Hypertrophic Cardiomyopathy (HCM)

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Hypertrophic Cardiomyopathy (HCM) 

  

Definition

  • Genetic disorder characterized by left ventricular hypertrophy (LVH) not explained by other causes (e.g., hypertension, aortic stenosis).

  • Two types:

    • HOCM (Hypertrophic Obstructive Cardiomyopathy): With LV outflow tract obstruction (LVOTO).

    • Nonobstructive HCM: Without LVOTO.

Epidemiology

  • Second most common cardiomyopathy.

  • HOCM ~70% of cases; nonobstructive ~30%.

  • Leading cause of sudden cardiac death (SCD) in young people, esp. athletes.

Etiology

  • Genetic, autosomal dominant with variable penetrance.

  • Mutations in sarcomeric protein genes:

    • MYH7 (β-myosin heavy chain, chr14).

    • MYBPC3 (myosin binding protein C, chr11).

  • → Myocyte disarray + fibrosis → LV hypertrophy.

  • Mimickers: HTN, aortic stenosis, Fabry disease, Friedreich ataxia, Noonan syndrome, amyloidosis.

Pathophysiology

  • Asymmetric septal hypertrophy → stiff ventricle → impaired relaxation (diastolic dysfunction).

  • Small LV cavity → ↓ stroke volume → ↓ perfusion → arrhythmias + risk of SCD.

  • HOCM mechanisms:

    • SAM (systolic anterior motion) of mitral valve → LVOTO ± MR.

    • Venturi effect + abnormal papillary muscles.

  • Obstruction worsened by: ↑ contractility, ↓ preload, ↓ afterload.

  • Exacerbating triggers: exercise, dehydration, valsalva, vasodilators, inotropes.

Clinical Features

  • Often asymptomatic.

  • Symptoms (worse with exercise, dehydration):

    • Dyspnea on exertion, angina, palpitations.

    • Dizziness, syncope.

    • Sudden cardiac death (esp. during exertion).

  • Exam:

    • Systolic ejection murmur (crescendo–decrescendo)

      • ↑ with Valsalva, standing.

      • ↓ with squatting, handgrip.

    • Possible MR murmur, S4, paradoxical S2 split, pulsus bisferiens.

Diagnosis

Echocardiography (gold standard)

  • Criteria:

    • LV wall thickness ≥ 15 mm.

    • No other cause of LVH.

  • Findings:

    • Asymmetric septal hypertrophy.

    • SAM of mitral valve ± MR.

    • LVOT gradient ≥ 30 mmHg.

    • Normal systolic function; diastolic dysfunction; LA enlargement.

ECG

  • LVH (Sokolow-Lyon criteria).

  • Deep Q waves (inferior, lateral leads).

  • T-wave inversions.

  • Arrhythmias (AF, VT).

Other

  • CXR: Normal/enlarged heart, LA enlargement, pulmonary congestion.

  • Cardiac MRI: Clarify morphology, fibrosis (late gadolinium enhancement).

  • Exercise testing: Detect latent obstruction, risk stratification.

  • Genetic testing + family screening.

  • Holter: Detect VT, AF, other arrhythmias.

Treatment

General

  • Lifestyle: Avoid dehydration, alcohol, strenuous exercise.

  • SCD prevention:

    • AICD if prior cardiac arrest, sustained VT/VF.

    • Consider if unexplained syncope, FHx SCD, wall thickness ≥ 30 mm, documented NSVT.

Pharmacologic

  • Goal: ↓ HR → ↑ LV filling + ↓ obstruction.

  • First-line: β-blockers (e.g., propranolol, atenolol, nadolol).

  • Second-line: Non-DHP CCBs (verapamil, diltiazem).

  • Additional: Disopyramide (esp. in obstructive HCM).

  • Diuretics: Only in volume overload, with caution.

  • Avoid: Digoxin, high-dose diuretics, vasodilators (nitrates, ACEI/ARB, DHP-CCB), inotropes.

Invasive

  • Septal myectomy (Morrow procedure): For refractory obstructive cases.

  • Alcohol septal ablation: Alternative if surgery high-risk.

  • Dual-chamber pacemaker: Sometimes for refractory symptoms.

  • Heart transplant: End-stage, nonobstructive HCM with systolic dysfunction.

Complications

  • Arrhythmias: AF, VT, VF → SCD.

  • Heart failure: Diastolic dysfunction, rarely systolic in late stage.

  • Mitral regurgitation.

  • Apical aneurysms.

  • Cardiogenic shock (rare, severe obstruction).

Prognosis

  • Variable; many live normal lifespan with monitoring.

  • High risk of SCD in young athletes if untreated.

  • Risk stratification + AICD crucial for prevention.

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