🫀 Chapter 488.2: Hypertrophic Cardiomyopathy
Nelson's Textbook of Pediatrics 22e | Asymmetric septal hypertrophy · LVOT obstruction · Diastolic dysfunction · Sudden death · Sarcomere genes · ICD · Myectomy · Beta-blockers
📚 Reference: www.paeds.online — Paediatric Resource Hub
📌 HCM – Definition & EpidemiologyLV hypertrophy (wall thickness Z-score >2) in absence of systemic hypertension or aortic stenosis. Most common genetic cardiomyopathy (1:500). Leading cause of sudden death in young athletes.
📌 Genetics – Sarcomere mutationsAutosomal dominant with variable penetrance. Most common: MYH7 (β-myosin heavy chain, ~40%), MYBPC3 (myosin-binding protein C, ~40%). Others: TNNT2, TNNI3, TPM1, ACTC1.
📌 Syndromic HCMNoonan syndrome, LEOPARD syndrome, Costello syndrome, cardiofaciocutaneous (CFC) – RASopathies (PTPN11, SOS1, RAF1, KRAS). Also Friedrich ataxia, Danon disease (LAMP2), Pompe disease, Fabry disease.
📌 PathophysiologyAsymmetric septal hypertrophy (ASH), dynamic left ventricular outflow tract (LVOT) obstruction, diastolic dysfunction (impaired relaxation), myocardial disarray, fibrosis, mitral regurgitation (systolic anterior motion SAM).
📌 Clinical presentationAsymptomatic (incidental murmur). Chest pain, dyspnea, fatigue, palpitations. Syncope (especially with exertion). Sudden cardiac death (SCD) – during exercise, post-exercise.
📌 Physical examHarsh systolic ejection murmur at LLSB and apex. Increases with Valsalva/standing (decreased preload). Decreases with squatting/handgrip (increased afterload). Bisferiens pulse, S4 gallop.
📌 ECG findingsLVH with deep septal Q waves (I, aVL, V5-V6), giant T-wave inversion, ST depression. Abnormal Q waves (pseudoinfarct). 90% have abnormal ECG.
📌 Echocardiogram – DiagnosticAsymmetric septal hypertrophy (septum:posterior wall ratio >1.3:1). LVOT gradient (resting or provocable). Systolic anterior motion (SAM) of mitral valve. Diastolic dysfunction.
📌 Sudden death risk stratificationMajor risk factors: prior cardiac arrest, syncope, family history SCD, NSVT, massive LVH (>30 mm), abnormal BP response to exercise, LV apical aneurysm. ICD indicated if ≥1 high-risk factor.
📌 Treatment & ICDBeta-blockers (propranolol, nadolol, atenolol) first-line. Disopyramide for refractory symptoms. Surgical septal myectomy (Morrow procedure) for severe obstruction. ICD for high-risk patients. Avoid competitive sports.
🔍 Step 1: Recognize presentation
Asymptomatic (heart murmur). Dyspnea on exertion (diastolic dysfunction). Chest pain (angina with normal coronaries). Palpitations (AF, VT). Syncope (especially during exercise). Family history of HCM or SCD.
📈 Step 2: Physical examination
Systolic ejection murmur LLSB/apex. Murmur intensity increases with Valsalva, standing, post-exercise. Decreases with squatting, handgrip, phenylephrine. S4 gallop. Bisferiens carotid pulse.
🩺 Step 3: ECG – almost always abnormal
LVH, deep narrow Q waves (septal), giant T-wave inversion (V2-V4). Arrhythmias (AF, PVCs, NSVT). Low voltage suggests alternate diagnosis.
🔄 Step 4: Echocardiogram with Doppler
Asymmetric septal hypertrophy, LVOT gradient (resting >30 mmHg, provocable >50 mmHg). Systolic anterior motion (SAM), mitral regurgitation. Diastolic dysfunction (E/A reversal, prolonged deceleration time).
🚨 Step 5: Sudden death risk assessment
Syncope, NSVT, massive LVH (>30 mm), family history SCD, abnormal BP response to exercise, LV apical aneurysm → ICD implantation.
1️⃣ Medical therapy – First-line (beta-blockers)
▪ Propranolol 2-4 mg/kg/day, nadolol 1-2 mg/kg/day, atenolol 1-2 mg/kg/day.
▪ Reduce symptoms, decrease LVOT gradient, improve diastolic filling.
▪ Avoid dehydration, vasodilators, digoxin (may worsen obstruction).
2️⃣ Second-line (disopyramide, verapamil)
▪ Disopyramide (class Ia antiarrhythmic) – negative inotrope, reduces gradient.
▪ Verapamil – calcium channel blocker for diastolic dysfunction (avoid in severe obstruction, hypotension).
3️⃣ Invasive therapies – Obstructive HCM
▪ Surgical septal myectomy (Morrow procedure) – gold standard for severe obstruction (gradient >50 mmHg, symptoms refractory to meds).
▪ Alcohol septal ablation (adults, limited pediatric data).
▪ Pacemaker (DDD) – limited efficacy, not first-line.
4️⃣ ICD implantation – Sudden death prevention
▪ Secondary prevention: survivors of cardiac arrest, sustained VT.
