FCPS Paediatrics TOACS · Secundum Atrial Septal Defect (ASD)

✅ Candidate's answer:
• ECG findings in secundum ASD:
  - Right axis deviation – QRS axis > +90° (or > +100° in children).
  - rsR' pattern in V1 – a minor right ventricular conduction delay (not true right bundle branch block).
  - Signs of RV volume overload: Tall R waves in V1, deep S waves in V5-V6.
  - Right atrial enlargement – tall, peaked P waves (P pulmonale) in leads II, III, aVF.
  - May be normal in small ASDs.
• Differentiation from ostium primum ASD: Primum ASD has left axis deviation (superior QRS axis), while secundum ASD has right axis deviation.
• Significance: The rsR' pattern reflects right ventricular volume overload due to the left-to-right shunt at the atrial level.

✅ Candidate's answer:
• Pathophysiology of secundum ASD:
  - Left-to-right shunt: Because the left ventricle is more compliant than the right ventricle, blood flows from the left atrium to the right atrium through the ASD.
  - Qp:Qs ratio: The shunt magnitude is determined by the size of the defect and the relative compliance of the ventricles. Qp:Qs typically ranges from 2:1 to 4:1.
  - RV volume overload: The increased volume of blood in the right atrium leads to right ventricular volume overload (RV dilation).
  - Pulmonary artery pressure: Usually normal (unless the shunt is very large or persists for decades).
  - No cyanosis: The shunt is left-to-right; cyanosis does not occur unless pulmonary hypertension develops (Eisenmenger syndrome) or there is a right-to-left shunt.
• Consequences: RV dilation, paradoxical embolism (if a clot passes from right to left), and in adulthood, atrial arrhythmias and heart failure.

✅ Candidate's answer:
• Auscultatory findings in secundum ASD:
  - Fixed widely split S2 – the hallmark of ASD. The split does not vary with respiration.
    - Mechanism: The increased right ventricular stroke volume prolongs RV ejection time, causing pulmonary valve closure to be delayed throughout the respiratory cycle.
  - Systolic ejection murmur at the left upper sternal border – due to increased flow across the pulmonary valve.
  - Mid-diastolic rumbling murmur at the left lower sternal border – due to increased flow across the tricuspid valve (indicates Qp:Qs ≥2:1).
  - No cyanosis – unless Eisenmenger syndrome develops.
• Key feature: The fixed split S2 is the most important physical finding and helps differentiate ASD from other causes of a split S2 (e.g., right bundle branch block).

✅ Candidate's answer:
• Indications for ASD closure:
  1️⃣ Qp:Qs >1.5:1 – significant left-to-right shunt.
  2️⃣ RV enlargement – RV end-diastolic volume index >120 mL/m².
  3️⃣ Paradoxical embolism – stroke or TIA due to right-to-left shunting.
  4️⃣ Symptoms – exercise intolerance, fatigue, palpitations, or arrhythmias.
  5️⃣ Atrial arrhythmias – atrial flutter or fibrillation.
• In this child:
  - If the echocardiogram shows RV enlargement (RVEDV index >120 mL/m²), closure is indicated.
  - If Qp:Qs is >1.5:1, closure is recommended.
  - Even if asymptomatic, closure is recommended to prevent late complications (pulmonary hypertension, atrial arrhythmias).
• Timing: Elective closure is usually performed at 2-4 years of age (before school age).

✅ Candidate's answer:
• Device: Amplatzer septal occluder (double-disc, nitinol mesh).
• Procedure: Deployed via the femoral vein → inferior vena cava → right atrium → across the ASD → left atrium. The device is delivered under transesophageal echocardiography (TEE) or intracardiac echocardiography (ICE) guidance.
• Criteria for device closure:
  - Secundum ASD (not primum or sinus venosus).
  - Defect size ≤38 mm.
  - Adequate septal rims (≥5 mm) – especially the aortic rim (deficient aortic rim is a contraindication due to risk of erosion).
  - Weight ≥10-15 kg.
  - No multiple fenestrations (if multiple, surgical closure may be needed).
• Success rate: >95%.
• Complications: Device embolization (<1%), erosion into aorta/atrium (rare, <0.3%), pericardial effusion, arrhythmias, thrombus, nickel allergy.
• Post-procedure: Aspirin 3-6 mg/kg/day for 6 months. Endocarditis prophylaxis not needed after 6 months.

✅ Candidate's answer:
• Indications for surgical closure:
  1️⃣ Large defects (>38 mm) – too large for device closure.
  2️⃣ Deficient septal rims – especially the aortic rim (<5 mm) – risk of device erosion.
  3️⃣ Multiple fenestrations – not suitable for a single device.
  4️⃣ Primum ASD or sinus venosus ASD – these are not suitable for device closure.
  5️⃣ Failed device closure – if the device embolizes or leaks.
  6️⃣ Inadequate vascular access – e.g., small child or venous thrombosis.
• Surgical approach: Median sternotomy or minimally invasive thoracotomy. Patch closure (pericardial or Dacron) is performed.
• Complications: Arrhythmias, pericardial effusion, residual shunt, heart block (rare).
• Outcome: Excellent, with low mortality (<1%).

