FCPS Paediatrics TOACS · Ostium Primum ASD (Partial AV Canal)
💙 5-year-old with murmur, fixed split S2, ECG: left axis deviation (superior QRS axis), rsR' in V1 – Primum ASD + cleft mitral valve, Down syndrome, surgical closure
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⚕️ OBSERVED STATION · CPSP FORMAT · 8 MINUTES · SEPARATE TABS · CLINICAL SCENARIO
📖 Problem-oriented Clinical Scenario – Ostium Primum ASD (Partial AV Canal)
👶🏻 Clinical Scenario (read aloud – 2 min):
A 5-year-old girl is referred to the pediatric cardiology clinic because of a heart murmur detected during a routine school physical examination. She is asymptomatic and has no history of cyanosis, exercise intolerance, or recurrent respiratory infections. She has had normal growth and development. She has a history of mild learning difficulties and was diagnosed with Down syndrome at birth. There is no history of syncope or palpitations.
Examination: Vital signs: HR 85 bpm, BP 105/65 mm Hg, RR 20/min, SpO2 98% on room air. Cardiovascular examination reveals a fixed widely split S2, a soft systolic ejection murmur at the left upper sternal border, and a holosystolic murmur at the apex. There is no cyanosis, clubbing, or hepatomegaly.
ECG (obtained in clinic):
Task for the candidate: You are the pediatric cardiologist. Evaluate this child, interpret the ECG (left axis deviation, superior QRS axis), discuss the pathophysiology of ostium primum ASD (partial AV canal), differentiate it from secundum ASD (normal axis), identify associated mitral valve cleft and mitral regurgitation, formulate a management plan (surgical closure + mitral valvuloplasty), and provide counseling to the parents about the association with Down syndrome and the need for surgical repair.
A 5-year-old girl is referred to the pediatric cardiology clinic because of a heart murmur detected during a routine school physical examination. She is asymptomatic and has no history of cyanosis, exercise intolerance, or recurrent respiratory infections. She has had normal growth and development. She has a history of mild learning difficulties and was diagnosed with Down syndrome at birth. There is no history of syncope or palpitations.
Examination: Vital signs: HR 85 bpm, BP 105/65 mm Hg, RR 20/min, SpO2 98% on room air. Cardiovascular examination reveals a fixed widely split S2, a soft systolic ejection murmur at the left upper sternal border, and a holosystolic murmur at the apex. There is no cyanosis, clubbing, or hepatomegaly.
ECG (obtained in clinic):
Figure: ECG shows left axis deviation (superior QRS axis) with counterclockwise inscription, rsR' pattern in V1 (right ventricular conduction delay), and biventricular hypertrophy pattern.
💡 Examiner instruction (interactive): This is a case of Ostium Primum ASD (Partial AV Canal) – a defect in the atrioventricular septum characterized by a primum ASD, intact ventricular septum, and a cleft anterior mitral leaflet (mitral regurgitation). The candidate must recognize the pathognomonic ECG finding: left axis deviation (superior QRS axis, -90 to -180 degrees) with counterclockwise inscription. This ECG pattern distinguishes primum ASD from secundum ASD (which has right axis deviation with rsR' in V1). The candidate should also understand that this defect is part of the AV canal spectrum, is associated with Down syndrome (40-50%), and requires surgical closure (patch ASD closure + mitral valvuloplasty). The candidate should discuss the indications for surgery (RV enlargement, mitral regurgitation) and the excellent surgical outcomes.
🔍 Examiner Questions (interactive) – Click to reveal model answers
❓ Q1 (Examiner): “Describe the ECG findings in this child. What is the pathognomonic ECG feature of ostium primum ASD?”
✅ Candidate's answer:
• ECG findings in ostium primum ASD:
- Left axis deviation (superior QRS axis): The QRS axis is typically between -90° and -180° (superior/leftward). This is due to abnormal formation of the left anterior fascicle (left anterior fascicular block pattern).
- Counterclockwise inscription – the QRS loop is directed counterclockwise in the frontal plane.
- Right ventricular conduction delay (rsR' in V1) – similar to secundum ASD, but with a leftward axis.
- Q wave in leads I and aVL – due to abnormal septal depolarization.
- Right atrial enlargement – tall, peaked P waves (P pulmonale).
• Pathognomonic feature: Left axis deviation (superior QRS axis) with counterclockwise inscription – this is the hallmark of ostium primum ASD and distinguishes it from secundum ASD (which has right axis deviation with rsR' in V1).
• Differential diagnosis: Tricuspid atresia also has left axis deviation, but with different clinical and echocardiographic findings (cyanosis, absent tricuspid valve).
