Cardiomyopathy, Hypertrophic

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Basics

Description

  • Genetic disorder affecting the sarcomere
  • Clinical diagnostic criteria: Hypertrophied (regionally or globally), nondilated left in the absence of another cause of degree of hypertrophy observed, such as hypertension or aortic stenosis
  • Hypertrophic cardiomyopathy (HCM) unifies over 75 different names historically used
  • 2 general types:
    • Obstructive – ≥30 mm Hg left ventricular outflow tract gradient:
      • 67% of patients
      • More severe – estimated 2% annual mortality
    • Nonobstructive – <30 mm Hg gradient:
      • 33% of patients
      • Estimated around 1% annual mortality
  • Global disease – >50 countries, all race/ethnic groups
  • 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
  • Average age of diagnosis in fifth decade:
    • CHF 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) persons, not just athletes
    • Most common cause of sudden death in athletes
  • Supraventricular arrhythmia incidence increases with age:
    • Atrial fibrillation both common and poorly tolerated
    • Stroke is a high-risk complication
  • Prevalence at least 1 in 500 adults:
    • Based on echocardiographic population studies
    • Much smaller number present for care, suggesting many undiagnosed with possible minimal to no adverse effect from phenotypic variety
  • 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 ‎ outflow obstruction
    • Atrial dilatation secondary to diastolic filling stiffness ‎ increased risk for atrial fibrillation
    • Impaired microvascular dilation associated with intimal thickening and perivascular collagen deposition ‎ increased risk for angina
  • 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
  • First cardiac disorder for which genetic basis identified (1989)
  • Autosomal-dominant inheritance:
    • >10 associated genes found:
      • Encode proteins of cardiac sarcomere
      • >1,500 distinct mutations recognized
    • High penetrance
  • Highly variable phenotypic expression
  • Some genotypes significantly more lethal:
    • Routine screening impractical at present:
      • Mutations do not predict individual clinical course
    • Screening routine for patient family members
      • Mutation negative – no need for further evaluation or follow-up
      • Mutation positive w/no LV hypertrophy – very likely to develop phenotypic manifestation in adulthood – close follow-up recommended, possible intervention
  • 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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Basics

Description

  • Genetic disorder affecting the sarcomere
  • Clinical diagnostic criteria: Hypertrophied (regionally or globally), nondilated left in the absence of another cause of degree of hypertrophy observed, such as hypertension or aortic stenosis
  • Hypertrophic cardiomyopathy (HCM) unifies over 75 different names historically used
  • 2 general types:
    • Obstructive – ≥30 mm Hg left ventricular outflow tract gradient:
      • 67% of patients
      • More severe – estimated 2% annual mortality
    • Nonobstructive – <30 mm Hg gradient:
      • 33% of patients
      • Estimated around 1% annual mortality
  • Global disease – >50 countries, all race/ethnic groups
  • 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
  • Average age of diagnosis in fifth decade:
    • CHF 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) persons, not just athletes
    • Most common cause of sudden death in athletes
  • Supraventricular arrhythmia incidence increases with age:
    • Atrial fibrillation both common and poorly tolerated
    • Stroke is a high-risk complication
  • Prevalence at least 1 in 500 adults:
    • Based on echocardiographic population studies
    • Much smaller number present for care, suggesting many undiagnosed with possible minimal to no adverse effect from phenotypic variety
  • 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 ‎ outflow obstruction
    • Atrial dilatation secondary to diastolic filling stiffness ‎ increased risk for atrial fibrillation
    • Impaired microvascular dilation associated with intimal thickening and perivascular collagen deposition ‎ increased risk for angina
  • 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
  • First cardiac disorder for which genetic basis identified (1989)
  • Autosomal-dominant inheritance:
    • >10 associated genes found:
      • Encode proteins of cardiac sarcomere
      • >1,500 distinct mutations recognized
    • High penetrance
  • Highly variable phenotypic expression
  • Some genotypes significantly more lethal:
    • Routine screening impractical at present:
      • Mutations do not predict individual clinical course
    • Screening routine for patient family members
      • Mutation negative – no need for further evaluation or follow-up
      • Mutation positive w/no LV hypertrophy – very likely to develop phenotypic manifestation in adulthood – close follow-up recommended, possible intervention
  • 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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