Atrial Septal Defect

Description

• Atrial septal defect (ASD) is a congenital defect of the interatrial septum characterized by absent or insufficient tissue. Patent foramen ovale (PFO) is not considered an ASD, because no septal tissue is missing.
• Types classified by location and abnormal embryogenesis (1)
  • 75%: ostium secundum defect, located in the midseptum
  • 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

Pediatric Considerations

• 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.

Epidemiology

Incidence

• Predominant age: present from birth, may be diagnosed at any age
• Female to male ratio 2–4:1
• No race predilection
• 1/1,500 live births
• Ostium secundum alone accounts for >90% of all congenital heart lesions in the adult population (2).

Prevalence
ASDs account for 13% of congenital heart disorders.

Etiology and Pathophysiology

• The flow across ASD is usually left-to-right 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.

Genetics

• Majority of cases are spontaneous, although rare familial cases exist.
• 25% prevalence in Down syndrome
• 5% with chromosomal abnormalities

Risk Factors

• Family history, other congenital heart defects
• Maternal age >35 years
• Gestational exposures: thalidomide, alcohol, tobacco, elevated blood glucose

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