Cardiomyopathy classification

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Lina Ya'qoub, MD

Overview

Cardiomyopathies refer to disorders of the heart muscle leading to its abnormal function and/or structure. It can generally be categorized into two groups (based on World Health Organization guidelines): extrinsic cardiomyopathies and intrinsic cardiomyopathies . Cardiomyopathy can be classified from a clinical standpoint, as to whether it is restrictive, dilated, or hypertrophic, and also by whether it is a primary cardiomyopathy or a secondary cardiomyopathy, as a result of another underlying process.

In 2013, the MOGE(S) classification for a phenotype-genotype nomenclature of cardiomyopathies was proposed by the World Heart Federation[6]. This classification suggests a nosology that addresses five characteristics of cardiomyopathic disorders: morphofunctional state (M), organ involvement (O), genetic inheritance (G), etiologic annotation (E) and functional state (S) according to ACC/AHA A-D stage and New York Heart Association (NYHA) I-IV functional class.

Classification

Cardiomyopathies are myocardial diseases that are independent of:

• Congenital Heart Disease
• Pericardial Disease
• Pulmonary hypertension / systemic hypertension
• Valvular heart disease
• Ischemic cardiac disease

Extrinsic Cardiomyopathies

These are cardiomyopathies where the primary pathology is outside the myocardium itself. Most cardiomyopathies are extrinsic, because by far the most common cause of a cardiomyopathy is ischemia. The World Health Organization calls these specific cardiomyopathies:

• Alcoholic cardiomyopathy
• Coronary Artery Disease
• Congenital Heart Disease
• Hypophosphatemia mediated myonecrosis as part of the refeeding syndrome
• Inflammatory cardiomyopathy
• Ischemic cardiomyopathy
• Hypertensive cardiomyopathy
• Nutritional diseases
• Systemic metabolic disease
• Valvular cardiomyopathy

Ischemic Cardiomyopathy

Ischemic cardiomyopathy is a weakness in the muscle of the heart due to inadequate oxygen delivery to the myocardium with coronary artery disease being the most common cause. Anemia and sleep apnea are other relatively common conditions that can contribute to ischemic myocardium and hyperthyroidism can cause a 'relative' ischemia secondary to high output heart failure. Individuals with ischemic cardiomyopathy typically have a history of myocardial infarction (heart attack), although longstanding ischemia can cause enough damage to the myocardium to precipitate a clinically significant cardiomyopathy even in the absence of myocardial infarction. In a typical presentation, the area of the heart affected by a myocardial infarction will initially become necrotic as it dies, and will then be replaced by scar tissue (fibrosis). This fibrotic tissue is akinetic; it is no longer muscle and cannot contribute to the heart's function as a pump. If the akinetic region of the heart is substantial enough, the affected side of the heart (i.e. the left or right side) will go into failure, and this failure is the functional result of an ischemic cardiomyopathy.

Cardiomyopathy Due to Systemic Diseases

Many diseases can result in cardiomyopathy. These include diseases like hemochromatosis, (an abnormal accumulation of iron in the liver and other organs), amyloidosis (an abnormal accumulation of the amyloid protein), diabetes, hyperthyroidism, lysosomal storage diseases and the muscular dystrophies.

Intrinsic Cardiomyopathies

An intrinsic cardiomyopathy is weakness in the muscle of the heart that is not due to an identifiable external cause. To make a diagnosis of an intrinsic cardiomyopathy, significant coronary artery disease should be ruled out (amongst other causes of extrinsic cardiomyopathy). The term intrinsic cardiomyopathy does not describe the specific etiology of weakened heart muscle. The intrinsic cardiomyopathies are a mixed-bag of disease states, each with their own causes.

Intrinsic cardiomyopathy has a number of causes including drug and alcohol toxicity, certain infections (including Hepatitis C), and various genetic and idiopathic (i.e., unknown) causes.

