What tests are used to diagnose Hypertrophic Cardiomyopathy (HCM)?

Diagnostic Tests for Hypertrophic Cardiomyopathy (HCM)

Transthoracic echocardiography (TTE) is the cornerstone diagnostic test for HCM and should be performed in all patients with suspected HCM as part of the initial evaluation. 1

Primary Diagnostic Tests

Transthoracic Echocardiography (TTE)

• Diagnostic criteria:
  • Adults: LV wall thickness ≥15 mm in one or more myocardial segments
  • Children: LV wall thickness >2 standard deviations above predicted mean (z-score >2) 2
• Essential for assessing:
  • Degree of myocardial hypertrophy
  • Dynamic left ventricular outflow tract obstruction (LVOTO)
  • Mitral regurgitation
  • Myocardial function 1
• For patients with resting LVOT gradient <50 mm Hg, TTE with provocative maneuvers should be performed 1
• Exercise TTE is recommended for symptomatic patients without resting or provocable outflow tract gradient ≥50 mm Hg to detect and quantify dynamic LVOTO 1

Electrocardiography

• 12-lead ECG: Recommended in the initial evaluation and periodic follow-up (every 1-2 years) 1
• Key findings include:
  • Left ventricular hypertrophy
  • Pathological Q-waves
  • T-wave inversion
  • Deep S-waves in V1-V3 or high R-waves in V4-V6 3
• Abnormal in 94-96% of adult HCM patients and >97% of pediatric patients 3
• Apical HCM often shows negative giant T-waves 3

24-48 Hour Ambulatory ECG Monitoring

• Recommended in initial evaluation and periodic follow-up (every 1-2 years) 1
• Essential for:
  • Detecting ventricular arrhythmias
  • Identifying patients at risk for sudden cardiac death
  • Guiding management of arrhythmias 1
• Extended monitoring (>24 hours) recommended for patients with palpitations or lightheadedness 1

Advanced Imaging

Cardiovascular Magnetic Resonance (CMR)

• Indications:
  • When echocardiography is inconclusive for diagnosis 1
  • When additional information is needed that may impact management decisions 1
  • To define apical hypertrophy and/or aneurysm if echocardiography is inconclusive 1
  • To differentiate HCM from phenocopies (amyloidosis, Fabry disease, LAMP2 cardiomyopathy) 1
• CMR provides more comprehensive diagnostic information in cases where echocardiography is of insufficient quality (approximately 37% of patients) 4

Exercise Testing

Exercise Stress Testing

• Recommended to:
  • Determine functional capacity
  • Provide prognostic information
  • Detect and quantify exercise-induced dynamic LVOTO 1
• Cardiopulmonary exercise testing should be performed in patients with advanced heart failure to quantify functional limitation 1

Coronary Assessment

Coronary Angiography

• Indicated in patients with:
  • Symptoms or evidence of myocardial ischemia 1
  • Risk factors for coronary atherosclerosis before surgical myectomy 1
• Can be performed via CT or invasive methods 1

Genetic Testing and Family Screening

Genetic Testing

• Reasonable in index patients to facilitate identification of first-degree family members at risk 1
• Should include genetic counseling before and after testing 2
• Primarily focuses on sarcomeric protein genes (MYBPC3, MYH7 most common) 2

Family Screening

• First-degree relatives should undergo:
  • 12-lead ECG
  • Transthoracic echocardiography
  • Clinical assessment 1, 2
• Screening intervals:
  • Children/adolescents: Every 12-18 months
  • Adults: Every 3-5 years 2
  • More frequent intervals appropriate in families with malignant clinical course 1

Laboratory Testing

• Blood tests primarily help exclude secondary causes rather than confirm HCM diagnosis 2
• Complete standard laboratory panel recommended:
  • CBC, metabolic panel, liver function
  • Cardiac biomarkers, thyroid function 2
• Specific tests to exclude phenocopies:
  • Alpha-galactosidase A (Fabry disease)
  • Immunoglobulin free light chain assay (amyloidosis)
  • Creatine phosphokinase (muscle disease) 2

Clinical Pitfalls and Caveats

1. Missed Diagnosis: TTE, while the gold standard, may miss some cases of adult-onset HCM, necessitating CMR in patients with persistent symptoms despite normal echocardiography 5

2. Phenocopies: Important to distinguish true sarcomeric HCM from conditions that mimic it:

   • Athlete's heart (differentiated by LV cavity dimension, diastolic function)
   • Hypertensive heart disease (typically LV thickness <25 mm)
   • Metabolic and infiltrative disorders 2

3. Normal ECG: A normal ECG does not exclude HCM, as 4-6% of adult patients may have normal ECGs despite having the condition 3

4. Provocable Obstruction: Patients without resting LVOT obstruction may develop significant gradients during exercise, making exercise TTE crucial for complete evaluation 1