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Restrictive Cardiomyopathy

(Infiltrative Cardiomyopathy)

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Restrictive cardiomyopathy includes a group of heart disorders in which the walls of the ventricles (the two lower chambers of the heart) 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, magnetic resonance imaging, cardiac biopsy, and cardiac catheterization.

  • Treatment is not often helpful, although sometimes doctors are able to treat the cause.

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.

Cardiomyopathy is a disorder of the heart muscle. 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:

  • The heart muscle is gradually replaced by scar tissue.

  • Abnormal substances accumulate in the heart muscle.

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.

Scarring

Scarring may result from injury due to radiation therapy that may be given for treatment of a co-existing chest tumor.

Accumulation of abnormal substances

Various substances may accumulate in the heart as a result of various disorders. The accumulated substances interfere with the heart muscle's ability to contract and relax.

For example, in people who have iron overload (hemochromatosis), the body contains too much iron, so iron may accumulate in the heart muscle.

In hypereosinophilic syndrome, eosinophils (a type of white blood cell) may accumulate in the heart muscle. Hypereosinophilic syndrome most often occurs in tropical regions.

In amyloidosis, amyloid (an unusual protein not normally present in the body) may accumulate in heart muscle and other tissues. Amyloidosis is more common among older people and can sometimes be hereditary.

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.

Symptoms

Restrictive cardiomyopathy causes heart failure with shortness of breath during exertion and when lying flat and fluid accumulation and swelling 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.

Diagnosis

  • Echocardiography and MRI

  • Sometimes, cardiac catheterization and cardiac biopsy

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. Cardiac catheterization is an invasive procedure in which a catheter is threaded from a blood vessel in the arm or leg into the heart. The procedure is used to measure pressures in the heart chambers and to 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).

Treatment

  • Treatment of the disorder causing restrictive cardiomyopathy

Survival varies depending on the cause. But prognosis is typically poor because the diagnosis is often made very late.

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. However, these drugs 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.