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Restrictive (infiltrative) cardiomyopathy includes a group of heart disorders in which the walls of the ventricles become stiff, but not necessarily thickened, and resist normal filling with blood between heartbeats.
Restrictive cardiomyopathy may occur when heart muscle is gradually infiltrated or replaced by scar tissue or when abnormal substances accumulate in the heart muscle.
Shortness of breath, fluid accumulation in the tissues, abnormal heart rhythms, and awareness of heartbeats are common symptoms.
The diagnosis is based on results of a physical examination, electrocardiography, echocardiography, and cardiac catheterization.
Treatment is not often helpful, although sometimes doctors are able to treat the cause.
The least common form of cardiomyopathy, restrictive cardiomyopathy, shares many features with hypertrophic cardiomyopathy. Its cause is usually unknown.
There are two basic types of restrictive cardiomyopathy:
Scarring may result from injury due to radiation therapy that may be given for treatment of a co-existent chest tumor.
For example, if the body contains too much iron, iron may accumulate in the heart muscle, as it does in people who have iron overload (hemochromatosis—see Hemochromatosis). Eosinophils, a type of blood cell, may infiltrate the heart muscle in people who have the hypereosinophilic syndrome (see Idiopathic hypereosinophilic syndrome), which most often occurs in tropical regions. Amyloid, an unusual protein not normally present in the body, may accumulate in heart muscle and other tissues, causing amyloidosis (see Amyloidosis). Amyloidosis is more common among older people. Other examples are tumors and granuloma tissue (abnormal collections of certain white blood cells that form in response to chronic inflammation), which, for example, develops in people who have sarcoidosis (see Sarcoidosis).
A congenital form of restrictive cardiomyopathy occurs in infants who have endocardial fibroelastosis. In this rare disorder, a thickened layer of fibrous tissue lines the left ventricle.
Restrictive cardiomyopathy causes heart failure (see Heart Failure) with shortness of breath during exertion and when lying flat and fluid accumulation in tissues (edema). Chest pain and fainting (syncope) are less likely than in hypertrophic cardiomyopathy, but abnormal heart rhythms (arrhythmias) are common. Fatigue may also occur. Usually, symptoms do not occur during rest, because in restrictive cardiomyopathy, the heart can supply the body with enough blood and oxygen during rest, even though the stiff heart resists filling with blood. Symptoms occur during exercise, when the stiff heart cannot pump enough blood to meet the body’s increased need for blood and oxygen.
Restrictive cardiomyopathy is one of the possible causes investigated when a person has heart failure. The diagnosis is based largely on the combined results of a physical examination, electrocardiography (ECG), chest x-ray, and echocardiography. ECG can typically detect abnormalities in the heart’s electrical activity, but these abnormalities are not specific enough for a diagnosis. Echocardiography shows that the atria are enlarged and that the heart is functioning normally only when the heart contracts (during systole). Magnetic resonance imaging (MRI) can detect abnormal texture in heart muscle due to accumulation of or infiltration with abnormal substances, such as iron and amyloid. Although the procedure is not often necessary, doctors sometimes do cardiac catheterization to measure pressures in the heart chambers and remove a sample of heart muscle for examination under a microscope (biopsy), which may enable doctors to identify an infiltrating substance. More than half the time, no specific cause for restrictive cardiomyopathy is found (idiopathic restrictive cardiomyopathy).
Survival varies depending on the cause. But on average, people with idiopathic restrictive cardiomyopathy survive about 7 years.
For most people, treatment is not very helpful. For example, diuretics, which are usually taken to treat heart failure, may help people who have troublesome leg swelling or shortness of breath but also reduce the amount of blood entering the heart, which can worsen restrictive cardiomyopathy instead of improving it. Drugs commonly used in heart failure to reduce the heart’s workload, such as angiotensin-converting enzyme (ACE) inhibitors, are usually not helpful because they reduce blood pressure too much. As a result, not enough blood reaches the rest of the body. Similarly, digoxin is usually not helpful and is sometimes harmful. Beta-blockers are poorly tolerated in people with restrictive cardiomyopathy and have not been shown to improve survival. Antiarrhythmics may be given to prevent or reduce symptoms in people with fast or irregular heart rhythms.
Sometimes, the disorder causing restrictive cardiomyopathy can be treated to prevent heart damage from worsening or even to partially reverse it. For example, removing blood at regular intervals reduces the amount of stored iron in people with iron overload. People who have sarcoidosis may take corticosteroids, which cause the granuloma tissue to disappear. Corticosteroids may also be helpful in eosinophilic infiltrative disorders. However, many cases of restrictive cardiomyopathy have no specific treatment.
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