Idiopathic Hypertrophic Subaortic Stenosis (IHSS): Hypertrophic Cardiomyopathy

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