HOCM vs DCM for MRCP Part 1
- Crack Medicine
- 9 hours ago
- 3 min read
TL;DR
Cardio: Cardiomyopathies: HOCM vs. DCM is a high-yield MRCP Part 1 topic that hinges on differentiating diastolic dysfunction with dynamic obstruction (HOCM) from systolic failure with ventricular dilatation (DCM). Key exam clues include murmur variation, echocardiographic findings, and complication profiles. Mastering these distinctions improves accuracy in vignette-based questions and pharmacology traps.
Why this matters
Cardiomyopathies are frequently tested in MRCP Part 1, often through subtle clinical scenarios involving exertional syncope, dyspnoea, or incidental murmurs. Candidates are expected to quickly distinguish hypertrophic obstructive cardiomyopathy (HOCM) from dilated cardiomyopathy (DCM)—two conditions with contrasting pathophysiology but overlapping presentations.
This topic integrates cardiology, genetics, and therapeutics. A strong grasp helps across multiple domains of the exam. For a structured approach to revision, start with the MRCP Part 1 overview and consolidate learning using Free MRCP MCQs.
Core sections
1. Definitions (Exam Foundation)
HOCM (Hypertrophic Obstructive Cardiomyopathy)
Characterised by asymmetric septal hypertrophy causing dynamic left ventricular outflow tract (LVOT) obstruction and diastolic dysfunction.
DCM (Dilated Cardiomyopathy)
Defined by ventricular dilatation with reduced systolic function and decreased ejection fraction.
2. Key Differences Table (High-Yield)
Feature | HOCM | DCM |
Ventricular size | Small LV cavity | Dilated ventricles |
Function | Diastolic dysfunction | Systolic dysfunction |
Ejection fraction | Normal or ↑ | Reduced |
Murmur | Dynamic ejection systolic | Functional MR/TR |
Genetics | Autosomal dominant (sarcomere mutations) | Often acquired |
Common causes | Genetic mutations | Alcohol, viral, idiopathic |
Major risk | Sudden cardiac death | Progressive heart failure |
3. Murmur Behaviour (Classic MRCP Point)
HOCM
Murmur increases with Valsalva or standing (↓ preload → ↑ obstruction)
Murmur decreases with squatting (↑ preload → ↓ obstruction)
DCM
Murmur typically due to mitral regurgitation
Does not vary significantly with manoeuvres
👉 This dynamic murmur behaviour is one of the most reliable differentiators in exams.
4. Echocardiographic Findings
HOCM
Asymmetric septal hypertrophy
Systolic anterior motion (SAM) of mitral valve
Small LV cavity
DCM
Dilated left (± right) ventricle
Global hypokinesia
Reduced ejection fraction (<40%)
5. Aetiology (Top Tested Causes)
HOCM
β-myosin heavy chain mutation
Autosomal dominant inheritance
Family history of sudden cardiac death
DCM
Alcohol excess
Viral myocarditis
Peripartum cardiomyopathy
Chemotherapy (e.g. anthracyclines)
Idiopathic
6. Clinical Presentation
HOCM
Exertional syncope
Dyspnoea
Palpitations
Sudden cardiac death (young individuals)
DCM
Fatigue
Dyspnoea (heart failure)
Peripheral oedema
Arrhythmias
7. Management Principles (Exam-Relevant)
HOCM
First-line: Beta-blockers
Alternatives: verapamil
Avoid: diuretics, nitrates (reduce preload → worsen obstruction)
Consider ICD in high-risk patients
DCM
Standard heart failure therapy:
ACE inhibitors / ARNI
Beta-blockers
Mineralocorticoid receptor antagonists
Diuretics
Device therapy: CRT/ICD where indicated
8. Complications
HOCM
Sudden cardiac death
Atrial fibrillation
Stroke
DCM
Chronic heart failure
Thromboembolism
Ventricular arrhythmias
9. High-Yield Exam Points (Must Revise)
HOCM murmur ↑ with Valsalva
DCM = reduced ejection fraction
HOCM = preserved EF but impaired filling
HOCM is inherited (screen relatives)
Alcohol is a key cause of DCM
HOCM causes sudden death in athletes
DCM presents with heart failure symptoms
Avoid preload-reducing drugs in HOCM
SAM of mitral valve = hallmark of HOCM
DCM commonly causes functional MR
Practical examples / mini-cases
MCQ
A 25-year-old athlete presents with exertional syncope. Examination reveals a systolic murmur that becomes louder on standing and softer on squatting. ECG shows left ventricular hypertrophy.
What is the most likely diagnosis?
A. Aortic stenosisB. Dilated cardiomyopathyC. Hypertrophic obstructive cardiomyopathyD. Mitral regurgitation
Answer: C. Hypertrophic obstructive cardiomyopathy
Explanation: The murmur’s increase with reduced preload (standing) is characteristic of HOCM. This reflects dynamic LVOT obstruction, a key MRCP Part 1 concept.
Common pitfalls (5 bullets)
Confusing HOCM with aortic stenosis (opposite murmur response)
Assuming normal EF excludes pathology (not true in HOCM)
Missing the importance of family screening in HOCM
Using vasodilators or diuretics in HOCM
Overlooking alcohol as a common DCM cause
FAQs
1. How is HOCM differentiated from aortic stenosis clinically?
HOCM murmur increases with Valsalva, whereas aortic stenosis murmur decreases. This manoeuvre-based distinction is frequently tested.
2. Why is ejection fraction preserved in HOCM?
Because systolic contraction is normal; the issue lies in impaired ventricular filling due to stiff hypertrophied myocardium.
3. What is the most common cause of DCM?
Idiopathic is most common, but alcohol and viral infections are high-yield causes in exams.
4. When should an ICD be considered in HOCM?
In patients with high-risk features such as syncope, family history of sudden death, or severe hypertrophy.
5. Can DCM be reversed?
In some cases (e.g. alcohol-induced or peripartum), partial or full recovery is possible with appropriate treatment.
Ready to start?
Strengthen your understanding by practising exam-style questions via Free MRCP MCQs or simulate real exam conditions with a Start a mock test.
For deeper cardiology revision, combine this topic with structured teaching from lectures and explore related blog topics such as valvular heart disease and heart failure.
Sources
MRCP(UK) Examination Blueprint: https://www.mrcpuk.org/mrcpuk-examinations/part-1
NICE Heart Failure Guidelines: https://www.nice.org.uk/guidance/ng106
ESC Cardiomyopathy Guidelines: https://www.escardio.org/Guidelines/Clinical-Practice-Guidelines/Cardiomyopathies
Kumar & Clark Clinical Medicine (Elsevier)
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