Standard 2D echocardiography is often adequate to image the interatrial septum and its defects.
The oval fossa is an area of demarkation in the RA aspect of the atrial septum depicting the line of fusion between the septum primum and seccundum. A part of the septum could remain open in upto 25% of adults. If there is significant patency this may allow blood to flow often from the right atrium to the left guided by the eustachian valve. This may lead to the persistance of a defect at he region of the foramen ovale as shown in the 3D movie below. There is an association between paradoxic embolism, stroke, migane, bends and patency of the oval fossa.
However, 3D echocardiography can be very helpful in assessing the size, contour and extensions of atrail septal defects when evaluating for transcatheter closure. The image below is a 3d view of an ASD, clearly displaying the margins.
The atrial septum is very rarely grossly abnormal. Below is such a case:
A new born baby weighing 2.3kgs born with critical pulmonary atresia, and hypoplastic Right Ventricle and a dysplastic mitral valve. She was Initially palliated with 3mm right BT shunt.
The atrial septum was known to have be aneurismal with multipple fenestrations. She needs an atrial communication for maintenance of cardiac output due to the small RV and pulmonary atresia. She acutely deteriorated with abdomanal distension and elevated CVP.
Displayed below is the 3D echo of the atrial aneurism.
Three Dimensional Images showing the aneurismal inter-atrial septum protruding in to the mitral valve. There are multipple small fenestrations in the aneurism. However, these openings were abutting on the mural leaflet of the mitral valve causing dynamic obstruction to the right atrial outflow and mitral inflow.
Resection of the aneurism restored stable haemodynamics.
Atrial Septal Defect and PFO
It is a very important question that arises during trans-catheter closure of ASDs. With the increased availability of trans oesophageal 3Dimensional echocardiography, this has become a much easier question of be resolved. Below is an example of a 35 year old man who presented with a large PFO with stroke, clubbing and positive contrast study. He was brought forward for trans-catheter closure of the PFO. Routine TOE showed a large PFO with predomineant right to left shunt. There were 2 ASDs seen one placed posterio-inferiorly, close to the IVC with no posterior margin. The 3D TOE is displayed below. This showed a PFO as described on standard TOE. But there was only one ASD with a tongue of tissue seperating the ASD into two parts as shown below. The standard TOE pictures will be inserted soon.
The first view is from the left atrium showing the ASD and PFO as labelled. As the image moves, you can see the PFO flap more clearly and the tongue of atrial tissue partially dividing the ASD into two to give the illusion of 2 ASDs on standard TOE. As the images is turned to view from the right atrium, you can appreciate the oval fossa and its opeing flap on its top. On live 3D it is interesting to note it opens only during atrial systole in to the left atrium giving rise to the right to left shunt. The ASd ios seen at the posterio inferior aspect as described.