Hypertrophic Cardiomyopathy vs. Dilated Cardiomyopathy: Clinical Differences, Evaluation, and Diagnosis
Hypertrophic cardiomyopathy (HCM) and dilated cardiomyopathy (DCM) represent distinct cardiac pathologies with fundamentally different structural abnormalities, clinical presentations, diagnostic features, and prognostic implications. 1
Fundamental Differences
Structural and Pathophysiological Differences
| Feature | Hypertrophic Cardiomyopathy | Dilated Cardiomyopathy |
|---|---|---|
| Definition | Heart muscle disease with unexplained LV hypertrophy, non-dilated ventricles, and preserved/increased ejection fraction | Heart muscle disease with LV dilatation and systolic dysfunction not attributable to abnormal loading conditions or CAD |
| Primary Structural Change | Increased wall thickness (≥15mm in adults) | Ventricular chamber enlargement |
| Sarcomere Changes | Addition of sarcomeres in parallel | Addition of sarcomeres in series |
| Histopathology | Myocyte hypertrophy, disarray, and interstitial fibrosis | Loss of myocytes and increased ECM |
| Genetics | Primarily sarcomeric mutations (MYBPC3, MYH7 most common) | Multiple genetic and acquired causes |
| Ejection Fraction | Preserved or increased | Reduced (<50%) |
Clinical Presentation
Symptoms and Signs
Hypertrophic Cardiomyopathy:
- Dyspnea (often due to diastolic dysfunction)
- Angina (from myocardial oxygen supply-demand mismatch)
- Syncope (particularly with exertion)
- Palpitations (from atrial fibrillation or ventricular arrhythmias)
- Systolic murmur that increases with Valsalva (in obstructive HCM)
- Sudden cardiac death (particularly in young athletes)
Dilated Cardiomyopathy:
- Progressive heart failure symptoms
- Fatigue and exercise intolerance
- Peripheral edema
- Elevated jugular venous pressure
- S3 gallop
- Higher prevalence of advanced heart failure symptoms at presentation 2
Diagnostic Evaluation
Echocardiography
Hypertrophic Cardiomyopathy:
- LV wall thickness ≥15mm in adults (or z-score >2 in children)
- Often asymmetric with predominant septal involvement
- Normal or small LV cavity
- Preserved or hyperdynamic ejection fraction
- Systolic anterior motion of mitral valve (in obstructive HCM)
- Dynamic LVOT obstruction (at rest in ~1/3, provokable in another 1/3)
- Diastolic dysfunction 3
Dilated Cardiomyopathy:
- LV dilatation (increased end-diastolic and end-systolic dimensions)
- Global systolic dysfunction (EF <50%)
- Functional mitral regurgitation
- Thinned ventricular walls relative to chamber size
- Spherical remodeling of LV 1
Electrocardiography
Hypertrophic Cardiomyopathy:
- LV hypertrophy
- Pathological Q waves
- T-wave inversions (particularly in lateral and inferior leads)
- Left atrial enlargement
- 4-6% may have normal ECGs despite disease 3
Dilated Cardiomyopathy:
- Left bundle branch block (common)
- Nonspecific ST-T wave changes
- Left atrial enlargement
- Atrial fibrillation (more common than in HCM) 4, 2
Cardiac MRI
Hypertrophic Cardiomyopathy:
- Confirms LV hypertrophy pattern
- Identifies apical variants missed by echo
- Late gadolinium enhancement (patchy, mid-wall)
- Useful for differentiating from phenocopies 3
Dilated Cardiomyopathy:
- Confirms LV dilatation and dysfunction
- Identifies non-ischemic patterns of fibrosis
- Helps exclude ischemic etiology
- Quantifies ventricular volumes precisely 1
Genetic Testing
Hypertrophic Cardiomyopathy:
- Highly genetic (30-60% yield in probands)
- Primarily autosomal dominant sarcomeric mutations
- MYBPC3 and MYH7 account for ~50% of genetic cases
- Genetic testing recommended for index cases 1, 3
Dilated Cardiomyopathy:
- Familial in 30-50% of cases
- More genetically heterogeneous than HCM
- Lower yield of genetic testing (30-40%)
- Multiple genes involved beyond sarcomeric proteins 1
Special Considerations
End-Stage Evolution
- Approximately 10-20% of HCM patients may progress to a dilated phase (D-HCM) with systolic dysfunction and cavity dilatation
- D-HCM has worse prognosis than primary DCM despite similar treatment approaches
- D-HCM shows more extensive fibrosis, particularly in the septum and anterior wall 4, 2, 5
Risk Stratification
Hypertrophic Cardiomyopathy:
- Risk factors for sudden death: family history of SCD, syncope, massive hypertrophy (≥30mm), non-sustained VT, abnormal BP response to exercise
- ICD recommended for high-risk patients 1, 6
Dilated Cardiomyopathy:
- Risk stratification primarily based on ejection fraction
- Additional factors: NYHA class, QRS duration, presence of LBBB
- ICD indicated for primary prevention when EF ≤35% despite optimal medical therapy 1
Diagnostic Algorithm
Initial Evaluation:
- Comprehensive history (family history, symptoms)
- Physical examination (murmurs, signs of heart failure)
- 12-lead ECG
- Transthoracic echocardiography
Differential Diagnosis:
- If LV hypertrophy with preserved EF → Consider HCM
- If LV dilatation with reduced EF → Consider DCM
Advanced Testing:
- Cardiac MRI to confirm diagnosis and exclude phenocopies
- Exercise testing (particularly for HCM to assess for provocable obstruction)
- Genetic testing (higher yield in HCM than DCM)
- Laboratory testing to exclude secondary causes
Family Screening:
- First-degree relatives: every 12-18 months for children/adolescents
- Every 3-5 years for adult relatives
- More frequent if family history of malignant course 3
Common Pitfalls and Caveats
- Athlete's heart can mimic mild HCM but typically has normal diastolic function and regresses with deconditioning
- End-stage HCM can mimic DCM; history of prior HCM diagnosis or family history is key
- Hypertensive heart disease can be confused with HCM, especially when wall thickness is 13-15mm
- Secondary causes of LV hypertrophy (aortic stenosis, infiltrative diseases) must be excluded before diagnosing HCM
- Not all DCM is idiopathic; ischemic, toxic, and inflammatory causes must be excluded 1, 3
Understanding these key differences is essential for proper diagnosis, risk stratification, and management of these distinct cardiomyopathies that significantly impact morbidity and mortality.