An atrial septal defect (ASD) is a congenital heart condition involving an opening in the septum, the wall that separates the heart’s two upper chambers (atria). This abnormal opening allows oxygen-rich blood from the left atrium to mix with oxygen-poor blood in the right atrium, potentially leading to increased blood flow to the lungs and long-term strain on the heart.
ASDs develop when the atrial septum does not form completely during fetal growth. Although the defect is present at birth, it may not be diagnosed until later in life, especially if the opening is small or the symptoms are subtle.
Atrial septal defects are among the more common congenital heart defects. In many cases, a small ASD will close on its own during infancy or early childhood. However, a large or persistent defect may require ongoing monitoring or medical intervention to prevent complications.
What Are the Types of Atrial Septal Defects?
ASDs are classified based on the location of the opening in the atrial septum and how the defect forms during fetal development. The main types include:
Secundum Atrial Septal Defect
The most common type of ASD, a secundum atrial septal defect occurs in the central portion of the atrial septum, where the foramen ovale—a natural opening that normally closes after birth—remains open or becomes abnormally large.
Primum Atrial Septal Defect
Located in the lower part of the atrial septum, a primum ASD is usually associated with another structural abnormality, such as a heart valve defect. Considered a form of atrioventricular septal defect, this type is less common than the secundum type.
Sinus Venosus Atrial Septal Defect
A sinus venosus ASD occurs near the connection of the superior or inferior vena cava with the right atrium. It is often associated with abnormal drainage of the pulmonary veins, a condition known as partial anomalous pulmonary venous return.
Coronary Sinus Atrial Septal Defect
This rare type of ASD involves an abnormal connection between the coronary sinus—a vein that returns blood from the heart muscle—and the left atrium. This defect can allow oxygenated and deoxygenated blood to mix.
Each type of atrial septal defect differs in terms of its location, associated abnormalities and potential complications. An accurate classification can help the physician determine whether and when treatment is necessary and guide appropriate monitoring.
What Are the Causes and Risk Factors for Atrial Septal Defects?
ASDs are congenital defects, which means they develop before birth when the septal wall of the heart does not form properly during fetal development. In most cases, the defect is isolated, with no identifiable genetic or environmental cause. The exact reason why an ASD occurs often remains unknown.
That said, some atrial septal defects are linked to a genetic or chromosomal condition, such as Down syndrome. In other cases, a mutation in a gene involved in heart formation may contribute to the condition. ASDs may also occur as part of a more complex congenital heart abnormality that affects multiple cardiac structures.
Several factors may increase the risk of an atrial septal defect, including:
- Advanced maternal age – A pregnancy in a woman aged 35 or older may carry a slightly elevated risk of certain congenital heart defects.
- Certain maternal health issues – During early pregnancy, an autoimmune condition such as lupus, poorly controlled diabetes and certain infections can increase the risk of congenital heart defects.
- Exposure to harmful substances during pregnancy – Use of alcohol, tobacco or certain prescription and recreational drugs during pregnancy can interfere with fetal heart development.
- Family history of congenital heart disease – Having a parent or sibling with a congenital heart defect may increase the likelihood of ASDs and related conditions.
- Genetic or chromosomal disorders – Conditions such as trisomy 21 (Down syndrome) are commonly associated with septal defects.
While these factors may contribute to the development of an atrial septal defect, many cases occur in infants with no known risk factors.
What Are the Warning Signs and Symptoms of an Atrial Septal Defect?
ASD symptoms can vary significantly based on the size of the defect and the patient’s age. A small atrial septal defect may go undetected until it is discovered incidentally during a medical evaluation performed for an unrelated condition, sometimes during adulthood. In contrast, a large defect can cause increased blood flow through the heart and lungs, leading to more apparent signs.
In an infant or child, the symptoms of a significant ASD may include:
- Fatigue or difficulty keeping up with peers
- Frequent respiratory infections
- Heart murmur
- Poor weight gain or slow growth
- Shortness of breath, particularly during feeding or activity
In an adult, an undiagnosed ASD may begin to cause symptoms due to long-term strain on the heart and lungs. Warning signs may include:
- Fatigue or reduced exercise capacity
- Palpitations or irregular heartbeat (arrhythmia)
- Shortness of breath during exertion
- Swelling in the abdomen, legs or feet
- Stroke, in rare cases, if a blood clot passes through the defect and enters the systemic circulation
Because the symptoms of an atrial septal defect can be subtle or absent for many years, the condition is often diagnosed later in life. Regular physical examinations and early evaluation of unexplained cardiac symptoms can help ensure timely identification and treatment.
