Atrial septal defect

An atrial septal defect (ASD) is the second most common congenital heart defect after VSD and the most common to become symptomatic in adulthood. It is characterised by an abnormal opening in the atrial septum allowing communication of blood between the right and left atria. Due to the low pressures of the atria the lesion is typically asymptomatic until adulthood despite 2 - 4 times the normal pulmonary blood flow. A gradual congestive cardiac failure (high output) eventually develops, becoming symptomatic usually around the age of 30. There may be greater female predilection.

Pathology

Classification

There are four major types of ASDs ⁴, distinguished according to their location within the septum. They are:

• secundum ASD
  • ~ 60 - 90% of all ASDs
  • usually an isolated abnormality
• primum ASD
  • 5 - 20%
  • associated with cleft anterior mitral valve leaflet (partial atrioventricular septal defect)
• sinus venosus 
  • 5%
  • associated with anomalous right pulmonary venous return to the superior vena cava or right atrium 
• coronary sinus type ASD 
  • < 1%

Associations

ASD's usually tend to be isolated anomalies, associations include

• Holt Oram syndrome
• Ellis van Creveld syndrome
• mitral valve prolapse
• Lutembacher syndrome
• anomalous pulmonary venous return (especially with sinus venosus defects)
  • total anomalous pulmonary venous return (TAPVR)
  • partial anomalous pulmonary venous return (PAPVR)

A patent foramen ovale (PFO) is a form of atrial septal defect.

Radiographic features

Plain film (CXR)

• can be normal is early stages +/- when the ASD is small
• signs of increased pulmonary flow (shunt vascularity)
  • enlarged pulmonary vessels
  • upper zone vascular prominence
  • vessels visible to the periphery of the film
  • eventual signs of pulmonary arterial hypertension
• chamber enlargement 
  • right atrium
  • right ventricle
  • note : left atrium is normal in size
  • note : aortic arch is small to normal

Complications

• In approximately 10% of patients pulmonary hypertension develops. In this situation flow through the shunt eventually reverses and becomes right to left. The patient then becomes cyanotic. This is known as the Eisenmenger syndrome.
• paradoxical emboli
• cardiac conduction defects (e.g. atrial fibrillation, flutter)

Treatment and prognosis

ASD's do not cause any impairment in cardiac function in utero and even most neonates are asymptomatic. Either a surgical closure or a percutaneous closure with an Amplatzer closure device can often performed. But careful evaluation has to be made to ensure lack of development of elevated right heart pressures or a right to left shunt prior to any intervention.