Definition and Overview

Atrial septal defect (ASD) is a congenital heart defect characterised by a hole in the atrial septum, or the wall the separates the right and left atria.

To understand this defect, it is important to know the normal flow of blood through the heart.

The heart has four chambers. The lower two are the ventricles and the upper two are the atria, which are separated by a wall of tissue called septum. The heart’s right side is responsible for pumping blood towards the lungs while its left side receives oxygen-enriched blood from the lungs. Deoxygenated blood flows from the right atrium to the right ventricle before being pumped to the lungs where it is oxygenated. From the lungs, the blood flows to the left atrium and left ventricle.

In patients with an ASD, this process is disrupted because freshly oxygenated blood flows from the left atrium to the right atrium through the hole in the atrial septum. This results in extra blood in the heart’s right side, which forces the heart to work harder to pump a sufficient amount of blood to the rest of the body. The increased blood flow to the lungs commonly results in a heart murmur.

There are four major types of ASDs; two of the most common are:

  • Ostium secundum atrial septal defect - Accounts for 70% of all ASDs and occurs when the atrial septum fails to develop fully.

  • Ostium primum atrial septal defect - Is linked to other mitral valve and ventricular septum defects.

Atrial septal defects are considered very rare. According to the Centres for Disease Control and Prevention (CDC), there are less than 2,000 babies in the United States that are born with the condition every year.

ASDs, unlike other congenital heart defects, are not always diagnosed early because most patients are asymptomatic. The condition is often found during an echocardiogram done for another reason. In many cases, ASDs are treated successfully with few or no complications, allowing patients to enjoy a normal life expectancy and go on to live healthy, active lives.

Causes of Condition

An ASD atrial septal defect occurs during the last stages of heart development, which occurs early in the pregnancy. The heart develops when two endocardial tubes fuse together to form a primitive heart tube consisting of primitive atriums and primitive ventricles. As the heart evolves, it creates partitions or walls to separate its left and right sides. An ASD occurs when this process is disrupted and the wall fails to close completely. What causes this error is yet to be established. However, doctors believe that both genetics and environmental factors that affect a woman during pregnancy have crucial roles to play in the development of congenital heart defects. These factors include:

  • Alcohol, tobacco or drug abuse

  • Genetic problems, such as Down syndrome

  • Lupus

  • Obesity

  • Rubella infection or German measles

Key Symptoms

The location and size of the hole in the atrial septum determine the kinds and severity of atrial septal defect symptoms that a patient will experience. Most patients with mild ASDs seem healthy and are generally asymptomatic. However, children with larger, more severe ASDs commonly present with the following symptoms:

  • Poor appetite

  • Poor growth

  • Fatigue

  • Breathing difficulties

  • Frequent lung problems and infections

  • Swollen legs, abdomen or feet

  • Heart palpitations

  • Atrial septal defect murmur, a whooshing sound that can be heard through a stethoscope

  • Tiring easily when playing

  • Sweating

Severe cases of untreated ASDs can cause serious health complications including atrial arrhythmia, increased risk for stroke, and pulmonary hypertension.

Who to See and Types of Treatments Available

Patients presenting with a heart murmur undergo an echocardiogram, a sonogram of the heart that can identify the cause of abnormal heart sounds as well as unexplained chest pain, arrhythmia, and an enlarged heart, among others. If doctors require more information, imaging tests, such as magnetic resonance imaging (MRI) and computerised tomography (CT) scans are performed.

Atrial septal defects do not always require treatment as small ASDs can close on their own during infancy without medical intervention. In such cases, medical monitoring is advised and patients are subjected to regular testing and imaging tests to ensure that the condition is not progressing and that the hole is closing on its own. If it has not closed by the time the child is old enough to start school, certain procedures are recommended to correct the condition.

Larger ASDs are highly unlikely to resolve on their own and must be medically treated as soon as possible. An atrial septal defect repair can be performed through cardiac catheterisation. This is a minimally invasive procedure that involves inserting a catheter into a blood vessel that leads to the heart so an implant can be positioned and used to permanently seal the ASD.

If atrial septal defect surgery is required, paediatric surgeons will perform an open-heart surgery wherein they make an incision in the chest to access the heart. The ASD may be sealed with stitches or with the use of a patch.

Kids who undergo ASD surgery have to stay in the hospital for a few days for close monitoring. The majority of patients recover fast and without any complications. They are scheduled for another echocardiogram weeks after surgery to ensure that the hole has closed completely. Once the wound has healed, patients are allowed to go back to their daily routine without limitations on activities.


  • Atrial septal defect (ASD). The Merck Manual Professional Edition.

  • Ferri FF. Ferri's Clinical Advisor 2015: 5 Books in 1. Philadelphia, Pa.: Mosby Elsevier; 2015.

  • St. John Sutton MG. Clinical manifestations and diagnosis of atrial septal defects in adults.

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