Closure of so-called "secundum" atrial septal defects with a device inserted on a catheter necessitates precise delineation of their morphology. Echocardiography is the diagnostic method of choice to demonstrate this morphology, and to differentiate such defects located within the oval fossa from the other variants producing an interatrial communication. Precordial echocardiography usually allows selection of cases likely to be suitable for closure in this fashion. This selection is based on the localisation and the size of the deficiency in the oval fossa, the length of the interatrial septum, and the adequacy of the infolded rims surrounding the defect. Suitability for closure is reevaluated by transesophageal echocardiography, either as a separate investigation or at the start of the interventional catheterisation. This investigation requires a multiplane transesophageal echocardiographic probe, since only oblique planes will demonstrate the entrance of the systemic and pulmonary veins and their relationship to the defect. Transesophageal echocardiography serves as an important monitoring tool during the interventional procedure. As such, it is a necessary adjunct to fluoroscopy. The stretched diameter of the defect measured with a balloon is the main determinant of the choice of the type and size of the device. This diameter can be measured fluoroscopically, as well as on echo. Colorflow mapping serves to rule out residual shunting during the occlusion of the defect with the balloon. During deployment of the device, constant echocardiographic visualisation of the device and its position relative to the atrial septum facilitates proper placement. Such constant visualisation can only be provided by repeated quick acquisitions of multiple planes. Once the device is released, the investigator should continue to record the position of the device, and assess the potential for residual shunting. Most of the devices show some subtle change in position during the first 20 minutes after implantation.