• ECG findings in ostium primum ASD:
- Left axis deviation (superior QRS axis): The QRS axis is typically between -90° and -180° (superior/leftward). This is due to abnormal formation of the left anterior fascicle (left anterior fascicular block pattern).
- Counterclockwise inscription – the QRS loop is directed counterclockwise in the frontal plane.
- Right ventricular conduction delay (rsR' in V1) – similar to secundum ASD, but with a leftward axis.
- Q wave in leads I and aVL – due to abnormal septal depolarization.
- Right atrial enlargement – tall, peaked P waves (P pulmonale).
• Pathognomonic feature: Left axis deviation (superior QRS axis) with counterclockwise inscription – this is the hallmark of ostium primum ASD and distinguishes it from secundum ASD (which has right axis deviation with rsR' in V1).
• Differential diagnosis: Tricuspid atresia also has left axis deviation, but with different clinical and echocardiographic findings (cyanosis, absent tricuspid valve).
❓ Q2 (Examiner): “What is the pathophysiology of ostium primum ASD? What are the anatomical abnormalities?”
✅ Candidate's answer:
• Anatomical abnormalities:
- Ostium primum atrial septal defect (ASD): A defect in the lower portion of the atrial septum, just above the atrioventricular valves.
- Cleft anterior mitral leaflet: A deficiency of the anterior mitral leaflet, causing mitral regurgitation (MR).
- Intact ventricular septum: No VSD (unlike complete AV canal).
- Common AV valve? In partial AVSD, the AV valves are separate but share a common annulus; there is a cleft in the mitral valve.
- Associated with: Down syndrome (40-50% of patients with Down syndrome have CHD; AVSD is the most common).
• Hemodynamics:
- Left-to-right shunt at atrial level: Due to the ASD (LA → RA → RV → PA).
- Mitral regurgitation: Due to the cleft mitral valve → left atrial volume overload → increased left-to-right shunt.
- Result: Right ventricular volume overload, right atrial enlargement, and left atrial enlargement (due to MR).
- Pulmonary artery pressure is usually normal (unless large shunt or late diagnosis).
- No cyanosis – unless pulmonary hypertension develops (rare).
• Anatomical abnormalities:
- Ostium primum atrial septal defect (ASD): A defect in the lower portion of the atrial septum, just above the atrioventricular valves.
- Cleft anterior mitral leaflet: A deficiency of the anterior mitral leaflet, causing mitral regurgitation (MR).
- Intact ventricular septum: No VSD (unlike complete AV canal).
- Common AV valve? In partial AVSD, the AV valves are separate but share a common annulus; there is a cleft in the mitral valve.
- Associated with: Down syndrome (40-50% of patients with Down syndrome have CHD; AVSD is the most common).
• Hemodynamics:
- Left-to-right shunt at atrial level: Due to the ASD (LA → RA → RV → PA).
- Mitral regurgitation: Due to the cleft mitral valve → left atrial volume overload → increased left-to-right shunt.
- Result: Right ventricular volume overload, right atrial enlargement, and left atrial enlargement (due to MR).
- Pulmonary artery pressure is usually normal (unless large shunt or late diagnosis).
- No cyanosis – unless pulmonary hypertension develops (rare).
❓ Q3 (Examiner): “How do you differentiate ostium primum ASD from secundum ASD clinically and on ECG?”
✅ Candidate's answer:
| Feature | Ostium Primum ASD | Secundum ASD |
|---|---|---|
| ECG Axis | Left axis deviation (superior QRS axis) | Right axis deviation |
| V1 Pattern | rsR' (RV conduction delay) with left axis | rsR' (RV conduction delay) with right axis |
| Mitral Valve | Cleft anterior mitral leaflet → MR | Normal |
| VSD | None (intact ventricular septum) | None |
| Murmur | Fixed split S2 + systolic murmur at LUSB + apical holosystolic murmur (MR) | Fixed split S2 + systolic murmur at LUSB (no MR) |
| Down Syndrome | Strong association (40-50%) | Less common |
| Surgery | ASD patch closure + mitral valvuloplasty | ASD patch or device closure only |
❓ Q4 (Examiner): “This child has Down syndrome. What is the association between Down syndrome and AVSD? What other cardiac defects are common?”
✅ Candidate's answer:
• Down syndrome (trisomy 21) and CHD:
- 40-50% of patients with Down syndrome have CHD.
- Atrioventricular septal defect (AVSD) is the most common cardiac defect in Down syndrome, occurring in approximately 40% of those with CHD.
- Spectrum of AVSD: Ostium primum ASD (partial), transitional AVSD, complete AVSD.
