Cardiomyopathy is a general term used to describe a diverse group of diseases of the heart muscle. For most people with cardiomyopathy, their hearts don't function normally because the heart has become either enlarged, abnormally thick, abnormally rigid, or unable to transmit electrical impulses in a normal fashion. These changes in the heart muscle correspond to the four principal types of cardiomyopathy—dilated cardiomyopathy, hypertrophic cardiomyopathy, restrictive cardiomyopathy, and arrhythmogenic right ventricular cardiomyopathy. Included in each of these categories are several dozen types of cardiomyopathy that are distinguished from one another based upon their individual cause.
Coronary artery disease, inflammatory diseases, viral or bacterial infections, chronic alcoholism, and metabolic and blood disorders are some of the more common conditions that can lead to cardiomyopathy. Genetic mutations, including some that run in families, can also cause cardiomyopathy. However, many forms of cardiomyopathy have no apparent cause; these are said to be idiopathic. Although it can affect people of all ages, sometimes even at birth, certain types of cardiomyopathy are more likely to occur in specific age groups, in men more than women, or in people of certain ethnic groups.
Many people can live long, healthy lives not even realizing that they have cardiomyopathy because they have no symptoms. For others, cardiomyopathy leads to serious complications including heart failure, abnormal heart rhythms, or sudden death. Cardiomyopathy is a leading cause for heart transplants and the most common identifiable cause of sudden death in young athletes. If the symptoms of heart failure develop, the outlook for people with cardiomyopathy can be discouraging—only one out of every three patients survives more than five years following the onset of heart failure.However, the symptoms and complications of many forms of cardiomyopathy can be effectively controlled using medication, surgery, and/or simple lifestyle changes.
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The structure of the heart is analogous to a two-story house with four rooms or chambers. On the main floor are the two largest rooms, the left and right ventricles. The ventricles are the main pumping chambers of the heart. In a healthy heart, the left ventricle is the stronger pumping chamber. The wall between these two rooms is called the ventricular septum. Upstairs, there are two smaller rooms, the left and right atria. The atria function primarily as receiving chambers for blood, but they also help out slightly with pumping. The wall between the two atria is called the atrial septum.
The valves of the heart function like one-way doors that help control the direction of blood flow; this keeps the heart working efficiently. The four valves in the heart are the tricuspid, mitral, pulmonary, and aortic valves. Proper functioning of the mitral valve, which connects the left atrium to the left ventricle, can be important for people suffering from heart failure associated with dilated cardiomyopathy. The mitral valve keeps the blood flowing into the left ventricle, where it is pumped out of the heart and circulated throughout the body.
The pulmonary and the aortic arteries are the main pathways for blood in and around the heart. The pulmonary artery shunts blood from the right ventricle to the lungs. The pulmonary veins channel blood from the lungs back to the heart into the left ventricle. The aorta channels blood from the heart to the body. The coronary arteries, which branch off the aorta, distribute blood to the heart itself.
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In general, the right side of the heart is responsible for pumping blood to the lungs. In a healthy heart, oxygen-depleted blood enters the heart at the right atrium, where it is pumped down into the right ventricle. When the right ventricle fills, the heart contracts strongly and pumps the blood through the pulmonary valve into the pulmonary artery, which carries the blood to the lungs. The pulmonary valve keeps the blood moving toward the lungs, preventing it from mixing with oxygen-rich blood.
In the lungs, the carbon dioxide in the blood is exchanged for oxygen. The oxygenated blood leaves the lungs and returns to the heart via the pulmonary veins, re-entering the heart at the left atrium. Exiting the left atrium through the mitral valve, the blood flows into the left ventricle. When the left ventricle fills with blood, the heart contracts strongly, pumping blood out through the aortic valve into the aorta to circulate oxygen to the rest of the body.
The primary pumping action of the heart is like a spring that contracts and relaxes. When the heart is relaxed, the ventricles simultaneously fill with blood. When the heart contracts, the ventricles eject a portion of the blood they contain to either the lungs (via the pulmonary artery from the right ventricle) or the rest of the body (via the aorta from the left ventricle). That exact portion of blood pumped out of the ventricles is called the ejection fraction. In a healthy heart, the ejection fraction is greater than 55-60 percent. If the ejection fraction falls below 55 percent, the heart is no longer able to circulate an adequate amount of blood to the body at a normal heart rate. A decrease in the volume of blood circulating throughout the body can cause a cascade of changes in the body's metabolism.
Like a spring, if a ventricle is continually overextended or stiff, it no longer functions properly. An overextended ventricle can lose the ability to contract, reducing the ejection fraction. The inverse problem can also occur where the ventricle is abnormally stiff. In this scenario, the ventricle no longer relaxes enough to fill adequately with blood. As a result, the volume of blood ejected from the heart is abnormally low because less blood has entered the heart.
