Atrial Septal Defect
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- Opening in the atrial septum allowing flow of blood between the two atria
- Patent foramen ovale is also an open communication between the atria, but it is not considered an ASD because no septal tissue is missing.
- Types (by location in the interatrial septum) (1)
- Classified based on their different anatomic location and abnormal embryogenesis: secundum ASD, primum ASD, sinus venosus ASD, coronary sinus ASD
- 70%: Ostium secundum defect occurs in the fossa ovalis region.
- 15–20%: Ostium primum defect occurs in the inferior septum; often associated with cleft mitral valve and failure of endocardial cushion development
- 5–10%: Sinus venosus defect occurs in the superior-posterior septum near the orifice of the superior vena cava; usually associated with partial anomalous right upper pulmonary venous return
- Less than 1%: coronary sinus defect: Part of the entire common wall between the coronary sinus and the LA is absent.
- Hemodynamic effects
- Left-to-right shunting in late ventricular systole and early diastole
- Degree depends on size of the defect and relative pressures of the two ventricles.
- Causes excessive blood flow through the right-sided circulation, ultimately leading to reactive pulmonary hypertension and heart failure
- Systems affected: cardiovascular; pulmonary
- Most cases of ASD are detected and corrected in the pediatric population.
- The smaller the defect and the younger the child, the greater the chance of spontaneous closure.
- Predominant age: present from birth, may be diagnosed at any age
- Slight female predominance (2)
- No race predilection
- 2/1,000 live births
ASDs account for 13% of congenital heart disorders.
Etiology and Pathophysiology
- Flow across ASD usually left-to-right shunt because of higher left-sided pressures:
- Minimal right-to-left shunting in early ventricular systole, especially during inspiration
- Increased right-sided pressure/pulmonary hypertension can cause reversal of shunt flow (Eisenmenger syndrome) with resulting cyanosis and clubbing.
- Symptoms typically occur due to right ventricular and pulmonary vascular volume overload and right-sided heart failure.
- Most cases are spontaneous.
- 5% with chromosomal abnormalities; other rare mutations exist.
- 25% prevalence in Down syndrome
- Other congenital heart defects
- Family history (~7–10% recurrence)
- Thalidomide, alcohol exposure in utero, smoking, maternal age >35 years, and elevated blood glucose have been associated with increased risk (2).
Commonly Associated Conditions
- ASDs may occur as a component of other complex cardiac structural defects.
- Important to exclude anomalous pulmonary venous return
- Occasionally can indicate underlying genetic syndromes, for example, Holt-Oram (ASD present in 66%), Ellis-van Creveld, VACTERL syndrome, or Noonan syndrome.
- Overall, ~70% isolated (1)