Atrial Septal Defect

Descriptive text is not available for this imageBASICS

DESCRIPTION

  • A communication in the atrial septum other than a patent foramen ovale (PFO)
  • Two major types of atrial septal defects (ASDs):
    • Secundum ASD
    • Primum ASD
  • Sinus venosus defects and coronary sinus defects are not true ASDs but result in similar physiology.
  • PFOs
    • Can be found in 25–30% of normal hearts at pathologic exam
    • Do not cause a significant intracardiac shunt.
  • Secundum ASDs
    • ~75% of all atrial communications
    • Vary in shape and may be fenestrated
  • Primum ASDs
    • ~20% of all atrial communications
    • Exist within the spectrum of atrioventricular (AV) defects due to an abnormality of the endocardial cushions
  • Sinus venosus defects
    • ~5% of all atrial communications
    • Can be of the superior or inferior vena caval (SVC or IVC) type due to deficiency of the sinus venosus septum
    • In the SVC type, the right upper pulmonary vein may drain anomalously to the SVC or right atrium.
    • In the IVC type, the right middle and/or lower pulmonary veins may drain anomalously to the right atrium.
  • Coronary sinus defects
    • <1% of all atrial communications
    • 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”)

EPIDEMIOLOGY

  • Females > males (2:1)
  • 100 per 100,000 live births
  • Represents ~8–10% of all congenital heart defects

ETIOLOGY

  • ASDs may be associated with partial or total anomalous pulmonary venous drainage, mitral valve anomalies, transposition of the great arteries, pulmonary atresia, tricuspid atresia, or hypoplastic left heart syndrome.
  • Although usually isolated, ASDs may occur as part of a syndrome (Holt-Oram [autosomal dominant]).

PATHOPHYSIOLOGY

  • A left-to-right shunt through a moderate or large ASD 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 vascular resistance decreases 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. In patients with elevated pulmonary artery pressure, a bidirectional or right-to-left shunt may be present.

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