The Cardiomyopathies

Cardiomyopathy refers to a variety of conditions involving chronic disease of the heart muscle. There are three categories of cardiomyopathy:

dilated (congestive) cardiomyopathy

hypertrophic cardiomyopathy

restrictive cardiomyopathy

Dilated cardiomyopathy is the commonest type. It is characterized by dilation of the left ventricle associated with its impaired performance, which can range from minor functional disturbance to intractable heart failure. Dilated cardiomyopathy is the result of various factors damaging the heart muscle. As a primary disease of the myocardium unrelated to cardiac overload, dilated cardiomyopathy is not associated with hypertrophy of cardiac ventricles.

Most cases of dilated cardiomyopathy develop as a primary disease without an identifiable cause (idiopathic cardiomyopathy). As mentioned, some cases may represent late affereffects of viral myocarditis. The onset of cardiomyopathy is usually inconspicuous (unless it is a continuation of acute myocarditis). The first symptoms are typically mild and nondisabling. Progression to disability may take many years, though occasionally the process moves rapidly.

In some cases dilated cardiomyopathy may have an identifiable cause or be associated with special situations. Myocardial damage may result from heavy alcohol abuse (alcoholic cardiomyopathy). Drugs or chemical substances may do permanent damage to the heart muscle (toxic cardiomyopathy). For example, in 1960 in the Great Lakes region of the United States and Canada an epidemic of cardiomyopathy was traced to cobalt mixed into the beer to stabilize the foam. Certain drugs used in chemotherapy to treat cancer exert a toxic effect on the heart. Cardiomyopathy related to child-birth (peripartum cardiomyopathy) is a rare complication that may develop during the last trimester of pregnancy or after delivery. Cardiomyopathy may also develop in the course of coronary-artery disease (see chap. 8).

The first symptom of dilated cardiomyopathy patients become aware of is shortness of breath. Tolerance for exercise may gradually decrease until other evidence of heart failure develops. Yet cardiomyopathy may be discovered by a physician before any symptoms are present. Changes in the electrocardiogram taken during a routine checkup, discovery of an arrhythmia, or cardiac enlargement on X-ray examination may trigger further cardiac evaluation. A finding of reduced contraction of either or both ventricles, demonstrated by

echocardiography or nuclide ventriculography, is central to the diagnosis (so long as there is no evidence of coronary-artery disease or valvular malfunction). Biopsy of the heart muscle by means of cardiac catheterization may be performed if unusual varieties of cardiomyopathy amenable to drug therapy are suspected.

No specific therapy for cardiomyopathy is available, except in rare cases where response to corticosteroids may be anticipated. The results of conventional treatment of heart failure vary. In many cases a disability can be managed for years. Yet deterioration into end-stage heart failure is inevitable. The only type of cardiomyopathy in which a complete regression of the disease is possible is peripartum cardiomyopathy.

Complications of cardiomyopathy include ventricular arrhythmias and intracardiac thrombi, possible sources of emboli. Treatment of complications includes the use of anticoagulants to prevent intracardiac thrombi and antiarrhythmic drugs to control serious ventricular arrhythmias. Dilated cardiomyopthy is the commonest indication for cardiac transplantation.

Hypertrophic cardiomyopathy is a hypertrophy, or excessive development, of the myocardium of the left ventricle, or both ventricles, without a corresponding increase in cardiac workload. Examination of the heart muscle in this condition under the microscope reveals abnormal structure of muscle fibers, which appear disorganized and thicker and larger than normal. The cause of hypertrophic cardiomyopathy is not known, but it often runs in families and in those cases may be due to a genetic error. Hypertrophic cardiomyopathy affects people of all ages; the hereditary variety may manifest itself in adolescents and young adults.

In contrast to work hypertrophy found in valvular and other cardiac diseases, hypertrophy in this variety of cardiomyopathy is not evenly distributed throughout the muscle of the left ventricle but affects primarily the cardiac septum, which bulges into the cavity of the left ventricle or, less commonly, both ventricles. This selective thickening of the septum is most frequent at its upper part, close to the mitral valve, and may obstruct the flow of blood ejected during systole into the aorta. The abnormal bulge can also interfere with the mitral leaflets, creating resistance to outflow from the left ventricle, much as in aortic stenosis, which results in abnormally high pressure in the left ventricle. As a further consequence,

the mitral valve, now in an abnormal position, may become incompetent. These abnormalities of outflow from the left ventricle produce symptoms in some patients, namely chest pain similar to angina pectoris and attacks of sudden weakness, dizziness, or syncope.

Manifestations of hypertrophic cardiomyopathy vary greatly. Many patients remain asymptomatic for years and often survive to old age. Symptoms, if present, may appear episodically or with disabling frequency. They can usually be controlled by drugs; if drugs prove ineffective, surgical treatment is also available. However, the condition does carry a risk of sudden cardiac death, assumed to be due to fatal arrhythmias.

Complications of hypertrophic cardiomyopathy include atrial and ventricular arrhythmias. There is some risk of stroke from systemic emboli, almost always associated with complicating atrial fibrillation. Mitral regurgitation, frequently present, is usually inconsequential, although in rare cases severe mitral regurgitation may necessitate mitral-valve replacement. There is also a small risk of infective endocarditis.

The diagnosis of hypertrophic cardiomyopathy, often suggested by physical examination, is definitively established by echocardiography, which displays the thickened septum and the abnormal motion of the mitral valve. Treatment of hypertrophic cardiomyopathy includes the use of drugs to reduce the force of left ventricular contraction, thereby reducing the obstruction. These include beta-adrenergic blocking agents and calcium channel blockers. Surgery is reserved for severely symptomatic patients unresponsive to medical therapy. It consists of resecting a portion of the hypertrophic septum located opposite the mitral valve to eliminate or greatly reduce the outflow obstruction and relieve symptoms. There are, however, disadvantages to surgical therapy: first, the desired effects are not always attainable; second, the average mortality of the procedure is higher than for valvular surgery; third, there is no definite evidence that successful operations influence longevity.

Restrictive cardiomyopathy is the rarest of the three cardiomyopathies. Unlike dilated cardiomyopathy, in restrictive cardiomyopathy the left ventricle is of normal size and contracts normally; however, the disease affects its relaxation. Thus inadequate cardiac

output is related to deficient filling; that is, not enough blood enters the ventricle. Dilated cardiomyopathy is caused by systolic ventricular malfunction, restrictive cardiomyopathy by diastolic ventricular malfunction. In other words, dilated hearts cannot empty, and stiff hearts cannot fill. At rest the affected ventricle accepts the normal amount of blood; but during periods of increased activity the needed additional blood remains in the left atrium. Hence pressure in that chamber may rise in diastole, producing a chain of sequelae in the pulmonary circulation identical to that of congestive cardiac failure.

Restrictive cardiomyopathy is most frequently caused by diseases infiltrating the heart and other organs, such as amyloidosis, sarcoidosis, and hemosiderosis. Inadequate diastolic filling of the ventricles occurs also in constrictive pericarditis (see below), and it is often difficult to determine which of the two conditions is the cause of diastolic heart failure in a given case.

Patients with restrictive cardiomyopathy develop shortness of breath, which may progress to congestive heart failure. Diagnosis follows a finding of congestive heart failure despite a normal ventricular ejection fraction and normal-sized heart. Definitive identification of its cause can often be made on the basis of a myocardial biopsy.