How to evaluate the severity of Hypertrophic Obstructive Cardiomyopathy (HOCM) by echocardiogram (echo)?

Echocardiographic Evaluation of HOCM Severity

Severity assessment of HOCM by echocardiography centers on quantifying the LVOT gradient (with ≥50 mm Hg defining hemodynamically significant obstruction), measuring maximal wall thickness (≥30 mm conferring highest sudden death risk), and comprehensively evaluating diastolic dysfunction, mitral regurgitation, and left atrial enlargement. 1

Core Severity Parameters

LVOT Gradient Assessment

• Measure peak instantaneous LVOT gradient using continuous wave Doppler at rest in multiple positions (supine, sitting, semi-supine) 1
• Gradients ≥50 mm Hg define obstructive physiology requiring treatment consideration 1
• Resting echocardiography misses up to 50% of obstructive cases due to the dynamic nature of LVOTO 1
• Perform provocative maneuvers when resting gradient <50 mm Hg: Valsalva maneuver in sitting and semi-supine positions, then standing from squatting if no gradient is provoked 1
• Exercise echocardiography is recommended for symptomatic patients with resting/provoked gradients <50 mm Hg to detect physiologic LVOTO 1, 2

Critical pitfall: Distinguish the LVOT gradient spectral profile from cavity obliteration and avoid contamination by mitral regurgitation signal 1

Maximal Wall Thickness

• Measure maximum diastolic wall thickness in all LV segments using 2D short-axis views from base to apex 1, 2
• Wall thickness ≥30 mm identifies highest sudden death risk (approximately 2% per year) 1, 3
• Wall thickness shows relatively linear association with sudden death risk across the spectrum 1

Diastolic Function Assessment

Comprehensive evaluation is mandatory and includes multiple parameters since no single measure is diagnostic 1:

• Mitral inflow pattern: E/A ratio ≥2 with E-wave deceleration time ≤150 ms defines restrictive filling pattern associated with adverse outcomes even with preserved ejection fraction 1
• Tissue Doppler velocities at mitral annulus: Elevated E/e' ratio correlates with raised LV end-diastolic pressure, reduced exercise capacity, and worse prognosis 1
• Pulmonary vein flow velocities 1
• Pulmonary artery systolic pressure 1
• Left atrial volume index: Values >34 mL/m² indicate chronic diastolic burden, predict abnormal filling, higher calculated LA pressure, and less favorable outcomes 1, 2

Mitral Valve and Regurgitation

• Assess systolic anterior motion (SAM) of the mitral valve as the primary mechanism of LVOTO 1
• Evaluate mitral leaflet length, coaptation point, and papillary muscle abnormalities that contribute to obstruction 1, 3
• Quantify mitral regurgitation severity: Posteriorly directed late systolic MR results from SAM-related leaflet malcoaptation 1, 2

Systolic Function

• Ejection fraction is typically normal or increased but is a poor measure of true systolic performance in hypertrophy 1
• Development of systolic dysfunction (reduced EF) heralds progressive heart failure with risk of transplantation or death 1
• Myocardial longitudinal strain and strain rate (via tissue Doppler or speckle tracking) are often reduced despite normal EF and may be abnormal before hypertrophy develops 1

Special Considerations for Severity Assessment

Apical Involvement

• Use contrast echocardiography with IV ultrasound-enhancing agents when apical hypertrophy or aneurysm is suspected, as near-field artifacts obscure the apex 1, 2
• LV apical aneurysm is a major sudden death risk factor regardless of size, defined by discrete thin-walled dyskinetic/akinetic segments 4
• CMR is superior to echo for detecting apical aneurysms, particularly small ones 4

Pattern of Hypertrophy

• Document distribution of hypertrophy (septal, anterolateral free wall, apical, posterior) using 2D imaging in multiple views 1, 5
• Most patients (52%) have Type III pattern involving both septum and anterolateral free wall, associated with more severe functional limitation and resting obstruction 5
• Extreme concentric LVH (≥30 mm) suggests specific etiologies like Danon or Pompe disease requiring alternative diagnosis consideration 1

Follow-Up Severity Monitoring

• Repeat TTE every 1-2 years in stable asymptomatic patients to assess progression of wall thickness, chamber size, LVOTO, systolic/diastolic function, and valvular disease 1, 2
• Immediate repeat TTE is required for any change in clinical status or new events 1, 2
• Post-septal reduction therapy TTE within 3-6 months evaluates procedural results 1, 2

Advanced Techniques for Unclear Cases

Transesophageal Echocardiography

• Consider TEE when TTE windows are poor as alternative to CMR 1
• TEE is particularly useful when LVOTO mechanism is unclear, for detailed mitral valve apparatus assessment before septal reduction, or when intrinsic mitral valve pathology causing severe MR is suspected 1
• Intraoperative TEE is mandatory during septal myectomy to guide surgical strategy, detect complications (VSD, aortic regurgitation), and assess residual LVOTO 1, 2

Contrast Echocardiography

• Intracoronary contrast echo is required during alcohol septal ablation to ensure correct localization of target septal perforator 1
• IV contrast for LV cavity opacification improves visualization when standard imaging is suboptimal 1, 2