- Other common defects in Down syndrome: VSD (30%), PDA (10%), TOF (5%), ASD secundum (5%).
• Why AVSD is common in Down syndrome: Abnormal development of the endocardial cushions → failure of fusion → AV canal defects.
• Clinical implications:
- All newborns with Down syndrome should have an echocardiogram to screen for CHD.
- If AVSD is present, early surgical repair is indicated (by 3-6 months for complete AVSD; ostium primum repair at 1-2 years).
- Pulmonary vascular disease develops earlier in Down syndrome → repair earlier.
- Also screen for hypothyroidism, atlantoaxial instability, and immune deficiency.
• Down syndrome (trisomy 21) and CHD:
- 40-50% of patients with Down syndrome have CHD.
- Atrioventricular septal defect (AVSD) is the most common cardiac defect in Down syndrome, occurring in approximately 40% of those with CHD.
- Spectrum of AVSD: Ostium primum ASD (partial), transitional AVSD, complete AVSD.
- Other common defects in Down syndrome: VSD (30%), PDA (10%), TOF (5%), ASD secundum (5%).
• Why AVSD is common in Down syndrome: Abnormal development of the endocardial cushions → failure of fusion → AV canal defects.
• Clinical implications:
- All newborns with Down syndrome should have an echocardiogram to screen for CHD.
- If AVSD is present, early surgical repair is indicated (by 3-6 months for complete AVSD; ostium primum repair at 1-2 years).
- Pulmonary vascular disease develops earlier in Down syndrome → repair earlier.
- Also screen for hypothyroidism, atlantoaxial instability, and immune deficiency.
❓ Q5 (Examiner): “Describe the auscultatory findings in ostium primum ASD. What is the significance of the apical holosystolic murmur?”
✅ Candidate's answer:
• Auscultatory findings in ostium primum ASD:
- Fixed widely split S2 – the hallmark of ASD (both primum and secundum). The split does not vary with respiration.
- Systolic ejection murmur at the left upper sternal border – due to increased flow across the pulmonary valve (increased RV stroke volume).
- Apical holosystolic murmur – due to mitral regurgitation from the cleft anterior mitral leaflet.
- Mid-diastolic rumbling murmur at the left lower sternal border – due to increased flow across the tricuspid valve (if Qp:Qs >2:1).
- No cyanosis – unless Eisenmenger syndrome develops (rare).
• Significance of apical holosystolic murmur:
- Indicates the presence of mitral regurgitation due to cleft mitral valve.
- The degree of MR determines the need for mitral valve repair during ASD closure.
- If MR is severe, it can cause left atrial enlargement, left ventricular volume overload, and pulmonary hypertension.
• Auscultatory findings in ostium primum ASD:
- Fixed widely split S2 – the hallmark of ASD (both primum and secundum). The split does not vary with respiration.
- Systolic ejection murmur at the left upper sternal border – due to increased flow across the pulmonary valve (increased RV stroke volume).
- Apical holosystolic murmur – due to mitral regurgitation from the cleft anterior mitral leaflet.
- Mid-diastolic rumbling murmur at the left lower sternal border – due to increased flow across the tricuspid valve (if Qp:Qs >2:1).
- No cyanosis – unless Eisenmenger syndrome develops (rare).
• Significance of apical holosystolic murmur:
- Indicates the presence of mitral regurgitation due to cleft mitral valve.
- The degree of MR determines the need for mitral valve repair during ASD closure.
- If MR is severe, it can cause left atrial enlargement, left ventricular volume overload, and pulmonary hypertension.
❓ Q6 (Examiner): “What are the echocardiographic findings in ostium primum ASD? What is the gooseneck deformity?”
✅ Candidate's answer:
• Echocardiographic findings in ostium primum ASD:
- Primum ASD: Defect in the lower portion of the atrial septum, adjacent to the atrioventricular valves.
- Cleft anterior mitral leaflet: A deficiency in the anterior mitral leaflet, best seen in the parasternal short-axis view or apical 4-chamber view.
- Mitral regurgitation (MR): Color Doppler shows a jet of MR originating from the cleft.
- Normal ventricular septum – no VSD.
- Right ventricular volume overload: RV dilatation, paradoxical septal motion.
- Gooseneck deformity: Abnormal elongation and narrowing of the left ventricular outflow tract (LVOT), seen on echocardiography or angiography. This is due to the abnormal anterior displacement of the mitral valve.
- Subsequent development: Subaortic stenosis may develop later due to the gooseneck deformity.
• LVOT gooseneck deformity: Is a hallmark of AVSD, seen in both primum and complete AVSD. It may progress to subaortic stenosis requiring surgical resection.
