atrial septal defect ( asd ) is one of the most common congenital heart diseases encountered in outpatient clinics .
surgical closure has traditionally been accepted as the gold standard treatment for an asd with volume overloading .
transcatheter device closure was developed as an alternative to surgery by king et al.1 ) in 1976 and accepted as a safe and effective treatment replacing surgical closure since the 2001 approval of the amplatzer septal occluder ( aso ) ( st .
however , due to the unfavorable anatomy of secundum asd , a detailed evaluation of asd has become crucial for device closure2,3 ) .
thus , an evaluation of asd in terms of successful transcatheter device closure is needed .
transthoracic echocardiography ( tte ) is the gold standard for diagnosing asd and has excellent sensitivity in young patients .
in general , the subcostal view will definitely show asd , and the apical four - chamber view and the parasternal short axis view are also helpful for making the diagnosis .
however , when tte imaging is poor due to obesity , previous thoracic surgery , or large breasts , transesophageal echocardiography ( tee ) is an alternative that provides excellent images .
high - resolution contrast computed tomography ( ct ) and advanced cardiac magnetic resonance imaging ( mri ) can also be used to delineate asd .
the general indications for closure include evidence of right cardiac volume overload even without symptoms . before deciding on closure , bidirectional shunt and pulmonary hypertension associated with asd should be evaluated with pulmonary vasodilators or the balloon occlusion test4 ) .
indications for the closure of asd in adults and children have been published by the american heart association5,6 ) .
most asds are asymptomatic , but symptomatic asds should be corrected surgically at any age .
elective surgical closure of asymptomatic asds is performed at 3 - 5 years of age7 ) .
transcatheter closure of an asd with the aso has been recommended for patients weighing > 15 kg .
however , the weight restriction has eased over time , and many authors reported safe and effective device closure in patients weighing < 15 kg8,9 ) .
the sinus venosus , coronary sinus , and primum types of asd require surgical closure while most secundum asds are amenable to transcatheter closure .
in addition to the size of the asd , the shape , number of defects , and surrounding rims are important for successful transcatheter closure . usually , four or five rims should be evaluated before deciding on device closure .
the anterior or retro - aortic rim can be evaluated on a parasternal short axis image .
the posterior rim and anterior - inferior rim can be seen in the apical four - chamber view .
the posterior - superior and posterior - inferior rims should be evaluated from the subcostal view or right parasternal view . in general
although retro - aortic rim deficiency is very common , most asds with deficient retro - aortic rims are closed successfully by the aso11,12 ) .
however , an asd with two or more deficient rims should not be closed with a device , as device embolization is highly expected in cases with significantly deficient posterior - inferior rims3 ) .
a sufficient rim is an indicator not only of length , but also of the floppiness of the rim tissue .
durongpisitkul et al.13 ) reported that a posterior - inferior rim length of at least 10 mm is safe for successful device closure of an asd .
1 ) , and tee has been accepted as the best method for a complete evaluation of the defect for the purpose of device closure14 ) ( fig .
2 ) . nevertheless , the evaluation of the posterior - inferior rim may be incomplete in some patients13 ) .
by contrast , cardiac ct offers superb spatial and temporal resolution with a short scanning time .
it allows for detailed imaging not only of intracardiac structures , but also of coexisting anomalies . in my experience ,
additive abnormal findings that include extracardiac lesions as well as cardiac lesions can be detected on ct images .
my experience includes the detection of silent coronary stenosis and lung problems outside of the asd on ct images .
some reports addressed the usefulness of cardiac ct for asd device closure and demonstrated superior resolution and measurement of the surrounding rims using cardiac ct15,16 ) ( fig .
however , the radiation hazard posed by ct should not be ignored despite the use of a minimal exposure technique .
we recommend cardiac ct for selected cases that have a complicated asd or a large asd with a rim deficiency .
very few reports are available on the use of cardiac mri for evaluating an asd prior to device closure17,18 ) .
it is not surprising that many asds are not circular in shape , and indeed complex asd shapes have been described by some authors16,19,20,21,22,23 ) .
three - dimensional ( 3d ) images should be reconstructed from 2d images for a complete understanding of defect shape .
this can be achieved by real - time 3d tee or 3d cardiac ct ( fig .
