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By far the most common type of
cardiomyopathy, the dilated (stretched) form occurs when
disease-affected muscle fibers lead to enlargement, or dilation, of
one or more chambers of the heart. This weakens the heart's pumping
ability. The heart tries to cope with the pumping limitation by
further enlarging and stretching - a process known as "compensation."
Congestive cardiomyopathy occurs most
often in middle-aged people and more often in men than women. However,
the disease has been diagnosed in people of all ages, including
children.
Causes
In most cases, a specific cause for the
damage is never identified.
But some factors have been linked to
the disease's occurrence. For instance, alcohol has a direct
suppressant effect on the heart. Dilated cardiomyopathy can be caused
by chronic, excessive consumption of alcohol, particularly in
combination with dietary deficiencies.
Also, dilated cardiomyopathy
occasionally occurs as a complication of pregnancy and childbirth.
Other factors are: various infections, mostly viral, which lead to an
inflammation of the heart muscle (myocarditis); toxins (such as
cobalt, once used in beers, for instance); and, rarely, heredity.
Some drugs, used to treat a different
medical condition, also can damage the heart and produce dilated
cardiomyopathy. Such drugs include doxorubicin and daunorubicin, both
used to treat cancer.
Whatever the cause, the clinical and
pathological manifestations of dilated cardiomyopathy are usually the
same.
Symptoms
Dilated cardiomyopathy can be present
for several years without causing significant symptoms. With time,
however, the enlarged heart gradually weakens.
This condition is commonly called "heart
failure," and it is the hallmark of dilated cardiomyopathy.
Typical signs and symptoms of heart failure include: fatigue;
weakness; shortness of breath, sometimes severe and accompanied by a
cough, particularly with exertion or when lying down; and swelling of
the legs and feet, resulting from fluid accumulation that may also
affect the lungs and other parts of the body. It also produces
abnormal weight gain. (The cough and congestion mimic and, therefore,
can be misdiagnosed as pneumonia or acute bronchitis.)
Because of the congestion, some
physicians use the older term "congestive cardiomyopathy" to refer to
dilated cardiomyopathy. In advanced stages of the disease, the
congestion may cause pain in the chest or abdomen.
In advanced stages, some patients
develop irregular heartbeats, which can be serious and even life
threatening.
Diagnosis
Once symptoms appear, the condition may
be tentatively diagnosed based on a physical examination and a
patient's medical history. More often, though, further examination is
needed to differentiate dilated cardiomyopathy from other causes of
heart failure.
A firm diagnosis typically requires a
chest x ray to show whether the heart is enlarged, an
electrocardiogram to reveal any abnormal electrical activity of
the heart, and an echocardiogram, which uses sound waves to
produce pictures of the heart.
Other, more specific tests may also be
needed. These include:
- A radionuclide ventriculogram.
This involves injecting low-dose radioactive material (usually equal
to that in a set of chest x rays) into a vein, through which it
flows to the heart. Pictures are generated by a special camera to
show how well the heart is functioning.
- A cardiac catheterization. In
this procedure, a thin plastic tube is inserted through a blood
vessel until it reaches the heart. A dye is injected and x rays
taken to assess the heart's structure and function.
Treatment
Since dilated cardiomyopathy is hard to
diagnose early, it is rarely treated in its beginning stage.
The goal of treatment is to relieve any
complicating factor, if known, control the symptoms, and stop the
disease's progression. However, no cure now exists.
Therapy begins with the elimination of
obvious risk factors, such as alcohol consumption. Weight loss and
dietary changes, especially salt restriction, may also be advised.
Drugs used to treat the condition
include:
- Diuretics,
which reduce excess fluid in the body;
- Vasodilators, such as angiotensin-converting
enzyme (ACE) inhibitors, which relax blood vessels, helping to
lower blood pressure and reducing the effort needed by the heart to
pump blood through the body;
- Digitalis, which helps to
improve pumping action and regulate heartbeat; and,
- Calcium blockers or beta
blockers, which may be used in some patients to help regulate
heartbeat and to alter the work of the heart muscle.
Also, patients with irregular
heartbeats may be put on any of various drugs to control the rhythm.
In critical cases where the condition
is advanced and the patient does not sufficiently respond to other
treatments, a heart transplantation may be needed. The patient's heart
is replaced with a donor heart. Most heart transplant recipients are
under age 60 and in good health other than their diseased heart.
Course of the disease
As the heart enlarges, it steadily
decreases its efficiency in pumping blood and the amount of blood it
can pump. As a result, some patients cannot perform even simple
physical activities.
However, the disease also may remain
fairly stable for years, especially with treatment and regular
evaluation by a physician.
Unfortunately, by the time it is
diagnosed, the disease often has reached an advanced stage and
heart failure has occurred.
Consequently, about 50 percent of patients with dilated cardiomyopathy
live 5 years once heart failure is diagnosed; about 25 percent live 10
years after such a diagnosis.
Typically, patients die from a
continued decline in heart muscle strength, but some die suddenly of
irregular heartbeats.
For patients with advanced disease,
heart transplantation greatly improves survival: 75 percent of
patients live 5 years after a transplantation. However, in the United
States, the scarcity of donor hearts limits the number of
transplantations to about 2,000 persons a year. Those who qualify for
heart transplantation often have to wait months, or even years, for a
suitable donor heart. Some patients with dilated cardiomyopathy die
awaiting a transplant but, according to recent studies, others improve
enough from aggressive medical treatment to be taken off the waiting
list.
Also, some critically ill
cardiomyopathy patients with declining heart function use a small,
implanted mechanical pump as a bridge to transplantation. Called
left ventricular assist devices (LVADs), these pumps take over
part or virtually all of the heart's blood pumping activity. The
devices provided only temporary assistance and are not now used as
substitutes for heart transplantation.
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