How Is an Atrial Septal Defect Diagnosed?
Most ASDs are diagnosed through a combination of clinical evaluation, imaging studies and specialized cardiac testing. In many cases, the condition is first suspected during an assessment for a heart murmur or unexplained symptoms, such as fatigue, shortness of breath or irregular heartbeat.
The diagnostic process for an ASD may include:
- Physical examination – During a routine medical checkup, the physician may detect a heart murmur or other abnormal heart sounds that suggest increased blood flow within the heart, prompting further investigation.
- Echocardiogram – This noninvasive ultrasound imaging test is the primary diagnostic tool for ASDs. It can provide clear images of the heart’s structure and may reveal the presence of a hole in the atrial septum. Doppler imaging may also be used to evaluate blood flow through the defect.
- Transesophageal echocardiogram (TEE) – If a standard echocardiogram does not provide sufficient detail, the physician may order a TEE. This diagnostic test uses an ultrasound probe inserted into the esophagus to capture high-resolution images of the atrial septum and surrounding structures.
- Electrocardiogram (EKG) – An EKG records the heart’s electrical activity and can detect abnormal rhythms or signs of heart enlargement that may indicate a septal defect.
- Chest X-ray – A chest X-ray can show changes in the size or shape of the heart and may reveal signs of increased blood flow to the lungs, which can occur with a large ASD.
- Cardiac magnetic resonance imaging (MRI) or computed tomography (CT) – These imaging techniques can provide detailed, cross-sectional views of the heart and major blood vessels, which can help the physician assess the size and location of the defect and plan treatment.
- Cardiac catheterization – In select cases, especially when other tests are inconclusive, cardiac catheterization may be performed to directly measure pressure and oxygen levels in the heart chambers and confirm the diagnosis.
Early detection of an atrial septal defect can allow for appropriate monitoring or treatment and can help prevent complications, such as heart failure, pulmonary hypertension and stroke.
How Is an Atrial Septal Defect Treated?
The most appropriate treatment for an ASD can vary depending on several factors, including the size and type of the defect, the presence of symptoms and the potential for complications. While a small ASD may close spontaneously or remain stable without intervention, a large or symptomatic defect may require treatment to help prevent long-term health issues. Options may include:
Watchful Waiting
If the defect is small and asymptomatic, the physician may recommend regular monitoring through periodic echocardiograms. This approach may be appropriate if the heart is functioning normally and there is no evidence of strain or related complications. In this scenario, formal treatment may be unnecessary unless changes occur over time.
Medications
Although medication cannot close an atrial septal defect, it may be used to manage the symptoms or reduce the risk of complications. Treatment may include:
- Antiarrhythmic medications or beta-blockers to help control irregular heart rhythms
- Anticoagulants to lower the risk of blood clots in a patient at increased risk of stroke
- Diuretics to minimize fluid retention and reduce the heart’s workload
Catheter-Based Closure
For a moderate to large ASD—especially the secundum type, with adequate rims of tissue—transcatheter closure may be considered. This minimally invasive procedure involves:
- Inserting a thin catheter through a vein in the groin
- Guiding the catheter to the heart using real-time imaging
- Deploying a closure device that seals the opening in the atrial septum
This outpatient procedure typically has a short recovery time and can eliminate the need for open-heart surgery in an appropriate candidate.
Surgical Repair
Surgical closure of an atrial septal defect may be necessary if:
- The ASD is a type not amenable to catheter-based treatment, such as a primum or sinus venosus defect
- The defect is too large or irregular for device closure
- The patient has an additional heart condition that requires surgery
Open-heart surgery is performed under general anesthesia. During the procedure, the surgeon will close the defect with sutures or a patch. With appropriate postoperative care, most patients recover fully and experience significant improvement in their symptoms and heart function.
What Are the Possible Complications and Long-Term Effects of an Atrial Septal Defect?