▪ Primary prevention: high-risk features (syncope, family history SCD, NSVT, massive LVH >30 mm, abnormal BP response).
▪ Implantable loop recorder if unexplained syncope.
5️⃣ Lifestyle modifications
▪ Avoid competitive sports (especially high-intensity, contact sports).
▪ Hydration (avoid dehydration that worsens obstruction).
▪ Avoid QT-prolonging drugs, stimulants (pseudoephedrine, caffeine).
6️⃣ Family screening
▪ First-degree relatives: ECG, echocardiogram, genetic testing.
▪ Serial screening every 1-2 years during childhood/adolescence.
▪ Genetic cascade testing if pathogenic variant identified.
7️⃣ Transition & pregnancy
▪ Pregnancy high-risk (especially if obstruction or NYHA III-IV). Avoid vasodilators, diuretics. Beta-blockers safe (propranolol, labetalol).
▪ Transition to adult cardiologist with expertise in HCM.
❓ Reflex prompt 1: A 14-year-old athlete collapses during basketball. ECG shows LVH. Echo: septal thickness 28 mm, LVOT gradient 60 mmHg. Next step?
✅ Answer: ICD for secondary prevention (aborted arrest). Beta-blocker therapy. No competitive sports.
❓ Reflex prompt 2: A 10-year-old with HCM, resting LVOT gradient 80 mmHg, NYHA III despite maximally tolerated beta-blockers. Next step?
✅ Answer: Surgical septal myectomy (Morrow procedure) – gold standard for obstructive HCM refractory to medical therapy.
❓ Reflex prompt 3: A 16-year-old with HCM and NSVT on Holter, family history of SCD. Indication for ICD?
✅ Answer: Primary prevention ICD (NSVT + family history SCD = high-risk).
❓ Reflex prompt 4: A 12-year-old with Noonan syndrome and HCM. Which additional cardiac finding is common?
✅ Answer: Pulmonary valve stenosis (dysplastic valve). Also ASD, hypertrophic cardiomyopathy.
❓ Reflex prompt 5: A 15-year-old with HCM and palpitations, ECG shows atrial fibrillation. Which drug is contraindicated?
✅ Answer: Digoxin (increases contractility, worsens LVOT obstruction). Use beta-blocker, amiodarone, or anticoagulation.
❓ Reflex prompt 6: A 7-year-old with HCM and hypotension after starting verapamil. Mechanism?
✅ Answer: Verapamil vasodilation worsens LVOT obstruction. Discontinue, treat with beta-blocker, IV fluids.
📌 Hypertrophic Cardiomyopathy – Core Concepts (Nelson 22e, Chapter 488.2)

1. Definition: LV hypertrophy (wall thickness Z-score >2) without apparent cause. Most common genetic cardiomyopathy (1:500). Leading cause of sudden death in young athletes.
2. Genetics: Autosomal dominant with variable penetrance. Sarcomere genes: MYH7 (β-myosin heavy chain) and MYBPC3 account for ~80% of familial cases. Other genes: TNNT2, TNNI3, TPM1, ACTC1.
3. Syndromic HCM: Noonan syndrome (PTPN11), LEOPARD, Costello, CFC (RASopathies), Friedreich ataxia, Danon disease (LAMP2), Pompe disease, Fabry disease.
4. Pathophysiology: Asymmetric septal hypertrophy (ASH), dynamic LVOT obstruction, diastolic dysfunction (impaired relaxation), myocardial disarray, fibrosis, systolic anterior motion (SAM) of mitral valve causing MR.
5. Clinical presentation: Asymptomatic (incidental murmur). Dyspnea, chest pain, palpitations, syncope (exertional). Sudden cardiac death.
6. Physical exam: Harsh systolic ejection murmur LLSB/apex. Increases with Valsalva/standing (decreased preload), decreases with squatting/handgrip. S4 gallop, bisferiens pulse.
7. Diagnosis: ECG (90% abnormal: LVH, deep Q waves, giant T inversion). Echocardiogram (septal:posterior wall ratio >1.3:1, LVOT gradient, SAM). Cardiac MRI (fibrosis, scar).
8. Treatment:
- Beta-blockers (propranolol, nadolol, atenolol) first-line.
- Disopyramide or verapamil for refractory symptoms.
- Surgical septal myectomy (Morrow) for severe obstruction (gradient >50 mmHg, symptoms).
- ICD for high-risk patients (secondary prevention: aborted arrest; primary: syncope, NSVT, family history SCD, massive LVH >30 mm, abnormal BP response).
9. Lifestyle: Avoid competitive sports, dehydration, stimulants. Pregnancy high-risk (beta-blockers safe).
10. Family screening: First-degree relatives require serial ECG and echo. Genetic testing if index case has pathogenic variant.
💡 Clinical pearls:
➤ HCM is the most common cause of sudden death in young athletes; preparticipation screening important.
➤ Murmur increases with Valsalva – differentiate from aortic stenosis (decreases).
➤ ICD for primary prevention in children with multiple risk factors.
➤ Avoid digoxin, vasodilators, and high-dose diuretics in HCM (worsen obstruction).