Spontaneous Closure of Atrial Septal Defects
December 1, 1999 5 minutes read
Special Report
Spontaneous Closure of Atrial Septal Defects
By Alan Friedman, MD, FAAP
It is well known that atrial septal defects (ASD) frequently close spontaneously during childhood, especially secundum ASDs, which are small. Large ASDs and primum or sinus venosus ASDs close less frequently and often require surgical or interventional transcatheter closure. A recent large study from Iceland evaluated the rate of ASD spontaneous closure, the closure rate for different sizes of ASDs, and determined the probability of intervention in relation to the size of the ASD at diagnosis.1 This was a cross-sectional study of all children born in Iceland between 1984 and 1993 who were diagnosed with an ASD. Patients who had an ASD associated with another congenital heart disease were excluded. An ASD was found in 91 patients, with an incidence of 2.1 per 1000 births and a male:female ratio of 1:2.2. The age at diagnosis ranged from 1 week to 10 years, with a mean age of 12.1 ± 13 months. Eighty patients with secundum ASDs were included in the study.
There were 29 children with defects less than 4 mm and spontaneous closure occurred in 62% at mean follow-up of 36 ± 12 months. Another 28% demonstrated a decrease in size to what was considered a patent foramen ovale. One defect got larger with time.
There were 17 children with ASDs measuring 5-6 mm in diameter and like the small defects, 64% demonstrated spontaneous closure during a follow-up period of 38 ± 16 months. Another 29% demonstrated smaller defects at follow-up. One defect got larger with time.
There were eight children with ASDs measuring 7-8 mm and only one of these spontaneously closed. However, 50% demonstrated a decrease in size. One defect got larger with time.
There were 26 children who were found to have an ASD of 8 mm or more at diagnosis and none of these demonstrated spontaneous closure over the 35 ± 12 months of follow-up. Two patients (8%) did have a decrease in ASD size to 4 mm. The necessity for surgical closure was low in the 4 mm group but was more than 90% in the 8 mm group.
ASD is the second most common cardiac defect in children and adults. It is not uncommon for ASDs to have minimal symptoms and findings that often include a soft murmur that may be interpreted as functional in nature. As a result, children with ASDs are often diagnosed after infancy and in the school-age years.
ASDs are classified by their anatomic position in the atrial septum. Primum ASDs are part of the endocardial cushion defect family often seen in children with trisomy 21. Sinus venosus ASDs are located in the region of the superior vena cava’s entrance to the right atrium and are frequently associated with anomalous return of the right pulmonary veins. Both of these defects typically require surgical repair, as they often result in right ventricular volume overload.
The most common defect is referred to as the secundum ASD because it is a defect in the embryological secundum atrial septum. These defects often occupy the central portion of the septum in the region of the fossa ovalis and can be further classified as small (< 4 mm), moderate (4-8 mm), or large (> 8 mm) in diameter. A clinical diagnosis of an ASD and its type can be determined by routine echocardiography, which is used to define both the location and size of the ASD.
It is known that secundum ASDs can undergo a spontaneous decrease in size or even demonstrate complete spontaneous closure. The necessity for surgical or transcatheter closure of a secundum ASD is dependent on its size, associated symptoms, and the degree of right ventricular volume overload. Small secundum ASDs rarely lead to the latter and so often don’t require closure, while large defects often need to be closed. Typically, closure is undertaken prior to school age (i.e., 3-6 years) or following diagnosis in the older child or adolescent who is diagnosed in later life.
The Icelandic study, which included virtually every child diagnosed in that small country over a decade, nicely documents the natural history of ASDs. Small defects particularly tend to spontaneously resolve to complete closure or to decrease to an insignificant flow comparable to that of a patent foramen ovale. In fact, 90% of defects that measure less than 4 mm at diagnosis will follow such a course and these children should not require surgical intervention. However, it was shown that a small number of these small defects actually increased in size over time, indicating that even small ASDs must be followed to verify that they have not become significantly larger.
Conversely, it is clear that an ASD that is large at diagnosis is likely to remain so, and often requires intervention at an appropriate age. Counseling of these families and patients at the time of diagnosis should include advising them of the probable necessity of intervention by either surgical or transcatheter technique at some time. Not surprisingly, moderately sized ASDs (4-8 mm) remain problematic because although most will resolve or become hemodynamically insignificant, some will require intervention. Again, a few ASDs in this intermediate group appear to increase in size.
The phenomenon of spontaneous closure is real in patients with an ASD and usually occurs during the preschool-age period. It continues to be unclear as to how this process occurs, although it may be related to postnatal growth of the septum secundum. Alternatively, tissue reaction to flow at the edges of the defects may lead to "filling in of the defect." What is perplexing is the apparent growth of some defects. Perhaps this is related to an elliptical shape of the secundum ASD and its relative stretching with cardiac growth. Whatever the reason, it is clear that a child found to have an ASD early in life should be followed according to their age, with repeat imaging study before the age of 4 years. v
Reference
1. Helgason H, Jonsdottir G. Spontaneous closure of atrial septal defects. Pediatr Cardiol 1999;20:195-199.
True statements concerning atrial septal defects include all of the following except:
a. a defect size of less than 4 mm often closes spontaneously.
b. a defect size of more than 8 mm often closes spontaneously.
c. a defect of the embryologic secundum atrial septum often closes spontaneously.
d. a defect in the region of the sinus venosus infrequently closes spontaneously.
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