Dilated cardiomyopathy

Dilated cardiomyopathy or DCM, also known as congestive cardiomyopathy, 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 and/or right ventricular systolic pump function of the heart is impaired, leading to progressive cardiac enlargement and hypertrophy, a process called remodeling.^[1]

Dilated cardiomyopathy is the most common form of cardiomyopathy. It occurs more frequently in men than in women, and is most common between the ages of 20 and 60 years.^[2] About one in three cases of congestive heart failure (CHF) is due to dilated cardiomyopathy.^[3] Dilated cardiomyopathy also occurs in children.

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Causes

Although no cause (etiology) is apparent in many cases, dilated cardiomyopathy is probably the end result of damage to the myocardium produced by a variety of toxic, metabolic, or infectious agents. It may be the late sequel of acute viral myocarditis, possibly mediated through an immunologic mechanism.^[4] Autoimmune mechanisms are also suggested as a cause for dilated cardiomyopathy.^[5] A reversible form of dilated cardiomyopathy may be found with alcohol abuse, pregnancy, thyroid disease, stimulant use, and chronic uncontrolled tachycardia. Many cases of dilated cardiomyopathy are described as idiopathic - meaning that the cause is unknown.

Genetics

About 20-40% of patients have familial forms of the disease, with mutations of genes encoding cytoskeletal, contractile, or other proteins present in myocardial cells.^[6] 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, and mitochondrial inheritance of the disease is also found.^[7] Relatives of dilated cardiomyopathy patients have been found to show preclinical, asymptomatic heart-muscle changes.^[8]

Although the disease is more common in African-Americans than in whites,^[9] it may occur in any patient population.

Associated symptoms

For many affected individuals, dilated cardiomyopathy is a condition which will not limit the quality or duration 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 concomitant ischemic heart disease. 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 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.^[10]

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.^[11][12][13] The majority of doctors doubt the effectiveness of these alternative treatments, but a few complement conventional treatment by suggesting Coenzyme Q10.

Dilated cardiomyopathy in dogs and cats

Dilated cardiomyopathy is a heritable disease in some dog breeds, including the Boxer, Dobermann, Great Dane, Irish Wolfhound and St Bernard.^[14] 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.

References