Atrial Septal Defect (ASD)

How an ASD affects the heart

Before birth, an opening between the atria (the foramen ovale) lets blood bypass the lungs. It normally seals after birth. An ASD is a true gap in the septum that does not close.

Because pressure is slightly higher on the left, oxygen-rich blood flows from the left atrium into the right atrium (a left-to-right shunt). The right atrium, right ventricle and lung arteries carry this extra volume. Over years, these chambers enlarge, and in some people pressure in the lung arteries rises.

A small patent foramen ovale (PFO), which about 1 in 4 adults have, is different: it is a flap-like opening rather than a missing piece of wall, and rarely needs closure.

Types of atrial septal defect

Symptoms

Many children have no symptoms, and an ASD is found because of a heart murmur. When symptoms occur, they often appear in adulthood, typically after age 30 to 40:

• shortness of breath, especially with exercise
• tiredness
• heart palpitations from atrial fibrillation or flutter
• swelling of the legs or abdomen (right heart failure)
• frequent lung infections
• in babies with large defects: fast breathing, poor feeding and slow weight gain (uncommon)

Causes and risk factors

Most ASDs occur by chance during heart development in the first weeks of pregnancy. Risk is higher with:

• a family history of congenital heart disease
• genetic syndromes such as Down syndrome and Holt-Oram syndrome
• maternal factors during pregnancy, including rubella infection, poorly controlled diabetes, smoking, alcohol and some medicines

Diagnosis

• Physical exam: a soft murmur and a characteristic "fixed split" second heart sound.
• ECG: may show right heart strain or rhythm problems.
• Chest X-ray: may show an enlarged heart and increased lung blood flow.
• Echocardiogram: the main test. It shows the hole, its size, the direction of flow and right heart enlargement.
• Transesophageal echo (TEE): a probe passed into the esophagus gives detailed images to plan closure.
• Cardiac MRI or CT: for sinus venosus defects and abnormal veins.
• Cardiac catheterization: measures lung pressures and shunt size when needed.

Treatment

Monitoring

Small secundum ASDs (under about 5 mm) often close by themselves in the first years of life and are monitored with periodic echocardiograms.

Closure

Closure is recommended when the defect causes right heart enlargement, symptoms, or (in selected cases) a stroke from a paradoxical clot. Options:

• Catheter device closure: a folded device is passed through a vein in the groin and opened to plug the hole. It is the standard treatment for suitable secundum ASDs. Recovery takes days.
• Surgical repair: open-heart surgery to close the hole with stitches or a patch. Needed for primum, sinus venosus and coronary sinus defects, and large or unusually shaped secundum defects.

Closure is generally done in childhood, often between ages 2 and 5, or whenever an important ASD is found in an adult. It is not advised when severe, irreversible pulmonary hypertension has developed, because the hole may then act as a pressure release.

Medicines

Medicines treat complications: rate or rhythm control and blood thinners for atrial fibrillation, and diuretics for heart failure. They do not close the hole.

Complications

Untreated large ASDs can cause:

• atrial fibrillation and flutter, increasingly common after age 40
• right heart failure
• pulmonary hypertension, and in rare advanced cases Eisenmenger syndrome, where flow reverses and causes cyanosis
• stroke from a clot crossing from the right to the left side (paradoxical embolism)

Outlook

Closure in childhood leads to a normal or near-normal life expectancy. Adults also benefit from closure, with improved symptoms and heart size, though rhythm problems may persist if they had already started. Long-term follow-up with a cardiologist experienced in congenital heart disease is recommended.

Pregnancy

Most women with a small or repaired ASD have uncomplicated pregnancies. Those with large unrepaired defects, pulmonary hypertension or rhythm problems need specialist assessment before conceiving.

Frequently asked questions

Is an atrial septal defect serious?

Small ASDs are usually harmless and may close on their own. Large defects can stay silent for years but eventually strain the right heart and lungs, cause irregular heart rhythms or, rarely, stroke. These are usually closed, after which the outlook is excellent.

Can an ASD close on its own?

Yes. Many small secundum ASDs, especially those under about 5 mm, close on their own during the first few years of life. Larger defects and other types rarely close without treatment.

What are the symptoms of an ASD in adults?

Adults may notice shortness of breath with exercise, tiredness, palpitations from atrial fibrillation, or leg swelling. Some have no symptoms and are diagnosed after a murmur is heard or an echocardiogram is done for another reason.

How is an atrial septal defect repaired?

Most secundum ASDs are closed with a device delivered through a catheter from a groin vein, with a short recovery. Other types, or very large defects, are closed with open-heart surgery using stitches or a patch.

What is the difference between an ASD and a PFO?

An ASD is a true hole where part of the atrial wall is missing. A PFO is a small flap-like opening left over from fetal circulation that failed to seal, found in about a quarter of adults. Most PFOs need no treatment.