Imaging of atrial septal defects

Atrial septal defect (ASD) is one of the most frequently encountered congenital heart defects, with an estimated incidence of 0.1% of live births. There are various types of ASDs, including secundum defect, primum defect, sinus venosus defect and coronary sinus defect, most common being secundum type accounting for 70-75% of the ASDs. The most frequently used imaging modality to diagnose ASD is transthoracic echocardiography utilizing 2D and 3D imaging along with color Doppler. It can provide information about the location, size, rims, hemodynamic effects of the ASD such as right heart dilatation and pulmonary hypertension and associated pulmonary venous anomalies. However, in patients with poor acoustic windows alternative imaging modalities have to be utilized, which includes transesophageal echocardiography, cardiac CT and/or MRI. Each type of imaging modality has advantages and limitations. Cardiac catheterization is primarily utilized for device closure of ASD and rarely used for diagnostic purposes. Transesophageal echocardiography is extremely useful during device closure of ASDs for assessment of accurate placement of the device, impingement on surrounding structures and residual shunts. MRI can diagnose and characterize ASDs, quantify the shunt and detect associated abnormalities, particularly vascular abnormalities. MRI can also be used for sizing the defect for surgeries and interventional procedures. CT is also a useful imaging modality, but is limited by the use of ionizing radiation. However, it provides rapid evaluation of ASDs without the need for anesthesia in infants and younger children. In this review, we will discuss and illustrate the role of these imaging modalities in the evaluation of ASD.