Cardiomyopathy, Hypertrophic

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Basics

Description

  • Hypertrophic cardiomyopathy (HCM):
    • Genetic disorder affecting the sarcomere:
      • Various mutations
      • Many phenotypic variations
    • Hypertrophied (regionally or globally), nondilated left or, rarely, right ventricle in the absence of another cause of degree of hypertrophy observed, such as hypertension or aortic stenosis
    • 2 general types:
      • Nonobstructive (HCM)—75% of patients. Estimated around 1% annual mortality
      • Obstructive (HOCM)—25% of patients. More severe—estimated 2% annual mortality
    • Manifests at all ages, from neonate to elderly:
      • Most manifest in childhood and adolescence—pubertal growth spurt
      • Usually more severe when diagnosed at younger age
      • Small percent progress to reduced LV function
    • Clinical presentation in mid and late life not uncommon
      • May initially be misdiagnosed as asthma, COPD, deconditioning or sleep apnea
    • Lethal arrhythmias more common in younger patients
      • Most common cause of atraumatic death in young (<35 yo) athletes
    • Supraventricular arrhythmias common with incidence increasing with age
      • Atrial fibrillation both common and poorly tolerated
  • Prevalence ∼1 in 500 adults general population:
    • Based on echocardiographic diagnosis
  • Structural pathology:
    • Irregular, marked ventricular wall thickening with disarray of myofibrils in the thickened regions and fibrin deposition:
      • Affects higher-pressure LV more than right and, in obstructive form, if obstruction removed, hypertrophy decreases
      • Some phenotypes have progressive wall thinning with age—usually associated with thicker wall early
    • Thickening usually asymmetric involving the septum to a greater extent than the free ventricular wall
    • Atrial dilatation secondary to diastolic filling stiffness
    • Impaired microvascular dilation associated with intimal thickening and perivascular collagen deposition
  • Outpatient long-term management
    • Avoidance of volume depletion and elevated cardiac demand—depending on degree and location of hypertrophy
    • Pharmacologic
      • β-Blockers or verapamil to slow and control rate, thus prolonging diastole
    • Implantable cardiac defibrillator
      • In patients with history of syncope, cardiac arrest, family member with sudden death, asymptomatic nonsustained ventricular tachycardia (VT), abnormal BP response to exercise, massive hypertrophy
    • Alcohol ablation of hypertrophic outflow-obstructing septal tissue
    • Surgical septal myectomy—improving statistics with more centers performing

Risk Factors

Genetics
  • 1st cardiac disorder for which genetic basis identified (1989)
  • Autosomal-dominant inheritance:
    • >10 associated genes found:
      • Most encode proteins for sarcomere
      • >700 distinct mutations recognized
    • High penetrance
    • Variable phenotypic expression
    • Some genotypes significantly more lethal:
      • Routine screening impractical at present
      • Increasing complexity with more understanding of interplay between primary sarcomere abnormalities and other genetic and nongenetic factors
      • Some mutations affect cell wall pumps—thus, association with dysrhythmias.

Etiology

See “Genetics.”

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Citation

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TY - ELEC T1 - Cardiomyopathy, Hypertrophic ID - 307578 Y1 - 2016 PB - 5-Minute Emergency Consult UR - https://emergency.unboundmedicine.com/emergency/view/5-Minute_Emergency_Consult/307578/all/Cardiomyopathy__Hypertrophic ER -