• Echocardiographic findings in ostium primum ASD:
- Primum ASD: Defect in the lower portion of the atrial septum, adjacent to the atrioventricular valves.
- Cleft anterior mitral leaflet: A deficiency in the anterior mitral leaflet, best seen in the parasternal short-axis view or apical 4-chamber view.
- Mitral regurgitation (MR): Color Doppler shows a jet of MR originating from the cleft.
- Normal ventricular septum – no VSD.
- Right ventricular volume overload: RV dilatation, paradoxical septal motion.
- Gooseneck deformity: Abnormal elongation and narrowing of the left ventricular outflow tract (LVOT), seen on echocardiography or angiography. This is due to the abnormal anterior displacement of the mitral valve.
- Subsequent development: Subaortic stenosis may develop later due to the gooseneck deformity.
• LVOT gooseneck deformity: Is a hallmark of AVSD, seen in both primum and complete AVSD. It may progress to subaortic stenosis requiring surgical resection.
❓ Q7 (Examiner): “What is the management of ostium primum ASD? When is surgical repair indicated?”
✅ Candidate's answer:
• Management of ostium primum ASD:
1️⃣ Medical management: If MR is mild and symptoms are absent, surgical closure is still indicated (to prevent late complications). Diuretics and ACE inhibitors may be used for heart failure symptoms (if MR is significant).
2️⃣ Surgical closure: The definitive treatment is surgical repair (transcatheter device closure is not suitable for primum ASD due to proximity to AV valves and conduction system).
3️⃣ Timing of surgery:
- Usually performed at 1-2 years of age (or when diagnosed, if significant shunt or MR).
- Earlier if severe MR or heart failure.
4️⃣ Surgical repair:
- Patch closure of ASD – using pericardial or synthetic patch.
- Mitral valvuloplasty – suture closure of the cleft anterior mitral leaflet.
- Anuloplasty – if significant mitral annular dilation.
5️⃣ Indications for surgery:
- Qp:Qs >1.5:1 (significant left-to-right shunt).
- RV enlargement on echo.
- Significant mitral regurgitation (moderate to severe).
- Symptoms (dyspnea, fatigue, exercise intolerance).
6️⃣ Prognosis: Excellent surgical outcomes with low mortality (<1-2%). Long-term complications: residual MR (5-10% require reoperation), subaortic stenosis, arrhythmias, heart block.
• Management of ostium primum ASD:
1️⃣ Medical management: If MR is mild and symptoms are absent, surgical closure is still indicated (to prevent late complications). Diuretics and ACE inhibitors may be used for heart failure symptoms (if MR is significant).
2️⃣ Surgical closure: The definitive treatment is surgical repair (transcatheter device closure is not suitable for primum ASD due to proximity to AV valves and conduction system).
3️⃣ Timing of surgery:
- Usually performed at 1-2 years of age (or when diagnosed, if significant shunt or MR).
- Earlier if severe MR or heart failure.
4️⃣ Surgical repair:
- Patch closure of ASD – using pericardial or synthetic patch.
- Mitral valvuloplasty – suture closure of the cleft anterior mitral leaflet.
- Anuloplasty – if significant mitral annular dilation.
5️⃣ Indications for surgery:
- Qp:Qs >1.5:1 (significant left-to-right shunt).
- RV enlargement on echo.
- Significant mitral regurgitation (moderate to severe).
- Symptoms (dyspnea, fatigue, exercise intolerance).
6️⃣ Prognosis: Excellent surgical outcomes with low mortality (<1-2%). Long-term complications: residual MR (5-10% require reoperation), subaortic stenosis, arrhythmias, heart block.
❓ Q8 (Examiner): “What is the surgical approach for ostium primum ASD repair? What are the risks?”
✅ Candidate's answer:
• Surgical approach:
- Median sternotomy or minimally invasive thoracotomy (for older children).
- Cardiopulmonary bypass is used.
- Repair:
1️⃣ Patch closure of the primum ASD: A patch (pericardial or synthetic) is sutured to close the ASD, avoiding the coronary sinus and AV node.
2️⃣ Mitral valvuloplasty: The cleft in the anterior mitral leaflet is sutured closed (to reduce MR). An annuloplasty ring may be placed if annular dilation is present.
3️⃣ Intraoperative TEE: To assess residual MR and shunt.
• Risks:
- Complete heart block: The AV node and bundle of His are located in the inferior-posterior position and are at risk during patch closure. Risk of heart block is 1-2% (requires pacemaker).
- Residual MR: Up to 10% of patients may have significant MR post-repair, requiring reoperation.
