There are three basic types of cardiomyopathy, which are distinguished by the kind of muscle problem involved:
- Dilated cardiomyopathy, in which the heart muscle becomes weak and the heart chambers subsequently dilate.
- Hypertrophic cardiomyopathy, in which the heart muscle itself is much thicker than normal.
- Restrictive cardiomyopathy, in which the heart becomes stiff and cannot fill efficiently during diastole, the period of the heartbeat when the chambers fill with blood.
Dilated cardiomyopathy refers to overall enlargement (dilatation) of the heart chambers, especially the ventricles. Although this enlargement is a key part of dilated cardiomyopathy, it is not the initial problem but rather the heart's own response to a weakness of heart muscle and poor pumping ability.
The weakness of the heart muscle in this condition is generalized ("global"); all parts of the myocardium are affected about equally. Enlargement of the heart is the heart's way of trying to compensate for the weakness of its muscle. If the heart muscle is weak, it is unable to pump out the same portion of blood that it could at normal strength.
Hypertrophic cardiomyopathy is an overgrowth of heart muscle that can impair blood flow both into and out of the heart. This type of cardiomyopathy is less common than dilated cardiomyopathy, but it is not rare and has been the focus of much medical interest.
Hypertrophic cardiomyopathy can result from abnormal thickening of the heart wall. The thickening can occur in several places throughout the ventricles. Most commonly, it occurs in the septum between the two ventricles just beneath the aortic valve. This is sometimes called idiopathic hypertrophic subaortic stenosis, abbreviated IHSS.
This overgrowth creates a bulge that protrudes into the ventricular chamber and impedes the flow of blood from the heart to the aorta and the rest of the body. When this obstruction is present, the cardiomyopathy is called hypertrophic cardiomyopathy (HOCM, often pronounced "HOKUM").
Restrictive cardiomyopathy is the least common type of cardiomyopathy. In this condition, the heart muscle is too stiff to allow blood in from the pulmonary veins. Obviously, blood has to get into the heart before it can be pumped out to the body. The heart cannot pump out blood that it does not receive. In restrictive cardiomyopathy, filling of the ventricle is rapid but ends abruptly when the stiff heart stops expanding. Because the "inflow" of blood into the heart is compromised, symptoms of heart failure can ensue.
Many toxic substances can cause weakening of the heart muscle. The most common is excessive alcohol intake, which can result in severe dilated cardiomyopathy. In some instances, this can be reversed if alcohol intake is stopped. The most common problem occurs when the heart muscle is scarred and the heart is dilated because of a previous heart attack or heart attacks, in which case the damage is irreversible.
The condition usually can be diagnosed by the medical history, characteristic physical findings, chest x-ray, electrocardiogram (EKG), echocardiogram and, if any doubt exists, cardiac catheterization and angiography.
Treatment depends on the patient's symptoms, age, general health, and the specific type and severity of cardiomyopathy. If a treatable underlying cause, such as alcoholism can be identified, it should be treated.
Depending on the type of cardiomyopathy, certain drugs may be prescribed to decrease the heart's workload, regulate the heartbeat, help prevent blood clot formation, and help prevent fluid accumulation in the body. These drugs include vasodilators, digitalis (digoxin), ACE (angiotensin converting enzyme) inhibitors, anticoagulants ("blood thinners") and diuretics ("water pills").
Congestive and dilated cardiomyopathies often respond well, at least initially, to medical therapy. Treatment of some cardiomyopathies that result from viral infections may not be effective. Therapy for those with restrictive cardiomyopathy may be particularly limited. If end-stage heart failure develops, heart transplantation may be necessary.