What is atrial septal defect (ASD)?

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atrial septal defect

Atrial septal defect (ASD) is a hole in the septum, or muscular tissue, between the left and right atria, the upper valves of the heart. The right side of a healthy heart pumps oxygen-poor blood on to the lungs; oxygen-enriched blood is pumped from the lungs through the left atrium and throughout the body. In a heart with an atrial septal defect, the hole allows the oxygen-poor blood to mix with the oxygen-enriched blood, preventing the heart from performing its job properly.

In the case of a large ASD, oxygenated blood is pumped into the lung arteries, making the heart and lungs work harder; potentially damaging the lung arteries.

If the hole is small, the patient may not be aware of symptoms or problems. In fact, many healthy adults have a small opening in the wall between the atria.

What causes an atrial septal defect (ASD)?

As the heart forms during the first eight weeks of pregnancy, it starts as a hollow tube and develops, creating a wall between the two sides of the heart. An ASD occurs when this partition remains incomplete, leaving a hole in the heart wall.

Like most congenital heart defects, ASDs are caused by a combination of factors including family history. A mother’s condition during pregnancy, such as alcohol/drug abuse, as well as diabetes, lupus and rubella can also be contributing factors.

What are the symptoms of ASD?

Because symptoms may not appear, patients often don’t know they have the defect. However, ASDs can show up as a murmur or irregular heartbeat, shortness of breath or fainting.

Other symptoms include:

  • Fatigue after mild exercise or other activity
  • Swelling in the feet, legs or abdomen
  • Heart palpitations

Types of ASDs

The four most common types of ASD include:

Ostium secundum atrial septal defect – affects nearly 70% of children with ASD. It occurs when part of the atrial septum doesn’t close completely.

Ostium primum atrial septal defect –  is a split in the mitral valve, which controls blood flow between the left atrium and left ventricle.

Sinus venosus atrial septal defect – a defect at the connection of the superior vena cava and right atrium, where deoxygenated blood typically enters the heart. This can cause flow of already-oxygenated blood through the right atrium and back through the lungs.

Coronary sinus atrial septal defect – the rarest ASD defect, affecting the coronary sinus, where the heart’s veins feed into the right atrium.

Risks of atrial septal defect (ASD)

Here are some common risks associated with ASD:

  • Enlargement of the right side of the heart – can lead to heart failure.
  • Abnormal heart rhythms – including atrial fibrillation or atrial flutter, affect 50- 60% of all patients over 40 with an ASD.
  • Stroke – small clots formed on the right side of the heart are normally filtered by the lungs; when bypassing the lungs through the ASD, clots can cause stroke.
  • Pulmonary hypertension –  high blood pressure in the pulmonary arteries supplying blood to the lungs.
  • Leaking tricuspid and mitral valves – caused by an enlarged heart.

Diagnosis of ASD

ASDs can be diagnosed with electrocardiogram as well as X-ray and electronic imaging.

Treatment of ASD

About half of ASDs in children close on their own over time. If not, a closure device is often inserted into the hole via catheterization. Surgery is typically called for only in the rare cases of ostium primum or sinus venosus ASDs.

atrial septal defect infographic

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