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.

• Coronary artery disease, viral infections, and some hormonal disorders are common causes of dilated cardiomyopathy.
• Shortness of breath and fatigue are often the first symptoms.
• Electrocardiography and echocardiography are used to diagnose dilated cardiomyopathy.
• Doctors try to treat the cause of dilated cardiomyopathy, usually by giving drugs.

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.

Causes

In North America, 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 also may be caused by an acute inflammation of the heart muscle (myocarditis) due to a viral infection. This disorder is called viral cardiomyopathy. In North America, infection with coxsackie B virus is the most common cause of viral cardiomyopathy. In other parts of the world, other viral infections are more common causes. 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, morbid obesity, a persistently rapid heart rate, 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. When no specific cause can be identified, the disorder is called an idiopathic dilated cardiomyopathy.

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 Heart Failure). When cardiomyopathy results from an infection, the first symptoms may be a sudden fever and flu-like symptoms. Whatever the cause of dilated cardiomyopathy, if the heart damage is severe enough, 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 and often leak. The valves most often affected are the mitral valve, which is positioned between the left atrium (upper heart chamber) and the left ventricle (lower heart chamber), and the tricuspid valve, which is positioned between the right atrium and the right ventricle. 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), which may cause awareness of heartbeats (palpitations) or death. 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, causing damage to the organ they supply. 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) may detect abnormalities in the electrical activity of the heart. However, these abnormalities are usually not sufficient evidence for a diagnosis. Echocardiography 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), which produces very detailed images of the heart, may be used to confirm the diagnosis (and sometimes identify the cause).

If the diagnosis remains in doubt, cardiac catheterization, an invasive procedure in which a catheter is threaded into the heart, can provide additional information about the pumping ability of the heart. During cardiac catheterization, doctors can also measure pressures in the heart chambers and determine the extent of coronary artery disease. During catheterization, doctors sometimes remove a tissue sample 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

About 70% of people die within 5 years of when their symptoms begin, and the prognosis worsens as the heart becomes more dilated and 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.

Treatment

If possible, doctors treat the underlying cause.

General treatment measures include avoiding stress, limiting salt in the diet, and having periods of rest, which help reduce strain on the heart, particularly when the cardiomyopathy is acute or severe.

Drugs, such as angiotensin-converting enzyme (ACE) inhibitors, angiotensin II receptor blockers, beta-blockers, spironolactone or eplerenone, and low-dose digoxin, improve the heart's pumping function, prolong life, and decrease persistent symptoms. Diuretics are used to reduce excess fluid in the lungs and decrease symptoms of swelling due to fluid retention, but they do not prolong life.

Antiarrhythmic drugs may be given to prevent abnormal heart rhythms. Most of these drugs are prescribed in small doses. Doses are increased in small increments, because if the dose is too large, an antiarrhythmic drug may worsen heart rhythm abnormalities or depress pumping function. Some people have an abnormality of the electrical conduction in the heart, which can be helped by a pacemaker. Doctors may consider an implantable cardioverter-defibrillator pacemaker in patients with persistent poor heart function and an increased risk of sudden death.

Regardless of the cause of dilated cardiomyopathy, doctors may give anticoagulants, such as warfarin, to prevent blood clots, which may form on the heart chamber walls of very dilated and poorly contracting ventricles.

Unless a specific cause of dilated cardiomyopathy can be treated, heart failure in dilated cardiomyopathy is often fatal. Because of this poor prognosis, dilated cardiomyopathy is the most common reason for heart transplantation (see Transplantation: Heart Transplantation). Successful heart transplantation cures the disorder, but it has its own complications and limitations.

Last full review/revision January 2008 by J. Malcolm O. Arnold, MD