- Residual ASD (rare).
- Subaortic stenosis – may develop later due to the gooseneck deformity.
- Arrhythmias: Atrial arrhythmias (flutter, fibrillation) can occur late.
• Post-operative: Aspirin for 6 months (if patch). Endocarditis prophylaxis for 6 months post-repair.
• Surgical approach:
- Median sternotomy or minimally invasive thoracotomy (for older children).
- Cardiopulmonary bypass is used.
- Repair:
1️⃣ Patch closure of the primum ASD: A patch (pericardial or synthetic) is sutured to close the ASD, avoiding the coronary sinus and AV node.
2️⃣ Mitral valvuloplasty: The cleft in the anterior mitral leaflet is sutured closed (to reduce MR). An annuloplasty ring may be placed if annular dilation is present.
3️⃣ Intraoperative TEE: To assess residual MR and shunt.
• Risks:
- Complete heart block: The AV node and bundle of His are located in the inferior-posterior position and are at risk during patch closure. Risk of heart block is 1-2% (requires pacemaker).
- Residual MR: Up to 10% of patients may have significant MR post-repair, requiring reoperation.
- Residual ASD (rare).
- Subaortic stenosis – may develop later due to the gooseneck deformity.
- Arrhythmias: Atrial arrhythmias (flutter, fibrillation) can occur late.
• Post-operative: Aspirin for 6 months (if patch). Endocarditis prophylaxis for 6 months post-repair.
❓ Q9 (Examiner): “What are the long-term complications after ostium primum ASD repair?”
✅ Candidate's answer:
• Long-term complications after primum ASD repair:
1️⃣ Mitral regurgitation (MR): Most common complication. 5-10% of patients require reoperation for residual or progressive MR. May develop years after repair.
2️⃣ Subaortic stenosis: Occurs in 5% of patients due to the gooseneck deformity (narrowing of LVOT) or fibrous ridge. Requires surgical resection.
3️⃣ Complete heart block: 1-2% risk; requires permanent pacemaker.
4️⃣ Residual atrial septal defect – rare.
5️⃣ Arrhythmias: Atrial flutter/fibrillation (especially if repaired later in adulthood).
6️⃣ Pulmonary hypertension: If repaired late, residual PH may persist.
7️⃣ Infective endocarditis: Risk is low, but prophylaxis is recommended for 6 months post-repair (or lifelong if prosthetic material).
• Follow-up: Annual echocardiograms to monitor MR, subaortic stenosis, and ventricular function. Regular cardiology follow-up lifelong.
• Long-term complications after primum ASD repair:
1️⃣ Mitral regurgitation (MR): Most common complication. 5-10% of patients require reoperation for residual or progressive MR. May develop years after repair.
2️⃣ Subaortic stenosis: Occurs in 5% of patients due to the gooseneck deformity (narrowing of LVOT) or fibrous ridge. Requires surgical resection.
3️⃣ Complete heart block: 1-2% risk; requires permanent pacemaker.
4️⃣ Residual atrial septal defect – rare.
5️⃣ Arrhythmias: Atrial flutter/fibrillation (especially if repaired later in adulthood).
6️⃣ Pulmonary hypertension: If repaired late, residual PH may persist.
7️⃣ Infective endocarditis: Risk is low, but prophylaxis is recommended for 6 months post-repair (or lifelong if prosthetic material).
• Follow-up: Annual echocardiograms to monitor MR, subaortic stenosis, and ventricular function. Regular cardiology follow-up lifelong.
❓ Q10 (Examiner): “Can ostium primum ASD be closed with a transcatheter device? Why or why not?”
✅ Candidate's answer:
• No, transcatheter device closure is NOT suitable for ostium primum ASD.
• Reasons:
- Anatomy: The primum ASD is located in the lower portion of the atrial septum, adjacent to the atrioventricular valves and the conduction system (AV node and His bundle).
- Risk of AV block: Device closure could impinge on the AV node or bundle of His, causing complete heart block.
- Mitral valve: The cleft mitral valve requires surgical repair (valvuloplasty), which cannot be done transcatheter.
- Inadequate rims: The primum ASD lacks adequate rims for device anchoring (especially the atrioventricular rim).
- Device embolization: Higher risk due to proximity to the valves.
• Therefore: Surgical repair is the only option for ostium primum ASD.
• Secundum ASD is suitable for transcatheter closure (Amplatzer device) because it has adequate rims and is away from the valves.
• No, transcatheter device closure is NOT suitable for ostium primum ASD.
• Reasons:
- Anatomy: The primum ASD is located in the lower portion of the atrial septum, adjacent to the atrioventricular valves and the conduction system (AV node and His bundle).
