Article: Cardiomyopathy

Cardiomyopathy, which literally means "heart muscle disease", is the deterioration of the function of the myocardium (i.e., the actual heart muscle) for any reason. Cardiomyopathy of any cause typically leads to signs and symptoms of heart failure as the pumping efficiency of the heart is diminished. People with cardiomyopathy are often at risk of arrhythmia and/or sudden cardiac death.

Cardiomyopathies can generally be categorized into two groups, based on WHO guidelines: extrinsic cardiomyopathies and intrinsic cardiomyopathies.

Extrinsic cardiomyopathies

These are cardiomyopathies where the primary pathology is outside the myocardium itself. Most cardiomyopathies are extrinsic, because by far the most common cause of a cardiomyopathy is ischemia. A reasonably complete list of extrinsic causes of cardiomyopathy would be:

• Ischemic cardiomyopathy (English spelling Ischaemic)
• Hypertensive cardiomyopathy
• Valvar cardiomyopathy
• Inflammatory cardiomyopathy
• Cardiomyopathy secondary to a systemic disease
• Alcoholic cardiomyopathy

Ischemic cardiomyopathy

Ischemic cardiomyopathy is a weakness in the muscle of the heart due to inadequate oxygen delivery to the myocardium with coronary artery disease being the most common cause. Anemia and sleep apnea are relatively common conditions that can contribute to ischemic myocardium and hyperthyroidism can cause a 'relative' ischemia secondary to high output heart failure. Individuals with ischemic cardiomyopathy typically have a history of myocardial infarction (heart attack), although longstanding ischemia can cause enough damage to the myocardium to precipitate a clinically significant cardiomyopathy even in the absence of myocardial infarction. In a typical presentation, the area of the heart affected by a myocardial infarction will initially become necrotic as it dies, and will then be replaced by scar tissue (fibrosis). This fibrotic tissue is akinetic; it is no longer muscle and cannot contribute to the heart's function as a pump. If this akinetic region of the heart is substantial enough, the affected side of the heart (i.e. the left or right side) will go into failure, and this failure is the functional result of an ischemic cardiomyopathy.

Cardiomyopathy due to systemic diseases

Many diseases can result in cardiomyopathy. These include diseases like hemochromatosis, (an abnormal accumulation of iron in the liver and other organs), amyloidosis (an abnormal accumulation of the amyloid protein), diabetes, hyperthyroidism, lysosomal storage diseases and the muscular dystrophies.

Intrinsic cardiomyopathies

An intrinsic cardiomyopathy is weakness in the muscle of the heart that is not due to an identifiable external cause. To make a diagnosis of an intrinsic cardiomyopathy, significant coronary artery disease should be ruled out (amongst other things). The term intrinsic cardiomyopathy does not describe the specific etiology of weakened heart muscle. The intrinsic cardiomyopathies are a mixed-bag of disease states, each with their own causes.

Intrinsic cardiomyopathy has a number of causes including drug and alcohol toxicity, certain infections (including Hepatitis C), and various genetic and idiopathic (i.e., unknown) causes.

There are four main types of intrinsic cardiomyopathy:

• Dilated cardiomyopathy (DCM), the most common form of cardiomyopathy, and one of the leading indications for heart transplantation. In DCM the heart (especially the left ventricle) is enlarged and weakened. Approximately 40% of cases are familial, but the genetics are poorly understood compared with HCM. In some cases it manifests as peripartum cardiomyopathy, and in other cases it may be associated with alcoholism.
• Hypertrophic cardiomyopathy (HCM or HOCM), a genetic disorder caused by various mutations in genes encoding sarcomeric proteins. In HCM the heart muscle is thickened, which can obstruct blood flow and prevent the heart from functioning properly.
• Arrhythmogenic right ventricular cardiomyopathy (ARVC) arises from an electrical disturbance of the heart in which heart muscle is replaced by fibrous scar tissue. The right ventricle is generally most affected.
• Restrictive cardiomyopathy (RCM) is the least common cardiomyopathy. The walls of the ventricles are stiff, but may not be thickened, and resist the normal filling of the heart with blood. A rare form of restrictive cardiomyopathy is the obliterative cardiomyopathy, seen in the hypereosinophilic syndrome. In this type of cardiomyopathy, the myocardium in the apicies of the left and right ventricles become thickened and fibrotic, causing a decrease in the volumes of the ventricles and a type of restrictive cardiomyopathy.

Treatment

Treatment depends on the type of cardiomyopathy, but may include medical therapy and implanted artificial pacemakers. The goal of treatment is often symptom relief, with the underlying condition unaffected. Some patients may eventually require a heart transplant. Treatment of cardiomyopathy (and other heart diseases) using alternative methods such as stem cell therapy is commercially available but is not supported by convincing evidence.