Key Facts

Atrial septal defect (ASD) is a congenital defect in the interatrial septum allowing communication between the left and right atria. It is the most common congenital heart defect presenting in adulthood.

Epidemiology

• ~10% of all congenital heart defects; most common CHD diagnosed in adulthood
• Female:male ratio ~2:1
• Prevalence: ~1-2 per 1,000 live births
• Many small ASDs close spontaneously in childhood

Types

• Secundum (~70%): defect in fossa ovalis region; most common; amenable to device closure
• Primum (~15-20%): defect in inferior septum near AV valves; associated with Down syndrome, AV canal defects, cleft mitral valve
• Sinus venosus (~5-10%): defect near SVC or IVC entry; often associated with anomalous pulmonary venous drainage
• Coronary sinus (<1%): unroofed coronary sinus

Pathophysiology

• Left atrial pressure > right atrial pressure → left-to-right shunt
• Chronic volume overload of RA and RV → RV dilatation, pulmonary overcirculation
• Long-standing overcirculation → pulmonary vascular remodelling → pulmonary hypertension
• Eisenmenger syndrome: irreversible pulmonary hypertension → shunt reversal (right-to-left) → cyanosis
• Paradoxical embolism: venous thrombus crosses ASD to arterial circulation → stroke

Typical Presentation

• Many patients are asymptomatic in childhood and young adulthood
• Exertional dyspnoea, fatigue (typically presents in 3rd-4th decade)
• Palpitations (atrial arrhythmias: AF, atrial flutter — especially after 40 years)
• Recurrent chest infections (children)
• Paradoxical embolism → stroke (may be first presentation)

Examination Findings

• Fixed widely split S2 (pathognomonic): splitting does not vary with respiration because RV volume is constantly increased
• Ejection systolic murmur at LUSE: increased flow across pulmonary valve (not the ASD itself)
• Mid-diastolic tricuspid flow murmur: if large shunt
• Right ventricular heave (RV volume overload)
• In Eisenmenger: central cyanosis, clubbing, loud P2

Red Flags

• Stroke in a young patient (paradoxical embolism)
• Progressive dyspnoea with RV dilatation
• New AF/atrial flutter in a young adult
• Signs of Eisenmenger syndrome (cyanosis, clubbing) — closure contraindicated

Bedside

• ECG: RAD (secundum), LAD (primum), RBBB or rSR' in V1, P pulmonale, AF

Bloods

• BNP/NT-proBNP: if heart failure suspected
• Routine bloods: FBC, U&Es

Imaging

• Transthoracic echocardiography: ASD visualisation (especially secundum), RV dilatation, paradoxical septal motion, shunt direction (colour Doppler)
• TOE with bubble contrast: gold standard for ASD detection and sizing (especially sinus venosus type); exclude anomalous pulmonary veins
• Cardiac MRI: quantify shunt (Qp:Qs ratio), RV volumes and function, pulmonary vein anatomy
• CXR: cardiomegaly (RA/RV dilatation), pulmonary plethora (increased pulmonary vascular markings), small aortic knuckle

Special Tests

• Right heart catheterisation: measure pulmonary pressures, calculate Qp:Qs, assess pulmonary vascular resistance
  • Qp:Qs >1.5:1 = haemodynamically significant shunt
• Bubble contrast echocardiography: demonstrates right-to-left shunt (bubbles crossing to left heart)
• Pulse oximetry: desaturation in Eisenmenger syndrome

Non-pharmacological

• Small ASDs with no RV dilatation: monitor with serial echo (3-5 yearly)
• Endocarditis prophylaxis: not routinely needed (only for 6 months post-closure or if residual shunt)

Pharmacological

• AF management: rate/rhythm control, anticoagulation
• Heart failure: diuretics, ACEi if needed
• Eisenmenger syndrome: pulmonary vasodilators (bosentan, sildenafil, prostanoids) — closure CONTRAINDICATED
• Anticoagulation/antiplatelet: post-device closure (aspirin 75mg for 6 months; clopidogrel for 3 months; or as per interventionist)

Surgical/Interventional

• Transcatheter device closure (Amplatzer device): standard for secundum ASD with sufficient rims
  • Indicated if Qp:Qs >1.5:1 with RV volume overload
  • Success rate >95%; low complication rate
  • Requires adequate septal rims (not suitable for primum or sinus venosus)
• Surgical closure (patch or direct suture): for primum, sinus venosus, or large secundum ASDs not suitable for device
  • Also indicated if associated anomalous pulmonary venous drainage
  • Operative mortality <1%
• Closure CONTRAINDICATED in Eisenmenger syndrome (shunt reversal maintains systemic output)

Referral Criteria

• All haemodynamically significant ASDs: congenital heart disease specialist
• Cryptogenic stroke in young patient: investigate for PFO/ASD
• Primum ASD: surgical assessment
• Pulmonary hypertension with ASD: specialist assessment for operability

• Small ASD with no RV dilatation: excellent prognosis, may never need intervention
• Post-closure (device or surgical): excellent long-term outcomes; RV remodelling and improvement over months
• Closure before age 25: near-normal life expectancy
• Closure after age 40: symptoms improve but may not fully normalise; AF may persist
• Eisenmenger syndrome: poor prognosis; median survival ~40-50 years without transplant
• Surgical closure mortality: <1% in experienced centres
• Device closure complication rate: ~1-2% (erosion, embolisation, arrhythmia)

ASD Types Comparison

Fixed vs Variable S2 Splitting