Hypertrophic cardiomyopathy (HCM - HOCM) ✅

Related Subjects: |Dilated Cardiomyopathy |Hypertrophic cardiomyopathy (HCM - HOCM) |Peripartum cardiomyopathy |Restrictive Cardiomyopathy |Takotsubo Cardiomyopathy

💔 Hypertrophic cardiomyopathy (HCM) is an inherited myocardial disease that may present with exertional dyspnoea, chest pain, palpitations, syncope, atrial fibrillation, ventricular arrhythmia, or rarely sudden cardiac death, including in young people. 🧬 Even if no pathogenic variant is identified in the proband, first-degree relatives still require clinical screening because a negative genomic test does not exclude a genetic basis.

📖 About

• Defined in adults as otherwise unexplained LV wall thickness ≥15 mm in one or more myocardial segments.
• In first-degree relatives or genotype-positive individuals, a lower threshold such as ≥13 mm may support diagnosis in the right clinical context.
• Commonly caused by autosomal dominant variants affecting sarcomere proteins.
• Prevalence is often quoted as about 1 in 500.
• Causes diastolic dysfunction, myocardial ischaemia, atrial and ventricular arrhythmias, and sometimes dynamic LV outflow tract obstruction (LVOTO).
• Obstructive HCM is usually defined by an LVOT gradient ≥30 mmHg at rest or with provocation.
• A gradient ≥50 mmHg is often used as the threshold for considering invasive septal reduction therapy in symptomatic patients despite optimal treatment.

🧬 Pathophysiology

• Myocyte hypertrophy and disarray produce a stiff, non-compliant ventricle → diastolic dysfunction and raised filling pressures.
• Asymmetric septal hypertrophy may narrow the LV outflow tract.
• Systolic anterior motion of the mitral valve can worsen obstruction and cause mitral regurgitation.
• Small-vessel disease, hypertrophy and increased oxygen demand can cause angina-like chest pain even without obstructive coronary disease.
• Myocardial fibrosis creates an arrhythmogenic substrate, increasing risk of AF, NSVT and sudden cardiac death.

🩺 Clinical Features

🔍 Examination

• Jerky / bifid carotid pulse may be present in obstructive HCM.
• Double apical impulse may be felt due to forceful atrial contraction and LV hypertrophy.
• Ejection systolic murmur at the left sternal edge or apex, often louder with standing or Valsalva.
• Murmur may become softer with squatting or passive leg raise because increased preload reduces dynamic obstruction.
• There may be a pansystolic murmur from associated mitral regurgitation.
• Examination can be normal, especially in non-obstructive disease.

🧪 Investigations

👶 Family Screening

• If a pathogenic or likely pathogenic variant is identified → offer cascade genetic testing to relatives.
• If genomic testing is non-diagnostic → clinical screening of first-degree relatives is still recommended.
• Clinical screening usually includes history, examination, ECG and echocardiography.
• Children/adolescents from genotype-positive or early-onset families: every 1–2 years.
• Other children/adolescents: every 2–3 years, starting no later than puberty.
• Adults: every 3–5 years, or sooner if symptoms develop.
• Screen earlier or more frequently if there is a malignant family history, early-onset disease, symptoms, competitive sport participation, or concerning ECG/echo changes.

⚠️ Sudden Cardiac Death Risk

• Important markers include family history of SCD, recent unexplained syncope, NSVT, massive LVH, apical aneurysm, extensive LGE/fibrosis on CMR, and impaired LV systolic function.
• Previous cardiac arrest or sustained VT is a strong indication for secondary-prevention ICD assessment.
• 🧠 ICD decisions should follow specialist risk stratification; avoid saying “ICD indicated” on the basis of 2–3 isolated exam features alone.
• Risk should be reassessed periodically and when symptoms, imaging or rhythm findings change.

💊 Management

⚠️ Drugs / Situations to Use Caution With

• Avoid dehydration and excessive preload reduction in obstructive HCM.
• Use caution with nitrates, potent vasodilators and aggressive diuresis, as they may worsen LVOTO.
• Avoid combining beta-blockers with verapamil or diltiazem unless specialist-directed because of bradycardia and heart block risk.
• Consider coronary disease separately in older patients or those with vascular risk factors; HCM does not exclude ACS.

💡 Clinical Pearls

• HCM is not just “a thick septum”; it is a disease of myocardial architecture, diastolic filling, dynamic obstruction and arrhythmia risk.
• The murmur of obstructive HCM usually gets louder with standing or Valsalva and softer with squatting.
• Syncope during exertion is a major red flag and needs urgent specialist assessment.
• A normal coronary angiogram does not exclude HCM-related chest pain because microvascular ischaemia is common.
• First-degree relatives need a structured family-screening plan even if the proband’s genetic test is negative or inconclusive.

📚 References

• 📘 NICE TA913: Mavacamten for treating symptomatic obstructive hypertrophic cardiomyopathy. NICE, 2023.
• 🧬 NHS Genomics Education: Hypertrophic cardiomyopathy – Knowledge Hub.
• 🌍 ESC Guidelines 2023: Guidelines for the management of cardiomyopathies.
• 🇺🇸 AHA/ACC 2024: Guideline for the Management of Hypertrophic Cardiomyopathy.