What Is Atrial Septal Defect?

Overview

Atrial septal defect (ASD) is a congenital heart defect that occurs when there is a hole in the wall (septum) that divides the top two chambers of the heart (atria).²  

During the heart's developmental phase, the heart divides into two separate sections, eventually becoming the chamber walls. During this process, if there are any complications, a hole can appear in the atrial wall that divides the left and right sides of the heart. This communication failure between the left and right atria allows for oxygen-rich blood to leak into chambers of the heart with oxygen-poor blood, increasing the amount of blood that flows to the lungs. During pregnancy, as the baby's heart develops, there are numerous openings in the atria, however, these usually close up later in the pregnancy or shortly after birth. The hole size can vary, with minor atrial septal defects typically closing naturally during early childhood. However, surgical intervention may be required for more significant defects that do not close, to prevent later complications, namely, stroke, dysrhythmias and pulmonary hypertension.

Types of atrial septal defect

Secundum 

The most common type, occurs in the central part of the atrial septum, resulting in the shunting of blood between the systemic and pulmonary circulations.¹

Primum

Develops in the lower part of the atrial septum and can be linked to tricuspid and mitral valve defects.¹

Sinus venosus

There are two types, superior defect and inferior defect.

• The superior defect is usually located at the superior aspect of the atrial septum, close to the right-sided pulmonary veins (PV). It usually occurs when the superior vena cava (SVC) opening overrides the atrial septum draining the left and right atria
• The inferior defect is located close to the junction of the inferior vena cava (IVC) and right atrium

Both types are linked to partial anomalous pulmonary venous return (PAPVR), a rare congenital heart defect affecting adults and causing abnormal blood flow from the lungs to the heart.¹

Coronary sinus

This defect is rare and often labelled as an abnormal communication between the coronary sinus and the left atrium. It is usually part of a more convoluted cardiac defect.¹

Causes of atrial septal defect

ASD is a congenital heart defect that occurs during fetal development. Though it occurs as a singular defect, causes may be genetic, as some genetic syndromes can result in chromosome mutations associated with ASD. Some associated genetic disorders include Down syndrome, and associated heart defects include mitral valve disease and pulmonary stenosis.

Another cause is Mendelism, referring to how certain traits are inherited and passed on from parents to offspring. Maternal exposure to drugs, like cocaine and alcohol, can cause the unborn foetus to be predisposed to developing ASD. However, in the majority of ASD cases, there are no obvious causes.²

Signs and symptoms of atrial septal defect

Signs and symptoms in children

The majority of children born with ASD do not experience any symptoms. However, depending on the size, location and severity of the defect, symptoms may include:

• Heart murmur
• Poor weight gain
• Growth delays
• Increasing susceptibility to respiratory infections
• Arrhythmia (irregular heartbeat)
• Difficulties breathing/ shortness of breath

Signs and symptoms in adults

Adults with ASD start experiencing the following symptoms by 40 years: 

• Tachycardia
• Heart palpitations
• Shortness of breath with exercise
• Swelling of extremities
• Syncope (fainting)
• Fatigue

Diagnosis of atrial septal defect 

ASD is generally found when a murmur is detected by listening to a person's heart with a stethoscope. After this, an echocardiogram (ultrasound of the heart) is requested to confirm the diagnosis; this is the gold standard for ASD evaluation. Other diagnostic tests include:²

• Electrocardiogram (ECG/EKG): Records the heart's electrical activity to check for heart conditions, such as arrhythmias
• Transoesophageal echocardiogram (TOE): Unlike an echocardiogram, a TOE involves a thin tube that passes through the mouth, down the throat and into the oesophagus. Due to the proximity of the oesophagus to the heart's upper chambers, a TOE can obtain very clear images of the heart's structure and valves
• Intracardiac echocardiography (ICE): Provides high-resolution real-time visualisations of cardiac structures, has largely replaced TOEs as an ideal imaging modality for guiding procedures, such as ASD closure
• Chest X-ray: Can diagnose ASD as an X-ray will show if there is an enlargement of the heart or any changes to the lungs that may have caused blood to flow differently than it should

Management and treatment for atrial septal defect

Spontaneous closure of atrial septal defects of less than 5mm usually occurs within the first year of life. However, more significant defects may require medical/ surgical interventions to close the defect. Treatment depends on the age at diagnosis, severity of the symptoms, size of the hole, and presence of any additional conditions.² 

Medication

Children with ASD are monitored to see if the hole closes whilst medications treat symptoms. However, there are currently no medications that can close the hole. Patients with atrial dysrhythmias primarily require anticoagulation medications to control the abnormal rhythm. Individuals with a history of transient ischaemic attack (TIA) or stroke require a more aggressive monitoring approach or possibly surgical intervention.²

Closure

Closure of the hole is recommended in children with large atrial septal defects, including those with very few symptoms, to prevent an increased risk of problems in later life. Closure is recommended for adults with severe symptoms, including: ²

• Percutaneous closure: It is far less invasive than surgical repair, and it can close most secundum ASDs and some sinus venosus ASDs with a comparable success rate, making it a favourable method. 
• Surgical intervention: It is safe and effective for ASD with little morbidity and mortality. It typically involves the use of a tissue patch to close the ASD, with the tissue usually being taken from the pericardium (a fluid-filled sac around the heart). However, certain secundum ASDs can be closed with the use of sutures alone.

Risk factors

Some risk factors that can lead to ASD are:

• Maternal exposure to drugs and alcohol
• Family history of ASD
• Diabetes
• Lupus

Complications

Complications of ASD include:

• Increases the risk of TIA/ stroke
• Atrial arrhythmias
• Right-sided heart failure
• Pulmonary artery hypertension (high blood pressure in the lung arteries)
• Eisenmenger syndrome is a late complication that occurs secondary to pulmonary hypertension in ASD patients who go untreated.

FAQs

How common is atrial septal defect?

ASD occurs in almost 25% of children making it one of the most common types of congenital heart defects.² 

How can I prevent atrial septal defect?

Preventing ASD may not be possible, however, receiving appropriate prenatal care is highly important. When planning to get pregnant, you must visit a healthcare provider and discuss any current health conditions, medications and family medical history.

When should I see a doctor?

Large ASDs are often diagnosed before or soon after a child is born. However, contact your healthcare provider if you or your child is experiencing:

• Shortness of breath
• Fatigue
• Swelling of the legs or feet
• Palpitations or skipped heartbeats

Summary

ASD is a common congenital heart defect that occurs when there is a hole in the atrial septum. ASD can be clinically asymptomatic or cause pulmonary hypertension and vascular complications such as strokes. Most ASDs are small and spontaneously close in the first year of life. However, larger defects require surgical intervention for closure. Closure of a defect is indicated when significant shunting occurs, causing enlargement of right heart structures. SDs are often diagnosed before or soon after a child is born. However, contact your healthcare provider if you or your child is experiencing any symptoms like shortness of breath, fatigue, swelling of the legs or feet, palpitations, skipped heartbeats etc.