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 (1).
• Current classification scheme attempt to differentiate between myocardial diseases confined to the myocardium (primary) and those due to systemic disorders (secondary). Specific causes of myocardial dysfunction due to other cardiovascular disorders are considered a third, separate category (1).
• Classification of cardiomyopathies
  • Primary (mainly involves the myocardium)
    • 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 below)
    • Specific: ischemic, valvular, hypertensive, and congenital heart disease
• Patients with end-stage cardiomyopathy have stage D heart failure or severe symptoms at rest refractory to standard medical therapy.
• Systems affected: cardiovascular, renal, hepatic, and pulmonary

Pediatric Considerations
Progressive course and early diagnosis may alter disease course. Causes: DCM, HCM, RCM, LVNC in childhood, endocrine, uremic, nutritional

Pregnancy Considerations
Peripartum cardiomyopathy (PPCM) may occur in peripartum women well before and up to months after delivery.

Epidemiology

Predominant age: Ischemic cardiomyopathy is the most common etiology; predominantly in patients aged >50 years. Consider uncommon causes in young. In the young, HCM is the most common cause of sudden cardiac death and important underlying cause of heart failure disability.

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

Prevalence

• DCM: roughly 1:2,500; third most common cause of heart failure and most common reason for heart transplantation
• HCM: at least 1:500 of the adult population
• RCM: more commonly seen in the tropics

Etiology and Pathophysiology

• HCM: hypertrophied, nondilated left ventricle without other systemic or cardiac disease which could produce wall thickening
• 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
• 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 (2): 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
Autosomal dominant HCM is the most common form of primary genetic cardiomyopathy, which is commonly caused by many mutations that encode contractile proteins of the cardiac sarcomere. Genetic causes of DCM are less common, accounting for 1/3 cases, with mostly autosomal dominant inheritance. LVNC and ARVC are also inherited in an autosomal dominant fashion in addition to LQTS and other ion-channel disorders.

Risk Factors

• Hypertension
• Hyperlipidemia
• Obesity
• Coronary artery disease
• Diabetes mellitus
• Smoking
• Physical inactivity
• Excessive alcohol intake
• Dietary sodium
• Obstructive sleep apnea
• Chemotherapy

General Prevention

Reduce salt and water intake, and perform home blood pressure (BP) and daily weight measurements.