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Idiopathic Hypertrophic Subaortic Stenosis (IHSS): Hypertrophic Cardiomyopathy

  • What is it?
      • Disease characterized by marked hypertrophy of the left ventricle
      • Involves interventricular septum & left ventricular outflow tract
      • Usually asymmetric
      • Obstructive vs nonobstructive
      • More common in males
      • Most common cause of sudden cardiac arrest (SCA) in young athletes
  • Etiology
      • Most commonly a mutation of MYH7, beta-myosin heavy chain gene in heart muscle protein
  • What is happening?
      • Muscle fibers are thickened & shorter
      • Muscle bundles in left ventricle arranged in a bizarre fashion
      • Possibly LVOT abnormality → creates turbulence in blood flow → progressive LVOT thickening, fibrosis, and scarring
      • During systole, the hypertrophied muscle in the outflow tract bulges into right ventricular outflow tract and often the left → narrows this region → produce obstruction to left ventricular ejection
  • Common consequences?
      • Damage heart muscle → arrhythmias
      • Increase blood pressure
      • Marked enlargement of the papillary muscles and trabeculae carneae
      • Deformation of the mitral valve by the thickened ventricular septum
      • Thickening of the anterior mitral leaflet / mitral regurgitation
  • Signs and symptoms
      • Ejection type systolic heart murmur with thrill – mid left sternal border *often first sign*
        • Valsalva: increases murmur
        • Leg lifting: decreases murmur
      • Dyspnea
      • Angina
      • Dizziness
      • Syncope
      • Enlarged heart with double apical impulse
      • Apex cardiograms: abnormally tall presystolic expansion wave (a wave)
  • Diagnosis
  • Definitive: Echocardiogram
      • Continuous wave Doppler: to determine gradient and degree of obstruction  
      • EKG: shows LVH
      • CXR: normal or cardiomegaly
      • Cardiac catheterization: gradient across valve, measurement of cardiac output, & degree of aortic regurgitation
  • Treatment and management
      • Patients are told to avoid strenuous activity, stay hydrated, and have close follow up
      • Meds: Beta blockers or Ca2+ channel blockers
      • ICD placement
      • Definitive: Surgical correction of obstruction
        • Surgical resection of the subvalvar membrane or fibrous crescent, with myectomy
        • High rate of reoccurrence
        • “Prevention” of aortic regurgitation alone is not a criterion for surgery
        • We defer surgery in the first decade of life if obstruction is moderate or less (maximum instantaneous Doppler gradient ≤50 mmHg or mean LVOT gradient <30 mmHg) and regurgitation is no more than trivial
        • Patients with more severe obstruction or with progressive aortic regurgitation are surgically corrected
        • Children with a LVOT gradient <30 mmHg and no significant LVH are followed closely
  • Pearls
    • No antibiotic prophylaxis (for endocarditis) is recommended anymore
    • Second most common form of AS
    • Patients are not born with it, develops later
    • Mortality after surgery is very low

Overview Video

https://youtu.be/KodyU7tUVO8

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