Atrial Septal Defect
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- 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
- 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”).
Females > males (2:1)
- Difficult to determine
- Represents 6–10% of all cardiac anomalies encountered
- 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.
- 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]).