What are the key echocardiographic findings and velocity measurements in a patient suspected of having Hypertrophic Obstructive Cardiomyopathy (HOCM)?

Echocardiographic Findings and Velocity Measurements in HOCM

Key Diagnostic Findings

Transthoracic echocardiography is the gold standard for diagnosing HOCM and should comprehensively assess the pattern of hypertrophy, left ventricular outflow tract obstruction, mitral valve function, and systolic anterior motion. 1, 2

Structural Abnormalities to Identify

• Asymmetric septal hypertrophy: Measure maximum diastolic wall thickness using 2D short-axis views in all LV segments from base to apex to characterize the extent and pattern of hypertrophy 2, 3
• Systolic anterior motion (SAM) of the mitral valve: This is a hallmark finding that contributes to LVOT obstruction and often causes mitral regurgitation 2, 3, 4
• Mid-systolic closure of the aortic valve: A characteristic finding reflecting dynamic LVOT obstruction 3
• Left ventricular apical aneurysms: These are major risk factors for sudden cardiac death and require CMR if echocardiography is inconclusive 1, 5
• Systolic obliteration of the left ventricle: May be visible on imaging 3

Velocity Measurements and Gradient Assessment

Continuous-Wave Doppler Technique

Use continuous-wave Doppler aligned with the LVOT to measure peak velocities, which are then converted to gradients using the modified Bernoulli equation (gradient = 4 × velocity²). 2, 4

Critical Gradient Thresholds

• <30 mm Hg: Non-obstructive, clinically insignificant 6
• 30-49 mm Hg: Pathologic obstruction warranting medical management if symptomatic 6
• ≥50 mm Hg: Severe obstruction, the threshold for considering septal reduction therapy in symptomatic patients refractory to medical management 1, 6

Dynamic Nature Requires Provocative Testing

LVOT gradients are highly dynamic and influenced by loading conditions; resting echocardiography misses up to 50% of obstructive cases, making provocative maneuvers essential. 2, 6

Recommended Provocative Maneuvers

• Valsalva maneuver: Perform in sitting and semi-supine positions if resting gradient is <50 mm Hg 2
• Exercise echocardiography: Recommended for symptomatic patients to detect provocable LVOTO and exercise-induced mitral regurgitation 1, 2
• Postural changes: Assess gradients in different positions as they can vary dramatically 6

Distinguishing LVOT Obstruction from Aortic Stenosis

When both LVOT obstruction and aortic stenosis coexist, use the timing of peak gradient on continuous-wave Doppler—LVOT obstruction peaks later in systole (late-peaking "dagger-shaped" profile) while aortic stenosis peaks earlier. 4 If uncertainty persists, invasive hemodynamic assessment with simultaneous LV and aortic pressure measurements is recommended 1

Comprehensive Diastolic Function Assessment

Evaluate LV diastolic function using multiple parameters: 2

• Pulsed Doppler of mitral valve inflow (E and A waves)
• Tissue Doppler velocities at mitral annulus (e' velocity)
• Pulmonary vein flow velocities
• Pulmonary artery systolic pressure
• Left atrial size and volume 2

Special Imaging Considerations

When Standard TTE is Inadequate

• Use intravenous ultrasound-enhancing agents for patients with suboptimal images or suspected apical hypertrophy/aneurysm 1, 2
• Consider transesophageal echocardiography (TEE) if TTE is inconclusive for clinical decision-making, planning myectomy, or assessing mitral valve structural abnormalities 1, 2
• CMR imaging is indicated when echocardiography is inconclusive for diagnosis or when additional anatomic detail is needed for surgical planning 1

Perioperative and Post-Procedure Assessment

• Intraoperative TEE is mandatory during surgical septal myectomy to assess mitral valve anatomy and adequacy of septal resection 1
• TTE within 3-6 months after septal reduction therapy is recommended to evaluate procedural results 1, 2
• For alcohol septal ablation, TTE or intraoperative TEE with intracoronary contrast injection of candidate septal perforators is recommended 1

Follow-Up Imaging Protocol

Serial TTE every 1-2 years is recommended for routine follow-up to assess changes in LV systolic and diastolic function, wall thickness, chamber size, and valvular disease 2, 5