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Atrial Septal Defect (ASD)

Clinical Subject Page

Atrial Septal Defect (ASD)

ICD-10

Q21.1

Specialty

Cardiology

Onset

Chronic

Reviewed

July 2026

On This Page

Overview

Atrial Septal Defect (ASD) is A defect in the atrial septum caused by impaired growth or excessive resorption of the atrial septum

Etiology & Risk Factors

  • – Down syndrome
    – Fetal alcohol syndrome
    – Intrauterine infections (e.g., TORCH)
    – Holt-Oram syndrome (hand-heart syndrome)
    – Autosomal dominant
    – Characterized by:
    – Atrial septal defect
    – First-degree heart block
    – Upper limb abnormalities (e.g., absent radial bones)

Pathophysiology

  • Impaired growth or excessive resorption of the atrial septum during fetal development creates a defect in the atrial septum.
  • This allows oxygenated blood to flow from the left atrium (LA) to the right atrium (RA) because left atrial pressure is higher than right atrial pressure.
  • The left-to-right shunt increases:
    • Right atrial blood volume
    • Right ventricular blood volume
    • Pulmonary blood flow
  • Small Atrial Septal Defect (ASD) usually cause a low-pressure, low-volume shunt, so patients are often asymptomatic.
  • Large Atrial Septal Defect (ASD) can lead to:
    • Right heart volume overload
    • Pulmonary hypertension
    • Supraventricular arrhythmias
    • Eisenmenger syndrome (late reversal to right-to-left shunt)

Simple Flow

Defect in atrial septum → Left-to-right shunt (LA → RA) → ↑ Blood flow to RA, RV & lungs → Right heart volume overload → Pulmonary hypertension → Arrhythmias ± Eisenmenger syndrome (late)

Clinical Presentation

  • Small Atrial Septal Defect (ASD) :
    – Usually asymptomatic
  • Medium to Large Atrial Septal Defect (ASD) 
  • Symptoms often develop in adulthood (around 30–40 years):
  • Exertional dyspnea
  • Fatigue
  • Recurrent respiratory infections
  • Palpitations (supraventricular arrhythmias)
  • Syncope
  • Heart failure symptoms (e.g., peripheral edema)
  • Stroke or TIA due to paradoxical embolism 
    -Auscultation
    Mid-systolic ejection murmur at the 2nd left intercostal space
    – Fixed, widely split second heart sound (S2)
    – Soft mid-diastolic murmur at the lower left sternal border

History Taking

Evaluate for:
– Exertional dyspnea
– Fatigue
– Palpitations
– Recurrent respiratory infections
– Syncope
– Heart failure symptoms
– Previous stroke or TIA (suggesting paradoxical embolism)

Investigations

  • Echocardiography (Confirmatory Test)
    – Transthoracic echocardiography (TTE) with Doppler
    – Confirms interatrial communication
    – Best seen in apical four-chamber and subcostal views
    – Agitated saline study if findings are equivocal
    – TEE if TTE is limited or for intraoperative guidance

    ECG
    May show:
    – Right ventricular hypertrophy
    – Right axis deviation
    – P pulmonale
    – PR prolongation
    – Complete or incomplete right bundle branch block
    – Atrial fibrillation/flutter (common in adults)

    Chest X-ray
    – Enlarged right atrium
    – Enlarged right ventricle
    – Enlarged pulmonary artery
    – Increased pulmonary vascular markings
    Pulse Oximetry
    – At rest and during exercise
    – Helps assess magnitude and direction of shunt

Diagnosis

  • Diagnosis of Atrial Septal Defect (ASD) is confirmed by:
    – Transthoracic echocardiography with Doppler (first-line confirmatory investigation)
    Supportive findings:
    – ECG abnormalities
    – Chest X-ray changes
    – Cardiac MRI/CT
    – Cardiac catheterization when detailed hemodynamics are required

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Management

General Principles
– Managed by a congenital cardiologist
– Treat associated conditions:
– Atrial fibrillation
– Tachyarrhythmias
– Pulmonary hypertension
– Small/asymptomatic ASD:
– Clinical follow-up
– Serial echocardiography
– Larger or symptomatic Atrial Septal Defect (ASD) :

– Surgical closure
Indications for Closure
– Large left-to-right shunt (Qp:Qs ≥1.5:1 without pulmonary hypertension)
– Right atrial or ventricular hypertrophy
– Heart failure symptoms
– Previous paradoxical embolism
– Platypnea-orthodeoxia syndrome
Contraindications
– Severe pulmonary hypertension
– Eisenmenger syndrome (right-to-left shunt)
Closure Methods
– Transcatheter closure
– Patch repair
– Open surgical repair- Surgical closure
Indications for Closure
– Large left-to-right shunt (Qp:Qs ≥1.5:1 without pulmonary hypertension)
– Right atrial or ventricular hypertrophy
– Heart failure symptoms
– Previous paradoxical embolism
– Platypnea-orthodeoxia syndrome
Contraindications
– Severe pulmonary hypertension
– Eisenmenger syndrome (right-to-left shunt)
Closure Methods
– Transcatheter closure
– Patch repair
– Open surgical repair

 

Complications

  • Paradoxical embolism leading to ischemic stroke
  • Heart failure

Prognosis

  • – Up to 40% of ASDs close spontaneously by 5 years of age.
    – Larger symptomatic defects generally require closure.
    – Surgical repair is contraindicated in patients with Eisenmenger syndrome or right-to-left shunting.

Key Points / Clinical Pearls

  • – VSD is the most common congenital heart defect.
    – Most defects are membranous.
    – Small VSDs produce louder murmurs than large VSDs.
    – Classic murmur: harsh holosystolic murmur at the left lower sternal border.
    – Confirmatory test: transthoracic echocardiography with Doppler.
    – Many small VSDs close spontaneously.
    – Close significant defects before irreversible pulmonary hypertension develops.
    – Do not close VSDs in patients with Eisenmenger syndrome.