What are the principal types of atrial septal defect (ASD) based on anatomic location?

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Last updated: October 27, 2026 • View editorial policy

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ASD Classification by Anatomic Location

Atrial septal defects are classified into four principal anatomic types: secundum ASD (75-80% of cases), primum ASD (15-20%), sinus venosus defects (5-10%), and coronary sinus septal defects (<1%). 1, 2

The Four Principal Types

1. Secundum ASD (75-80%)

  • Location: Within the fossa ovalis region, centrally positioned in the atrial septum
  • Pathology: Results from deficiency of septum primum tissue, though septum secundum deficiency may also contribute 3
  • Most amenable to percutaneous device closure when anatomically suitable 4

2. Primum ASD (15-20%)

  • Location: Positioned inferiorly near the crux of the heart, just above the atrioventricular valves
  • Key distinction: This is actually a variant of atrioventricular septal defect (AVSD), not a true atrial septal defect 1, 2
  • Associated lesion: Nearly always accompanied by a cleft in the anterior mitral valve leaflet 1
  • Important caveat: The bridging leaflets are bound down to the ventricular septum, allowing shunting only at the atrial level 3

3. Sinus Venosus Defects (5-10%)

These are not true atrial septal defects from a morphological standpoint—they represent interatrial communications outside the true atrial septum 4

Two subtypes:

  • Superior sinus venosus defect (more common, ~5%): Located near the superior vena cava entry 1, 2

    • Frequently associated with partial anomalous pulmonary venous drainage of right pulmonary veins to the SVC or right atrium 1

  • Inferior sinus venosus defect (rare, <1%): Located near the inferior vena cava entry 2

4. Coronary Sinus Septal Defect (<1%)

  • Location: Defect in the roof of the coronary sinus (unroofed coronary sinus)
  • Mechanism: Creates direct communication between left atrium and coronary sinus 1, 3
  • Associated lesions: May occur with partial or total anomalous pulmonary venous connection and/or persistent left superior vena cava draining to the coronary sinus 1
  • Technical note: Not technically an ASD but causes shunting through the ostium of the coronary sinus 1

Important Distinction: Patent Foramen Ovale

PFO is NOT a true ASD 4. It represents a flaplike, tunnel-like communication where septum primum overlaps the superior limbic band of septum secundum in the anterosuperior atrial septum, with no actual tissue deficiency 1. This distinction matters for clinical management and intervention planning.

Clinical Relevance of Classification

The anatomic type determines:

  • Natural history and complications: Primum ASDs have higher rates of AV valve regurgitation; sinus venosus defects have higher rates of sinus node dysfunction, especially with older surgical techniques 5
  • Closure approach: Secundum ASDs are typically amenable to percutaneous device closure, while primum and sinus venosus defects require surgical repair 6, 7
  • Associated anomalies: Sinus venosus defects have anomalous pulmonary venous drainage in the majority of cases 1, 2

References

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