Classification of Cardiomyopathy¶
Chapter 266 | Part 6: Disorders of the Cardiovascular System
KEY CLINICAL POINTS¶
- Cardiomyopathies are classified into hypertrophic (HCM), dilated (DCM), restrictive (RCM), and arrhythmogenic (ACM) phenotypes with distinct diagnostic criteria.
- Regional variations in treatment response and patient demographics (e.g., North America vs. Europe) impact clinical outcomes and therapeutic generalizability.
- Genetic mutations and imaging techniques (e.g., late gadolinium enhancement) are critical for early diagnosis and differentiation of cardiomyopathies.
- Management includes ICDs for primary prevention, beta-blockers, spironolactone, and tailored therapies based on phenotype and comorbidities.
- Overlap between phenotypes (e.g., HCM evolving to DCM) and two-hit models (genetic predisposition + acquired triggers) complicate diagnosis.
1. DEFINITION & OVERVIEW¶
Cardiomyopathy refers to primary disease of the heart muscle, excluding secondary causes like ischemia or valvular disease. Modern classification includes four main phenotypes: hypertrophic (HCM), dilated (DCM), restrictive (RCM), and arrhythmogenic (ACM). Diagnostic criteria, morphology, and challenges in differentiation are outlined in Table 266-1.
Table 266-1 Classification of Cardiomyopathies¶
| CARDIOMYOPATH Y (CM) | PHENOTYPE | DIAGNOSTIC CRITERIA | OTHER MORPHOLOGY | COMMON CHALLENGES IN DIAGNOSIS |
|---|---|---|---|---|
| Hypertrophic cardiomyopathy (HCM) | Mid-range LVEF includes rare transition to HCM with LV systolic dysfunction (LVEF <0.50) | Septal thickness in men ‡15 mm, ‡13 mm in women. 13–14 mm may be diagnostic in relatives of proband with known HCM or positive genetic test. LVEF ‡ normal, usually >0.60. LV chamber volume £normal. | Patterns of LV hypertrophy (LVH): asymmetric septal, inverse (sigmoid pattern) septal, concentric LVH, apical hypertrophy | Distinction from athlete’s heart and severe chronic hypertension. Exclude aortic stenosis. In older patients, exclude amyloidosis. |
| CARDIOMYOPATH Y (CM) | PHENOTYPE | DIAGNOSTIC CRITERIA | OTHER MORPHOLOGY | COMMON CHALLENGES IN DIAGNOSIS |
|---|---|---|---|---|
| Restrictive cardiomyopathy (RCM) | Functional diagnosis based on moderate-severe diastolic dysfunction and/or elevated cardiac filling pressures | Usually marked atrial enlargement. Wall thickness often increased but can appear normal. LVEF usually mildly reduced, occasionally normal. | Marked wall thickness suggests amyloidosis, inherited storage diseases, inborn metabolic diseases | Differentiate from scleroderma-type connective tissue diseases, sarcoidosis, and structural heart disease. |
| Dilated cardiomyopathy (DCM) | Mid-range LVEF is often a transition in DCM, either deterioration from normal for age/sex or early DCM, or improvement into DCM remission | LV dilated cardiomyopathy (DCM): early LVEF £0.50 and/or LVEDV >112% normal for age/sex or LVEDD >95% predicted sex/height. LVEF £0.40: threshold for recommended therapies for heart failure with low LVEF. | Can involve LV alone or with RV involvement from primary cause or secondary RV failure due to elevated pulmonary artery pressures | Structural heart disease (e.g., coronary artery disease, valve disease) must be excluded. |
| Arrhythmogenic CM Dominant in LV (ACM-LV) | Ventricular tachyarrhythmias dominate without or before severely reduced LVEF and heart failure | Primary prevention ICD considered even when LVEF >0.35 | Suggestive but not conclusive differences in late gadolinium enhancement patterns between variants | Differentiate from genetic CM causing arrhythmias and structural changes. |
| Arrhythmogenic CM Dominant in RV (ACM-RV; also termed ARVC) | Modified task force criteria from 2010 include combinations of major and minor criteria. Biventricular ACM often diagnosed from LGE in ventricle with less involvement | Abnormal RV function or structure. Cardiac sarcoidosis can cause predominantly RV involvement with ventricular arrhythmias, wall motion abnormalities, aneurysms, and dilation | Differentiate from cardiac sarcoidosis and other storage diseases | |
| Trait of LV noncompaction (LVNC) | Often assessed by maximum ratio of no ncompacted/compac ted LV myocardium >2.3 and other criteria | Can occur with HCM, DCM, some dystrophies, and other syndromic presentations | Can occur in normal hearts, pregnancy, and athletic hearts |
1.1 Cardiomyopathy Classification¶
The traditional morphologic classification defines HCM (LV hypertrophy), DCM (LV dilation), and RCM (diastolic dysfunction). ACM (arrhythmogenic) is a fourth phenotype with genetic and structural basis. Phenotypes overlap clinically, with DCM showing 'reverse remodeling' and HCM evolving to reduced ejection fraction (HCM-rEF).
