Atrial Septal Defect (ASD)

Definition | Aetiology | Pathophysiology | Risk Factors | Signs and Symptoms | Investigations | Management | Patient Advice

Definition

Atrial Septal Defect (ASD) is a congenital heart defect characterised by an abnormal opening in the atrial septum, allowing blood to flow between the left and right atria. It can result in a left-to-right shunt and volume overload in the right side of the heart.

Aetiology

ASD is typically a congenital defect and can occur as an isolated anomaly or as part of a syndrome:

• Secundum ASD: The most common type, located at the fossa ovalis.
• Primum ASD: Associated with atrioventricular septal defects, often seen in Down syndrome.
• Sinus Venosus ASD: Less common, located near the superior vena cava or inferior vena cava.
• Unroofed Coronary Sinus: A rare form of ASD.

Pathophysiology

The defect allows left-to-right shunting, resulting in the following changes:

• Increased Right-sided Volume Load: The right atrium and ventricle handle an excessive volume of blood, leading to dilation.
• Increased Pulmonary Blood Flow: Leads to pulmonary hypertension over time.
• Right Ventricular Hypertrophy: Chronic overload may lead to hypertrophy.
• Paradoxical Embolism: In rare cases, right-to-left shunting (e.g., during Valsalva) can lead to embolism and stroke.

Risk Factors

Risk factors for ASD include:

• Family history of congenital heart defects.
• Chromosomal abnormalities (e.g., Down syndrome).
• Maternal infections during pregnancy (e.g., rubella).
• Exposure to teratogens, such as alcohol or medications during pregnancy.

Signs and Symptoms

Clinical features depend on the size of the defect:

• Small ASD: Often asymptomatic and detected incidentally by a murmur.
• Moderate to Large ASD:
  • Heart Murmur: Ejection systolic murmur at the left upper sternal border due to increased flow across the pulmonary valve.
  • Exertional Dyspnoea: Shortness of breath during physical activity.
  • Fatigue: Generalised tiredness, particularly with exertion.
  • Palpitations: Due to atrial arrhythmias like atrial fibrillation or flutter.
  • Stroke or Transient Ischaemic Attack: In cases of paradoxical embolism.

Investigations

Diagnostic tests and findings include:

• Clinical Examination: May reveal a murmur or fixed splitting of the second heart sound (S2).
• Electrocardiogram (ECG):
  • Right axis deviation.
  • Incomplete or complete right bundle branch block (RBBB).
• Chest X-ray: May show cardiomegaly and increased pulmonary vascular markings.
• Echocardiography: Diagnostic test of choice:
  • Demonstrates left-to-right shunting across the defect.
  • Bubble contrast studies can identify right-to-left shunting.
• Cardiac MRI or CT: Useful for detailed assessment of anatomy and associated anomalies.

Management

1. Medical Management

• Observation: Small ASDs with minimal shunting may close spontaneously in infancy.
• Anticoagulation: For prevention of stroke in patients with atrial arrhythmias or paradoxical embolism.

2. Surgical and Interventional Management

• Transcatheter Device Closure: Preferred for secundum ASDs in suitable patients.
• Surgical Repair: Open-heart surgery with patch closure, indicated for large or complex defects.

3. Specialist Referral

Referral to a paediatric or adult congenital cardiologist is essential for assessment and management planning, particularly for moderate to large ASDs.

Patient Advice

Key advice includes:

• Attend regular follow-up appointments with a cardiologist.
• Maintain good oral hygiene to prevent infective endocarditis.
• Report symptoms such as increased breathlessness, palpitations, or fatigue immediately.
• Educate parents or patients about the condition, its implications, and the importance of follow-up care.