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The Merck Manual of Medical Information--Home Edition
Section 3. Heart and Blood Vessel Disorders
Chapter 18


Cardiomyopathy is a progressive disorder that alters the structure or impairs the function of the muscular wall of the lower chambers of the heart (ventricles). (see illustration, page 69)

Cardiomyopathy can be caused by many known diseases, or it may have no identifiable cause.

Dilated Congestive Cardiomyopathy

Dilated congestive cardiomyopathy is a group of heart disorders in which the ventricles enlarge but aren't able to pump enough blood for the body's needs, resulting in heart failure.

In the United States, the most common identifiable cause of dilated congestive cardiomyopathy is widespread coronary artery disease. (see page 121 in Chapter 27, Coronary Artery Disease) Such coronary artery disease results in inadequate blood supply to the heart muscle, which can lead to permanent injury. The remaining uninjured heart muscle then stretches to compensate for the lost pumping action. When this stretching doesn't adequately compensate, dilated congestive cardiomyopathy develops.

An acute inflammation of the heart muscle (myocarditis) from a viral infection may weaken the heart muscle and produce dilated congestive cardiomyopathy (sometimes called viral cardiomyopathy). In the United States, infection with coxsackievirus B is the most common cause of viral cardiomyopathy. Certain chronic hormonal disorders such as diabetes and thyroid disease can eventually result in dilated congestive cardiomyopathy. Dilated congestive cardiomyopathy also can be caused by drugs such as alcohol, cocaine, and antidepressants. Alcoholic cardiomyopathy may develop after about 10 years of heavy alcohol abuse. Rarely, pregnancy or connective tissue diseases such as rheumatoid arthritis may cause dilated congestive cardiomyopathy.

Symptoms and Diagnosis

The usual first symptoms of dilated congestive cardiomyopathy--becoming short of breath on exertion and tiring easily--result from a weakening of the heart's pumping action (heart failure). (see page 87 in Chapter 17, Heart Failure) When cardiomyopathy results from an infection, the first symptoms may be a sudden fever and flulike symptoms. Whatever the cause, the heart rate speeds up, blood pressure is normal or low, fluid is retained in the legs and abdomen, and the lungs fill with fluid. The enlargement of the heart causes the heart valves to open and close improperly, and those leading to the ventricles (the mitral and tricuspid valves) often leak. Improper valve closure causes murmurs, which a doctor can hear with a stethoscope. Damage to and stretching of the heart muscle may make the heart rhythm abnormally fast or slow. These abnormalities interfere further with the heart's pumping action.

The diagnosis is based on the symptoms and a physical examination. Electrocardiography (a test that examines the electrical activity of the heart) may show characteristic changes. Echocardiography (a test that uses ultrasound waves to create an image of the heart structures) (see page 76 in Chapter 15, Diagnosis of Heart Disease) and magnetic resonance imaging (MRI) may be used to confirm the diagnosis. If the diagnosis remains in doubt, a catheter that measures pressures is inserted into the heart for more precise evaluation. During catheterization, a tissue sample can be removed for microscopic examination (biopsy) to confirm the diagnosis and often to detect the cause.

Prognosis and Treatment

About 70 percent of people with dilated congestive cardiomyopathy die within 5 years of when their symptoms begin, and the prognosis worsens as the heart walls become thinner and heart function decreases. Abnormal heart rhythms also indicate a worse prognosis. Overall, men survive only half as long as women, and blacks half as long as whites. About 50 percent of the deaths are sudden, probably resulting from an abnormal heart rhythm.

Treating specific underlying causes such as alcohol abuse or an infection can prolong life. If alcohol abuse is the cause, the person must abstain from alcohol. If a bacterial infection causes sudden inflammation of the heart muscle, it's treated with an antibiotic.

In a person with coronary artery disease, the poor blood supply may cause angina (chest pain caused by heart disease), (see page 121 in Chapter 27, Coronary Artery Disease) requiring treatment with a nitrate, beta-blocker, or calcium channel blocker. Beta-blockers and calcium channel blockers may reduce the force of heart contractions. Getting enough rest and sleep and avoiding stress help reduce strain on the heart.

Pooling of blood in the swollen heart may cause clots to form on the chamber walls. Anticoagulant drugs are usually given to prevent clotting. Most drugs used to prevent abnormal heart rhythms are prescribed in small doses, and the doses are adjusted in small increments because the drugs may reduce the force of heart contractions. Heart failure also is treated with drugs--an angiotensin converting enzyme inhibitor, often with a diuretic. However, unless a specific cause of the dilated congestive cardiomyopathy can be treated, the heart failure is likely to eventually be fatal. Because of this poor prognosis, dilated congestive cardiomyopathy is the most common reason for heart transplants.

