What is the role of 2D (two-dimensional) echo in diagnosing and managing Hypertrophic Obstructive Cardiomyopathy (HOCM)?

Role of 2D Echocardiography in Hypertrophic Obstructive Cardiomyopathy (HOCM)

Two-dimensional echocardiography is the cornerstone imaging modality for diagnosing, risk stratifying, and managing patients with hypertrophic obstructive cardiomyopathy, providing essential information about cardiac morphology, function, and hemodynamics that directly impacts treatment decisions and patient outcomes. 1

Diagnostic Role

• Comprehensive 2D echocardiography establishes the diagnosis of HOCM by determining the pattern of hypertrophy, presence of left ventricular apical aneurysms, LV systolic and diastolic function, mitral valve function, and presence and severity of left ventricular outflow tract obstruction (LVOTO) 1

• 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

• 2D echo can identify diverse patterns of myocardial hypertrophy that may be more extensive than appreciated by M-Mode echocardiography alone, with four basic patterns commonly 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 2

Assessment of Obstruction

• LVOT gradients are dynamic and influenced by loading conditions; recumbent resting echocardiography tends to underestimate the presence and severity of ambulatory LVOTO, with up to 50% of obstructive cases missed on resting studies 1

• If resting gradient is <50 mm Hg, provocative maneuvers are essential to uncover LVOTO:

  • Valsalva maneuver in sitting and semi-supine positions
  • Standing position if no gradient is provoked with Valsalva
  • Exercise echocardiography for symptomatic patients 1

• For symptomatic patients with resting or provoked LVOT gradient <50 mm Hg, exercise echocardiography in standing, sitting, or semi-supine positions is recommended to detect provocable LVOTO and exercise-induced mitral regurgitation 1

• To attribute effort-related symptoms to LVOTO, the resting or provoked gradient typically needs to exceed 50 mm Hg 1

Evaluation of Associated Abnormalities

• 2D echo allows assessment of mitral valve abnormalities that contribute to LVOTO, including:

  • Anterior mitral leaflet length
  • Abnormal chordal attachments to base of anterior mitral leaflet
  • Systolic anterior motion (SAM) of the mitral valve 3

• Comprehensive evaluation of LV diastolic function is recommended, including:

  • Pulsed Doppler of mitral valve inflow
  • Tissue Doppler velocities at mitral annulus
  • Pulmonary vein flow velocities
  • Pulmonary artery systolic pressure
  • Left atrial size and volume 1

• Papillary muscle abnormalities can be assessed, including number and area of papillary muscle heads and bifid papillary muscle mobility, which may contribute to obstruction even without severe septal hypertrophy 3

Management and Follow-up

• Routine follow-up with serial TTE every 1-2 years is recommended for asymptomatic patients to assess changes in:

  • LV systolic and diastolic function
  • Wall thickness
  • Chamber size
  • LVOTO
  • Concomitant valvular disease 1

• For patients undergoing septal reduction therapy (SRT), TTE within 3-6 months after the procedure is recommended to evaluate procedural results 1

• In patients undergoing septal myectomy, perioperative transesophageal echocardiography (TEE) is recommended to:

  • Guide surgical strategy
  • Assess post-surgical complications (ventricular septal defect, aortic regurgitation)
  • Detect residual LVOTO 1

Special Considerations

• For patients with suboptimal images or suspected apical hypertrophy or aneurysm, TTE with LV cavity opacification using intravenous ultrasound-enhancing agents should be considered, particularly if CMR is not readily available or contraindicated 1

• TEE can be useful if TTE is inconclusive for clinical decision-making regarding medical therapy, planning for myectomy, excluding subaortic membrane, or assessing mitral regurgitation secondary to structural abnormalities 1

• For patients undergoing alcohol septal ablation, TTE or intraoperative TEE with intracoronary contrast injection of candidate septal perforator arteries is recommended to guide the procedure 1

Screening

• TTE is recommended for first-degree relatives of patients with HCM as part of initial family screening and periodic follow-up 1

• In genotype-positive, phenotype-negative individuals, echocardiography is recommended at periodic intervals:

  • Every 1-2 years in children and adolescents
  • Every 3-5 years in adults
  • More frequently with change in clinical status 1

Pitfalls and Limitations

• LVOT gradients can be missed on resting echocardiography in up to 50% of patients with obstructive physiology 1

• Provocative maneuvers during resting TTE (such as Valsalva) can be variable due to inconsistencies in instruction and patient effort 1

• Exercise testing may not be helpful in young children (typically <7-8 years of age) who often cannot cooperate with these maneuvers 1

• Some patterns of hypertrophy (Type IV) may be inaccessible to conventional M-mode and require comprehensive 2D imaging for diagnosis 2