Atrial septal defect (ASD) with bidirectional shunt
Subcostal four chamber view shows a large defect in the interatrial septum (ASD). Right atrium (RA) and right ventricle (RV) are dilated, while left atrium (LA) and left ventricle (LV) are not. Blue color on colour flow mapping indicates right to left shunt across the atrial septal defect (R>L Shunt) in the subcostal view as the flow is away from the transducer.
This view shows red coloured flow across the ASD indicating a left to right shunt (L>R shunt). In addition there is a mosaic (multi colored) jet spreading from the closed tricuspid valve into the right atrium, due to tricuspid regurgitation (TR jet).
Bidirectional shunt can occur in ASD even without pulmonary hypertension. This is because transient right to left shunt can occur in certain phases of respiration. The volume of that right to left shunt is so small that there won’t be any clinical cyanosis. But here there is severe pulmonary hypertension which has caused reversal of shunt, though some left to right shunting is also persisting. As the pulmonary hypertension progresses, the shunt may become fully right to left.