Hypertrophic Cardiomyopathy

Hypertrophic cardiomyopathy is a group of heart disorders in which the walls of the ventricles thicken.

Hypertrophic cardiomyopathy may occur as a birth defect. It also may occur in adults with acromegaly, a condition resulting from excessive growth hormone in the blood, or in people who have pheochromocytoma, a tumor that produces adrenaline. People with neurofibromatosis, a hereditary condition, may also develop hypertrophic cardiomyopathy.

Usually, any thickening of the muscular walls of the heart represents the muscle's reaction to an increased workload. Typical causes include high blood pressure, narrowing of the aortic valve (aortic valve stenosis), and other conditions that increase resistance to blood flow from the heart. But people who have hypertrophic cardiomyopathy don't have these conditions. Instead, the thickening in hypertrophic cardiomyopathy usually results from an inherited genetic defect.

The heart becomes thicker and stiffer than normal and more resistant to filling with blood from the lungs. One result is back pressure in the lung veins, which can cause fluid to accumulate in the lungs, so the person is chronically short of breath. Also, as the ventricle walls thicken, they may block the flow of blood, preventing the heart from filling properly.

Symptoms and Diagnosis

Symptoms include faintness, chest pain, palpitations produced by irregular heartbeats, and heart failure with shortness of breath. Sudden death may result from irregular heartbeats.

A doctor can usually identify hypertrophic cardiomyopathy by physical examination. For instance, the heart sounds heard through a stethoscope are usually characteristic. The diagnosis usually is confirmed by an echocardiogram, electrocardiogram (ECG), or chest x-ray. Cardiac catheterization to measure pressures within the heart may be necessary if surgery is being considered.

Prognosis and Treatment

About 4 percent of people with hypertrophic cardiomyopathy die each year. Death is usually sudden. Death from chronic heart failure is less common. People who learn that they've inherited this disorder may wish to obtain genetic counseling when planning a family.

Treatment is aimed primarily at reducing the heart's resistance to filling with blood between heartbeats. Taken alone or together, beta-blockers and calcium channel blockers are the main treatment. Surgery to remove some heart muscle improves the outflow of blood from the heart, but it's performed only on people whose symptoms are incapacitating despite drug therapy. Surgery can relieve symptoms, but it doesn't lower the risk of death.

Before dental work or a surgical procedure, antibiotics may be given to reduce the risk of infection of the inside lining of the heart (infective endocarditis).

Restrictive Cardiomyopathy

Restrictive cardiomyopathy is a group of disorders of the heart muscle in which the walls of the ventricles become stiff, but not necessarily thickened, and resist normal filling with blood between heartbeats.

The least common form of cardiomyopathy, restrictive cardiomyopathy shares many features with hypertrophic cardiomyopathy. Its cause is usually unknown. In one of its two basic types, the heart muscle is gradually replaced by scar tissue. In the other, the heart muscle is infiltrated by abnormal material, such as white blood cells. Other causes of infiltration include amyloidosis and sarcoidosis. If the body contains too much iron, it may accumulate in the heart muscle, as in iron overload (hemochromatosis). The cause may also be a tumor invading the heart tissue.

Because the heart resists filling with blood, the amount of blood pumped out is adequate when the person is resting but not when the person is exercising.

Symptoms and Diagnosis

Restrictive cardiomyopathy causes heart failure with shortness of breath and tissue swelling (edema). Chest pain and fainting are less likely than in hypertrophic cardiomyopathy, but abnormal heart rhythms and palpitations are common.

Restrictive cardiomyopathy is one of the possible causes investigated when a person has heart failure. The diagnosis is based largely on a physical examination, an electrocardiogram (ECG), and an echocardiogram. Magnetic resonance imaging (MRI) can provide additional information about the structure of the heart. A precise diagnosis usually requires catheterization of the heart to measure pressures and a biopsy of the heart muscle (removal and microscopic examination of a specimen), which may enable the doctor to identify the infiltrating substance.

Prognosis and Treatment

About 70 percent of people with restrictive cardiomyopathy die within 5 years of when symptoms begin. For most, no therapy is satisfactory. For instance, diuretics, which normally are used to treat heart failure, may reduce the amount of blood entering the heart, worsening the condition instead of improving it. Drugs normally used in heart failure to reduce the heart's workload usually aren't helpful because they may reduce blood pressure too much.

Sometimes the cause of restrictive cardiomyopathy can be treated to prevent heart damage from getting worse or even to partially reverse it. For example, removing blood at regular intervals reduces the stored iron in people with iron overload. Those who have sarcoidosis may take corticosteroids.

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