Chapter 20. Hypertrophic Cardiomyopathy (HCM)

Also called Idiopathic Hypertrophic Subaortic Stenosis (IHSS).

Etiology

• Autosomic dominant with variable genetic penetrance
• Highest incidence in 13–22 years old
• Males = females
• Highest incidence of sudden cardiac death (SCD) in all patients
• Features (Figure 20-1):
  • Hypertrophy of left ventricle involving intraventricular septum
  • Enlargement of one or both papillary muscles
  • Septal bulging into the LVOT:
    • Partial or complete LVOT outflow obstruction
  • Paradoxical motion of anterior leaflet of mitral valve (systolic anterior motion [SAM]):
    • Worsens LVOT obstruction
    • Causes MR in 30%
  • Exceptional RV involvement
• Diagnosis of exclusion based on echo findings

Diagnosis

• Most common symptoms are dyspnea, angina, dizziness, and syncope:
  • May be late signs or nonapparent in older patients
• Abnormal S4 heart sounds, systolic flow murmur
• Misplaced apical impulse
• Nonspecific EKG changes (atrial enlargement, LVH, inferolateral Q waves, PVCs)
• Echo findings:
  • Pressure gradient through the LVOT:
    • This varies widely between patients
  • SAM of mitral valve:
    • Dynamic outflow obstruction
    • Due to following conditions:
      • Anterior position of the mitral valve in the LV
      • Altered LV geometry due to septal bulge (hypertrophy)
      • Chordal slack
      • Venturi forces in the outflow tract (drop in pressure because of narrowed channel attracts anterior leaflet of mitral valve)
    • Described as closure of LVOT during systole
  • Mitral regurgitation

Treatment

• Medical:
  • Focused on HR control and negative inotropy:
    • Beta-blockers
    • Calcium channel blockers
  • Often works for nonsymptomatic patients
  • ICD implantation for avoidance of sudden cardiac death (SCD)
• Surgical:
  • Surgical myomectomy
  • Ablative procedures:
    • Decrease in mass of the ventricular hypertrophy
    • May be combined with corrective procedures to change aberrant anatomical problems with mitral valve

• Rule out associated myopathy
• Know the patients’ functional status and the disease progression (i.e., symptoms they have had ongoing)
• ICD often present to prevent SCD (see chapter 19 on ICD) must be deactivated prior to surgery (interrogation by company representative, or magnet if not possible)
• Premedicate as appropriate to avoid anxiety-related tachycardia

Monitors

• Arterial line, depending on:
  • Severity of hypertrophic cardiomyopathy (HCM) (i.e., symptomatic vs. incidental finding)
  • Nature and invasiveness of surgical procedure
• TEE (and practitioner able to interpret) available to diagnose cause of hemodynamic deterioration

Hemodynamic Principles

• Avoid factors that worsen obstruction:
  • Tachycardia (sympathetic stimulation, vagolysis)
  • Positive inotropes
  • Peripheral vasodilators
  • Hypovolemia
• Have immediately available:
  • Esmolol, diltiazem
  • Phenylephrine

Induction

• Balanced technique:
  • Avoid induction agents that decrease afterload (e.g., propofol) or increase HR (e.g., ketamine):...