a.k.a. "Idiopathic hypertrophic subaortic stenosis (IHSS)" and "hypertrophic obstructive cardiomyopathy"

I. Pathophysiology

  1. A genetic (autosomal dominant) cardiac disease, involving mutations in any of 10 genes encoding portions of the cardiac sarcomere
  2. Markedly variable in clinical expression
  3. Common features
    1. Left ventricular hypertrophy
      1. Usually present by age 18, but can appear at any time of life
      2. Can progress to dilated cardiomyopathy and in some patients
      3. Heart Failure may result from dilated cardiomyopathy or, earlier in disease course, from "diastolic dysfunction"
      4. May produce "outflow obstruction,"  i.e. LV outflow gradient of 50mm Hg or more at rest or with provocative maneuvers, but the role of such obstruction in adverse outcomes in HCM is unclear.
    2. Small vessel disease leading to myocardial ischemia is common
    3. Myocardial scarring predisposing to Atrial Fibrillation (occurs in 20-25% of pts with HCM) and/or Ventricular Arrhythmias, the latter with a risk of sudden cardiac death

II. Diagnosis

  1. Left ventricular hypertrophy in absence of other disease capable of causing same (e.g. hypertension, aortic stenosis)--most easily confirmed with echocardiography
  2. Systolic murmur
  3. Family history of sudden cardiac death at an early age or HCM diagnosis
  4. Abnormal ECG (particularly, signs of Left Ventricular Hypertrophy)

III. Treatment

  1. Meds that may improve cardiac function in patients with HCM:
    1. Beta-Blockers
    2. Calcium channel blockers (may reduce cardiac output in some patients with severely elevated outflow gradients and heart failure)
    3. Disopyramide
    4. Diuretics
  2. Surgical Treatment
    1. Percutaneous transluminal septal myocardial ablation (PTSMA)
    2. Septal myomectomy + mitral leaflet extension (the latter increases the hemodynamic results)
    3. Comparisons
      1. In a nonrandomized study in 72 pts with hypertrophic cardiomyopathy with enlarged anterior mitral valve leaflet who received either PTSMA or septal myomectomy + mitral leaflet extension, PTSMA was associated with higher incidence of periprocedural complications and more reinterventions, but inferior hemodynamic results (Circ. 112:482, 2005--abst)
  3. Patients felt to be at high risk for sudden cardiac death are candidates for an implantable cardioverter-defibrillator.  Risk factors include:
    1. Prior cardiac arrest, spontaneous sustained ventricular tachycardia, or recurrent or prolonged non-sustained ventricular tachycardia
    2. Family history of premature HCM-related death
    3. Syncope or exertional pre-syncope
    4. Hypotensive response to exercise
    5. LV wall thickness 30mm or greater
    6. Relation of outflow obstruction and/or presence of inducible arrhythmias on cardiac electrophysiologic testing with risk of sudden death is unclear as of 2004
  4. Patients with Atrial Fibrillation should be treated accordingly
  5. Patients with Heart Failure should also be treated accordingly, and if refractory to standard treatments, treatment options include:
    1. Heart transplantation
    2. If LV outlet obstruction is present:
      1. Ventricular-septal myotomy-myomectomy ("Morrow" procedure)
      2. Alcohol septal ablation (may be less effective than the Morrow procedure)
      3. Duel-chamber pacing
  6. Restriction from vigorous athletic activity is often advised

(Source: JAMA 287:1308, 2002, and other sources as cited)