Key 2D Echocardiographic Findings in Hypertrophic Obstructive Cardiomyopathy (HOCM)
Comprehensive 2D echocardiography is essential for establishing the diagnosis of HOCM by determining the pattern of hypertrophy, presence of left ventricular apical aneurysms, LV function, mitral valve function, and presence and severity of left ventricular outflow tract obstruction (LVOTO). 1, 2
Diagnostic Findings
- Asymmetric septal hypertrophy: Measurement of maximum diastolic wall thickness using 2D short-axis views in all LV segments from base to apex is recommended to characterize the extent and pattern of hypertrophy 1, 2
- Distribution patterns of hypertrophy: Four basic patterns can be identified:
- Type I: Hypertrophy confined to anterior portion of ventricular septum
- Type II: Hypertrophy involving entire septum but not free wall
- Type III: Hypertrophy involving both ventricular septum and anterolateral free wall (most common, 52% of patients)
- Type IV: Hypertrophy limited to regions other than basal anterior septum (posterior septum, anterolateral free wall, or apical segment) 3
- Left ventricular outflow tract obstruction (LVOTO): Identified by increased velocities across LVOT with characteristic late-peaking "dagger-shaped" Doppler flow pattern 1, 2
- Systolic anterior motion (SAM) of mitral valve: Characteristic finding causing dynamic LVOTO 1, 4
- Mitral regurgitation: Often secondary to SAM and distortion of mitral valve apparatus 1
Assessment of Obstruction
- Dynamic LVOT gradient: LVOT gradients are dynamic and influenced by loading conditions; resting echocardiography tends to underestimate obstruction, with up to 50% of obstructive cases missed on resting studies 1, 2
- Provocative maneuvers: If resting gradient is <50 mm Hg, provocative maneuvers are essential:
- Significant obstruction threshold: Peak instantaneous gradient ≥50 mm Hg is considered hemodynamically significant 1
Associated Abnormalities
- Left ventricular diastolic dysfunction: Comprehensive evaluation includes:
- Left atrial enlargement: Measurement of LA size and volume is important for risk stratification 1, 2
- Apical aneurysms: Discrete thin-walled dyskinetic or akinetic segments at the most distal portion of the LV chamber, associated with increased risk of sudden cardiac death 1, 5
- Right ventricular hypertrophy: May be present in some cases, particularly with specific etiologies 1
Special Considerations
- Contrast echocardiography: For patients with suboptimal images or suspected apical hypertrophy or aneurysm, TTE with LV cavity opacification using intravenous ultrasound-enhancing agents should be considered 1, 2
- Transesophageal echocardiography (TEE): Useful when TTE is inconclusive, for assessing mitral valve apparatus before septal reduction procedures, or when severe mitral regurgitation from intrinsic valve abnormalities is suspected 1, 2
- Fixed vs. dynamic obstruction: Careful assessment needed to differentiate dynamic LVOTO from fixed obstruction (e.g., subaortic membrane, accessory mitral tissue), which requires different treatment approaches 4
Follow-up Recommendations
- Routine monitoring: Serial TTE every 1-2 years for asymptomatic patients to assess changes in LV function, wall thickness, chamber size, and valvular disease 1, 2
- Post-intervention assessment: TTE within 3-6 months after septal reduction therapy to evaluate procedural results 2
- Perioperative TEE: Essential for patients undergoing septal myectomy to guide surgical strategy, assess complications, and detect residual LVOTO 1, 2
Pitfalls and Caveats
- Missed diagnoses: Type IV patterns of hypertrophy may be missed by conventional M-mode echocardiography and require comprehensive 2D imaging 3
- Differential diagnosis: Echocardiography should help differentiate HOCM from hypertensive heart disease, athlete's heart, and other causes of LV hypertrophy 6, 7
- Limitations: CMR may be superior for detecting apical aneurysms, particularly when small 5