ATRIAL SEPTAL DEFECTS 

 

EMBRYOLOGY

During embryogenesis, the septum primum extends from the base of the heart towards the endocardial cushion. The space between the two is called the ostium primum. When the fusion between the septum primum and the endocardial cushion has occurred, the septum primum fenestrates. The resulting communication between the two atria is called the ostium secundum. A second septum extends on the right side of the septum primum and covers part of the ostium secundum. The orifice that remains is the foramen ovale. The foramen ovale flap is the lower part of the septum primum.
 

ULTRASOUND

 

Link to Ultrasound

 

CLASSIFICATION

 

 

Ostium primum

- Defects that are close to the endocardial cushion. They are located postero-inferiorly near the IVC.

Ostium secundum

- Defects in the area of the foramen ovale (most common type). Tissue present between defect and mitral / tricuspid valve leaflets as well as between the defect and back wall of the atria
- Difficult to diagnose as it is in the same position as the foramen ovale
- Usually isolated
- May be related to other cardiac lesions with interatrial shunts (mitral, pulmonary, tricuspid or aortic atresia)
- Associated syndromes:
* Holt-Oram syndrome, pulmonary valve stenosis, tricuspid atresia, hypoplastic left heart, interrupted aortic arch, total anomalous pulmonary venous drainage.

Sinus Venosus

- Defect is high in the posterior septum near the inlet of the SVC or IVC, and is difficult to image antenatally
- Associated anomalies:
* Partial anomalous pulmonary venous return (90%)
* Holt-Oram syndrome
* Ellis van Creveld syndrome.

Coronary Sinus

- Rare type located at the site of the ostium of the coronary sinus in the right atrium. The "unroofed" coronary sinus opens via a defect in its distal wall directly into the left atrium. The coronary sinus may enlarge from the increased flow. Rarely the completely absent (cyanotic soon after birth, as SVC blood drains directly into the left atrium mixing with and diluting oxygenated blood from the lungs).

 

MATERNAL CONDITIONS ASSOCIATED WITH ASD’S

 

Link to Maternal Conditions Associated with ASDs

 

FETAL ANOMALIES AND SYNDROMES ASSOCIATED WITH ASD’S

 

Link to Fetal Anomalies and Syndromes Associated with ASDs