Description

• Anatomy
  • 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
  • <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

Epidemiology

• Predominant age: present from birth, may be diagnosed at any age
• Slight female predominance (2)
• No race predilection
• 2/1,000 live births

Prevalence
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

Risk Factors

• 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)