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Page 2 of 18 Zimmermann et al. Vessel Plus 2019;3:31 I http://dx.doi.org/10.20517/2574-1209.2019.010

intervention. Obstacles to device employment and countermeasures to overcome operational challenges will also
be discussed. To this end, variations or similarities of currently approved devices will be emphasized throughout this
discussion where possible. Lastly, we will offer insights into device evolution trends with the expectation of new device
developments on the horizon. We will briefly discuss up and coming areas of active research, including the emerging
fields of novel biomaterials and gene therapy.

Keywords: Atrial septal defect repair, transcatheter, endovascular, elderly, current methods

INTRODUCTION
Atrial septal defects (ASD) are one of the most common congenital cardiac abnormalities reported both
in adolescent and adult populations. The incidence of newly diagnosed atrial septal defects are second
only to bicuspid aortic valves as the most common congenital heart disease in children, with ASDs
[1]
accounting for the majority of congenital malformations diagnosed in adults . ASDs may be detected in
asymptomatic patients, though physical findings may be subtle at best making detection prior to associated
[2]
symptoms difficult in most clinical settings . Though patients with ASDs may remain asymptomatic well
into adulthood, undetected ASDs may lead to potentially irreversible complications such as arrhythmias,
[3,4]
pulmonary hypertension, stroke or their associated sequelae . The true incidence of ASD may be
significantly underestimated due to the nature of their relatively silent clinical course. One study estimates
941 per one million live births have an ASD based on the metanalysis of 43 studies, which accounts for an
[5-7]
estimated 30%-40% of adult congenital cardiac abnormalities . Ostium secundum defects are the most
commonly reported ASD as compared to defects associated with the septum primum, sinus venosus, or
[8]
unroofed coronary sinus which occur in descending frequency respectively . Although surgical closure
of ASD is considered to be safe, efficacious, and time-tested, it requires open heart surgery, longer hospital
stays, and may not be suitable for elderly patients with concomitant comorbidities .
[9]

MORPHOLOGY AND CLINICAL FEATURES OF ASDS
Location, Morphology, and suitability for surgery vs. transcatheter intervention
It is important to note that morphological variations of different types of ASDs, which determines whether
a particular defect is amenable for transcatheter closure. Briefly, ASDs fit into four major classes: ostium
secundum, ostium primum, sinus venosus, and unroofed coronary sinus [Figure 1]. Ostium secundum
defects are characterized by enlarged foramen ovale with insufficient septem secondum development,
causing incomplete closure and fusion of the atrial septum. Secundum type defects are the most common
[10]
atrial septal malformation accounting for up to 80% of ASDs . Secundum type defects are considered ideal
for transcatheter ASD closure due to their size and surrounding tissue for device fixture. Ostium primum
defects, also known as endocardial cushion defects, are defects at the level left or right atrioventricular
valves. Sinus venosus defects are located in proximity to either the superior or inferior vena cava. Lastly,
coronary sinus septal defects are characterized as an “unroofing” of the coronary sinus in which allows
communication between the coronary sinus and the LA. Mixed defects, or those involving multiple defect
types are also possible, though less commonly reported are also typically repaired with open surgery.
Although, surgical repair is considered as the standard method of treatment for all but secundum type
defects, case reports are exist describing multiple ASDs and coronary sinus defects which transcatheter
closure was successful without significant valvular impairment or conduction disturbance [11,12] .

ASD variation with age
Clinical characteristics of ASDs differ significantly in pediatric populations as compared to adults.
ASDs are detected in asymptomatic children with increasing frequency due to non-invasive screening
modalities such as echocardiography, routine ECG, and even prior to birth during routine obstetric