- Risk of AV block: Device closure could impinge on the AV node or bundle of His, causing complete heart block.
- Mitral valve: The cleft mitral valve requires surgical repair (valvuloplasty), which cannot be done transcatheter.
- Inadequate rims: The primum ASD lacks adequate rims for device anchoring (especially the atrioventricular rim).
- Device embolization: Higher risk due to proximity to the valves.
• Therefore: Surgical repair is the only option for ostium primum ASD.
• Secundum ASD is suitable for transcatheter closure (Amplatzer device) because it has adequate rims and is away from the valves.
❓ Q11 (Examiner): “This child is 5 years old and asymptomatic. Is there a risk of pulmonary hypertension? When does it develop?”
✅ Candidate's answer:
• Pulmonary hypertension in primum ASD:
- Less common than in complete AVSD because there is no VSD and the shunt is only at the atrial level.
- However, if the ASD is large and mitral regurgitation is significant, the left-to-right shunt can be substantial → volume overload → eventual pulmonary hypertension.
- Pulmonary artery pressure is usually normal or mildly elevated in childhood.
- If left unrepaired, pulmonary hypertension can develop in adulthood (3rd-4th decade).
- Risk factors: Large shunt (Qp:Qs >2:1), significant MR, delayed repair.
- Down syndrome patients: May develop pulmonary hypertension earlier than non-Down patients.
• Indication for early repair: To prevent pulmonary vascular disease. Repair before school age (1-2 years) is recommended.
• Pulmonary hypertension in primum ASD:
- Less common than in complete AVSD because there is no VSD and the shunt is only at the atrial level.
- However, if the ASD is large and mitral regurgitation is significant, the left-to-right shunt can be substantial → volume overload → eventual pulmonary hypertension.
- Pulmonary artery pressure is usually normal or mildly elevated in childhood.
- If left unrepaired, pulmonary hypertension can develop in adulthood (3rd-4th decade).
- Risk factors: Large shunt (Qp:Qs >2:1), significant MR, delayed repair.
- Down syndrome patients: May develop pulmonary hypertension earlier than non-Down patients.
• Indication for early repair: To prevent pulmonary vascular disease. Repair before school age (1-2 years) is recommended.
❓ Q12 (Examiner): “What is the differential diagnosis of ostium primum ASD? What other conditions can cause left axis deviation on ECG?”
✅ Candidate's answer:
• Differential diagnosis of primum ASD:
1️⃣ Secundum ASD: Right axis deviation, no MR, no cleft mitral valve.
2️⃣ Tricuspid atresia: Left axis deviation + cyanosis + absent tricuspid valve.
3️⃣ Complete AVSD: Primum ASD + inlet VSD + common AV valve (usually presents with heart failure in infancy).
4️⃣ Pulmonary stenosis: Right axis deviation, ejection click, RVH.
5️⃣ Left anterior fascicular block (LAFB): Can cause left axis deviation without CHD.
• Conditions causing left axis deviation:
- Ostium primum ASD (most common cause in children).
- Tricuspid atresia.
- Complete AVSD.
- Left anterior fascicular block (idiopathic or post-surgical).
- Myocardial infarction (rare in children).
• Echocardiography: Is essential to differentiate these conditions.
• Differential diagnosis of primum ASD:
1️⃣ Secundum ASD: Right axis deviation, no MR, no cleft mitral valve.
2️⃣ Tricuspid atresia: Left axis deviation + cyanosis + absent tricuspid valve.
3️⃣ Complete AVSD: Primum ASD + inlet VSD + common AV valve (usually presents with heart failure in infancy).
4️⃣ Pulmonary stenosis: Right axis deviation, ejection click, RVH.
5️⃣ Left anterior fascicular block (LAFB): Can cause left axis deviation without CHD.
• Conditions causing left axis deviation:
- Ostium primum ASD (most common cause in children).
- Tricuspid atresia.
- Complete AVSD.
- Left anterior fascicular block (idiopathic or post-surgical).
- Myocardial infarction (rare in children).
• Echocardiography: Is essential to differentiate these conditions.
❓ Q13 (Examiner): “A 10-year-old with repaired primum ASD presents with a systolic ejection murmur at the left upper sternal border and a new systolic thrill. Echocardiogram shows a gradient of 60 mmHg across the LVOT. What is the diagnosis and management?”
✅ Candidate's answer:
• Diagnosis: Subaortic stenosis – a known complication after primum ASD repair (due to the gooseneck deformity or fibrous ridge).
