Restrictive Cardiomyopathy

Restrictive cardiomyopathy is the least common of the three general categories of cardiomyopathy, or disease of the heart muscle. The other two categories are dilated cardiomyopathy, and hypertrophic cardiomyopathy. 

Restrictive cardiomyopathy is important because it often produces heart failure, and depending on the underlying cause, the heart failure may be difficult to treat effectively. Because the treatment of this disorder can be tricky, anyone with restrictive cardiomyopathy should be under the care of a cardiologist.

In restrictive cardiomyopathy, for one reason or another the heart muscle develops an abnormal "stiffness." While the stiffened heart muscle is still able to contract normally, and thus is able to pump blood, it is unable to fully relax during the diastolic phase of the heart beat. (Diastole is the “filling” phase of the cardiac cycle—the time in between heart beats, when the ventricles are filling with blood.) This relaxation failure makes it more difficult for the ventricles to fill adequately with blood during diastole. 

The restricted filling of the heart (which gives this condition its name) causes the blood to "back up" as it tries to enter the ventricles, which can produce congestion in the lungs and in other organs.

Another name for restricted filling of the heart during diastole is “diastolic dysfunction,” and the kind of heart failure it produces is called diastolic heart failure. Essentially, restrictive cardiomyopathy is one of the many causes of diastolic heart failure, though a relatively rare one.

There are several conditions that may produce restrictive cardiomyopathy. In some cases, no specific cause can be identified, in which case the restrictive cardiomyopathy is said to be ”idiopathic.” However, idiopathic restrictive cardiomyopathy should be diagnosed only when all the other potential causes have been looked for, and ruled out. These other causes include:

• Infiltrative diseases such as amyloidosis, sarcoidosis, Hurler syndrome, Gaucher disease and fatty infiltration.
• Several familial disorders that are genetic in nature, including pseuoxanthoma elasticum.
• Storage diseases including Fabry disease, glycogen storage disease, and hemochromatosis.
• Other miscellaneous conditions including scleroderma, hypereosinophilic syndrome, endomyocardial fibrosis, carcinoid syndrome, metastatic cancer, radiation therapy or chemotherapy.

What all these causative disorders have in common is that they produce some process that interferes with the normal functioning of the heart muscle, such as abnormal cellular infiltration, or abnormal deposits. These processes tend not to interfere too much with the contraction of heart muscle, but they reduce the elasticity of the heart muscle and thus restrict the filling of the ventricles with blood.

The symptoms people experience with restrictive cardiomyopathy are similar to the symptoms that occur with other forms of heart failure. Symptoms are mainly due to congestion of the lungs, congestion of other organs, and an inability to adequately increase the amount of blood the heart pumps during exertion.

Consequently, the most prominent symptoms with restrictive cardiomyopathy are dyspnea (shortness of breath), edema (swelling of the feet and ankles), weakness, fatigue, a greatly reduced tolerance for exercise, and palpitations. With severe restrictive cardiomyopathy, congestion of the abdominal organs can occur, producing an enlarged liver and spleen, and ascites (fluid accumulation in the abdominal cavity.)

As with most forms of heart failure, the diagnosis of restrictive cardiomyopathy depends first on the doctor becoming alert to the possibility that this condition may be present when performing a medical history and physical examination.

People with significant restrictive cardiomyopathy may have a relative tachycardia (rapid heart rate) at rest, and distention of the veins in the neck. These physical findings, as well as the symptoms, tend to be similar to those seen with constrictive pericarditis. In fact, differentiating restrictive cardiomyopathy from constrictive pericarditis is a classic problem that cardiologists inevitably face on their board certification exams. (On the test, the answer has to do with the esoteric heart sounds produced by these two conditions — an “s3 gallop” with restrictive cardiomyopathy vs. a “pericardial knock” with constrictive pericarditis.)

The diagnosis of restrictive cardiomyopathy can usually be confirmed by performing echocardiography, which shows diastolic dysfunction and evidence of restrictive filling of the ventricles. If the underlying cause is an infiltrative disease such as amyloidosis, the echo test may also show evidence of abnormal deposits in the ventricular muscle. Cardiac MRI scanning can also help make the diagnosis, and in some cases, can help identify an underlying cause. A heart muscle biopsy can also be very useful in making the diagnosis when an infiltrative or storage disease is present.

If an underlying cause of restrictive cardiomyopathy has been identified, aggressively treating that underlying cause may help to reverse or halt the progression of restrictive cardiomyopathy. Unfortunately, there is no specific therapy that directly reverses the restrictive cardiomyopathy itself.

Managing restrictive cardiomyopathy is directed toward controlling lung congestion and edema in order to reduce symptoms. This is accomplished by using many of the same drugs that are used for heart failure due to dilated cardiomyopathy.

Diuretics, such as Lasix (furosemide), tend to offer the most obvious benefit in treating people with restrictive cardiomyopathy. However, it is possible to make people with this condition “too dry” with diuretics, further reducing the filling of the ventricles during diastole. So close monitoring of their condition is necessary, measuring weight at least daily and periodically checking blood tests to look for evidence of chronic dehydration. The optimal dose of diuretics may change over time, so this vigilance is a chronic requirement.

The use of calcium channel blockers can be helpful by directly improving the heart’s diastolic function, and by slowing the heart rate to allow more time for filling the ventricles between heart beats. For similar reasons, beta-blockers can also be helpful.

There is some evidence that ACE inhibitors may be of benefit to at least some people with restrictive cardiomyopathy, possibly by reducing heart muscle stiffness.

If atrial fibrillation is present, it is critical to control the heart rate to allow adequate time to fill the ventricles. The use of calcium channel blockers and beta blockers can usually accomplish this goal.

If medical therapy fails to control the symptoms of restrictive cardiomyopathy, cardiac transplantation may become an option that should be considered.

The prognosis of restrictive cardiomyopathy tends to be worse in men, in people over 70 years of age, and in people whose cardiomyopathy is caused by a condition with a poor prognosis, such as amyloidosis.

Summary

Restrictive cardiomyopathy is an uncommon form of heart failure. Anyone who has this condition needs a full medical work-up to look for underlying causes, and also needs careful and ongoing medical management to minimize symptoms and optimize long-term outcomes.