Atrial Septal Defect

Description

• An opening in the atrial septum, other than a patent foramen ovale (PFO)
• Four major types of atrial septal defects (ASDs)
  • Secundum ASD
  • Primum ASD
  • Sinus venosus ASD
  • Coronary sinus ASD
• PFO
  • Usually does not cause a significant intracardiac shunt
  • A probe-patent PFO can be found in up to 15–25% of normal hearts at pathologic exam.
• Secundum defects
  • Make up 60–70% of all ASDs
  • Usually, there is a shunt from the left atrium to the right atrium.
• Primum defects
  • Occur in ~30% of all ASDs
  • They are usually associated with a cleft mitral valve. This defect is the result of an abnormality of the endocardial cushions and therefore is also referred to as an incomplete atrioventricular (AV) canal defect.
• Sinus venosus defects
  • Can be of the superior or inferior vena caval type and occur in ~5–10% of all ASDs
  • In ASDs of the superior vena caval type, the right pulmonary veins (usually right upper lobe) may drain anomalously to the superior vena cava or right atrium.
• Coronary sinus ASDs
  • Rare and occur in <1% of all ASDs
  • They are often associated with absence of the coronary sinus and a persistent left superior vena cava that joins the roof of the left atrium (also known as an “unroofed coronary sinus”).

Epidemiology

Females > males (2:1)

Pathophysiology

• A left-to-right shunt occurs through the ASD. For large defects, this results in right atrial and right ventricular volume overload.
• There is usually increased pulmonary blood flow.
• The left-to-right shunt generally increases with time as pulmonary resistance drops and right ventricular compliance normalizes.
• Moderate and large defects are associated with a Qp/Qs ratio of >2:1.
• The direction of atrial shunting is determined by the relative compliance of the right and left ventricles.

Etiology

• ASDs may be associated with partial or total anomalous pulmonary venous drainage, mitral valve anomalies, transposition of the great arteries, or tricuspid atresia.
• Although usually isolated, ASDs may occur as part of a syndrome (Holt-Oram [autosomal dominant]).