Atrial Septal Defect (ASD)

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Atrial Septal Defect (ASD)  

1. Definition

  • ASD is a defect in the atrial wall, specifically in the interatrial septum, allowing abnormal blood flow between the left atrium (LA) and right atrium (RA).

  • It results from impaired growth or excessive resorption of the atrial septum during fetal development.

2. Types of ASD

  1. Ostium secundum (ASD II)

    • Most common (~70% of ASDs)

    • Usually isolated

  2. Ostium primum (ASD I)

    • ~15–20% of cases

    • Often associated with other heart defects (e.g., AVSD)

Minor ASDs are often low-pressure, low-volume shunts, so patients may remain asymptomatic for years.

3. Epidemiology

  • Third most common CHD (~1/2,000 live births)

  • Female predominance (♀ > ♂)

4. Etiology / Risk Factors

  • Genetic syndromes:

    • Down syndrome

    • Holt-Oram syndrome (hand-heart syndrome) → includes ASD, first-degree heart block, upper limb abnormalities like absent thumbs or radial bones

  • Maternal factors:

    • Fetal alcohol syndrome

    • Intrauterine infections (TORCH: Toxoplasmosis, Other, Rubella, CMV, Herpes)

5. Pathophysiology

  • Impaired septal tissue → left-to-right shunt: oxygenated blood flows from LA → RA → RV → pulmonary circulation

  • Hemodynamic consequences:

    • Mild defects → minimal shunt → usually asymptomatic

    • Moderate-to-large defects → RA and RV volume overload → eventual pulmonary hypertension, supraventricular arrhythmias, or Eisenmenger syndrome (rare in childhood)


6. Clinical Features

Small ASDs

  • Usually asymptomatic

  • May be detected incidentally on imaging

Moderate to Large ASDs

  • Symptoms often manifest later in life (30–40 years old)

  • Cardiovascular:

    • Exertional dyspnea

    • Fatigue

    • Palpitations (supraventricular arrhythmias)

    • Syncope (rare)

    • Heart failure signs: peripheral edema, exertional intolerance

  • Neurological:

    • Stroke or transient ischemic attack due to paradoxical embolism

7. Auscultation / Murmur Findings

  • Mid-systolic ejection murmur at 2nd left intercostal space (parasternal) → caused by increased flow across the pulmonary valve

  • Widely split, fixed S2 → classic sign (does not vary with respiration)

  • Soft mid-diastolic murmur at lower left sternal border → due to increased flow across tricuspid valve

8. Diagnostics

Echocardiography (TTE)

  • Confirms interatrial communication

  • Doppler study shows left-to-right shunt

  • Apical four-chamber and subcostal views are most informative

  • Agitated saline study for doubtful cases

Electrocardiogram (ECG)

  • Signs of RV hypertrophy: right axis deviation, P pulmonale

  • Complete or incomplete right bundle branch block (RBBB)

  • Atrial arrhythmias (atrial fibrillation or flutter) are common in adults

Chest X-ray

  • RA/RV enlargement

  • Prominent pulmonary vascular markings

  • Rounding of left heart border

Pulse Oximetry

  • Detects oxygen saturation at rest and during exercise

  • Assesses shunt magnitude

Additional Testing

  • Cardiac MRI / CT: anatomy, Qp:Qs ratio (pulmonary/systemic flow ratio)

  • Cardiac catheterization: detailed hemodynamics, shunt magnitude, pulmonary artery pressure; reserved for patients with CAD risk or unclear anatomy

9. Management

General Principles

  • Follow-up by a congenital cardiologist

  • Manage associated complications: arrhythmias, pulmonary hypertension, paradoxical embolism

Small / Asymptomatic ASDs

  • Observation

  • Periodic echocardiography

  • Up to 40% may close spontaneously by age 5

Large / Symptomatic ASDs

  • Indications for closure:

    • Qp:Qs ≥ 1.5:1 (significant left-to-right shunt)

    • RA/RV enlargement

    • Heart failure symptoms

    • History of paradoxical embolism

    • Platypnea-orthodeoxia syndrome

  • Contraindication: Severe pulmonary hypertension with right-to-left shunt (Eisenmenger)

Surgical / Interventional Repair

  • Transcatheter closure (most common if anatomy suitable)

  • Patch repair (surgical)

  • Open surgical repair for complex defects

  • Post-repair follow-up:

    • Echocardiography

    • Endocarditis prophylaxis

    • Monitoring for arrhythmias, residual shunts, or symptoms

10. Complications

  • Paradoxical embolism: embolus passes RA → LA → systemic circulation → stroke

  • Heart failure in untreated large ASDs

  • Arrhythmias (especially in adults with longstanding defects)

  • Pulmonary hypertension (rare if treated early)

Summary

  • ASD is a common congenital heart defect with a spectrum from asymptomatic to heart failure later in life.

  • Diagnosis relies on echocardiography, ECG, CXR, and sometimes catheterization.

  • Management ranges from observation to transcatheter or surgical closure, depending on size, symptoms, and shunt magnitude.

  • Early detection and treatment prevent long-term complications such as arrhythmias, stroke, and heart failure.

 👌  Good luck & Thank you

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