About This Page
This is a clinician-written, evidence-based summary aligned to the 2026 MLA Content Map. It is intended for medical students and junior doctors preparing for the UKMLA. Always cross-reference with NICE guidance, local protocols, and clinical judgement.
The Bottom Line
- HCM = LV wall thickness ≥15 mm not explained by loading conditions (hypertension, aortic stenosis). Usually asymmetric septal hypertrophy
- Autosomal dominant — sarcomeric gene mutations (MYH7, MYBPC3 account for ~70%). Prevalence ~1:500
- Most common cause of SCD in young athletes. Assess 5-year SCD risk with ESC HCM Risk-SCD calculator
- LVOT obstruction present in ~70% (dynamic, worsened by reduced preload/afterload). Systolic murmur that increases with Valsalva/standing
- Management: beta-blockers (first-line), avoid strenuous exercise, ICD if high SCD risk (≥6%/5 years); myectomy or alcohol septal ablation for refractory LVOT obstruction; mavacamten (cardiac myosin inhibitor) for symptomatic obstructive HCM
Overview
Hypertrophic cardiomyopathy (HCM) is a genetically determined heart muscle disease characterised by LV hypertrophy (typically ≥15 mm) that cannot be attributed to another cardiac or systemic condition. The hypertrophy is usually asymmetric, predominantly affecting the interventricular septum. Approximately 70% of patients have dynamic LVOT obstruction (HOCM — hypertrophic obstructive cardiomyopathy), where systolic anterior motion (SAM) of the mitral valve leaflet creates a pressure gradient. HCM is the most common inherited cardiac condition and the leading cause of sudden cardiac death in young athletes. Pathological features include myocyte disarray, fibrosis, and small vessel disease.
Epidemiology
HCM has a prevalence of approximately 1 in 500 (0.2% of the population). It follows autosomal dominant inheritance with variable penetrance. Sarcomeric protein gene mutations are identified in approximately 60% of cases — MYH7 (beta-myosin heavy chain) and MYBPC3 (myosin-binding protein C) are the commonest. Many cases are diagnosed incidentally. SCD risk is approximately 1% per year overall but higher in certain subgroups. HCM is compatible with normal life expectancy in most patients with appropriate risk stratification.
Clinical Features
Symptoms
Exertional dyspnoea (diastolic dysfunction, LVOT obstruction)
Chest pain (myocardial ischaemia from supply-demand mismatch, small vessel disease)
Palpitations (AF, VT)
Syncope or presyncope (LVOT obstruction, arrhythmia)
Sudden cardiac death — may be first presentation, especially during/after vigorous exercise
Many patients are asymptomatic — diagnosed on family screening or incidental echo
Signs
Ejection systolic murmur at left sternal edge — increases with Valsalva manoeuvre and standing (reduced preload worsens obstruction)
Murmur decreases with squatting (increased preload reduces obstruction)
Jerky pulse (rapid initial upstroke then obstruction — bisferiens quality)
Prominent A wave in JVP (reduced ventricular compliance)
S4 (stiff, hypertrophied ventricle)
Double apex beat (palpable S4 + systolic impulse)
Investigations
First-line
EchocardiographyAsymmetric septal hypertrophy (≥15 mm), SAM of mitral valve, dynamic LVOT gradient (provoked with Valsalva if resting gradient <30 mmHg), small LV cavity, preserved/hyperdynamic systolic function
ECGAbnormal in ~95%: LVH, deep T-wave inversions (especially V4–V6 and lateral leads), pathological Q waves (septal hypertrophy mimicking infarction), LA enlargement
Second-line
Cardiac MRIQuantify hypertrophy, assess for apical variant (may be missed on echo), late gadolinium enhancement (fibrosis — prognostic significance)
Ambulatory ECG (48h)Detect NSVT — component of SCD risk assessment
Exercise stress testAssess exercise tolerance, blood pressure response (failure to augment or drop in SBP = adverse prognostic factor)
Specialist
Genetic testingIdentify pathogenic variant. Cascade family screening with targeted testing
ESC HCM Risk-SCD calculatorEstimates 5-year SCD risk using: age, max LV wall thickness, LA diameter, max LVOT gradient, NSVT, unexplained syncope, family history of SCD
1
Lifestyle and general
- Avoid competitive and high-intensity exercise (SCD risk)
- Adequate hydration, avoid dehydration (reduces preload, worsens obstruction)
- Genetic counselling and cascade family screening (first-degree relatives: echo + ECG)
2
Symptomatic obstructive HCM
- Beta-blocker (first-line): bisoprolol, propranolol — reduces HR, improves filling time, reduces LVOT gradient
- Verapamil (if beta-blocker not tolerated) — avoid combining with beta-blocker
- Disopyramide (add-on): negative inotrope, reduces LVOT gradient
- Mavacamten (cardiac myosin inhibitor): NICE TA1011 — for symptomatic obstructive HCM refractory to standard therapy
- Avoid vasodilators (ACEi, nitrates), diuretics (reduce preload), and digoxin (positive inotrope) — all worsen LVOT obstruction
3
Refractory LVOT obstruction
- Surgical septal myectomy (gold standard — Morrow procedure)
- Alcohol septal ablation (percutaneous — controlled infarction of hypertrophied septum via first septal perforator branch)
4
Sudden cardiac death prevention
- ESC HCM Risk-SCD score ≥6% at 5 years → offer ICD
- Score 4–6% → consider ICD after shared decision-making
- Score <4% → ICD not routinely indicated (unless additional risk features)
5
Atrial fibrillation
- Anticoagulate ALL HCM patients with AF (irrespective of CHA₂DS₂-VASc — high stroke risk)
- Rate or rhythm control as per standard AF guidelines
Complications
- Sudden cardiac death: VT/VF — particularly during/after vigorous exercise in young people
- Heart failure: Diastolic dysfunction (HFpEF) or progression to systolic failure (burnt-out HCM)
- Atrial fibrillation: Common — high stroke risk in HCM (anticoagulate regardless of CHA₂DS₂-VASc)
- Stroke: Thromboembolism from AF or intracavitary thrombus
- Infective endocarditis: Especially with LVOT obstruction and mitral valve involvement
UKMLA Exam Tips
- 1HCM murmur INCREASES with Valsalva/standing (reduced preload) and DECREASES with squatting (increased preload) — opposite of most other murmurs
- 2Most common cause of sudden cardiac death in young athletes — classic exam scenario
- 3ECG is abnormal in ~95% of HCM — deep T inversions, LVH, pathological Q waves
- 4HCM + AF = anticoagulate ALL patients (do NOT use CHA₂DS₂-VASc to decide)
- 5Avoid vasodilators, diuretics, and digoxin in obstructive HCM — they all worsen the gradient
- 6Mavacamten is a newer therapy for symptomatic obstructive HCM — may appear in updated exam questions
practicetest your knowledge on hypertrophic cardiomyopathyApply what you've learnt with UKMLA-style questions from the iatroX Q-Bank — cardiovascular and beyond.
open q-bank