What is the management of Hypertrophic Obstructive Cardiomyopathy (HOCM) with Systolic Anterior Motion (SAM) and moderate to severe Mitral Regurgitation (MR)?

Management of Hypertrophic Obstructive Cardiomyopathy (HOCM) with Systolic Anterior Motion (SAM) and Moderate to Severe Mitral Regurgitation (MR)

For patients with HOCM complicated by SAM and moderate to severe MR, a stepwise approach beginning with non-vasodilating beta-blockers as first-line therapy, followed by non-dihydropyridine calcium channel blockers or disopyramide if needed, with invasive septal reduction therapy reserved for drug-refractory cases with gradients ≥50 mm Hg is strongly recommended. 1

Pathophysiology

HOCM with SAM and MR involves several interrelated mechanisms:

• Left Ventricular Outflow Tract Obstruction (LVOTO): Caused by SAM of the mitral valve leaflets making mid-systolic contact with the hypertrophied ventricular septum 2
• Systolic Anterior Motion (SAM): Results from drag effect or possibly Venturi phenomenon 2
• Mitral Regurgitation: Secondary to SAM with specific characteristics:
  • Typically mid-to-late systolic in timing
  • Usually posterior or lateral in orientation due to anterior distortion of the mitral valve
  • Caused by compromised leaflet coaptation 2
• Dynamic Nature: LVOTO is sensitive to ventricular preload, afterload, and contractility, with gradients varying based on heart rate, blood pressure, volume status, activity, medications, food, and alcohol intake 2

Diagnostic Assessment

• Echocardiography with Doppler: Primary tool to assess:
  • LVOT gradient (obstruction present if ≥30 mm Hg)
  • SAM of the mitral valve
  • MR severity and jet direction (posterior/lateral jets suggest SAM-related MR) 2, 1
• Provocative Maneuvers: For minimal resting gradients (<30 mm Hg):
  • Standing
  • Valsalva maneuver
  • Exercise echocardiography 2, 1
  • Avoid dobutamine due to lack of specificity 2
• Assessment of MR:
  • Evaluate timing (mid-to-late systolic)
  • Direction (posterior/lateral suggests SAM-related)
  • Severity (moderate to severe) 2
  • Rule out intrinsic mitral valve abnormalities (if central or anterior jets are present) 2

Medical Management

1. First-Line Therapy:

   • Non-vasodilating beta-blockers (e.g., propranolol)
   • Target heart rate: 55-65 bpm at rest
   • Titrate to maximum tolerated dose 1

2. Second-Line Options (if symptoms persist):

   • Non-dihydropyridine calcium channel blockers (verapamil)
   • Disopyramide added to beta-blockers 1

3. Avoid:

   • Vasodilators (can worsen LVOTO)
   • Diuretics (can reduce preload and worsen obstruction) 1

4. Hemodynamic Optimization:

   • Maintain adequate preload
   • Avoid tachycardia
   • Control hypertension carefully 2, 1

Invasive Management

For drug-refractory symptoms with LVOT gradients ≥50 mm Hg:

1. Surgical Septal Myectomy (gold standard):

   • Reduces septal thickness
   • Eliminates SAM
   • Typically reduces LVOT gradients to <10 mm Hg
   • Usually resolves SAM-related MR without direct mitral valve intervention 1, 3

2. Mitral Valve Assessment:

   • Close examination required before septal reduction therapy
   • Direct mitral valve intervention only needed if intrinsic mitral valve disease present (e.g., leaflet prolapse, chordal rupture, leaflet cleft) 4, 3

3. Mitral Valve Techniques (if needed for intrinsic MV disease):

   • Edge-to-edge repair (quick, reproducible procedure) 4
   • Anterior leaflet plication/extension 5
   • Reorientation of papillary muscles 5
   • Mitral valve replacement (rarely necessary) 6

4. Alcohol Septal Ablation:

   • Alternative for high-surgical-risk patients
   • Creates controlled infarction of the basal septum 1

Clinical Pearls and Pitfalls

• Key Pitfall: Assuming all MR in HOCM requires direct mitral valve intervention. In most cases, adequate septal myectomy alone resolves SAM and associated MR 3

• Important Distinction: Differentiate between SAM-related MR (posterior/lateral jets) and intrinsic mitral valve disease (central/anterior jets or multiple jets) 2

• Hemodynamic Considerations:

  • MR severity in HOCM is dynamic and varies with loading conditions
  • MR can increase with maneuvers that decrease LV preload in patients with mitral valve prolapse and HOCM 2
  • Afterload reduction increases MR severity in HOCM 2

• Monitoring: Color Doppler can overestimate MR severity in high LV systolic pressure conditions like HOCM 2