Atrial Septal Defect
- Opening in the atrial septum allowing flow of blood between the two atria
- Patent foramen ovale is not considered an atrial septal defect (ASD) because no septal tissue is missing.
- Types classified by location and abnormal embryogenesis (1)
- 75%: ostium secundum defect, located in the mid-septum
- 15–20%: ostium primum defect, located in the inferior septum, associated with cleft mitral valve and failure of endocardial cushion development
- 5–10%: sinus venosus defect, located in the superior-posterior septum near the orifice of the superior vena cava, associated with partial defect in right upper pulmonary venous return
- < 1%: coronary sinus defect, absence of the entire common wall between the coronary sinus and the left atrium
- 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
- Female-to-male ratio 2–4:1 (2)
- No race predilection
- 1/1,500 live births (2)
- Ostium secundum alone accounts for >90% of all congenital heart lesions in the adult population (3)
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 arterial 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.
- Majority of cases are spontaneous, although rare familial cases exist (2).
- 25% prevalence in Down syndrome
- 5% with chromosomal abnormalities
- Family history, other congenital heart defects
- Maternal age >35 years
- Gestational exposures: thalidomide, alcohol, tobacco, elevated blood glucose (4).
Commonly Associated Conditions
- 70% ASDs are isolated but may occur as a component of other complex cardiac structural defects, including anomalous pulmonary venous return.
- May be associated with rare underlying genetic syndromes, including Holt-Oram (ASD present in 66%), Ellis-van Creveld, VACTERL syndrome, Down syndrome, or Noonan syndrome (4)
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