ASD most commonly stands for atrial septal defect, a hole in the wall between the two upper chambers of the heart. It’s one of the most common congenital heart defects, affecting roughly 13 out of every 10,000 babies born in the United States, or about 5,240 newborns each year. (You may also see “ASD” used as shorthand for autism spectrum disorder, which is a completely different condition. This article covers the heart defect.)
How a Normal Heart Compares to One With an ASD
In a healthy heart, a solid wall called the septum separates the left and right upper chambers (the atria). This wall keeps oxygen-rich blood on the left side from mixing with oxygen-poor blood on the right. When a hole exists in that wall, blood leaks from the left atrium into the right atrium, forcing the right side of the heart and lungs to handle more blood than they should.
Small holes may never cause problems and sometimes close on their own during infancy. Larger holes push significantly more blood into the right side of the heart, gradually stretching and enlarging it. Over years or decades, that extra workload can damage the heart and the blood vessels in the lungs.
Symptoms in Children and Adults
Many people with a small ASD have no symptoms at all, which is why the defect sometimes goes undetected until adulthood. A doctor may first suspect it after hearing an unusual heart murmur during a routine exam.
When a hole is large enough to matter, the most common symptoms include shortness of breath (especially during exercise), fatigue with activity, and swelling in the legs, feet, or abdomen. Adults who were never diagnosed as children sometimes notice these symptoms creeping in during their 30s or 40s as the heart’s extra workload takes a cumulative toll.
How It’s Diagnosed
An echocardiogram is the primary tool for diagnosing an ASD. It uses sound waves to create real-time images of the heart, showing the size and location of the hole and how much extra blood is crossing from left to right. An electrocardiogram (EKG) is often done alongside it to check for irregular heart rhythms that can develop as a result of the defect. In cases where the echocardiogram doesn’t give a clear enough picture, a cardiac MRI can provide more detailed images of the heart’s structure.
What Happens if an ASD Goes Untreated
A small ASD that causes no symptoms may never need treatment. But a significant hole left open for years puts you at increasing risk for several serious problems. The right side of the heart can enlarge to the point of heart failure. Irregular, rapid heartbeats called atrial fibrillation become more likely, particularly as you get older. The excess blood flow can damage the arteries in the lungs, raising the pressure inside them, a condition known as pulmonary hypertension. Stroke risk also goes up because blood clots that would normally be filtered by the lungs can pass through the hole and travel to the brain.
In the most severe cases, years of elevated lung pressure can cause a condition called Eisenmenger syndrome, where the pressure in the right side of the heart becomes so high that blood begins flowing in the wrong direction, from right to left. At that stage, closing the hole is no longer a safe option because the right side of the heart has come to depend on the opening as a pressure release valve.
Catheter Closure vs. Open-Heart Surgery
There are two main ways to close an ASD: a catheter-based procedure or open-heart surgery. The choice depends largely on the size, location, and type of hole.
Catheter-based closure is the less invasive option. A thin tube is threaded through a vein in the groin up to the heart, where a small device is guided through the catheter and positioned to plug the hole. This approach works best for the most common type of ASD (called a secundum defect) when the hole measures less than 38 millimeters across and has enough surrounding tissue to anchor the device. Recovery is significantly faster: patients typically return to normal daily activity within about two weeks, compared to roughly five and a half weeks after surgery.
Open-heart surgery is necessary for larger defects or those located in parts of the septum that a catheter device can’t reach. It involves a chest incision and the use of a heart-lung machine while a surgeon patches or stitches the hole closed. Hospital stays average about two and a half days longer than catheter procedures, and the overall complication rate is substantially higher. A large meta-analysis found a 31% complication rate for surgical patients compared to about 7% for catheter patients, with major complications running roughly 7% versus 2%. That said, surgery remains highly effective and is sometimes the only option.
Long-Term Outlook After Repair
Age at the time of repair is the single strongest predictor of how well someone does long term. A landmark study that followed patients for 27 to 32 years after surgical ASD closure found that people who had their defect repaired before age 25 had survival rates virtually identical to the general population, around 97% at 27 years for those treated in childhood and 93% for those treated between ages 12 and 24.
The picture changes for people repaired later in life. Those who had surgery between ages 25 and 41 had a 27-year survival rate of 84%, compared to 91% in a matched comparison group. For those over 41 at the time of repair, the rate dropped to 40% versus 59%. Late cardiac failure, stroke, and atrial fibrillation were all significantly more common when repair happened at older ages, likely because the heart and lungs had already sustained damage from decades of extra blood flow.
The takeaway is straightforward: early closure, before the right side of the heart has been permanently stretched and before lung pressures have risen, offers the best chance of a normal, healthy lifespan. People repaired later in life still benefit from closure but need ongoing monitoring for rhythm problems and heart function changes.