Intrinsic cardiomyopathies are generally classified into four types, but additional types are also recognized:

• Dilated cardiomyopathy (DCM), the most common form, and one of the leading indications for heart transplantation. In DCM the heart (especially the left ventricle) is enlarged and the pumping function is diminished. Approximately 40% of cases are familial, but the genetics are poorly understood compared with HCM. In some cases it manifests as peripartum cardiomyopathy, and in other cases it may be associated with alcoholism.
• Hypertrophic cardiomyopathy (HCM or HOCM), a genetic disorder caused by various mutations in genes encoding sarcomeric proteins. In HCM the heart muscle is thickened, which can obstruct blood flow and prevent the heart from functioning properly.
• Arrhythmogenic right ventricular cardiomyopathy (ARVC) arises from an electrical disturbance of the heart in which heart muscle is replaced by fibrous scar tissue. The right ventricle is generally most affected.
• Restrictive cardiomyopathy (RCM) is an uncommon cardiomyopathy. The walls of the ventricles are stiff, but may not be thickened, and resist the normal filling of the heart with blood. A rare form of restrictive cardiomyopathy is the obliterative cardiomyopathy, seen in the hypereosinophilic syndrome. In this type of cardiomyopathy, the myocardium in the apices of the left and right ventricles becomes thickened and fibrotic, causing a decrease in the volumes of the ventricles and a type of restrictive cardiomyopathy.
• Noncompaction cardiomyopathy has been recognized as a separate type since the 1980s. The term refers to a cardiomyopathy where the left ventricle wall has failed to grow properly from birth and has a spongy appearance when viewed during an echocardiogram.

Alternate Detailed Classification Schemes

There are other more detailed classification schemes with a more complete differential diagnosis as shown below:

Clinical Classification

• DILATED (D):

  • Left and/or right ventricular enlargement
  • Impaired systolic function
  • Congestive heart failure
  • Arrhythmias
  • Emboli

• RESTRICTIVE (R):

  • Endomyocardial scarring or myocardial infiltration resulting in restriction to left and/or right ventricular filling. This entity is more common in the tropics.

• HYPERTROPHIC (H):

  • Disproportionate left ventricular hypertrophy

    • Typically involving septum more than free wall
    • With or without an intraventricular systolic pressure gradient

      • Usually of a nondilated left ventricular cavity: the left ventricular cavity is either normal or reduced.

Primary Myocardial Involvement

• Idiopathic (D,R,H)
• Hereditary (D,R,H)

  • Up to 20% of dilated cardiomyopathy
  • Dominant, recessive, and x-linked

• Eosinophilic endomyocardial disease (R)
• Endomyocardial fibrosis (R)

Secondary Myocardial Involvement

• Sensitivity and toxic reactions (dilated cardiomyopathy)

  • Alcohol
  • Cocaine
  • Radiation
  • Doxorubicin

• Metabolic (dilated cardiomyopathy)

  • Selenium deficiency
  • Hypophosphatemia
  • Hypocalcemia
  • Thyroid disease

• Infectious (Dilated cardiomyopathy)

  • Viral myocarditis
  • Bacterial myocarditis
  • Fungal myocarditis
  • Protozoal myocarditis
  • Metazoal myocarditis
  • Spirochetal myocarditis
  • Rickettsial myocarditis

• Familial Storage Disease (dilated cardiomyopathy, restrictive cardiomyopathy)

  • Glycogen storage disease
  • Mucopolysaccharidoses
  • Hemochromatosis
  • Fabry’s disease

• Connective Tissue Disorders (dilated cardiomyopathy)

  • Systemic lupus erythematosus
  • Polyarteritis nodosa
  • Rheumatoid arthritis
  • Progressive systemic sclerosis
  • Dermatomyositis

• Infiltrative and Granulomatous (restrictive cardiomyopathy, dilated cardiomyopathy)

  • Amyloidosis
  • Sarcoidosis
  • Malignancy

• Neuromuscular (dilated cardiomyopathy)

  • Muscular dystrophy
  • Myotonic dystrophy
  • Friedreich’s ataxia (hypertrophic cardiomyopathy, dilated cardiomyopathy)

• Other (dilated cardiomyopathy)

  • Beta thallasemia cardiomyopathy
  • Uncontrolled tachycardia (tachycardia induced cardiomyopathy)
  • Right ventricular dysplasia

• Peripartum heart disease (dilated cardiomyopathy): which occurs in the last month of pregnancy, up to 6 months after delivery.