Atrial Septal Defect:
Clinical:
ASD accounts for 10% of congenital heart disease and is the most common type of CHD to go undetected until adult life as patients are acyanotic. Females are affected more than males (2-4:1). Most small ASD's will close spontaneously by age 3 years. Long standing ASD's can produce Eisenmenger's physiology or shunt reversal. In shunts which are greater than 2:1, chronic pulmonary overcirculation may lead to pulmonary arterial hypertension. This results in increased right ventricular work. The right ventricle subsequently hypertrophies and becomes less compliant which leads to a shunt reversal across the ASD (R->L) due to elevated right atrial pressures which can result in cyanosis. These patients are also at risk for paradoxical emboli. Generally, ASD's do not close spontaneously [2].Repair should be performed in patients with right atrial and right ventricular enlargement and in patients with paradoxical emboli [9]. Repair is also considered when the pulmonary-to-systemic flow ratio is greater than 1.5 (even in the absence of symptoms) [9]. Treatment is surgical closure and there is generally improved survival, except in instances in which pulmonary hypertension (greater than 40 mm Hg) is present. Although surgical repair has a high success rate, the morbidity associated with sternotomy, cardiopulmonary bypass, and a prolonged hospital stay make it a less than ideal treatment option [6]. Transcatheter closure of secundum ASD with a self-expanding Amplatzer septal occluder has become an alternative to surgical closure [6]. The occluder has a central waist for closure of the defect and two disks for fixation [6]. A successful percutaneous closure depends heavily on the anatomy of the defect and the presence of adequate surrounding tissue on which the closure device is to be secured [7].
ASD's may be associated with Ellis-van Creveld syndrome or Holt-Oram syndrome (triphalangeal hand and carpal fusion). Sites include:
1- Foramen/Ostium Secundum: Most common type of ASD (60%). The defect is located at the fossa ovalis (mid portion of the atrial septum at the site of the foramen ovale [9]). The defect can be distinguished from a patent foramen ovale by a large, direct communication between the atria [9]. This type of ASD is associated with mitral valve prolapse. Some secundum ASD's will close spontaneously- about 15% or less of ostium secundum ASD's close spontaneously by age 4 years [2] (when found during the neonatal period. However, if the ASD has not closed in the first year of life, there is a 90% chance it will never close [5]. Of the ASD's, a secundum ASD is the most common to be identified during late childhood or early adulthood [4].
2- Ostium Primum: The next most common type [3]. A large defect
in lower, anterior atrial septum associated with abnormalities of
the atrioventricular valves (especially a cleft in the septal
leaflet of the mitral valve) and endocardial cushion defects.
Ostium primum ASDs are strongly associated with Down syndrome (in
which 65% of cases involve an atrioventricular canal defect) [9].
3- Sinus Venosus: Defect is high in posterior portion of the interatrial septum located just inferior to the junction of the SVC and RA [5]- the SVC usually overrides the defect (and is committed to both atria [8]). Some authors feel that the term sinus venous atrial septal defect is a misnomer as the true atrial septum is not involved by the defect (the defect involves the wall that separates the SVC-RA junction from the posterior and superior aspect of the LA and is extraseptal in location) [8]. There are two variants of sinus venosus ASD- in the superior, or usual type, there is an ASD at the cavoatrial junction [9]. In the inferior type, there is a communication between the inferior caval-right atrial junction and the left atrium [9]. Both types of sinus venosus ASD's are associated with partial anomalous pulmonary venous return (esp. right upper pulmonary vein to the SVC or right atrium) in 15 to 25% (up to 90% [5]) of cases. Patients with total anomalous pulmonary venous return almost always have an associated ASD, most commonly of the sinus venosus type. Sinus venosus ASD's do not close spontaneously [5].
4- Coronary sinus ASD (posteroinferior or unroofed coronary sinus or ASD of the IVC): A rare form of ASD. An unroofed coronary sinus is caused by a lack of septation between the left atrium and the coronary sinus, resulting in a left to right shunt [9]. This septal defect occurs along a spectrum from multiple fenestrations in the coronary sinus to complete atresia of the the besian valve [9]. It is associated with absence of the coronary sinus and a left SVC. It is also commonly associated with other complex cardiovascular anomalies [10].
X-ray:
On plain film there is shunt vascularity with main pulmonary artery prominence (implies shunt greater than 2:1 if detected by CXR). RAE and RVE occur due to volume overload. The left atrium is typically normal sized as blood entering the left atrium is obligatorily shunted into the low pressure right atrium. If uncorrected, most patients will develop pulmonary artery hypertension by the 3rd to 4th decade (Eisenmenger's) which is characterized by marked dilatation of the central pulmonary arteries and pruning of peripheral arteries. Patients with long standing pulmonary venous hypertension may demonstrate calcification of the main pulmonary artery branches.REFERENCES:
(1) J Thorac Imag, 95, 10: p. 1-25
(2) Pediatric Clinics of North America 1999; Driscoll DJ. Left-to-right shunt lesions. 46(2): 355-368
(3) Radiographics 2007; Leschka S, et al. Pre- and postoperative evaluation of congenital heart disease in children and adults with 64-section CT. 27: 829-846
(4) AJR 2007; Cook AL, et al. Right heart dilatation in adults: congenital causes. 189: 592-601
(5) Radiology 2008; Gaca AM, et al. Repair of congenital heart disease: a primer- part 2. 248: 44-60
(6) AJR 2009; Ko SF, et al. Amplatzer septal occluder closure of atrial septal defect: evaluation of transthoracic echocardiography, cardiac CT, and transesophageal echocardiography. 193: 1522-1529
(7) J Cardiovasc Comput Tomogr 2010; Quaife RA, et al.
Pre-procedural planning for percutaneous atrial septal defect
closure: transesophageal echocardiography compared with cardiac
computed tomographic angiography. 4: 330-338
(8) Radiographics 2012; Vyas HV, et al. MR imaging and CT
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(9) Radiographics 2015; Malik SB, et al. The right atrium:
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(10) AJR 2018; Sun L, et al. Evaluation of unroofed coronary
sinus syndrome using cardiovascular CT angiography: an
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