Interventional Cardiology

Atrial septal defect

What is an atrial septal defect?

The heart is divided into four separate chambers. The upper chambers, or atria, are divided by a wall called the atrial septum.

A defect between the heart's two upper chambers (the atria) is called an atrial septal defect (ASD). Atrial septal defects are one of the most common heart defects, and are caused by incomplete growth of the septal wall during fetal development.

There are several types of atrial septal defects - they are classified by where they occur and their size. A secundum ASD is a hole in the middle of the atrial septum, which lets blood flow from the left chamber to the right chamber or from the right chamber to the left chamber, depending on the pressures in the atria.

When an atrial septal defect is present, blood flows through the hole, usually from the left atrium to the right atrium. This increases the blood volume in the right atrium, which causes more blood to be pumped to the lungs. Because it is receiving extra blood, the right side does more than the normal share of work. This may cause you to feel tired, have difficulty in breathing or be sick more often with respiratory infections such as cold or pneumonia. It also causes the right sided pumping chamber to become stretched and enlarged.

How do I know if I have an Atrial Septal Defect (ASD)?

Congenital heart problems are caused by specific genetic defects, meaning it is a defect that exists at the time of birth. In other words, the defect is an abnormality, not a disease. The septum between the two atria of the heart did not develop normally before birth. About 20 percent of ASDs that occur in infants close on their own in the first years of life.


Atrial Septal Defects (ASD) assessment and diagnosis may be performed using:

  • ECG – an electrocardiogram, a graph of the heart’s electrical activity (heartbeat).
  • Chest x-ray – to evaluate the size of the heart and lungs.
  • Transthoracic echocardiography – an ultrasound image of the heart combined with measurements of blood flow to assess the heart’s structure and function.
  • Transoesophageal echocardiography (TOE) – an ultrasound image obtained via the oesophagus to provide a clearer image of the atria, more precisely define the defect’s size and shape and to evaluate the function of the heart valves. Using TOE, the physician can determine the type of ASD.
  • Right heart catheterisation – a procedure during which a small thin tube (catheter) is inserted into the heart via the peripheral vein. Pressures are measured in each chamber as well as the oxygen saturations (how much oxygen is present in the blood). The latter measurements determine how much blood is flowing across the defect by measuring how much the oxygen level increases beyond the site of the defect.

Why do I need an ASD closure procedure?

ASD 2Under normal circumstances, the right side of the heart pumps blood low in oxygen saturation to the lungs, and left side pumps blood that is high in oxygen saturation to the body. When ASDs occur, oxygenated and deoxygenated blood gets mixed together, flowing to the lungs increasing the volume the right side of the heart needs to pump. The possible problems associated with ASDs are increased and more significant when the size of the defect is larger (greater than 2cm). 

These risks include:

  • Right heart enlargement (right heart failure);
  • Heart rhythm disturbances including atrial fibrillation or atrial flutter;
  • Stroke
  • Pulmonary hypertension (high blood pressure in the arteries that supply the lungs). If pulmonary hypertension is severe, flow across the ASD (normally left to right) can reverse (become right to left). As a result, oxygen levels in the blood will decrease, leading to a condition known as Eisenmenger syndrome.
  • Leaking tricuspid and mitral valves as a result of the enlargement of the heart.

ASD closure procedure