✅ Candidate's answer:
• Natural history of unrepaired secundum ASD:
  - Childhood: Usually asymptomatic. Small ASDs may close spontaneously in the first 2 years.
  - Adulthood (3rd-4th decade): Symptoms develop – exercise intolerance, palpitations, atrial arrhythmias (atrial flutter/fibrillation), pulmonary hypertension, right heart failure.
  - Eisenmenger syndrome: Rare (unlike VSD), but can occur if the defect is large and unrepaired for decades.
  - Paradoxical embolism: Can occur at any age.
• Why early closure is recommended:
  - Prevents late complications: Pulmonary hypertension, atrial arrhythmias, and right heart failure.
  - Reduces the risk of paradoxical embolism.
  - Improves long-term survival: Patients repaired in childhood have a normal life expectancy.
  - Optimal timing: 2-4 years of age (before school age) to minimize complications and allow the child to lead a normal life.

✅ Candidate's answer:
• Mechanism: Paradoxical embolism – a thrombus (usually from a deep vein thrombosis) passes from the right atrium to the left atrium through the ASD, causing a stroke or systemic embolism.
• Management:
  1️⃣ Immediate: Acute stroke management (thrombolysis if indicated).
  2️⃣ Anticoagulation: Warfarin or DOAC (direct oral anticoagulant) for secondary prevention.
  3️⃣ ASD closure: Device closure is indicated regardless of the size of the shunt, to prevent future paradoxical emboli.
  4️⃣ Evaluate for DVT: Doppler ultrasound of the legs to identify the source of the thrombus.
  5️⃣ Long-term: After device closure, anticoagulation may be continued for 3-6 months, then aspirin.

✅ Candidate's answer:

Feature	Secundum ASD	Ostium Primum ASD
ECG Axis	Right axis deviation	Left axis deviation (superior QRS axis)
V1 Pattern	rsR' (minor RV conduction delay)	rsR' (with left axis)
Mitral Valve	Normal	Cleft anterior mitral leaflet → MR
Down Syndrome	Less common	Strong association (40-50%)
Treatment	Device closure (Amplatzer)	Surgical closure + mitral valvuloplasty

✅ Candidate's answer:
• NKX2.5 gene mutation: Autosomal dominant mutation associated with familial ASD (secundum or primum) and progressive AV conduction disease (first-degree to complete heart block).
• Clinical features:
  - ASD (often secundum).
  - Progressive AV block (may require pacemaker).
  - May also be associated with ventricular septal defect or tetralogy of Fallot.
• Management:
  - Genetic testing for NKX2.5 mutation.
  - ECG monitoring: Annual ECGs to monitor for progression of heart block.
  - Pacemaker: May be needed if complete heart block develops.
  - Family screening: First-degree relatives should have ECG and echocardiogram.
• Other genes: TBX5 (Holt-Oram syndrome – ASD + upper limb anomalies), GATA4.

✅ Candidate's answer:
• Management: Observation with serial echocardiograms.
• Rationale: Small ASDs (<5-6 mm) have a high chance of spontaneous closure in the first 2 years of life.
• Follow-up:
  - Repeat echocardiogram at 2-3 years of age.
  - If the defect remains small (<5-6 mm) and there is no RV enlargement, no intervention is needed.
  - If the defect is still present at school age (4-5 years) and there is RV enlargement, closure is indicated.
• No medication needed – no endocarditis prophylaxis required for isolated ASD.

✅ Candidate's answer:
• Diagnosis: Device erosion into the aorta or atrium – a rare but serious complication of ASD device closure (incidence <0.3%).
• Clinical features: Chest pain, dyspnea, pericardial effusion, cardiac tamponade.
• Management:
  1️⃣ Urgent echocardiogram: To assess the pericardial effusion and signs of tamponade.
  2️⃣ Pericardiocentesis: If tamponade is present.
  3️⃣ Emergency surgical repair: To remove the device and repair the aortic/atrial erosion.
  4️⃣ If no tamponade: Close monitoring and possible surgical repair.
• Prevention: Careful selection of patients with adequate rims (especially aortic rim ≥5 mm) reduces the risk of erosion.

✅ Candidate's answer:
• Diagnosis: Eisenmenger syndrome – reversal of the shunt (right-to-left) due to severe, irreversible pulmonary hypertension.
• Pathophysiology: Long-standing left-to-right shunt leads to pulmonary vascular remodeling, increased pulmonary vascular resistance, and eventually reversal of the shunt (right-to-left), causing cyanosis.
• Management:
  1️⃣ ASD closure is CONTRAINDICATED – high mortality (increases right ventricular failure).
  2️⃣ Pulmonary vasodilators: Bosentan (endothelin receptor antagonist), sildenafil (PDE-5 inhibitor), or prostacyclin analogs.
  3️⃣ Anticoagulation: For thromboembolism prevention.
  4️⃣ Heart-lung transplantation: For end-stage disease.
  5️⃣ Avoid pregnancy: High mortality (30-50%).
• Prognosis: Poor without transplantation.

✅ Candidate's structured answer:
• “Your child has a condition called secundum atrial septal defect – a hole between the two upper chambers of the heart. This is the most common type of heart defect in children.”
• “The hole causes extra blood to flow to the lungs, which can enlarge the right side of the heart over time. But the good news is that this is very treatable.”
• “The ECG shows characteristic changes – a pattern called right axis deviation and rsR' in V1 – which are typical of this condition.”
• “We will close the hole using a procedure called transcatheter device closure – a small device is inserted through a vein in the leg and placed in the hole. This is very safe and effective, with a success rate >95%.”
• “The procedure is usually done before school age (2-4 years) to prevent future complications. After the procedure, your child will need to take aspirin for 6 months, but then will lead a normal life with no restrictions.”
• “There is a small risk of complications, but we will discuss these with you. Most children with this condition go on to live completely normal lives.”