(USMLE topics, cardiology) Cardiomyopathy: types of, causes, risk factors, genetics, treatment.

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Cardiomyopathy is a group of diseases that weaken the heart muscle - the myocardium, making it harder for the heart to pump blood. Cardiomyopathy reduces blood output, and may lead to heart failure. The condition may be inherited from a parent, or develop as a consequence of another disease or factor. Some patients do not experience any symptoms. When present, symptoms may include: shortness of breath, fatigue, rapid heartbeats, chest pain, swelling of lower limbs, dizziness and fainting. Progression of the disease varies greatly from person to person. In some people, symptoms may appear suddenly, and worsen quickly; while others see a gradual development over a long period of time.

There are 3 MAJOR types of cardiomyopathy:
- Hypertrophic cardiomyopathy, or HCM, is the thickening of the heart muscle. Most commonly, this occurs in the inter-ventricular septum facing the left ventricle. The thickened septum obstructs blood flow to the aorta, a condition called “outflow tract obstruction” or “obstructive hypertrophic cardiomyopathy”. Thickening elsewhere in the heart muscle causes non-obstructive HCM. In both cases, cardiac output is reduced. While HCM can develop as a result of high blood pressure or aging, it is most commonly inherited as an autosomal dominant trait: children of an affected parent have a 50% chance of inheriting the disease. Multiple mutations have been identified in genes encoding for proteins of the heart muscle. Genetic screening is recommended as the disease may progress rapidly, from asymptomatic to heart failure and cardiac arrest. In fact, HCM is the major cause of sudden cardiac death among young athletes. People who test positive for HCM are advised to avoid high-intensity activities.
- Dilated cardiomyopathy, DCM, is the thinning of the myocardium and enlargement of a heart chamber, most commonly the left ventricle. DCM is usually acquired and the cause is unknown in most cases. Risk factors include high blood pressure; damage to the myocardium caused by previous heart attacks, alcohol or cocaine use, toxins or infections; and obesity or diabetes. While DCM may develop in anyone at any age, it is more common in men of middle age. Some DCM cases are inherited.
- Restrictive cardiomyopathy, RCM, is when the heart muscle becomes rigid, lacking the elasticity required to properly fill and pump blood. RCM usually results from building-up of scar tissues or abnormal proteins, caused by a variety of conditions. RCM is more likely in older people.
Less common types of cardiomyopathy include: arrhythmogenic right ventricular dysplasia, a condition in which the right ventricle tissue is scarred, causing arrhythmias; and stress cardiomyopathy, or broken heart syndrome: a sudden temporary weakening of the heart muscle triggered by excessive emotional or physical stress.
Treatment varies depending on the type of cardiomyopathy, the underlying cause and severity of symptoms, and can range from life style changes, to medications and surgeries.

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