(See also Overview of Cardiomyopathy.)
Dilated cardiomyopathy is a group of heart muscle disorders in which the ventricles (the two lower chambers of the heart) enlarge (dilate) but are not able to pump enough blood for the body’s needs, resulting in heart failure.
Viral infections, and some hormonal disorders are common causes of dilated cardiomyopathy.
Shortness of breath and fatigue are often the first symptoms.
Electrocardiography, echocardiography, magnetic resonance imaging, and blood tests are used to diagnose dilated cardiomyopathy.
Doctors try to treat the cause of this cardiomyopathy, usually by giving drugs.
The term cardiomyopathy is used only when a disorder directly affects the heart muscle. Other heart disorders, such as coronary artery disease and heart valve disorders, also can eventually cause the ventricles to enlarge and heart failure. However, doctors do not classify the heart muscle problems caused by those disorders as cardiomyopathies.
Dilated cardiomyopathy can develop at any age but is more common among people aged 20 to 50 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.
The most common causes of dilated cardiomyopathy are
Some viral infections can cause an acute inflammation of the heart muscle (myocarditis). This disorder is called viral cardiomyopathy. In North America, infection with coxsackie B virus is the most common cause of viral cardiomyopathy. HIV infection also can cause cardiomyopathy. In other parts of the world, other viral infections are more common causes. Occasionally, dilated cardiomyopathy results from a bacterial infection, such as Chagas disease.
The virus or bacteria infects and weakens the heart muscle. As a result, the heart cannot pump as forcefully. The damaged heart muscle is replaced by fibrous (scar) tissue. The heart muscle then stretches resulting in enlargement of the heart chambers and reduced pumping ability. After that point heart failure develops.
Other causes of dilated cardiomyopathy include
Rare causes of dilated cardiomyopathy include pregnancy, iron overload, and connective tissue disorders such as rheumatoid arthritis, lupus, and systemic sclerosis. Extreme stress can also sometimes cause a type of dilated cardiomyopathy called Takotsubo cardiomyopathy. Diseases such as sarcoidosis can also cause dilated cardiomyopathy.
When no specific cause can be identified, the disorder is called an idiopathic dilated cardiomyopathy.
Usually, the first symptoms of dilated cardiomyopathy are becoming short of breath during exertion and tiring easily. These symptoms result from a weakening of the heart’s pumping action, which is called heart failure. Some people have chest pain.
When cardiomyopathy results from an infection, the first symptoms may be a sudden fever and flu-like symptoms.
Heart failure can develop whatever the cause of dilated cardiomyopathy, if the heart damage is severe enough. With heart failure, the fluid is retained in the legs and abdomen (causing swelling), and the lungs fill with fluid (causing shortness of breath with physical activity and while lying flat). With severe heart failure, blood pressure can be low.
Heart valve problems may develop. Because the heart is enlarged, the heart valves may be unable to close normally and often allow blood to leak back into the heart chamber rather than flowing into the next blood vessel or chamber (called regurgitation). 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 heart murmurs, which doctors can hear with a stethoscope.
Abnormal heart rhythms (arrhythmias) can result from damage to and stretching of the heart muscle. Arrhythmias may cause sensation of irregular heartbeats (palpitations) or death. The leakage of the valves and the abnormal heart rhythms may interfere further with the heart’s pumping action.
Blood clots may form on heart chamber walls because blood can pool in the enlarged heart, particularly when the ventricles are very dilated and poorly contracting. 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.
The diagnosis of dilated cardiomyopathy is based on the person's symptoms, the results of a physical examination, and additional tests. Doctors look for other causes of a dilated heart, such as a previous heart attack, chronic high blood pressure, or a damaged heart valve.
Blood tests for common viruses that can cause dilated cardiomyopathy are done when doctors suspect infection as a cause.
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 both the size and pumping action of the heart.
Cardiac magnetic resonance imaging (MRI), which produces very detailed images of the heart, is more often being 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 from a blood vessel in the arm or leg into the heart, can provide additional information about the pumping ability of the heart. During cardiac catheterization, doctors can also obtain a biopsy (remove a tissue sample from inside the heart for examination under a microscope), measure pressures in the heart chambers and exclude coronary artery disease.
The prognosis of dilated cardiomyopathy varies considerably depending on many factors. In general, 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 40 to 50% of deaths are sudden, probably resulting from an abnormal heart rhythm or an embolus that blocks blood flow in a critical area. Additional factors include the cause and severity of the cardiomyopathy, the person's age and ability to follow medical advice, access to specialized treatment, poor patient compliance with drugs, salt in the diet, and outpatient visits. However, in recent years overall prognosis has improved with current treatments, especially with the introduction of implantable cardioverter-defibrillators, cardiac resynchronization therapy, and other interventions.
If possible, doctors treat the disorder that is causing the dilated cardiomyopathy. For example, immunosuppressive drugs such as corticosteroids may be used to treat a connective tissue disorder that caused dilated cardiomyopathy.
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 used for heart failure, such as angiotensin-converting enzyme (ACE) inhibitors, angiotensin II receptor blockers, beta-blockers, aldosterone antagonists (spironolactone or eplerenone), the combination of hydralazine and nitrates, and neprilysin inhibitors, improve the heart’s pumping function, prolong life, and help to decrease persistent symptoms.
Diuretics (drugs that increase urination) are used to reduce excess fluid in the lungs and decrease symptoms of swelling due to fluid retention, but they do not prolong life.
Digoxin may decrease the number of hospitalizations for heart failure, but it does not prolong life.
Antiarrhythmic drugs may be given to treat abnormal heart rhythms. Most of these drugs are initially 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.
Drugs to prevent blood clots, such as warfarin or aspirin, may be used, particularly when ventricles are very dilated and contracting poorly.
Some people have an abnormality of the electrical conduction in the heart, which can be helped by an artificial pacemaker that stimulates first the atria and then the ventricles (cardiac resynchronization therapy). This type of pacemaker, when used in the right person, will help to return the contraction pattern of the heart toward normal and improve its function.
Doctors may also consider an implantable cardioverter-defibrillator pacemaker in patients with persistent poor heart function and an increased risk of arrhythmias leading to sudden death).
Heart failure in dilated cardiomyopathy can be progressive and ultimately fatal. Because of this poor prognosis, dilated cardiomyopathy is the most common reason for heart transplantation or mechanical heart support with a device. Successful heart transplantation cures the disorder, but it has its own complications and limitations.