What diagnostic tests are recommended for a patient suspected of having Hypertrophic Obstructive Cardiomyopathy (HOCM)?

Diagnostic Testing for Hypertrophic Obstructive Cardiomyopathy (HOCM)

A transthoracic echocardiogram (TTE) is the essential first-line diagnostic test for any patient suspected of having HOCM, and should be performed immediately after obtaining a 12-lead ECG, comprehensive physical examination with provocative maneuvers (Valsalva, squat-to-stand), and detailed 3-generation family history. 1

Initial Diagnostic Workup

Mandatory First-Line Tests

• 12-lead ECG should be obtained first to establish baseline rhythm, conduction abnormalities, and assess for left ventricular hypertrophy 1

  • Normal ECGs occur in less than 7% of symptomatic patients with HOCM, making an abnormal ECG highly sensitive but not specific 2
  • Repolarization abnormalities (81%) and ECG evidence of left ventricular hypertrophy (62%) are the most common findings 2
  • Any patient with an unusual and unexplained ECG should be suspected of having HCM even if physical examination is normal 2

• Transthoracic echocardiography (TTE) is the cornerstone diagnostic test and must assess: 1

  • Degree and distribution of left ventricular hypertrophy
  • Presence and severity of left ventricular outflow tract (LVOT) obstruction
  • Mitral valve anatomy, systolic anterior motion (SAM), and degree of mitral regurgitation
  • Left ventricular systolic and diastolic function
  • Left atrial size

Provocative Testing When Initial TTE Shows Low Gradient

• TTE with provocative maneuvers (Valsalva, standing from squatting) is mandatory if the resting LVOT gradient is <50 mm Hg 1, 3

  • This distinguishes true non-obstructive HCM from latent obstruction that only manifests with physiologic stress

• Exercise stress echocardiography is required for symptomatic patients who do not have a resting or provocable gradient ≥50 mm Hg on standard TTE 1

  • This represents the most physiologic form of provocation and is superior to bedside maneuvers for detecting dynamic LVOTO 1, 4
  • Intraventricular gradients increase significantly in the orthostatic position and increase considerably during treadmill exercise 4
  • Gradients measured during recovery do not reflect what happens during exercise or daily activities 4

• Exercise stress echocardiography is also reasonable for asymptomatic patients without resting/provocable gradients ≥50 mm Hg to detect occult obstruction 1

Advanced Cardiac Imaging

Cardiovascular magnetic resonance (CMR) imaging has specific Class I indications: 1

• When echocardiography is inconclusive for diagnosis
• To differentiate HCM from alternative diagnoses (infiltrative/storage diseases, athlete's heart)
• For sudden cardiac death risk stratification when clinical assessment (including echo and Holter) leaves uncertainty about ICD placement
• To assess maximum LV wall thickness, ejection fraction, LV apical aneurysm, and extent of late gadolinium enhancement (myocardial fibrosis)
• When the anatomic mechanism of obstruction is unclear on echo and septal reduction therapy is being considered

Cardiac CT may be considered if echocardiogram is non-diagnostic and CMR is unavailable or contraindicated, though this is a weaker recommendation 1

Arrhythmia Assessment

• 24-48 hour ambulatory (Holter) monitoring is mandatory in the initial evaluation for: 1, 3

  • Sudden cardiac death risk stratification (detecting non-sustained ventricular tachycardia)
  • Screening for atrial fibrillation
  • Guiding management of arrhythmias

• Extended ambulatory monitoring (>24 hours) or event recording is required for patients who develop palpitations or lightheadedness 1

  • Should not be considered diagnostic unless symptoms occur during monitoring

• Extended ambulatory monitoring is reasonable for patients with additional AF risk factors (left atrial dilatation, advanced age, NYHA class III-IV heart failure) who are eligible for anticoagulation 1

Family Screening Protocol

First-degree relatives require screening with both ECG and TTE at specific intervals: 1

• Children/adolescents from genotype-positive families or families with early-onset HCM: Screen at time of diagnosis in family member, repeat every 1-2 years
• All other children/adolescents: Screen any time after family diagnosis but no later than puberty, repeat every 2-3 years
• Adults: Screen at time of diagnosis in family member, repeat every 3-5 years

Genotype-positive, phenotype-negative individuals require serial echocardiography every 1-2 years (children/adolescents) or 3-5 years (adults) 1

Additional Testing in Specific Clinical Scenarios

Invasive Hemodynamic Assessment

Cardiac catheterization with invasive hemodynamic assessment is useful when: 1

• Non-invasive testing is inconclusive regarding presence or severity of LVOT obstruction
• Coexistent valvular aortic stenosis is present and contribution of each lesion needs clarification
• Coronary angiography is indicated (patients with atherosclerotic risk factors, chest pain unresponsive to medical therapy, or pre-operative evaluation before surgical myectomy)

Functional Capacity Assessment

Cardiopulmonary exercise testing (CPET) is reasonable for: 1

• Determining functional capacity and providing prognostic information as part of initial evaluation
• Quantifying degree of functional limitation in patients with non-obstructive HCM and advanced heart failure (NYHA class III-IV) to aid in selection for transplantation or mechanical circulatory support

Common Diagnostic Pitfalls

• Do not rely on recovery period gradients after exercise testing, as they significantly underestimate peak exercise gradients and do not reflect daily activity demands 4
• Do not assume a normal physical examination excludes HOCM, particularly in non-obstructive patients who may have entirely normal examinations 1
• Do not skip provocative maneuvers during initial TTE, as up to 70% of patients have latent obstruction only revealed with provocation 1, 5
• Do not use nuclear stress testing as a primary diagnostic tool, as it has high false-positive rates in HCM patients 1

Ongoing Surveillance Testing

• Repeat TTE every 1-2 years in stable patients to assess disease progression 1, 3
• Repeat TTE immediately for any change in clinical status or new clinical event 1
• Annual 12-lead ECG and repeat Holter monitoring every 1-2 years for ongoing arrhythmia surveillance 1, 3
• Repeat contrast-enhanced CMR every 3-5 years may be considered for SCD risk stratification to evaluate changes in late gadolinium enhancement, ejection fraction, or development of apical aneurysm 1