Transposition of the great arteries

Transposition of the great arteries (TGA) is the most common cyanotic congenital cardiac anomaly with cyanosis in the first 24 hours of life. It accounts for up to 7% of all congenital cardiac anomalies 1  and can be assessed with echocardiography, gated cardiac CT, or cardiac MRI.

The estimated incidence is at ~1 in 5000 births. Transposition of the great arteries is an isolated abnormality in 90% of those affected and rarely is associated with a syndrome or an extra-cardiac malformation. It is most common in infants of diabetic mothers 1.

Occurs as a result of ventriculoarterial discordance, with the aorta arising from the right ventricle and the pulmonary trunk from the left ventricle. It can be subdivided into two main types depending on the positional relationship of the aortic valve with the pulmonary valve:

This article mainly focuses on the D-loop transposition.

An isolated TGA is incompatible with life at birth without one of the following additional anomalies (which are a common occurrence 2):

Unstable associations account for 60-65% of occurrences.

Associations

Approximately 90% of TGAs occur as an isolated finding, and extracardiac syndromic associations are rare. Associations have been described with:

Plain radiograph

A frontal chest radiograph classically shows cardiomegaly with cardiac contours classically described as appearing like an egg on string 1. There is often an apparent narrowing of the superior mediastinum as the result of the aortic and pulmonary arterial configuration, i.e. parallel in D-loop transposition, with the main pulmonary artery posterior to the aorta.

Echocardiography 

Allows direct visualisation of abnormal anatomy with the aorta and pulmonary trunk lying in parallel with an absence of crossing (best seen in the base view of the fetal heart) 4.

CT/CTA

Allows direct visualisation of abnormal great vessel anatomy. Cardiac-gated cine CT can additionally assess function.

Cardiac MRI 

Allows direct visualisation of abnormal anatomy. SSFP cine sequences can additionally determine flow dynamics.

Initial Rashkind septoplasty is usually done as a palliative procedure in neonates.

Definitive surgical correction

Previously TGAs were treated with atrial switch operations, such as a Mustard repair or Senning repair, which have been superseded by arterial switch procedures 5.

Congenital heart disease

There is more than one way to present the variety of congenital heart diseases. Whichever way they are categorised, it is helpful to have a working understanding of normal and fetal circulation, as well as an understanding of the segmental approach to imaging in congenital heart disease.

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Article Information

rID: 7367
Section: Pathology
Synonyms or Alternate Spellings:
  • Transposition of the great arteries (TGA)
  • TGA

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Cases and Figures

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Previous Mus...
    Case 1: TGA with subsequent Mustard repair
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    Case 2
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    Case 3: D-TGA with VSD
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    TGA
    Case 4
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    Case 5
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    Case 6: egg-on-a-string sign
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