• Pathophysiology: Abnormal anatomy of the LVOT (elongated and narrowed) leads to a fibrous ridge or membrane that obstructs LV outflow.
• Management:
- Surgical resection of the subaortic membrane (subaortic myectomy or membranectomy).
- If associated with mitral valve abnormalities, may need concomitant mitral valve surgery.
- Follow-up: Monitor for recurrence (can grow back) – repeat echocardiograms.
- If significant aortic regurgitation develops – may require aortic valve surgery.
• Prevention: Early repair of primum ASD may reduce the risk of subaortic stenosis, but it can still develop due to the inherent anatomy.
• Diagnosis: Subaortic stenosis – a known complication after primum ASD repair (due to the gooseneck deformity or fibrous ridge).
• Pathophysiology: Abnormal anatomy of the LVOT (elongated and narrowed) leads to a fibrous ridge or membrane that obstructs LV outflow.
• Management:
- Surgical resection of the subaortic membrane (subaortic myectomy or membranectomy).
- If associated with mitral valve abnormalities, may need concomitant mitral valve surgery.
- Follow-up: Monitor for recurrence (can grow back) – repeat echocardiograms.
- If significant aortic regurgitation develops – may require aortic valve surgery.
• Prevention: Early repair of primum ASD may reduce the risk of subaortic stenosis, but it can still develop due to the inherent anatomy.
❓ Q14 (Examiner): “The parents are anxious about their child's heart condition. How will you counsel them?”
✅ Candidate's structured answer:
• “Your child has a condition called ostium primum atrial septal defect – a hole in the lower part of the wall between the upper chambers of the heart. This is part of a spectrum of heart defects called AV canal defects, which are common in children with Down syndrome.”
• “The hole causes extra blood to flow to the lungs, which can enlarge the right side of the heart over time. Your child also has a leaky mitral valve (mitral regurgitation) due to a cleft in the valve leaflet.”
• “The good news is that this condition is very treatable with surgery. Your child will need an operation to close the hole and repair the mitral valve. This is usually done at 1-2 years of age and has excellent outcomes – more than 95% of children do well.”
• “After surgery, your child will need regular follow-up with a cardiologist to monitor the repair, but most children go on to lead normal, active lives.”
• “We will also screen for other conditions associated with Down syndrome, such as thyroid problems, and provide comprehensive care.”
• “Your child has a condition called ostium primum atrial septal defect – a hole in the lower part of the wall between the upper chambers of the heart. This is part of a spectrum of heart defects called AV canal defects, which are common in children with Down syndrome.”
• “The hole causes extra blood to flow to the lungs, which can enlarge the right side of the heart over time. Your child also has a leaky mitral valve (mitral regurgitation) due to a cleft in the valve leaflet.”
• “The good news is that this condition is very treatable with surgery. Your child will need an operation to close the hole and repair the mitral valve. This is usually done at 1-2 years of age and has excellent outcomes – more than 95% of children do well.”
• “After surgery, your child will need regular follow-up with a cardiologist to monitor the repair, but most children go on to lead normal, active lives.”
• “We will also screen for other conditions associated with Down syndrome, such as thyroid problems, and provide comprehensive care.”
🗣️ Examiner's probing / high-yield points (Ostium Primum ASD):
• "What is the pathognomonic ECG feature of primum ASD?" → Left axis deviation (superior QRS axis).
• "What is the most common associated valve abnormality?" → Cleft anterior mitral leaflet (mitral regurgitation).
• "What is the difference between primum and secundum ASD?" → Primum: left axis deviation + MR + Down syndrome association. Secundum: right axis deviation + no MR.
• "Is transcatheter closure possible for primum ASD?" → No, surgical repair is required.
• "What is the surgical procedure?" → Patch closure of ASD + mitral valvuloplasty.
• "What are the long-term complications?" → MR (5-10% require reoperation), subaortic stenosis, heart block, arrhythmias.
• "What is the gooseneck deformity?" → Narrowing of LVOT due to abnormal anatomy in AVSD.
• "What is the association with Down syndrome?" → 40-50% of AVSD patients have Down syndrome.
• "What is the pathognomonic ECG feature of primum ASD?" → Left axis deviation (superior QRS axis).
• "What is the most common associated valve abnormality?" → Cleft anterior mitral leaflet (mitral regurgitation).
• "What is the difference between primum and secundum ASD?" → Primum: left axis deviation + MR + Down syndrome association. Secundum: right axis deviation + no MR.
• "Is transcatheter closure possible for primum ASD?" → No, surgical repair is required.
• "What is the surgical procedure?" → Patch closure of ASD + mitral valvuloplasty.
