What is the diagnostic formulation and management approach for Obstructive Hypertrophic Septal Cardiomyopathy (OHS)?

Diagnostic Formulation for Obstructive Hypertrophic Cardiomyopathy

The diagnosis of obstructive HCM requires transthoracic echocardiography (TTE) as the primary diagnostic modality to confirm left ventricular hypertrophy and quantify left ventricular outflow tract (LVOT) obstruction, with a diagnostic threshold of ≥50 mmHg gradient at rest or with provocation. 1

Initial Diagnostic Workup

Electrocardiography

• Obtain a 12-lead ECG immediately to identify characteristic findings including left ventricular hypertrophy patterns, deep T-wave inversions (particularly in V3-V4), pathological Q-waves, and conduction abnormalities 1
• Perform 24-hour Holter monitoring in the initial evaluation to detect ventricular tachycardia and identify candidates for ICD therapy, as this is a Class I recommendation for risk stratification 1
• Repeat Holter monitoring or event recording is mandatory if patients develop palpitations or lightheadedness 1

Echocardiographic Assessment

• TTE is the cornerstone diagnostic test (Class I recommendation) for all patients with suspected HCM, providing assessment of septal thickness, LVOT gradient, systolic anterior motion (SAM) of the mitral valve, and mitral regurgitation 1
• Measure LVOT gradients at rest and with provocation (Valsalva maneuver or exercise) to detect dynamic obstruction, as some patients have latent obstruction only evident with physiologic stress 1
• Exercise TTE is reasonable (Class IIa) when resting gradients are <50 mmHg to detect and quantify exercise-induced dynamic LVOT obstruction 1
• Document left atrial volume index, as values ≥34 mL/m² indicate chronically elevated filling pressures, predict worse outcomes, and may justify earlier intervention 1

Advanced Imaging

• Consider cardiac MRI (CMR) when TTE images are suboptimal, to evaluate apical variants (missed in ~10% by echo alone), detect apical aneurysms, or assess for late gadolinium enhancement indicating fibrosis 1
• Transesophageal echocardiography (TEE) is reasonable (Class IIa) when TTE is inconclusive for clinical decision-making, to exclude subaortic membrane, assess intrinsic mitral valve pathology, or plan septal reduction therapy 1

Exercise Testing

• Treadmill exercise testing with ECG and blood pressure monitoring is reasonable (Class IIa) for sudden cardiac death risk stratification, as abnormal blood pressure response (failure to increase ≥20 mmHg or drop ≥20 mmHg) identifies high-risk patients 1
• Exercise testing also determines functional capacity and response to therapy 1

Diagnostic Criteria for Obstructive HCM

The diagnosis requires all three components:

1. Anatomic: Left ventricular wall thickness ≥15 mm (or ≥13 mm with positive family history) in the absence of other causes of hypertrophy 1

2. Hemodynamic: Dynamic LVOT gradient ≥50 mmHg at rest or with provocation, associated with SAM of the mitral valve 1, 2

3. Clinical: Symptoms including dyspnea, chest pain, syncope, or presyncope that correlate with obstruction 1, 2

Key Diagnostic Pitfalls to Avoid

• Do not perform TTE more frequently than every 12 months in stable patients when changes are unlikely to impact clinical decisions (Class III: No Benefit) 1
• Distinguish from aortic stenosis with secondary hypertrophy in elderly patients—HCM typically shows asymmetric septal hypertrophy with wall thickness often >15 mm, while aortic stenosis shows more symmetric, milder hypertrophy that correlates with valve severity 1
• Exclude subaortic membrane as a cause of fixed obstruction, which may coexist with or mimic dynamic obstruction—TEE is superior for this assessment 1
• Recognize apical variants that require contrast echocardiography or CMR, as standard TTE misses these in 10% of cases 1
• Assess for apical aneurysms using CMR in patients with apical hypertrophy, as these carry increased risk and alter management 1

Differential Diagnosis Considerations

• Evaluate for infiltrative diseases (amyloidosis, Fabry disease) if clinical features are atypical, as these require different management 1
• Consider athlete's heart in young athletic individuals—wall thickness rarely exceeds 13 mm, cavity is enlarged, and hypertrophy regresses with deconditioning 1
• Rule out hypertensive heart disease—typically shows concentric hypertrophy with wall thickness <15 mm and correlates with blood pressure severity 1

Family Screening Algorithm

• Perform TTE and 12-lead ECG on all first-degree relatives unless genotype-negative in families with known definitive mutations (Class I) 1
• Screen children starting at age 12 years (or earlier if growth spurt, puberty, or plans for competitive sports) with TTE every 12-18 months 1
• Adult relatives require screening every 5 years when genetic status is unknown (Class IIa) 1