Atrial septal defect classification
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-In-Chief: Priyamvada Singh, M.B.B.S. [2]; Assistant Editor(s)-In-Chief: Kristin Feeney, B.S. [3]
Overview
The normal septal development requires a proper alignment and fusion of the two interatrial septums i.e. septum primum and septum secundum. Failure to do so may lead to a patent fossa ovalis and the development of atrial septal defects (ASDs). Atrial septal defects are classified into various types based on their location and the nature of the embryological defect. The types of atrial septal defects that can occur are: ostium primum, ostium secundum, sinus venosus, common or single atrium and coronary sinus defects. Patent foramen ovale, commonly associated with atrial septal defects, is a sister condition involving communication between the two atria. Patent foramen ovale is not a true atrial septal defect as flap like tissue that functions usually like a one way valve is present in a PFO.
Classification
Atrial septal defects are classified into various types based on their location and the nature of the embryological defect.[1]. Isolated ASDs occur due to abnormal development of the septa between the right and left atrium of the heart and normally are not associated with other cardiac defects.
Ostium Secundum ASD
Ostium secundum ASD at the fossa ovalis account for 75% of all atrial septal defects.
Ostrium Primum ASD
An ostium primum defect or endocardial cushion defect usually occurs due to the failure in fusion of the septum primum with the endocardial cushion. This defect is commonly associated with other cardiac anomalies in the septum such as ventricular septal defect, mitral valve cleft, pulmonary stenosis, subaortic stenosis, left superior vena cava, coarctation and atrioventricular septal defect.
Sinus venosus ASD
Sinus venosus ASD defects can be of two types depending on their location in comparison to the fossa ovalis. They form 5-10% of all the atrial septal defects.
Superior Sinus Venosus Type ASD (Superior Vena Caval Defect)
The defect is superior to fossa ovalis
Inferior Sinus Venosus Type ASD (Inferior Vena Caval Defect)
The defect is inferior to the fossa ovalis.
Coronary Sinus Defects
Accounting for less than 1% of all atrial septal defects, this rare atrial septal defect occurs at the site of the coronary sinus drainage.
Patent Foramen Ovale
ASD Associated with other Malformations
ASDs are associated with other malformations in 30% of cases of atrial septal defect.
Associated defects include:
- Ostium primum ASDs /Atrioventricular canal defects: Occur due to malformation of the partitioning of the atrioventricular (AV) canal by the endocardial cushions (accounts for 15% to 20% of all atrial septal defects) and is located inferiorly near the crux of heart. It is most commonly associated with other malformations such as cleft in the anterior mitral valve leaflet. AV canal defects can be classified as: complete, incomplete, and common atrium.
- Ostium primum ASD or Ostium secundum ASD: Aneurysmal formations found in some patients and may have multiple small fenestrations.
- Patent foramen ovale (PFO): A flap like formation where communication exists between the right and left atria. It is commonly associated with atrial septal defects, however, it is not technically considered a true atrial septal defect as no septal tissue is missing. There is not continuous flow across a PFO as there is with an ASD. There is only flow across a PFO when there is an increase in right atrial pressure such as occurs during the valsalva maneuver.