• "What are the long-term complications?" → MR (5-10% require reoperation), subaortic stenosis, heart block, arrhythmias.
• "What is the gooseneck deformity?" → Narrowing of LVOT due to abnormal anatomy in AVSD.
• "What is the association with Down syndrome?" → 40-50% of AVSD patients have Down syndrome.
📘 Ostium Primum ASD – Core Revision for TOACS
💙 Definition
Partial AV canal defect with primum ASD + cleft anterior mitral leaflet + intact ventricular septum. Associated with Down syndrome (40-50%).
Partial AV canal defect with primum ASD + cleft anterior mitral leaflet + intact ventricular septum. Associated with Down syndrome (40-50%).
📊 ECG
Left axis deviation (superior QRS axis, -90 to -180°) – pathognomonic. Counterclockwise inscription, rsR' in V1, right atrial enlargement.
Left axis deviation (superior QRS axis, -90 to -180°) – pathognomonic. Counterclockwise inscription, rsR' in V1, right atrial enlargement.
🔍 Clinical Features
Asymptomatic in childhood. Fixed widely split S2, systolic ejection murmur at LUSB, apical holosystolic murmur (MR). No cyanosis.
Asymptomatic in childhood. Fixed widely split S2, systolic ejection murmur at LUSB, apical holosystolic murmur (MR). No cyanosis.
🩺 Echocardiogram
Primum ASD, cleft anterior mitral leaflet with MR, gooseneck deformity of LVOT, RV volume overload, normal ventricular septum.
Primum ASD, cleft anterior mitral leaflet with MR, gooseneck deformity of LVOT, RV volume overload, normal ventricular septum.
💊 Management
Surgical repair: patch closure of ASD + mitral valvuloplasty (suture cleft, annuloplasty). Transcatheter closure NOT possible.
Surgical repair: patch closure of ASD + mitral valvuloplasty (suture cleft, annuloplasty). Transcatheter closure NOT possible.
📈 Complications
Mitral regurgitation (5-10% reoperation), subaortic stenosis (5%), heart block (1-2%), arrhythmias.
Mitral regurgitation (5-10% reoperation), subaortic stenosis (5%), heart block (1-2%), arrhythmias.
⭐ High-yield pearls for TOACS (Ostium Primum ASD):
• ECG: Left axis deviation (superior QRS axis) is pathognomonic.
• Associated with: Down syndrome (40-50%).
• Key murmur: Apical holosystolic (mitral regurgitation).
• Surgery: Patch ASD closure + mitral valvuloplasty.
• Transcatheter closure: NOT possible.
• Complications: MR, subaortic stenosis, heart block.
• Differentiate from secundum ASD: left vs right axis deviation.
• ECG: Left axis deviation (superior QRS axis) is pathognomonic.
• Associated with: Down syndrome (40-50%).
• Key murmur: Apical holosystolic (mitral regurgitation).
• Surgery: Patch ASD closure + mitral valvuloplasty.
• Transcatheter closure: NOT possible.
• Complications: MR, subaortic stenosis, heart block.
• Differentiate from secundum ASD: left vs right axis deviation.
🗣️ Candidate's role-play & examiner feedback
💬 To the candidate (role‑play): You will be asked the 14 questions from the Examiner Q&A tab. This station tests knowledge of Ostium Primum ASD – ECG interpretation (left axis deviation, superior QRS axis), pathophysiology (primum ASD + cleft mitral valve + MR), differentiation from secundum ASD (left vs right axis), association with Down syndrome, management (surgical repair – patch closure + mitral valvuloplasty), and complications (MR, subaortic stenosis, heart block). Provide empathetic counseling to parents about the need for surgery and the excellent prognosis.
📝 Examiner Marking Grid (Ostium Primum ASD – TOACS station):
- ✅ Interprets ECG: left axis deviation (superior QRS axis) – pathognomonic
- ✅ Describes pathophysiology: primum ASD + cleft mitral valve + MR
- ✅ Differentiates from secundum ASD (left vs right axis deviation)
- ✅ States association with Down syndrome (40-50%)
- ✅ Describes physical exam: fixed split S2, systolic murmur LUSB, apical holosystolic (MR)
- ✅ States that transcatheter closure is NOT possible (surgical repair required)
- ✅ Describes surgical repair: patch closure ASD + mitral valvuloplasty
- ✅ Lists complications: MR (5-10% reoperation), subaortic stenosis, heart block
- ✅ Provides compassionate counseling and discusses prognosis
📚 Key references: Nelson Textbook of Pediatrics 22e (Section 475.5 – Atrioventricular Septal Defects), Pediatric Cardiology guidelines.