Transposition of the great arteries (TGA) is a form of cyanotic congenital heart disease. It is caused by the failure of the aorticopulmonary septum to spiral during septation.

Children of diabetic mothers are at an increased risk of TGA.

Aetiology

• In normal development, the aortopulmonary septum spirals
• In TGA, this spiral doesn't happen, which means that the aorta leaves the right ventricle and supplies the body while the pulmonary artery leaves the left ventricle and supplies the lungs
• This in effect creates two parallel circulations and is not compatible with life without shunting via the ductus arteriosus and sometimes septal defects

Clinical features

• cyanosis
• tachypnoea
• loud single S2
• prominent right ventricular impulse

*Most diagnosis are made antenatally

*Neonates may be diagnosed postnatally when they are cyanotic at birth - or become cyanotic as ductus arteriosis closes

Investigations

• Pulse oximetry - Sats can be quite low
• 'egg-on-side' appearance on chest x-ray