If left untreated, an ASD can lead to a range of complications. The likelihood and severity of these issues can vary depending on the size of the defect, the volume of excess blood flow between the heart chambers and the patient’s overall health.
Possible long-term effects of an atrial septal defect include:
Arrhythmias
Chronic dilation of the atria from a long-standing ASD may lead to irregular heart rhythms, such as atrial fibrillation (AFib) or atrial flutter. These arrhythmias can impair heart function and increase the risk of blood clots and stroke.
Eisenmenger Syndrome
In rare cases, severe and prolonged pulmonary hypertension can lead to Eisenmenger syndrome. This condition causes a reversal of blood flow through the defect, allowing oxygen-poor blood to circulate throughout the body. A hallmark sign is a bluish or purplish discoloration of the skin and mucous membranes due to low oxygen levels in the blood (cyanosis).
Heart Enlargement
A significant atrial septal defect can allow increased blood flow into the right atrium and right ventricle, leading to enlargement of these heart chambers. Over time, the added strain can weaken the heart muscle and reduce its ability to pump blood efficiently.
Heart Failure
Persistent volume overload from an untreated ASD can contribute to heart failure, particularly in an older adult. Symptoms may include fatigue, shortness of breath and fluid buildup in the abdomen, legs or feet.
Pulmonary Hypertension
Excess blood flow to the lungs can increase pressure in the pulmonary arteries. This condition, known as pulmonary hypertension, can further burden the right side of the heart and may eventually result in heart failure if left untreated.
Stroke
A blood clot may pass through the septal defect from the right atrium to the left atrium and then enter the systemic circulation. If the clot travels to the brain, it may cause a stroke. The risk is higher in an adult with an undiagnosed or untreated ASD.
Early detection and appropriate management of an atrial septal defect can help prevent these complications. With timely treatment, most individuals can maintain good heart function and lead a healthy, active lifestyle.
Can Atrial Septal Defects Be Prevented?
ASDs are congenital heart conditions that develop during fetal growth and are present at birth. Because they form early in pregnancy, the defects generally cannot be prevented. However, certain steps during preconception and prenatal care may help reduce the overall risk of congenital heart defects. These include:
Avoiding Harmful Substances
A pregnant woman should not consume alcoholic beverages, smoke or use illicit drugs, all of which are associated with an increased risk of birth defects, including ASDs and other heart abnormalities.
Considering Genetic Factors
Some ASDs occur as part of an inherited genetic syndrome or run in families. If there is a known family history of congenital heart defects, genetic counseling may help identify risks and inform decisions about testing or monitoring.
Managing Health Conditions
Controlling chronic medical conditions—such as diabetes, obesity and autoimmune disorders—both before and during pregnancy can support healthy fetal development and reduce the likelihood of structural heart defects.
Preventing Infections and Using Safe Medications
To help protect fetal development, a pregnant woman should stay current on vaccinations and consult a physician before taking any medications. Certain infections and medications taken during pregnancy may interfere with fetal heart formation.
Taking Prenatal Vitamins
Folic acid and other essential nutrients play a key role in fetal development. Taking recommended prenatal vitamins before and during pregnancy may lower the risk of congenital anomalies, including heart defects.
While atrial septal defects cannot be fully prevented, following these guidelines can help promote optimal fetal health and reduce the risk of congenital heart conditions.
Living With an Atrial Septal Defect
The experience of living with an ASD can vary significantly based on the size of the defect and whether it has been treated. Many individuals with a small or successfully repaired atrial septal defect can lead a full, active lifestyle with few or no limitations. In some cases, the defect causes no symptoms and does not require treatment.
However, a large or untreated ASD may result in ongoing symptoms, such as fatigue, shortness of breath or heart palpitations, which can interfere with daily activities. In this scenario, regular medical monitoring and lifestyle modifications may be necessary. If complications arise, such as arrhythmias or pulmonary hypertension, additional treatment and close follow-up may be required.
With a timely diagnosis and appropriate care, most individuals with an ASD can maintain a good quality of life and avoid serious long-term complications.
Benefit From World-Class Care at TGH
If you would like to learn more about atrial septal defects, you can request a consultation with a specialist at TGH’s nationally recognized Heart and Vascular Institute by calling (800) 844-3900 or emailing heart-vascular@tgh.org.