the preprocedural evaluation of an asd undergoing device closure should be different from that used before surgical closure .
devices used for asd closure do not reflect the various defect shapes , and all asds are assumed to be circular based on the longest diameter .
device closure of an asd that is 10 mm in the long diameter and 5 mm in the short diameter can differ from the closure of a nearly circular defect with a 10-mm diameter .
song et al.16 ) reported that an oval shaped asd with a short diameter that was 75% smaller than the long diameter could be closed safely with an aso smaller than that used for a circular defect .
they also reported their experience of a successful transcatheter closure of an asd that was 45 mm in the long diameter and 24 mm in the short diameter with a 38-mm aso16 ) .
it is well known that defects within 7 mm of each other can frequently be closed with a single device .
we experienced the successful closure of multiple asds with multiple asos or a cribriform device24 ) .
two - dimensional echocardiographic images have difficulty in comprehensively defining the shape of an asd or multiple asds . by contrast , the excellence of 3d images has been reported by many interventionists .
reconstructed en - face ct or tee images are superior for visualizing the morphology and the number of defects16,22,23,24,25 ) .
the morphology and location of the defect may be more easily understood on 3d images obtained from ct than those obtained from tee .
however , in the case of an asd with a very thin or floppy interatrial septum , defect size and morphology can easily be distorted on the basis of ct images . even though understanding anatomy and location based on tee images can be complicated
, real - time 3d tee is used widely due to the much shorter time required for 3d reconstruction .
balloon sizing has been accepted as an integral part of asd device closure with an aso , but several reports described techniques that did not use balloon sizing16,23,26,27 ) .
oversizing has been suspected to play an important role in cardiac erosion after implantation and should be avoided during size selection .
it is not surprising that a stretched balloon sizing technique results in frequent oversizing , which is why the stop - flow technique has replaced stretched balloon sizing28 ) .
several reports have indicated that sizing with 3d tee has similar results to those of the balloon sizing technique29,30 ) .
the longest diameter at the end - systole phase has been used to size the device , but defect morphology is often ignored when selecting device size .
seo et al.31 ) found that devices implanted using the balloon sizing technique in large oval shaped defects were smaller than those used in large circular defects , and suggested that device size could be selected using 3d tee linear parameters .
by contrast , song et al.23 ) measured defect area by planimetry on an en - face 3d tee image and found that the defect area correlated nicely with the device size selected by the stop - flow technique ( fig .
these data indicate that oversizing can be avoided by considering defect morphology in 3d images of the asd .
2d tee or intracardiac echocardiography ( ice ) has been used during the procedure even though tte can be used in some cases .
although it necessitates other venous access and a biplane image is not obtainable , ice can be conveniently used by the same operator simultaneously . in particular
, ice provides a more accurate image of the posterior - inferior rim that is superior to a tee image . an accurate size evaluation for adequate device size selection during the procedure
rigatelli et al.35 ) reported their experience with ice during asd device closure , achieving a good outcome even without the use of balloon sizing methods .
real - time 3d tee provides several benefits during asd device closure , such as visualization of the catheter and wire course , position of the device , and the interaction between the device and surrounding structures after implantation36 ) . in the case of multiple asds or a multifenestrated asd
, wire selection should be monitored for successful complete closure , and real - time 3d tee is very helpful37 ) .
although transcatheter closure of an asd is technically simple and straightforward , an imaging study is potentially very important for the successful completion of the procedure .
three - dimensional tee or ct reconstructed images are helpful for an accurate understanding of the morphology and preprocedure sizing . in cases of multiple asds
 transcatheter closure of atrial septal defects has become a popular procedure . 
 the availability of a preprocedural imaging study is crucial for a safe and successful closure . 
 both the anatomy and morphology of the defect should be precisely evaluated before the procedure . 
 three - dimensional ( 3d ) echocardiography and cardiac computed tomography are helpful for understanding the morphology of a defect , which is important because different defect morphologies could variously impact the results . during the procedure 
 , real - time 3d echocardiography can be used to guide an accurate closure . 
 the safety and efficiency of transcatheter closures of atrial septal defects could be improved through the use of detailed imaging studies . 
Introduction
Diagnosis and indications for closure
Anatomical evaluation
Shape and multiplicity
Size evaluation
Guiding images
Conclusions