Diagnostic Criteria for Cardiomyopathy
Cardiomyopathies are diagnosed using a phenotype-first approach based on morphological and functional imaging characteristics, with five major phenotypes recognized: dilated cardiomyopathy (DCM), hypertrophic cardiomyopathy (HCM), restrictive cardiomyopathy (RCM), arrhythmogenic right ventricular cardiomyopathy (ARVC), and non-dilated left ventricular cardiomyopathy (NDLVC). 1
Algorithmic Diagnostic Approach
1. Hypertrophic Cardiomyopathy (HCM)
Primary diagnostic criterion: Asymmetric left ventricular wall hypertrophy 2, 3
- Wall thickness: Look for asymmetric hypertrophy, typically affecting the interventricular septum
- Chamber size: Small left ventricular cavity
- Systolic function: Usually preserved or hyperdynamic
- Diastolic function: Abnormal relaxation pattern with E/A ratio < 1 on Doppler echocardiography 2
- Obstructive features: Systolic anterior motion of the mitral valve (when present) 3
- Tissue characterization: Endomyocardial biopsy shows myocyte disarray; CMR demonstrates fibrosis patterns for risk stratification 4, 5
2. Dilated Cardiomyopathy (DCM)
Primary diagnostic criteria: Ventricular dilation with systolic dysfunction 2, 3
- Wall thickness: Normal or decreased
- LV dimensions: End-diastolic dimension > 70 mm indicates poor prognosis 2
- Systolic function: Reduced ejection fraction (EF < 25% carries poor prognosis) 2
- Diastolic filling: Abnormal patterns; restrictive profile (E/A ratio > 2) indicates severe disease 2
- Mitral deceleration time: < 150 msec predicts poor outcome 2
- Genetic testing: Indicated in familial or suspected genetic cases; approximately 50% have genetic causes 6
Critical pitfall: Distinguish from secondary causes (ischemic, toxic, metabolic) before labeling as primary DCM 7
3. Restrictive Cardiomyopathy (RCM)
Primary diagnostic criteria: Non-dilated ventricles with atrial enlargement and preserved systolic function 4, 1
- Ventricular size: Normal or small chamber dimensions
- Wall thickness: May show symmetrical thickening (especially in amyloidosis) 2
- Atrial size: Marked biatrial enlargement is characteristic 4
- Systolic function: Nearly normal or mildly reduced
- Diastolic pattern: Restrictive filling with dip-plateau phenomenon on hemodynamics 4
- Advanced disease markers: E/A ratio > 2 and deceleration time < 150 msec indicate rapidly fatal outcome 2
- Endomyocardial biopsy: Essential to identify secondary causes (amyloidosis most common) 4
4. Arrhythmogenic Right Ventricular Cardiomyopathy (ARVC)
Diagnosis based on standardized Task Force criteria incorporating major and minor criteria across multiple domains 8, 9
The diagnostic framework includes:
- Structural abnormalities: Fibro-fatty replacement of RV free wall; myocardial atrophy 8
- Tissue characterization: CMR superior for detecting RV structural abnormalities and fibrosis 5
- Arrhythmic features: Ventricular tachycardia with left bundle branch block morphology 8
- ECG abnormalities: Epsilon waves, T-wave inversions in right precordial leads
- Histopathology: Fibro-fatty replacement on endomyocardial biopsy
- Genetic factors: Desmosomal gene mutations (most common) 9
Important evolution: Disease may progress from isolated RV involvement to biventricular involvement and eventually to dilated phenotype 9, 6
5. Non-Dilated Left Ventricular Cardiomyopathy (NDLVC)
Newer phenotypic category encompassing left-dominant ACM variants 9, 1
- Defining features: Non-ischemic LV scarring or fatty replacement without significant dilation
- Wall motion: May have regional abnormalities or isolated global hypokinesia
- Systolic function: Low-normal to mildly reduced EF
- Imaging hallmark: Subepicardial late gadolinium enhancement on CMR 9
- Genetic correlation: Often associated with desmoplakin, filamin C mutations 9
Critical distinction: The ESC categorizes this as NDLVC, while other societies may classify the same patient as arrhythmogenic left ventricular cardiomyopathy (ALVC) depending on genetic and clinical criteria 9
Key Diagnostic Nuances
Phenotypic overlap is common: Some cardiomyopathies evolve from one phenotype to another during disease progression. ARVC, HCM, and LVNC can all develop dilated features over time 6, 1. The distinction between dilated ACM and DCM is particularly complex, as they differ in pathogenesis despite similar morphology 9.
Imaging hierarchy:
- Echocardiography remains first-line for initial assessment 5
- CMR provides superior tissue characterization, fibrosis detection, and prognostic information 5
- Cardiac CT primarily excludes coronary disease and complements CMR 5
Genetic testing integration: Increasingly important for phenotype-genotype correlation, family screening, and personalized management, particularly in DCM (50% genetic), HCM (predominantly sarcomeric), and ARVC (desmosomal) 6, 10