Atrial Septal Defect (ASD): What Is It, What Are the Symptoms, and How Is It Treated?

The heart is a four-chambered organ consisting of two ventricles and two atria. It pumps blood throughout the body to maintain circulation and transports deoxygenated blood to the lungs, where it is purified and delivered to the tissues. The upper chambers of the heart are called atria, and the lower chambers are called ventricles. Certain congenital heart diseases, which are present from birth, may involve structural abnormalities in these chambers. One of these conditions is called atrial septal defect, or ASD for short.

The heart has a four-chamber structure made up of two ventricles and two atria. It ensures circulation by pumping blood to the body, while also carrying deoxygenated blood to the lungs to be cleansed and transported to tissues. The heart’s upper chambers are the atria, and the lower chambers are the ventricles. Some congenital heart diseases, present from birth, may lead to structural abnormalities in these chambers. One such condition is atrial septal defect, or ASD.

The heart is structured with four chambers: two ventricles and two atria. It provides circulation by pumping blood to the body and transferring deoxygenated blood to the lungs for purification, which then reaches the tissues. The upper chambers are known as the atria, while the lower chambers are called the ventricles. Some congenital heart diseases may result in structural abnormalities within these chambers. One example is atrial septal defect, commonly referred to as ASD.

What Is Atrial Septal Defect (ASD)?

Atrial septal defect is a condition characterized by a hole in the wall between the atria of the heart. These defects occur in the septum separating the two upper chambers, also known as the atria. Commonly referred to as a “hole in the heart,” this condition allows blood to pass between the atria. Deoxygenated blood, known as "dirty" blood, mixes with oxygen-rich blood from the lungs, lowering the overall oxygen levels in the blood. Depending on the size of the hole, this can potentially damage the heart and lungs. A small hole in the atrial septum may persist without causing health issues or may close over time. Larger holes, however, may cause symptoms and require intervention.

The most common type of ASD is the ostium secundum defect, in which a hole appears in the middle portion of the atrial septum. In ostium primum defect, the hole is located in the lower part of the septum, while in sinus venosus defect, it appears closer to the upper part of the wall. Another rare type, known as coronary sinus defect, involves a hole in the wall between the coronary sinus (a major vein) and the left atrium. Each type has different characteristics and effects, so accurately identifying the type of ASD is essential for determining an appropriate treatment plan.

Prevalence of ASD in Children and Adults

While a baby’s heart development is largely complete before birth, every child is born with one or more small openings between the atria. These fetal openings help divert blood away from the lungs during prenatal development. After birth, as the baby’s lungs start functioning, these openings are no longer needed and typically close within a few weeks or months. In cases of atrial septal defect (ASD), however, this opening is larger than normal and does not close on its own after birth. As a result, blood from the left atrium flows through this hole into the right atrium and pulmonary artery. This extra workload on the heart and lungs can cause damage if left untreated. ASD affects approximately one in every 1,500–2,000 births and accounts for 10–15% of all congenital heart defects.

Symptoms of ASD (Atrial Septal Defect)

In most infants born with an atrial septal defect, no symptoms are observed initially. However, if the defect is large or does not close as the child grows, certain symptoms may start to appear, such as:

• Rapid breathing
• Difficulty in breathing
• Fatigue and shortness of breath during daily activities or exercise
• Swelling in various parts of the body, such as the feet, legs, or abdomen
• A murmur or whooshing sound heard when listening to the heart with a stethoscope
• Noticeable irregularities in heartbeats or palpitations
• Feeding difficulties in infants
• Stroke

In some cases, smaller septal defects may not cause any symptoms until adulthood, at which point the condition may be diagnosed in later life.

ASD Diagnosis and Treatment

The diagnosis of atrial septal defect (ASD) can sometimes be made in advanced cases during pregnancy or, for smaller defects, after birth. However, in many cases, severe symptoms are not present, so it is often diagnosed closer to adulthood. Anyone exhibiting symptoms similar to those of ASD should be examined by a cardiologist. During an examination with a stethoscope, the sound of a murmur can raise suspicion for ASD. Common diagnostic tests for symptomatic patients include transthoracic echocardiography and electrocardiography (ECG). Additional tests, such as cardiac ultrasound, chest X-rays, or computed tomography (CT) scans, may also be required.

For infants, children, or adults diagnosed with ASD, a treatment plan is determined based on the size of the opening between the chambers and the severity of the symptoms. If the defect is not severe in infants, monitoring is often recommended to allow the hole to close or shrink over time. In severe cases or in adults with significant symptoms, surgical intervention is performed.

Long-Term Effects of ASD

For individuals with small ASD openings, the defect may not cause any issues or damage. Many adults may have a very small remaining opening known as a patent foramen ovale (PFO), which generally does not cause problems or impact their lives. However, if the opening does not close and is significantly large, an excessive amount of blood is pumped to the pulmonary artery, causing the heart and lungs to work harder. Over time, this can lead to damage in the pulmonary artery. The impact of ASD varies greatly depending on its type, severity, the size of the hole, and the patient's other health conditions. Long-term adverse effects are seen in individuals with larger ASDs who neglect treatment or avoid surgery, making careful monitoring and timely treatment essential.

Non-Surgical ASD Repair

In infants diagnosed with atrial septal defect, if the opening in the wall between the atria is smaller than 5 millimeters, it often heals on its own. For such cases, regular check-ups are generally recommended. Defects larger than 1 centimeter typically require treatment with medication or surgery. Medications do not cure ASD but help alleviate the symptoms and complications it causes. For suitable cases that require ASD repair, non-surgical options may be considered first.

For the most common type, secundum ASD, a non-surgical (percutaneous) repair is usually the first choice if measurements are appropriate. In this method, a thin tube called a catheter is inserted through a vein in the groin and guided to the heart. The closure device, attached to the catheter, opens like an umbrella when released to close the septal opening. Over time, tissue grows over the implant, integrating it with the heart. After the procedure, blood-thinning medication is prescribed to prevent clotting.

Non-surgical ASD repair is only an option for defects of appropriate type and location. Therefore, the decision for surgical or non-surgical treatment is made by the physician based on the patient's condition.