Dilated cardiomyopathy

Dilated cardiomyopathy or DCM is a condition in which the heart becomes weakened and enlarged and cannot pump blood efficiently. The decreased heart function can affect the lungs, liver, and other body systems.

DCM is one of the cardiomyopathies, a group of diseases that primarily affect the myocardium (the muscle of the heart). Different cardiomyopathies have different causes and affect the heart in different ways. In DCM a portion of the myocardium is dilated, often without any obvious cause. Left or right ventricular systolic pump function of the heart is impaired, leading to progressive cardiac enlargement and hypertrophy, a process called remodeling.

Dilated cardiomyopathy is the most common form of non-ischemic cardiomyopathy. It occurs more frequently in men than in women, and is most common between the ages of 20 and 60 years. About one in three cases of congestive heart failure (CHF) is due to dilated cardiomyopathy. Dilated cardiomyopathy also occurs in children.

Causes
Although in many cases no cause (etiology) is apparent, dilated cardiomyopathy is probably the result of damage to the myocardium produced by a variety of toxic, metabolic, or infectious agents. It may be due to fibrous change of the myocardium from a previous myocardial infarction. Or, it may be the late sequel of acute viral myocarditis, such as with coxsackievirus B and other enteroviruses, possibly mediated through an immunologic mechanism. Autoimmune mechanisms are also suggested as a cause for dilated cardiomyopathy.

Dilated cardiomyopathy can also be caused by alcohol abuse (Alcoholic cardiomyopathy), or other toxic exposure, although the cause-and-effect relationship with alcohol alone is debated. Nonalcoholic toxic insults include administration of certain chemotherapeutic agents, particularly doxorubicin(Adriamycin), and cobalt.

Other potential causes include thyroid disease, stimulant use, and chronic uncontrolled tachycardia. Many cases of dilated cardiomyopathy are described as idiopathic - meaning that the cause is unknown.

Recent studies have shown that those subjects who have an extremely high occurrence (several thousands a day) of premature ventricular contractions (extrasystole) can develop dilated cardiomyopathy. In these cases, if the extrasystole are reduced or removed (for example, via ablation therapy) the cardiomyopathy usually regresses.

Dilated cardiomyopathy also occurs more frequently in pregnancy than in the normal population. It occurs late in gestation or several weeks to months postpartum as a peripartum cardiomyopathy. It is reversible in half of cases.

Genetics
About 25-35% of patients have familial forms of the disease, with most mutations affecting genes encoding cytoskeletal proteins, while some affect other proteins involved in contraction. The disease is genetically heterogeneous, but the most common form of its transmission is an autosomal dominant pattern. Autosomal recessive (as found, for example, in Alström syndrome ), X-linked (as in Duchenne muscular dystrophy), and mitochondrial inheritance of the disease is also found. Some relatives of patients with dilated cardiomyopathy have preclinical, asymptomatic heart-muscle changes. Other cytoskeletal proteins involved in DCM include α-cardiac actin, desmin, and the nuclear lamins A and C. Mitochondrial deletions and mutations presumably cause DCM by altering myocardial ATP generation.

Although the disease is more common in African-Americans than in Caucasians, it may occur in any patient population.

Associations include:

Associated symptoms
For many affected individuals, dilated cardiomyopathy is a condition which will not limit the quality of life. A minority, however, experience significant symptoms and there is sometimes a risk of sudden death. Evaluation by a cardiologist is recommended to confirm the diagnosis and to assess the outlook and particularly the risk of complications. In some patients, symptoms of left- and right-sided congestive heart failure develop gradually. Left ventricular dilatation may be present for months or even years before the patient becomes symptomatic.

Vague chest pain may be present, but typical angina pectoris is unusual and suggests the presence of ischemic heart disease as well. Syncope due to arrhythmias and systemic embolism may occur.

Physical examination
The patient may present variable degrees of cardiac enlargement, and findings of congestive heart failure. In advanced stages of the disease, the pulse pressure is narrowed and the jugular venous pressure is elevated. Third and fourth heart sounds are common. Mitral or tricuspid regurgitation may occur, presented by systolic murmurs upon auscultation (see mitral regurgitation and tricuspid insufficiency for more details about the findings).

Laboratory examinations
Generalized enlargement of the heart is seen upon normal chest X-ray. Pleural effusion may also be noticed, which is due to pulmonary venous hypertension.

The electrocardiogram often shows sinus tachycardia or atrial fibrillation, ventricular arrhythmias, left atrial abnormality, and sometimes intraventricular conduction defects and low voltage. Echocardiogram shows left ventricular dilatation with normal or thinned walls and reduced ejection fraction. Cardiac catheterization and coronary angiography are often performed to exclude ischemic heart disease.

Treatment
Years ago the statistic was that the majority of patients, particularly those over 13 (if passed on genetically and has taken place earlier in life) and over 55 years of age, died within 3 years of the onset of symptoms (stage 5 of CHF) – and such figures can still be found in many textbooks. The situation has improved dramatically in recent years with drug therapy that can slow down progression and in some cases even improve the heart condition. Death is due to either congestive heart failure or ventricular tachy- or bradyarrhythmias.

Patients are given the standard therapy for heart failure, typically including salt restriction, angiotensin-converting enzyme (ACE) inhibitors, diuretics, and digitalis. Anticoagulants may also be used. Alcohol should be avoided. Artificial pacemakers may be used in patients with intraventricular conduction delay, and implantable cardioverter-defibrillators in those at risk of arrhythmia. These forms of treatment have been shown to improve symptoms and reduce hospitalization.

In patients with advanced disease who are refractory to medical therapy, cardiac transplantation may be considered.

Reverse remodeling
The progression of heart failure is associated with left ventricular remodeling, which manifests as gradual increases in left ventricular end-diastolic and end-systolic volumes, wall thinning, and a change in chamber geometry to a more spherical, less elongated shape. This process is usually associated with a continuous decline in ejection fraction. The concept of cardiac remodeling was initially developed to describe changes which occur in the days and months following myocardial infarction. It has been extended to cardiomyopathies of non-ischemic origin, such as idiopathic dilated cardiomyopathy or chronic myocarditis, suggesting common mechanisms for the progression of cardiac dysfunction. Literally, reverse remodeling is the process of reversing the remodeling, or in other words,it is a process of a temporary or a permanent correction of the heart. A 2004 article gives a description of the current therapies that support reverse remodeling and suggests a new approach to the prognosis of cardiomyopathies.

Alternative treatment
Alternative treatments are promoted by some, including food supplements Coenzyme Q10, L-Carnitine, Taurine and D-Ribose, and there is some evidence for the benefits of Coenzyme Q10 in treating heart failure.

Dilated cardiomyopathy in dogs, cats and other pets
Dilated cardiomyopathy is a heritable disease in some dog breeds, including the Boxer, Dobermann, Great Dane, Irish Wolfhound and St Bernard. Treatment is based on medication, including ACE inhibitors, loop diuretics and phosphodiesterase inhibitors.

Dilated cardiomyopathy is also a disease affecting some cat breeds, including the Oriental Shorthair, Burmese, Persian, and Abyssinian. As opposed to these hereditary forms, non-hereditary DCM used to be common in the overall cat population before the addition of taurine to commercial cat food.

There is also a high incidence of heritable dilated cardiomyopathy in captive Golden Hamsters (mesocricetus auratus), thanks in no small part to their being highly inbred. The incidence is high enough that several strains of Golden Hamster have been developed to serve as animal models in clinical testing for human forms of the disease.