UNDERSTANDING CARDIOMYOPATHY, OR "WEAK HEART MUSCLE"
Peter J. Sharis, MD
What is cardiomyopathy ("weak heart muscle"), and how is it classified?
The cardiomyopathies are a group of diseases in which the primary feature is direct involvement and weakening of the heart muscle (myocardium only). Cardiomyopathies are increasing in incidence and are a significant cause of death. Dilated cardiomyopathy, the most common type of cardiomyopathy, is reported to occur in 5 to 8 people per 100,000 population per year.
Cardiomyopathies occur more frequently in blacks than whites and more commonly in men than women. Factors that are associated with increased death rates in cardiomyopathy patients include the following:
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Weak heart function (left ventricular ejection fraction < 35%)
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Aging (age greater than 55 years)
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Reduced functional capacity
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Electrical abnormalities
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Low blood sodium level (hyponatremia)
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Worsening kidney function.
Cardiomyopathy can be classified as primary, which is heart muscle disease of unknown cause, or secondary, which is heart muscle disease due to specific causes (such as narrowing of the heart arteries [coronary artery disease], heart valve disease, high blood pressure).
The World Health Organization (WHO) classifies cardiomyopathy into 3 major groups:
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Dilated
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Hypertrophic
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Restrictive.
What are the features and causes of dilated cardiomyopathy (DCM)?
Dilated cardiomyopathy (DCM) is typically characterized by significant enlargement of the 2 pumping chambers of the heart—the left ventricle (which pumps blood to the body) and the right ventricle (which pumps blood to the lungs). As a result of the chamber enlargement, there is some degree of reduction in the pumping power of the ventricle (reduced ejection fraction).
While there are many causes of DCM (nearly 80 specific diseases have been associated with DCM), a clear cause is often not identified in many individuals, and these cases are described as idiopathic. Alcohol abuse is a common cause of DCM, as long-term ingestion leads to cardiac cell (myocyte) damage with subsequent heart dysfunction. Many patients can see significant improvement if they stop drinking. Cocaine abuse can lead to DCM in some individuals; in 1 large study, more than 10% of cocaine users had at least mild left ventricular dysfunction.
Infectious causes can also lead to DCM. Viral infections can attack the heart muscle and lead to significant cardiac dysfunction; in many cases, the damage can be irreversible and severe. In young adults, severe viral-related DCM is the top reason to be "listed" for heart transplantation. Human immunodeficiency virus (HIV), the cause of AIDS, can also lead to DCM in a minority of causes. Vitamin deficiencies (such as thiamine) can lead to DCM, though such cases occur more commonly in Third World countries.
