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Transposition of the great arteries

Dr Abhilash Sandhyala and Dr Yuranga Weerakkody et al.

Transposition of the great arteries (TGA) is one of the commonest cyanotic congenital cardiac anomalies and can account for up to 7% of all congenital cardiac anomalies ¹.

Epidemiology

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.

Pathology

Occurs as a result of ventriculo-atrial discordance with the aorta arising from the right ventricle and the pulmonary trunk from the left ventricle. It can be sub divided into two main types depending on the positional relationship of the aortic valve with the pulmonary valve.

The article mainly focuses on the D type transposition.

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

atrial septal defect (ASD) : uncommon
ventricular septal defect (VSD) : ~ 35 %
patent ductus arteriosus (PDA) : unstable due closure following birth
patent foramen ovale (PFO) : unstable

Unstable associations account for 60 - 65 % of occurrences.

Associations

Approximately 90% of TGA's occur as an isolated finding and extra cardiac syndromic associations are generally rare. associations have been described with

maternal diabetes *
congential coronary arterial anomalies

Radiographic features

Plain film

A frontal chest radiograph classically shows cardiomegaly with a cardiac contours classically described as appearing like an egg on a string ¹. There is often an apparent narrowing of the superior mediastinum as result of the aortic and pulmonary arterial configuration.

Echocardiography - ultrasound

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

Contrast CT / CTA

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

Cardiac MRI

Allows direct visualisation of anomlaous anatomy. SSFP cine sequences can additionally assess flow dynamics.

Treatment

Initially TGAs were treated with atrial switch operations, such as a Mustard repair or Senning repair, which have been superseded by arterial switch procedures ⁵.