Types of cardiomyopathy fall into four principal categories based upon the muscle problem involved. These include, in order of prevalence:
- Dilated cardiomyopathy—an abnormally enlarged heart muscle
- Hypertrophic cardiomyopathy—an abnormally thick heart muscle
- Restrictive cardiomyopathy—an abnormally stiff heart muscle
- Arrhythmogenic right ventricular dysplasia (ARVD)—abnormal transmission of electrical impulses by the heart muscle
Within these categories, cardiomyopathies are further distinguished based upon the cause, if known. For example, dilated cardiomyopathy caused by alcoholism is called alcoholic cardiomyopathy. Frequently, the cause is unknown. In these cases the condition is referred to as idiopathic cardiomyopathy.
Dilated cardiomyopathy, a common form of cardiomyopathy, is characterized by an overall enlargement or stretching of the heart muscle accompanied by a decrease in the heart's ability to contract. Dilated cardiomyopathy usually begins with stretching of the left ventricle; in some cases, the right ventricle may become affected as well. Dilated cardiomyopathy can lead to heart failure, a decrease in the heart's ability to contract and pump blood out into the arteries of the body. Other complications include disturbances in the heart's electrical system known as arrhythmias, blood clots forming within the heart, and sudden death, any of which can occur at any stage of the disease.
Although it can occur in infants and the elderly, dilated cardiomyopathy occurs most frequently between the ages of 20 and 60. It is three times more common in men than women and more common in African-Americans than Caucasians.
The progression of dilated cardiomyopathy can be rapid; some studies have found that 50 percent of deaths due to dilated cardiomyopathy occur within two years of diagnosis, although the risk of dying within one year for all patients with heart failure symptoms is about 12 percent. In general, the worse the symptoms, the worse the outlook. For example, a patient with mild breathlessness during significant exertion may have a 5 percent chance of dying within a year, while a person who has these symptoms while sitting in a chair may have a 30-50 percent risk of dying within a year.
When cardiomyopathy is caused by coronary artery disease (CAD) it is known as ischemic cardiomyopathy, the most common type of cardiomyopathy. People with ischemic cardiomyopathy often develop the same signs and symptoms as those with other forms of dilated cardiomyopathy. However, with ischemic cardiomyopathy, the symptoms are caused by narrowed or blocked coronary blood vessels restricting blood flow and oxygen to the heart tissue, which damages the heart muscle. Even though the signs and symptoms are the same, ischemic cardiomyopathy has traditionally been considered separate from dilated cardiomyopathy because coronary artery disease typically causes localized damage to the heart as opposed to the generalized damage of all heart cells associated with dilated cardiomyopathy. More importantly, the damage to heart muscle associated with ischemic cardiomyopathy can be reversed in some patients by opening the blockages caused by CAD. For this reason, almost all patients with a new diagnosis of dilated cardiomyopathy undergo a cornary angiogram to evaluate the condition of their coronary arteries.
Dilated cardiomyopathies can be caused by many other conditions or the cause may never be identified. In the United States, dilated cardiomyopathies other than ischemic cardiomyopathy account for 50,000 hospitalizations and over 10,000 deaths annually—and these statistics are on the rise. Other common types of dilated cardiomyopathy include:
Inflammatory cardiomyopathy can develop as the result of viral, bacterial, or autoimmune infection as well as myocardial inflammatory disease. Some of the infectious and inflammatory conditions that have been linked to inflammatory dilated cardiomyopathy are lymphocytic and giant cell myocarditis, Lyme disease, HIV, mumps, influenza, Epstein-Barr, and hepatitis B and C.
Familial (genetic) cardiomyopathy accounts for roughly 20 percent of all cases of dilated cardiomyopathy where no other cause can be identified. The details of the genetic link are not well understood but it's clear there is a genetic prediposition to developing dilated cardiomyopathy in some families. As such, evaluation of all first-degree relatives to rule out a "silent" familial cardiomyopathy is recommended for people whose dilated cardiomyopathy can not be attributed to a specific cause.
Alcoholic cardiomyopathyusually begins to develop after about 10 years of heavy alcohol consumption.
Toxic cardiomyopathy may develop after exposure to certain toxins including cocaine, methamphetamines and some chemotherapy drugs.
Peripartum cardiomyopathy can develop in women during the last trimester of pregnancy or within five months after childbirth. Women often recover completely from peripartum cardiomyopathy, but it may recur with future pregnancies.
Valvular cardiomyopathy can develop when the workload on the heart in increased due to a malfunctioning heart valve.
