It is well known that morphological variations of ASD are frequent, and appropriate patient selection for transcatheter ASD closure is crucial for successful procedure. ASDs are grouped into four major categories: ostium primum, ostium secundum, sinus venosus, and coronary sinus septal defect. Secundum defect is the most common type of ASDs in which the defect involves the region of fossa ovale, and this type is indicated for transcatheter ASD closure. Coronary sinus septal defect is a rare type, in which a communication occurs between the coronary sinus and the left atrium as a result of unroofed coronary sinus. Primum septal defect and sinus venosus defect are indicated for surgical repair. Regarding coronary sinus septal defect, although surgical repair is the standard treatment for this type of ASD, there are some case reports in which transcatheter closure was successful without any conduction disturbance [16].

In patients with secundum septal defect, two crucial parameters, those are the maximal ASD diameter in order to select a device with the appropriate size and the surrounding rim dimensions to optimize the placement of the device, which should be assessed to select patients for procedure. The maximum defect diameter must be less than 38 mm. Most of ASDs have ellipsoidal shape, and it varies during cardiac cycle. The major axis diameter of the defect measured in the phase of ventricular end systole is mandatory for selecting the optimal device size, especially in patients undergone the procedure without balloon sizing or multiple defects. Transcatheter closure of large ASD with a maximal native diameter of >30 mm is still challenging, and alternative special techniques for deployment of the device are usually required. In regard to the classification of surrounding rims, although there are some differences among studies, distances from ASD to aorta (superoanterior rim), superior vena cava (superoposterior rim), right upper pulmonary vein (posterior rim), inferior vena cava (inferoposterior rim), coronary sinus, and atrioventricular valve (inferoanterior rim) are assessed. The definition of rim deficiency varies among different studies; any rim was considered deficient if its length is <5 mm (Fig. 7.2) [17].

In patients with superoanterior rim deficiency, the risk of serious complication, so-called cardiac erosion may increase after the device implantation. Although the definite mechanism of “cardiac erosion” has not been established completely, previous clinical experiences suggested that an aortic rim deficiency and oversized occlusion device might be at highly related with cardiac erosion [18, 19]. However, a large number of cases with an aortic rim deficiency resulted in a successful deployment without complicating cardiac erosion. Morphological factors additional to an aortic rim deficiency should be considered in cases with cardiac erosion.

Atrial septal malalignment is a morphological characteristic frequently encountered in cases with a deficient aortic rim. Surfaces arising from septum primum and septum secundum are different in a defect with malaligned atrial septum resulting in vertical displacement and tight impingement of the right atrial disk toward the right atrium. As the device is deployed against the atrial septum from the left atrium side, the right atrium disk moved toward to the left atrium side after the release. Atrial septal malalignment causes a change in the device axis angle against the aortic root and may be a risk for cardiac erosion in catheter closure of ASD using Amplatzer Septal Occluder (Fig. 7.2). Although the observation of the both side of the disks before and after the release of the device is important, assessment of this situation before the device deployment is difficult. Device deployment against an ASD complicated with a deficient aortic rim can result in a splay of the disks across the aortic root with impingement of the device. Atrial septal malalignment can swell the tight impingement of the device, especially after releasing the cable. Thus, atrial septal malalignment may be a potential risk factor for cardiac erosion [20].

Recently, the instruction for user (IFU) of Amplatzer Septal occluder has been updated especially for avoiding cardiac erosion [19]. That is, the contraindication for defect margins less than 5 mm has been updated to include the inferior vena cava rim, because such defect character tend to be caused of oversized device selection.

Two dimensional (2D) and color Doppler transthoracic echocardiography (TTE) can demonstrate the presence of ASDs, chamber dilatation, estimated pulmonary artery pressure, shunt ratio, and other coexisting heart disease with high sensitivity and specificity in real time. And the advent of tissue Doppler imaging could facilitate the understanding of cardiac diastolic function in which impaired cardiac function before ASD closure may lead to the development of congestive heart failure after ASD closure especially in elderly patients [20]. However, in terms of accurate assessment of ASD morphology including measurements of maximal diameter and surrounding rims, 2D TTE has sometimes limited ability to visualize ASDs in detail clearly especially in adult patients; thus precise evaluation using transesophageal echocardiography (TEE) are necessary in most ASD patients.

Three-dimensional (3D) echocardiography provides better spatial visualization, and 3D TEE can delineate the 3D structure with high-resolution image. As the result, 3D echocardiography offers the ability to improve display and our understanding of complex lesions such as valvular and congenital heart disease [19–24]. In addition, although 3D echocardiography was initially based on reconstructed image from serial 2D images, which required cumbersome acquisition and time-consuming offline analysis, recently real-time 3D echocardiography using matrix array transducer has been available in TTE as well as TEE. 3D TTE is a promising modality to provide comprehensible en face image of ASD because of its noninvasiveness, low cost, portability, and wide availability (Fig. 7.3). In terms of patient selection for transcatheter ASD closure, 3D TTE has a potential to provide accurate information of ASD morphology including location, size, and surrounding rims for the treatment both in children and adults. However, there are several limitations of 3D TTE at present such as dependence on the skill of the operator, restrictive echo window especially in elderly patients, and echo dropout in the region of the mid portion which can lead to false diagnoses of large defects and both lower temporal and spatial resolutions compared to 2D TTE. On the other hand, ASD morphology can be recognized with high-quality en face image using 3D TEE. Real-time 3D TEE allows for the evaluation of various shape of ASD especially in patients with complex-shaped ASD like multiple ASDs (Fig. 7.4) [19, 22, 23]. Nowadays, intracardiac echocardiography is also available for acceptable echocardiographic guidance for this procedure, especially in simple and small defect (Fig. 7.5).

Various technical modifications were reported for transcatheter ASD closure. These are the modification of delivery sheath, deployment position, or additional material to hold the left atrial disk inside the left atrium, avoiding the left atrial disk slipping into the right atrial side [24].

Rotation of the delivery sheath within the heart, or increasing the curvature of the sheath by remolding outside the body, has been described to improve alignment [25]. Some have advocated deployment of the left atrial disk in the right or left upper pulmonary vein followed by pulling of the sheath into the right atrium to improve the approach to the atrial septum in large defects [26]. Concerns exist in this technique causing injury of the pulmonary vein. A specially designed sheath (Hausdorf sheath, Cook, Bloomington, IN) can be used to help align the left atrial disk parallel to the atrial septum [26–28]. Favorable changes in the approach to the interatrial septum and increased ability to deliver the device have been reported with the Hausdorf sheath [28]. Kutty and colleagues developed a method to modify a Mullins transseptal sheath to enhance delivery [29]. The resulting sheath is straight and has an exit orifice essential in the side of the distal portion of the sheath-a straight, side-hole delivery sheath [29]. The use of a balloon catheter [30] or a long dilator [31] to support the left atrial disk and prevent its prolapse into the right atrium during deployment has been described. Although this technique requires additional venous access, the procedure, especially balloon-assist technique, is relatively simple and less traumatic. Even in the large ASD, high procedure success can be expected. Operators are not required to be familiarized all of these techniques; however, operators should master one or two of different techniques to achieve the procedure successfully for difficult patients or defect anatomy.