In an earlier post it was shown that false echo dropouts can occur in the interatrial septum as the ultrasound beam is parallel to the structure being imaged. It was also mentioned that subcostal view is best for imaging the interatrial septum. This picture in subcostal view gives an excellent image of the interatrial septum (IAS) between the right atrium (RA) above and the left atrium (LA) below. LV: Left ventricle. Most echocardiographers use this orientation for subcostal view, though it is anatomically an inverted view as the transducer is kept below the structures being imaged. On the contrary, most paediatric echocardiographers invert the image in the machine while imaging from the subcostal view in order to get a more straight forward anatomical oriented of structures being imaged.
Colour Doppler imaging of interatrial flow across and atrial septal defect or patent foramen ovale is also good in this view as the principle of Doppler is that the imaging is better when the flow being imaged is parallel to the ultrasound beam. Left to right flow will be seen as red and reversal of shunt will be shown as blue, in this view. Gradient across the defect in IAS is also accurately measured by this approach. The gradient will be significant in restrictive defects while it will be negligible in a large defect.
Reverse flow across the IAS in the absence of features of pulmonary hypertension should alert us to the possibility of total anomalous pulmonary venous drainage. This will initiate a meticulous imaging of pulmonary venous connections.