Tachycardia-induced cardiomyopathy, caused by chronic rapid heart rate, is important to identify because the symptoms of heart failure can be reversed in these people by treating the arrhythmia.
Hypertrophic cardiomyopathy, a genetic disease affecting 1 in 500 people, is characterized by an overdeveloped heart muscle with fibers that have become disorganized. The severity of the disease varies widely, with most people experiencing few or no limitations on quality or length of their life; however, for a small minority of people, HCM is lethal. HCM is the most common identifiable cause of sudden death in young people, particularly athletes.
Restrictive cardiomyopathy occurs when the heart muscle becomes stiff and loses its ability to relax between contractions, impairing the heart's ability to fill with blood. It frequently causes heart block, the inability of the heart to successfully transmit the electrical signals needed to generate a heart beat. Although heart block can be treated by surgically implanting a cardiac pacemaker, treatment of restrictive cardiomyopathy is largely ineffective. Surgery usually is not considered; but a heart transplant may be an option for some people with restrictive cardiomyopathy.
Usually occurring around age 50, restrictive cardiomyopathy affects men and women equally. Typically it is not inherited, but some of the diseases that can cause restrictive cardiomyopathy can be inherited.
In the United States and other industrial nations in temperate climates, restrictive cardiomyopathy is relatively rare, associated with unusual blood or metabolic disorders or radiation therapy to the chest. In tropical regions of Africa, India, South and Central America, and parts of Asia, restrictive cardiomyopathy is a common cause of death associated with the high rates of fibrosis of the tissues of the heart in people living those regions.
Accurate diagnosis of restrictive cardiomyopathy can be difficult because the signs and symptoms are very similar to another heart disease, constrictive pericarditis. Unlike restrictive cardiomyopathy, constrictive pericarditis can be effectively treated with surgery. The distinction between the two conditions can be detected with careful imaging of the heart using echocardiography, magnetic resonance imaging, and/or CT scan, but in some cases cardiac catheterization may be necessary.
Arrhythmogenic right ventricular dysplasia (ARVD), also known as right ventricular cardiomyopathy, is a rare type of cardiomyopathy diagnosed primarily in teenagers and young adults. For people with ARVD, the muscle tissue of the right ventricle has been replaced by fatty and/or fibrous scar tissue that inhibits the transmission of electrical signals within the heart. As the disease progresses, the right ventricle may dilate, compromising the pumping efficiency of the heart. ARVD is associated with arrhythmias that can cause strong or irregular heartbeats and fainting after exercise, or even sudden death in some people.
A difficult disease to diagnosis, ARVD is estimated to occur in 1 in 5,000 people. In many patients the disease is familial. The exact cause of ARVD is not well understood.
The change in the heart muscle associated with the principal types of cardiomyopathy is the result of the interplay of a variety of factors. Genetic mutations in the cells of the heart muscle, other diseases, environmental and lifestyle factors, and the body's own survival mechanism can contribute to the development of cardiomyopathy.
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- Causes of Dilated Cardiomyopathy
- Causes of Restrictive Cardiomyopathy
- Causes of Hypertrophic Cardiomyopathy
Dilated cardiomyopathy can be thought of as a compensatory reaction of the heart to a weakened heart muscle. The cause of the weakening may be unknown or it may be associated with many different risk factors including viral infections, exposure to toxins and drugs, or coronary artery disease, as in ischemic cardiomyopathy.
In people with dilated cardiomyopathy, the heart enlarges to compensate for the inability of a weakened muscle to eject the amount of blood needed by the body. Stretching helps compensate for the weakened muscle in two ways. First, the overall volume of the heart is increased, thereby increasing the volume of blood ejected into the circulatory system. This action is analogous to a person squeezing a flexible plastic bottle. A strong person might be able to squirt out 50 percent of the contents of the bottle with each squeeze. If the person's grip is weakened and he is only able to eject 25 percent of the contents, only half as much liquid will exit the bottle. However, if the person had a bottle that holds twice as much, 25 percent of that bottle would be twice as much volume. In dilated cardiomyopathy, the heart is acting like the plastic squeeze bottle, dilating its chambers to try to maintain the amount of blood pumped to the tissues of the body by a heart whose ejection fraction is diminishing.
Stretching the heart muscle can also increase the strength of the contraction. Starling's Law, a basic principle involving the function of the heart, describes this phenomenon: the more the heart muscle stretches, the greater the force of its squeeze. The heart functions much like a spring whose coils are overstretched and then released to snap back into shape. If this action continues repeatedly, the heart will eventually lose the ability to regain its original shape, like an overstretched spring.
