Atrial septal defect classifications


 * Associate Editor(s)-In-Chief: Priyamvada Singh, M.B.B.S. [mailto:psingh@perfuse.org]; Assistant Editor(s)-In-Chief: Kristin Feeney, B.S. [mailto:kfeeney@perfuse.org]

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, are a sister condition involving communication between the two atria. It is not a true classification of atrial septal defect as no septal tissue is anatomically absent. However, hemodynamically similar issues exist.

Atrial septal defect classifications
Atrial septal defects are classified into various types based on their location and the nature of the embryological defect.


 * Isolated ASDs: Occur due to abnormal development of the septa between right and left atrium of the heart and normally not associated with other cardiac defects.
 * Ostium secundum ASD: ASDs at the fossa ovalis (accounts for 75% of all atrial septal defects).
 * Sinus venosus ASD: They 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. In superior sinus venosus type ASD (Superior vena caval defect) the defect is superior to fossa ovalis whereas in inferior sinus venosus type ASD (inferior vena caval defect) the defect is inferior to the fossa ovalis.
 * Coronary sinus defects (accounts for less than 1% of all atrial septal defects)


 * ASD associated with other malformations: Found i 30% of cases atrial septal defects, commonly associated with other defects.
 * 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.