S. [5]

Patients with tricuspid atresia should be differentiated from other cardiac and non-cardiac causes of cyanosis-

Cardiac causes (starts with ‘t’)-

• Tetralogy of Fallot
• Truncus arteriosus
• Total anomalous pulmonary venous connection
• Other tricuspid valve abnormalities like tricuspid regurgitaton, tricuspid stenosis

Other less common causes are- pulmonary atresia, hypoplastic left heart syndrome, anomalous systemic venous connection.

Non-cardiac causes

• Pulmonary diseases – Structural abnormalities of the lung, V/P (ventilation-perfusion mismatch), airway obstruction, pneumothorax, and hypoventilation.
• Abnormal hemoglobin like methemoglobin, polycythemia
• Peripheral cyanosis for e.g. sepsis, hypoglycemia, dehydration, and hypoadrenalism.

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-In-Chief: Priyamvada Singh, M.B.B.S. [2]; Cafer Zorkun, M.D., Ph.D. [3]; Keri Shafer, M.D. [4]; Assistant Editor(s)-In-Chief: Kristin Feeney, B.S. [5]

Among patients with congenital heart disease, CCTGA has an incidence of 0.5%, with a slight male predominance.

• Among patients with congenital heart disease, CCTGA has an incidence of 0.5%, with a slight male predominance. 95% of CCTGA occurs in “situs solitus”.
• Transposition of the great arteries TGA is one of the most common cyanotic congenital heart defects present in the first 24 hours of life.
• TGA represents 5-7% of all CHD with an incidence at birth of 20-30 in 100000 live births and almost 20 percent of all cyanotic CHD defects
• TGA is more common in infants of diabetic mothers.
• Boys outnumber girls with an approximate ratio of 2:1.
• Without treatment, 30% of infants die within the first week of life, 50% will die in the first month, 70% will die in the first 6 months and 90% of infants will die before the end of the first year.
• Heart defects are the most common birth defect, occurring in approximately 1% of live births
• Approximately one million people worldwide are currently living with a CHD
• Having a child with a CHD increases an individual’s chances of having another child with a CHD from 1% to 3%. Subsequent children born with a CHD increase that individual’s chances further.

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