Hypertrophic Cardiomyopathy

Clinically diverse disease consisting of variable LV hypertrophy. May lead to:

• Dynamic LVOT obstruction
  Present in 20-30% of patients, may precipitate sudden cardiac death.
• Diastolic dysfunction
• Systolic dysfunction
• Ischaemia
• Mitral regurgitation
• Cardiac failure

Epidemiology and Risk Factors

Autosomal dominant with variable phenotypic expression:

• Many patients may be relatively unaffected

Pathophysiology

LVOT obstruction occurs dynamically during systole:

• Systolic Anterior Motion of the mitral valve results in the distance between the LV septum and the tip of the anterior leaflet of the mitral valve narrowing during systole
• This distance is further reduced in HCM due to:
  • Hypertrophic LV septum
  • Apically positioned papillary muscles
  • Longer anterior leaflet
• The narrowing of the outflow tract impedes ejection, resulting in a pressure gradient between the LV cavity and the aortic root
• Ejection of blood from the LVOT also creates a drag effect on the anterior leaflet, pulling it towards the septum
• Obstruction occurs and resolves dynamically, and worsens with:
  • Reduced preload
  • Reduced afterload
  • ↑ contractility
  • High CO states

Aetiology

Autosomal dominant disease with a large number of potential gene mutations on many different chromosomes.

Assessment

Presentation may be:

• Family history of sudden cardiac death
• Fatigue
• Dyspnoea
• Chest pain
• Palpitations
• Cardiac syncope

Diagnostic Approach and DDx

Investigations

Echocardiography:

• LV hypertrophy
  May be:
  • Eccentric or concentric
  • Diffuse or focal
• LVOT gradient
  Gradient >70% is present in most patients at rest or with exercise.

Management

Medical management of dynamic obstruction:

• β-blockade
  • Negative inotropy
  • Negative chronotropy
• Non-dihydropyridine calcium channel blockers
  • Verapamil
• Positioning
  • Fontan position ↑ preload and reduces afterload
    Squatting or supine with hips and knees flexed.

Procedural:

• Alcohol ablation
• Open myectomy

Anaesthetic Considerations

• C
  • Often β-blockade or calcium-channel blockade pre-operatively
  • Often have AICD
  • Arterial line
  • 5-lead ECG
  • Dynamic LVOT obstruction
    
    • Maintain sinus rhythm
      Aggressive treatment of arrhythmia.
    • Low-normal heart rate
    • Maintain or ↑ preload
      Maintain cavity size.
    • Maintain or ↑ afterload
      
      • Vasopressors
      • Prepare for anaesthetic vasodilation
    • ↓ Inotropy
      Volatile is excellent choice.

Marginal and Ineffective Therapies

Complications

Prognosis

• Related to degree of LVOT obstruction
  

Key Studies

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References

1. Davies MR, Cousins J. Cardiomyopathy and anaesthesia. Contin Educ Anaesth Crit Care Pain. 2009;9(6):189-193. doi:10.1093/bjaceaccp/mkp032