Restrictive Cardiomyopathy
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.
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. In one type, the heart muscle is gradually replaced by scar tissue. Scarring may result from injury due to radiation therapy for cancer. In the other type, abnormal substances accumulate in or infiltrate the heart muscle. 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 Section 12, Chapter 155)). Amyloid, an unusual protein not normally present in the body, may accumulate in heart muscle and other tissues, causing amyloidosis (see Section 25, Chapter 304). 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 Section 4, Chapter 50).
Symptoms and Diagnosis
Restrictive cardiomyopathy causes heart failure (see Section 3, Chapter 25) with shortness of breath and fluid accumulation in tissues (edema). Chest pain and fainting (syncope) are less likely than in hypertrophic cardiomyopathy, but abnormal heart rhythms (arrhythmias) and awareness of heartbeats (palpitations) are common. 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 results of a physical examination, electrocardiography (ECG), and echocardiography. ECG can typically detect abnormalities in the heart's electrical activity, but they 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. A precise diagnosis usually requires cardiac catheterization to measure pressures in the heart chambers and removal of a sample of heart muscle for examination under a microscope (biopsy), which may enable doctors to identify the infiltrating substance.
Prognosis and Treatment
About 70% of people with restrictive cardiomyopathy die within 5 years of when symptoms begin. For most people, treatment is not very helpful. For example, diuretics, which are usually taken to treat heart failure, may reduce the amount of blood entering the heart, worsening the disorder instead of improving it. Drugs commonly used in heart failure to reduce the heart's workload, such as 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.
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.
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