Section 3. Heart and Blood Vessel Disorders

Chapter 26. Cardiomyopathy

Topics: Introduction | Dilated Cardiomyopathy | Hypertrophic Cardiomyopathy | Restrictive Cardiomyopathy

Dilated Cardiomyopathy

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

Dilated cardiomyopathy can develop at any age but is more common among people aged 20 to 60 years. About 10% of people who develop dilated cardiomyopathy are older than 65. The disorder occurs in about 3 times as many men as women and 3 times as many blacks as whites. About 5 to 8 of every 100,000 people develop the disorder each year.

In the United States, the most common identifiable cause of dilated cardiomyopathy is extensive coronary artery disease. Such coronary artery disease results in an inadequate blood supply to the heart muscle, which leads to permanent injury and death of heart muscle. As a result, the heart cannot pump as forcefully. The dead heart muscle is replaced by fibrous (scar) tissue. The remaining uninjured heart muscle then stretches and thickens (hypertrophies) to compensate for the lost pumping action. The more the heart muscle is stretched, the more forcefully it contracts or pumps but only up to a point. After that point, the stretching and thickening do not adequately compensate, and dilated cardiomyopathy with heart failure develops.

Dilated cardiomyopathy may be caused by an acute inflammation of the heart muscle (myocarditis) due to a viral infection. This disorder is called viral cardiomyopathy. In the United States, infection with coxsackie B virus is the most common cause of viral cardiomyopathy. The virus infects and weakens the heart muscle. As in coronary artery disease, the weakened heart stretches in an attempt to compensate, resulting in dilated cardiomyopathy and often heart failure. Occasionally, dilated cardiomyopathy results from a bacterial infection.

Other causes of dilated cardiomyopathy include certain chronic hormonal disorders such as long-standing, poorly controlled diabetes or thyroid disease. Dilated cardiomyopathy also can be caused by use of certain substances, especially alcohol (when intake is heavy and malnutrition is also present), cocaine, antidepressants, and a few chemotherapy drugs. Rare causes of dilated cardiomyopathy include pregnancy and connective tissue disorders such as rheumatoid arthritis.

Symptoms

Usually, the first symptoms of dilated cardiomyopathy are becoming short of breath during exertion and tiring easily. They result from a weakening of the heart's pumping action, which is called heart failure (see Section 3, Chapter 25). When cardiomyopathy results from an infection, the first symptoms may be a sudden fever and flu-like symptoms. Whatever the cause of dilated cardiomyopathy, the heart rate eventually speeds up, blood pressure is normal or low, fluid is retained in the legs and abdomen, and the lungs fill with fluid.

Because the heart is enlarged, the heart valves may be unable to close normally. The mitral valve, which opens from the left atrium (upper heart chamber) into the left ventricle (lower heart chamber), and the tricuspid valve, which opens from the right atrium into the right ventricle, often leak. Leakage causes murmurs, which doctors can hear with a stethoscope. Damage to and stretching of the heart muscle may result in abnormal heart rhythms (arrhythmias). The leakage of the valves and the abnormal heart rhythms may interfere further with the heart's pumping action.

Blood pools in the enlarged heart, increasing the risk of blood clots forming on heart chamber walls. The clots can break into pieces (becoming emboli), travel from the heart to blood vessels elsewhere in the body, and block them. If the blood supply to the brain is blocked, a stroke can result.

Diagnosis

The diagnosis is based on the symptoms and the results of a physical examination. Electrocardiography (ECG) (see Section 3, Chapter 21) may detect abnormalities in the electrical activity of the heart. However, these abnormalities are usually not sufficient evidence for a diagnosis. Echocardiography (see Section 3, Chapter 21), which uses ultrasound waves to produce an image of the heart, is the most useful procedure because it can show the size and pumping action of the heart. Magnetic resonance imaging (MRI) (see Section 3, Chapter 21), which produces very detailed images of the heart, may be used to confirm the diagnosis.

If the diagnosis remains in doubt, cardiac catheterization (see Section 3, Chapter 21), an invasive procedure, can provide additional information about the pumping ability of the heart or help confirm the diagnosis. A catheter threaded into the heart can measure pressures in the heart chambers. Also during catheterization, a tissue sample can be removed for examination under a microscope (biopsy). A biopsy can sometimes identify the characteristic microscopic changes of some disorders that cause dilated cardiomyopathy (such as a viral infection that has just developed) and thus confirm the diagnosis. However, usually, the results of a biopsy are not specific enough to help with the diagnosis.

Prognosis and Treatment

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

Treating the cause, such as alcohol abuse (by abstaining from alcohol) or a bacterial infection (by using antibiotics), can prolong life.

People who also have coronary artery disease may require treatment for it. Such treatment may include a nitrate, a beta-blocker, or a calcium channel blocker (see Section 3, Chapter 33). However, calcium channel blockers may reduce the force of heart contractions and thus may worsen the heart failure that accompanies dilated cardiomyopathy. Getting enough rest and avoiding stress help reduce strain on the heart.

Antiarrhythmic drugs may be given to prevent abnormal heart rhythms (see Section 3, Chapter 27). Most of these drugs are prescribed in small doses. They are increased in small increments, because if the dose is too large, an antiarrhythmic drug may reduce the force of heart contractions and thereby worsen heart failure.

Heart failure is treated with an angiotensin-converting enzyme (ACE) inhibitor, a beta-blocker, digoxin, and often a diuretic (see Section 3, Chapter 25). However, unless a specific cause of dilated cardiomyopathy can be treated, the heart failure is likely to eventually be fatal. Because of this poor prognosis, dilated cardiomyopathy is the most common reason for heart transplantation (see Section 16, Chapter 187). Successful heart transplantation cures the disorder, but it has its own complications and limitations.

Regardless of the cause of dilated cardiomyopathy, anticoagulants, such as warfarin, are usually given to prevent blood clots, which may form on the heart chamber walls.