Atrial Septal Defect - ASD (Paediatric Cardiology/Ostium Secundum Defect)

What is Atrial Septal Defect - ASD?

Atrial septal defect (ASD) is a congenital heart defect. In fetal circulation there is normally an opening between the two atria (the upper chambers of the heart) to allow blood to bypass the lungs. This opening usually closes about the time the baby is born. If the opening is persistent it is called an ASD, and thus blood continues to bypass the lungs. This is called a shunt.

Atrial Septal Defect - ASD (Paediatric Cardiology)

Statistics on Atrial Septal Defect - ASD?

About 1 in 2000 live births.

Risk Factors for Atrial Septal Defect - ASD

The aetiology of congenital heart defects is not understood but several factors are known to be associated:1) Maternal drug abuse, alcohol abuse and radiation exposure.2) Maternal infection, particularly rubella.3) Genetic abnormalities.4) Chromosomal abnormalities (septal defects are associated with Trisomy 21- Down's syndrome).

Progression of Atrial Septal Defect - ASD

ASDs may occur in isolation or may be associated with other malformations:

Spontaneous closure of ASDs is rare after the first 2 years of life.
ASDs allow shunting of blood from one side of the circulation to the other. There are no great pressure differentials across the two atria and shunting is usually from left to right due to the greater compliance of the right heart chambers. Flow rates across the defect are usually not high².
Increased flow to the pulmonary circulation eventually leads to pulmonary hypertension, usually by the 4th decade. Atrial arrhythmias, particularly AF are common due to the physical distention of the atria⁵.
In severe cases the shunt can eventually reverse so that blood bypasses the lungs - this is termed Eisenmenger's syndrome and is a poor prognostic factor².

How is Atrial Septal Defect - ASD Diagnosed?

Chest x-ray: Prominent pulmonary vasculature may be seen. Right ventricular hypertrophy may be seen. ECG: May show some right bundle branch block and right axis deviation.

Prognosis of Atrial Septal Defect - ASD

Most commonly symptoms dont develop until the twenties when evidence of pulmonary vascular disease becomes apparent. With increasing age, risk of developing cardiac rhythm disturbances increases. By the age of 40 most patients are severely symptomatic.Cardiac failure is the most common cause of death. Others include emboli and infections.

How is Atrial Septal Defect - ASD Treated?

Large ASDs (where pulmonary blood flow is greater than 150% normal) should be repaired surgically as early as possible, preferably before 10 years. The outlook is good if pulmonary hypertension (high blood pressure in the lungs) has not developed. Otherwise, medical management of heart failure and other complications such as arrhythmias should be instigated.

Atrial Septal Defect - ASD References

[1] Anderson et al. Paediatric Cardiology. Churchill Livingstone 1987.[2] Behrman, Kliegman, Jenson. Nelson Textbook of Paediatrics 17th Ed. Saunders 2004.[3] Hurst's The Heart 8th Edition, McGRAW-HILL 1994.[4] Kumar and Clark Clinical Medicine 4th Edition, W.B SAUNDERS 1998.[5] Rudolph et al. Rudolphs's Paediatrics (21st edition). McGraw-Hill 2003.