What is the diagnostic approach for cardiomyopathy?

How Cardiomyopathy is Diagnosed

Cardiomyopathy diagnosis begins with demonstrating ventricular dysfunction or abnormal wall thickness on cardiac imaging (echocardiography, CMR, or CT), followed by systematic exclusion of coronary artery disease and identification of the underlying etiology through multimodal testing. 1

Diagnostic Criteria by Phenotype

Dilated Cardiomyopathy (DCM)

• **LVEF <45% with or without LV dilatation** (dilatation defined as end-diastolic volumes/diameters >2 SD above normal, corrected for body surface area and age) 1
• Must exclude abnormal loading conditions and coronary artery disease as primary causes

Hypertrophic Cardiomyopathy (HCM)

• LV wall thickness ≥15 mm in adults in one or more myocardial segments on any imaging modality (echo, CMR, or CT), unexplained by loading conditions 2
• Wall thickness 13-14 mm requires additional evaluation: family history, ECG abnormalities, non-cardiac symptoms, and advanced imaging 2
• In children: LV wall thickness >2 SD above predicted mean (z-score >2) 2
• In first-degree relatives: threshold lowered to ≥13 mm 2

Algorithmic Diagnostic Approach

Step 1: Initial Cardiac Imaging

Transthoracic echocardiography is the first-line modality to assess:

• LV/RV dimensions and volumes
• Systolic function (LVEF, global longitudinal strain)
• Diastolic function (tissue Doppler imaging)
• Wall thickness and regional abnormalities
• Valvular function (particularly secondary mitral/tricuspid regurgitation)
• Presence of thrombus (contrast may be needed) 1

Step 2: Exclude Coronary Artery Disease

Choose one of three modalities 1:

1. Cardiac CT angiography - highly accurate for excluding epicardial coronary disease; also useful for device planning
2. Radionuclide perfusion imaging - particularly valuable for distinguishing DCM from ischemic cardiomyopathy
3. Cardiovascular magnetic resonance (CMR) - can exclude ischemic component while providing tissue characterization

Step 3: Cardiovascular Magnetic Resonance (CMR)

CMR should be performed at initial evaluation (Class I recommendation) 3 for:

• Tissue characterization: detecting myocardial edema, scarring, fibrosis, infiltration, and iron overload 1
• Late gadolinium enhancement (LGE): distinguishes ischemic from non-ischemic scarring; predicts arrhythmic events, mortality, and functional recovery 3
• T1 mapping and extracellular volume: assesses diffuse myocardial fibrosis 3
• Prognostic stratification: presence and pattern of fibrosis guides risk assessment

Step 4: Etiologic Investigation

Obtain detailed history focusing on 2:

• Age at presentation (metabolic disorders in infants; amyloidosis in elderly men >65 years)
• Three-generation family pedigree: sudden cardiac deaths, heart failure, transplants, devices, systemic disease (stroke, muscle weakness, renal dysfunction, diabetes, deafness) 2
• Toxic exposures: alcohol, cocaine, chemotherapy agents (anthracyclines), tacrolimus, hydroxychloroquine 1, 2
• Systemic symptoms: suggesting sarcoidosis, amyloidosis, hemochromatosis, autoimmune disease

Laboratory testing for specific etiologies 1:

• Infectious: viral serology (if chronic myocarditis suspected)
• Infiltrative: serum/urine protein electrophoresis, free light chains (amyloidosis)
• Storage: serum ferritin and transferrin saturation (hemochromatosis); alpha-galactosidase A (Fabry disease)
• Endocrine: thyroid function, growth hormone (acromegaly)
• Nutritional: selenium, thiamine, carnitine levels
• Autoimmune markers

Advanced imaging for specific diagnoses:

• 18F-FDG-PET scanning: if cardiac sarcoidosis suspected (Class IIa) 3
• Cardiac MRI T2 sequences*: for iron overload quantification 4

Step 5: Genetic Testing and Counseling

Genetic testing is a Class I recommendation for patients meeting diagnostic criteria 3:

• Enables cascade screening of family members
• Identifies ~50% of DCM cases (titin gene most common) 1
• Identifies ~60% of HCM cases (sarcomere protein genes) 2
• Must be accompanied by pre- and post-test genetic counseling 3
• Consider referral to specialized centers for comprehensive genetic evaluation 4

Step 6: Endomyocardial Biopsy

Reserved for specific scenarios 3:

• When other investigations suggest myocarditis requiring immunosuppression
• Suspected infiltrative disease (amyloidosis, sarcoidosis) when non-invasive testing inconclusive
• Suspected storage diseases (Fabry, Pompe)
• Low sensitivity but remains gold standard for myocarditis diagnosis 5

Early Detection in Asymptomatic Patients

Screen high-risk individuals 1:

• First-degree relatives of cardiomyopathy patients
• Carriers of pathogenic variants (genotype-positive/phenotype-negative)
• Those with uncontrolled cardiovascular risk factors

Advanced techniques detect subclinical disease 1:

• Global longitudinal strain (GLS) analysis
• Tissue Doppler imaging
• Serial assessment of LV size and diastolic function
• Early detection allows preventive therapy that reduces morbidity and mortality 1

Critical Diagnostic Pitfalls

1. Athlete's heart vs. HCM: Athletes show balanced RV/LV enlargement, normal TAPSE, normal strain values; HCM shows asymmetric hypertrophy, abnormal strain, ECG abnormalities 5

2. Isolated basal septal hypertrophy in elderly: May represent normal aging variant rather than HCM 2

3. Hypertension-related LVH: Not conventionally classified as DCM despite ventricular dysfunction 4

4. Late-stage DCM: May present with wall thinning and dilated/hypokinetic ventricle, obscuring original phenotype 2

5. Left-dominant arrhythmogenic cardiomyopathy: Can mimic DCM; frequent arrhythmias and subepicardial fibro-fatty replacement on CMR favor arrhythmogenic diagnosis 5

Follow-Up Imaging

• Echocardiography: for clinically stable DCM (Class IIa) and with clinical status changes (Class I) 3
• CMR during follow-up: to monitor disease progression and aid risk stratification (Class IIa) 3
• Serial screening in genotype-positive/phenotype-negative relatives: CMR recommended (Class IIa) 3