The heart can also compensate by beating faster. Although beating faster can improve circulation temporarily—normal hearts do this during exercise—a chronic increase in heart rate (tachycardia) can lead to dilated cardiomyopathy or serious arrhythmias.
The kidneys may also try to compensate for the decreased circulation by increasing the volume of blood and fluid in the circulatory system. Ironically, this compensatory mechanism exacerbates the situation by causing swelling in the legs and abdomen, and fluid accumulation in the lungs.
All of these compensatory mechanisms—dilating, stretching, beating faster, retaining fluid—evolved to keep the blood pumping to the body on a short-term basis following an injury or dehydration. In the long term, though, the heart responds like a spring that's been overextended; eventually, it can no longer return to its shape and function effectively. Then the dilated heart becomes more of a dam than a pump, with blood pooling inside an enlarged heart that is no longer capable of circulating blood. The most effective treatments for dilated cardiomyopathy focus on blocking these compensatory responses.
For people with restrictive cardiomyopathy, the ventricles become stiff and rigid due to the accumulation of abnormal material within the tissue of the heart muscle. Foreign material in the tissues keeps the heart muscle from relaxing normally, which inhibits the ventricles from adequately filling with blood. This in turn can cause the atria to enlarge. Eventually, blood flow in the heart is reduced, and complications such as heart failure or arrhythmias can develop.
Restrictive cardiomyopathy can be idiopathic—occurring for no known reason—or it can develop as the result of radiation treatment to the chest, infection, scarring of the heart muscle after surgery, or other diseases. Connective tissue disorders such as progressive systemic sclerosis (scleroderma) and pseudoxanthoma elasticum may cause restrictive cardiomyopathy. Other diseases that deposit abnormal material in the tissues of the heart, including amyloidosis and hemochromatosis, can also lead to restrictive cardiomyopathy. Unfortunately, these underlying causes of restrictive cardiomyopathy are often not treatable. Restrictive cardiomyopathy can also lead to dilated cardiomyopathy.
People who have defects in the genes controlling heart muscle growth are predisposed to developing HCM. These genetic defects or mutations cause the heart muscle to develop abnormally, causing thickening that can interfere with its pumping efficiency.
Medical research continues to reveal how different risk factors interact to influence a person's health and lifespan. Understanding your risks allows you to develop a strategy and make lifestyle choices accordingly. Your decisions then balance the value you place on your health with the risks that may compromise your health in the future. An increased risk does not mean the disease is inevitable; risk refers to the possibility that a disease could occur in the future.
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The risk factors for dilated cardiomyopathy include both lifestyle choices as well as genetic traits. Many of the risk factors are actually other diseases. Uncommon bacterial or viral infections, rare blood disorders, and other inflammatory diseases can lead to dilated cardiomyopathy in some people.
The more common risk factors for dilated cardiomyopathy include:
- Coronary artery disease (ischemic cardiomyopathy)
- Exposure to toxic agents such as cocaine, methamphetamines, cobalt, and certain cancer-treating drugs including doxorubicin and daunorubicin
- Family members with dilated cardiomyopathy of unknown cause
- Heart valve defects
- Myocarditis, or inflammation of the walls of the heart
- Sleep apnea
- Sustained, untreated high blood pressure
- Sustained heavy alcohol consumption
Risk factors for hypertrophic cardiomyopathy:
- Although hypertrophic cardiomyopathy is considered primarily a genetic disease, environmental factors can increase your risk of developing this condition. If you have a genetic mutation for hypertrophic cardiomyopathy, you are predisposed to developing this disease. If you have a blood relative with the disease, you may have one of the genetic mutations that increase your risk of developing the disease. For more about the risk factors for hypertrophic cardiomyopathy, see Hypertrophic Cardiomyopathy.
Risk factors for restrictive cardiomyopathy generally fall into three categories, which include:
- Familial. In most cases restrictive cardiomyopathy itself is not inherited but the diseases that can lead to restrictive cardiomyopathy can be.
- Cancer treatment. Radiation to the chest and some chemotherapy drugs, such as anthracycline, increase the risk of developing restrictive cardiomyopathy.
- Other disease. Dozens of diseases and conditions have been linked to restrictive cardiomyopathy. In the United States the most common of these are amyloidosis and hemochromatosis, in which protein (amyloid) or iron, respectively, are deposited in the cells of the heart muscle. Other less common diseases that can lead to restrictive cardiomyopathy include connective tissue disorders such as scleroderma and pseudoxanthoma elasticum; neoplastic diseases, in which abnormal tissue growths develop; metabolic disorders, including acromegaly and hypothyroidism; and endomyocardial fibrosis, the growth of abnormal fibers within the tissue of the heart.
Last reviewed on 12/31/2008
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