What is the workup and management for a patient with systolic anterior motion (SAM) on echocardiogram (echo)?

Systolic Anterior Motion (SAM) on Echocardiogram: Workup and Management

Systolic anterior motion (SAM) of the mitral valve is defined as the displacement of the anterior mitral valve leaflet towards the left ventricular outflow tract, resulting in left ventricular outflow tract obstruction (LVOTO) and is most commonly associated with hypertrophic cardiomyopathy (HCM). 1

Definition and Mechanism

• SAM occurs when the anterior mitral valve leaflet moves toward the interventricular septum during systole, creating obstruction to left ventricular outflow 1
• This movement often results in failure of normal leaflet coaptation and mitral regurgitation, typically mid-to-late systolic and inferolaterally oriented 1
• SAM can be caused by elongated anterior mitral valve leaflets, papillary muscle abnormalities (hypertrophy, anterior displacement, direct insertion into anterior leaflet), and mitral leaflet abnormalities 1
• While most commonly associated with HCM, SAM can also occur in structurally normal hearts, after mitral valve repair, or in hypercontractile states 1, 2, 3

Initial Evaluation

• Transthoracic echocardiography (TTE) is the cornerstone for diagnosis and assessment of SAM 1
• Clinical examination may reveal a harsh crescendo-decrescendo systolic murmur, prominent apical point of maximal impulse, abnormal carotid pulse, and fourth heart sound 1
• By convention, LVOTO is defined as an instantaneous peak Doppler gradient ≥30 mm Hg at rest or during provocation; a gradient ≥50 mm Hg is considered hemodynamically significant 1
• Standard 12-lead ECG should be performed to aid diagnosis and provide clues to underlying etiology, particularly HCM 1

Comprehensive Workup Algorithm

Step 1: Confirm and Characterize SAM

• Perform comprehensive TTE to:
  • Document the presence and severity of SAM 1
  • Measure the LVOT gradient at rest 1
  • Assess mitral valve anatomy and function (leaflet length, papillary muscle position) 1
  • Evaluate for mitral regurgitation (typically posteriorly directed in SAM) 1
  • Measure left ventricular wall thickness to assess for HCM 1

Step 2: Provocative Testing

• For patients with resting LVOT gradient <50 mm Hg, perform TTE with provocative maneuvers 1:
  • Valsalva maneuver in sitting and semi-supine positions 1
  • Standing from squatting position 1
  • If bedside maneuvers fail to induce significant gradient in symptomatic patients, perform exercise TTE 1

Step 3: Determine Underlying Etiology

• Evaluate for HCM (most common cause of SAM) 1
• Consider other causes:
  • Post-mitral valve repair 3, 4
  • Hypovolemia or hypercontractile states 2
  • Mitral valve abnormalities (elongated leaflets, abnormal papillary muscles) 1
  • Exclude other conditions that can mimic LVOTO (sub-aortic membrane, mid-cavity obstruction) 1

Step 4: Family Screening (if HCM is diagnosed)

• Screen first-degree relatives with ECG and TTE 1
• Follow age-specific screening protocols:
  • Pediatric patients: screen at time of HCM diagnosis in family, repeat every 1-2 years 1
  • Other children/adolescents: screen by puberty, repeat every 2-3 years 1
  • Adults: screen at time of HCM diagnosis in family, repeat every 3-5 years 1

Management Approach

For SAM Associated with HCM:

1. Medical therapy:

   • Beta-blockers to reduce contractility and heart rate 1
   • Non-dihydropyridine calcium channel blockers if beta-blockers are contraindicated 1
   • Avoid vasodilators, diuretics, and positive inotropes which can worsen obstruction 1

2. For persistent symptoms despite medical therapy with LVOT gradient ≥50 mm Hg:

   • Consider septal reduction therapy (SRT) 1:
     • Surgical septal myectomy (with intraoperative TEE to guide adequacy) 1
     • Alcohol septal ablation with TTE/TEE guidance 1
   • Follow-up TTE within 3-6 months after SRT to evaluate results 1

For Transient SAM (non-HCM related):

1. Address underlying causes:

   • Volume repletion for hypovolemia 2
   • Reduce or discontinue inotropes/vasopressors if possible 2
   • Beta-blockers to reduce hypercontractility 3, 4

2. For SAM after mitral valve repair:

   • Stepwise approach: medical therapy with volume loading and beta-blockade 3, 4
   • If severe or persistent, surgical revision may be required 4

Follow-up Recommendations

• For patients with HCM and SAM:

  • Repeat TTE every 1-2 years in children/adolescents 1
  • Repeat TTE every 2-3 years in adults with stable symptoms 1
  • Immediate repeat TTE for any change in clinical status 1

• For non-HCM related SAM:

  • Follow-up TTE after resolution of acute precipitating factors 2
  • In post-mitral valve repair patients, close monitoring in the immediate post-operative period 4

Common Pitfalls and Caveats

• SAM with LVOTO can be mistaken for aortic stenosis; careful echocardiographic assessment is essential 1
• Not all systolic murmurs in HCM are due to SAM; other causes like intrinsic mitral valve disease should be considered 1
• SAM-related mitral regurgitation is dynamic and varies with the degree of LVOTO 1
• Central or anteriorly directed mitral regurgitation jets suggest intrinsic mitral valve abnormality rather than SAM 1
• Patients with SAM during dobutamine stress echocardiography may not develop it during exercise, limiting clinical significance in some cases 5
• Persistent SAM after septal reduction therapy may be related to anterior papillary muscle displacement and mitral valve malcoaptation 6