Idiopathic Hypertrophic Subaortic Stenosis (IHSS): Hypertrophic Cardiomyopathy
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- 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
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- Most commonly a mutation of MYH7, beta-myosin heavy chain gene in heart muscle protein
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- 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
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- 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
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- 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)
- Definitive: Echocardiogram
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- 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
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- 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
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- 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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