2. EPIDEMIOLOGY¶
Regional variations in cardiomyopathy incidence and treatment response are significant. Patients from North America have higher comorbidity burden, revascularization, and device use rates compared to South America or Eastern Europe. Geographic differences in baseline characteristics and outcomes affect therapeutic generalizability.
2.1 Demographics¶
Eastern European ADHF patients tend to be younger with higher EFs and lower natriuretic peptide levels. South American patients have lowest comorbidities, revascularization, and device use. North American patients have highest comorbidity burden and device use.
3. ETIOLOGY & PATHOPHYSIOLOGY¶
Cardiomyopathies arise from genetic mutations, acquired conditions (e.g., infections, toxic exposures), and structural heart disease. Genetic variants (e.g., GLA, PRKAG2, LAMP2) and immune-mediated inflammation contribute to pathogenesis. New imaging techniques enable early detection of genetic cardiomyopathies.
3.1 Genetic Basis¶
Heritable cardiomyopathies are linked to pathogenic genetic variants. Arrhythmogenic cardiomyopathy (ACM) has genetic causes, while acquired conditions (e.g., sarcoidosis, Chagas’ disease) can mimic ACM phenotypes.
4. CLINICAL FEATURES¶
Early symptoms include exertional intolerance, breathlessness, fatigue, and arrhythmias. Congestive heart failure syndrome (fluid retention, elevated filling pressures) may present with dyspnea, edema, and orthopnea. Embolic events and atrial fibrillation-related thrombi are common presenting features.
4.1 Congestive Heart Failure Syndrome¶
The term 'congestive heart failure' is a nonspecific syndrome requiring thorough evaluation of etiology. It may result from diverse causes including congenital heart disease, pulmonary hypertension, and structural valve disease.
5. DIFFERENTIAL DIAGNOSIS¶
Differentiate cardiomyopathies from structural heart disease (e.g., aortic stenosis, coronary artery disease), valvular disease, and systemic conditions (e.g., amyloidosis, sarcoidosis). Genetic testing and imaging are critical for accurate diagnosis.
6. INVESTIGATIONS & DIAGNOSIS¶
Echocardiography is the initial imaging modality for morphology and function. Magnetic resonance imaging (MRI) provides tissue characterization, late gadolinium enhancement, and T1/T2 mapping for fibrosis and inflammation. Diagnostic criteria are outlined in Table 266-1.
6.1 Diagnostic Algorithms¶
Use echocardiography to assess LV dimensions, wall thickness, and function. MRI is used for advanced tissue characterization. Late gadolinium enhancement helps differentiate ACM variants and identify fibrosis.
7. MANAGEMENT & TREATMENT¶
Management includes pharmacologic therapies (beta-blockers, spironolactone), ICDs for primary prevention, and surgical interventions (e.g., valve repair). Non-pharmacologic strategies include lifestyle modifications and monitoring for complications.
7.1 Therapeutic Strategies¶
ICDs are recommended for primary prevention in ACM-RV and ACM-LV with LVEF >0.35. Spironolactone improves outcomes in HFrEF. Beta-blockers reduce mortality in HCM and DCM. Surgical revascularization and valve repair are indicated for structural causes.
8. PROGNOSIS & COMPLICATIONS¶
Prognosis varies by phenotype. HCM may progress to HCM-rEF, while DCM can show reverse remodeling. Complications include arrhythmias, heart failure, and sudden cardiac death. Genetic factors and acquired triggers (e.g., infections) influence disease progression.
9. SPECIAL CONSIDERATIONS¶
Pregnancy and athletic hearts may present with LVNC or HCM. Elderly patients require careful evaluation for amyloidosis. Genetic counseling is essential for heritable cardiomyopathies. Special attention is needed for sarcoidosis and Chagas’ disease.
10. KEY POINTS & CLINICAL PEARLS¶
- Cardiomyopathies are classified into HCM, DCM, RCM, and ACM with distinct diagnostic criteria. 2. Regional variations in treatment response and patient demographics impact outcomes. 3. Genetic testing and MRI are critical for early diagnosis. 4. ICDs and targeted therapies improve outcomes in high-risk phenotypes. 5. Differentiate from structural heart disease and systemic conditions using imaging and genetic analysis.