Atrial septal defect (ASD)

Learning objectives

Atrial septal defect (ASD) is one of the most common types of congenital heart defects, occurring in about 25% of children
Failure to close the septum between the right and left atria
Small defects usually close spontaneously during childhood
Large defects that do not close spontaneously may require percutaneous or surgical intervention
Blood flows from the left atrium to the right atrium causing a left-to-right shunt
Increase in pulmonary vascular resistance due to chronic volume overload, resulting in pulmonary hypertension
Once pulmonary pressures equal systemic pressures, the shunt across the ASD reverses, and deoxygenated blood flows into the left atrium and systemically (Eisenmenger syndrome)
Other complications:
- Atrial dysrhythmias
- Right-sided congestive heart failure
- Transient ischemic attack/stroke

Secondary to inherited disorder	Down syndrome
	Treacher-Collins syndrome
	Thrombocytopenia-absent radii syndrome
	Turner syndrome
	Noonan syndrome
Maternal exposures	Rubella
	Alcohol
	Drugs, e.g., cocaine

Ostium secundum defect: Increased reabsorption of the septum primum in the atrium’s roof, or the septum secundum does not occlude the ostium secundum
Ostium primum defect: Failure of the septum primum to fuse with the endocardial cushions
Sinus venosus defect: Superior and inferior defects occur, and neither involves the true membranous septum:
- Superior defect: The orifice of the superior vena cava overrides the atrial septum above the oval fossa and drains both the left and right atria
- Inferior defect: The orifice of the inferior vena cava overrides both atria
Coronary sinus defect: A defect or hole in the common wall between the left atrium and the coronary sinus creates a communication between the right and left atria

Transthoracic echocardiogram (gold standard diagnostic imaging modality)
Cardiac CT and MRI
Exercise testing can help determine the reversibility of shunt flow and the response of patients with pulmonary artery hypertension to activity
Cardiac catheterization is contraindicated in young patients who present with small, uncomplicated ASDs.
Differential diagnosis:
- Atrioventricular septal defect
- Ventricular septal defect
- Cyanotic congenital heart disease (sinus venosus defects and coronary sinus defects)
  - Total anomalous pulmonary venous return
  - Pulmonary stenosis
  - Truncus arteriosus
  - Tricuspid atresia

SVR, systemic vascular resistance; PVR, pulmonary vascular resistance