Description

• Cardiomyopathies are myocardial diseases which result in structural and functional heart abnormalities in the absence of coronary artery disease, congenital heart disease, valvular disease, or hypertension which could sufficiently explain the clinical myocardial dysfunction.
• Results in 5–10% of cases of heart failure
• Classification of cardiomyopathies
  • Primary (mainly involves the heart)
    • Genetic
      • Hypertrophic cardiomyopathy (HCM)
      • Arrhythmogenic right ventricular cardiomyopathy/dysplasia (ARVC/D)
      • Left ventricular (LV) noncompaction (LVNC)
      • Glycogen storage (Danon type, PRKAG2)
      • Conduction defects
      • Mitochondrial myopathies
      • Ion channel disorders: long QT syndrome (LQTS), Brugada syndrome, short QT syndrome, and catecholaminergic polymorphic ventricular tachycardia (CPVT)
    • Mixed (genetic and nongenetic)
      • Dilated cardiomyopathy (DCM)
      • Restrictive (nonhypertrophied and nondilated)
    • Acquired
      • Myocarditis, stress cardiomyopathy, peripartum, tachycardia induced, infants of type 1 diabetic mothers
  • Secondary (multiorgan involvement; see list)
    • Specific: ischemic, valvular, hypertensive, and congenital heart disease

Epidemiology

Incidence
DCM: 5 to 8 new cases per 100,000 population annually

Prevalence

• DCM: roughly 1:2,500; most common reason for heart transplantation
• HCM: 1:500 of the adult population; 50% sporadic and rest are familial

Etiology and Pathophysiology

• HCM: hypertrophied (>15 mm), nondilated left and/or right ventricle which is disproportionate to hemodynamic stress on the heart
• ARVC/D: involves the right ventricle with progressive loss of myocytes and fatty/fibrofatty tissue replacement; can be associated with myocarditis (adenovirus or enterovirus)
• LVNC: congenital cardiomyopathies with “spongy” appearance of the LV myocardium
• LQTS: most common ion channelopathy with prolonged ventricular repolarization and QTc
• DCM: Ventricular chamber enlargement and systolic dysfunction with normal LV wall thickness result in progressive heart failure and further complications; strong genetic component with infectious and toxic etiologies
• RCM: normal/decreased ventricular volume with restrictive physiology, biatrial enlargement, and impaired ventricular filling
• Myocarditis: acute or chronic inflammation of the myocardium produced by toxins, drugs, or infectious causes
• Peripartum cardiomyopathy (PPCM): a form of DCM with LV systolic dysfunction and heart failure of unknown etiology
• Stress cardiomyopathies: triggered by profound psychological stress resulting in acute but rapidly reversible LV systolic dysfunction
• Endocrine: diabetes mellitus, hyperthyroidism, hypothyroidism, hyperparathyroidism, pheochromocytoma, acromegaly
• Nutritional deficiencies: beriberi, pellagra, scurvy, selenium, carnitine, kwashiorkor
• Autoimmune/collagen: systemic lupus erythematosus, dermatomyositis, rheumatoid arthritis, scleroderma, polyarteritis nodosa
• Infectious causes
  • Viral (e.g., HIV, coxsackievirus, adenovirus)
  • Bacterial and mycobacterial (e.g., diphtheria, rheumatic fever)
  • Parasitic (e.g., toxoplasmosis, Trypanosoma cruzi)
• Infiltrative (1): amyloidosis, Gaucher disease, Hurler disease, Hunter disease, Fabry disease
• Storage: hemochromatosis, glycogen storage disease (type II, Pompe), Niemann-Pick disease
• Neuromuscular/neurologic: Duchenne and Emery-Dreifuss muscular dystrophies, Friedreich ataxia, myotonic dystrophy, neurofibromatosis, tuberous sclerosis
• Toxic: alcohol, drugs and chemotherapy (anthracyclines, cyclophosphamide, trastuzumab [Herceptin]), radiation, heavy metal, chemical agents
• Inflammatory (granulomatous): sarcoidosis
• Idiopathic
• Endomyocardial: endomyocardial fibrosis, hypereosinophilic syndrome (Loeffler endocarditis)

Genetics

• Genetic causes well recognized in HCM; less common in DCM
• Most familial cardiomyopathies are inherited in autosomal dominant pattern.
• Involves mutations in sarcomere contractile proteins.

Risk Factors

Same as etiology