Chapter Ten
Diseases of the
Myocardium and Pericardium

Diseases of the Myocardium

This chapter deals with rarer varieties of heart muscle disease caused by conditions other than coronary disease. The life-sustaining function of the heart depends on the pumping capacity of the left ventricular heart muscle, and, to a lesser extent, that of the right ventricular muscle. The commonest cause of impairment of left ventricular function is destruction of heart muscle cells produced by myocardial ischemia as a part of coronary disease (see "Pump Failure," chapter 8).

Acute Myocarditis

Any inflammatory process affecting the heart muscle is referred to as myocarditis . In most cases myocarditis results from an infection, although there are other causes as well. Involvement of the myocardium occurs commonly in some acute infectious diseases, especially those caused by viruses; but owing to the benign nature of myocarditis, it routinely goes unrecognized.

Many viral childhood diseases—mumps, measles, poliomyelitis—may lead to myocarditis. As a rule, they do not produce any symptoms, and hence the myocarditis cannot be recognized on physical examination; its presence can only be detected by special tests. Since it usually has no significant sequelae, testing for myocarditis is not indicated. However, in rare cases myocarditis may

lead to heart failure and even death. It is believed that myocarditis is principally responsible for the rare deaths from influenza. In the past, when diphtheria was common, myocarditis due to a toxin of the diphtheria bacillus was a dreaded complication of that disease. Myocarditis may coexist with viral pericarditis, to be discussed later in this chapter. It can also be caused by some drugs and by radiation therapy. As a part of the hypersensitivity mechanism, myocarditis is often a manifestation of diseases related to allergic reaction, such as acute rheumatic fever. Myocardial involvement occurs occasionally in infectious mononucleosis, viral hepatitis, and Lyme disease.

Even in those rare cases where heart failure results from acute myocarditis, complete recovery is the commonest outcome. Occasionally viral myocarditis may initiate dilated cardiomyopathy (see below). Heart failure caused by myocarditis may persist beyond the acute stage, turning into dilated cardiomyopathy. More often, however, there is an apparent recovery from acute myocarditis, with cardiomyopathy developing gradually months or years later. The possibility that some cases of dilated cardiomyopathy of unknown cause may also be the consequence of past, unrecognized myocarditis has been suggested, though not proved.

Clinically significant acute myocarditis presents itself usually by the onset of dyspnea. Signs of heart failure appear without obvious cause but are often associated with a fever. Diagnostic studies may show electrocardiographic abnormalities, which are particularly significant if day-to-day changes are observed. Chest X ray may reveal enlargement of the heart shadow. Echocardiography and nuclide ventriculogram are the definitive tests for determining the degree to which ventricular function is impaired.

Because of the self-limiting nature of myocarditis, in most cases no treatment is necessary. If a contributive allergic factor is suspected, the use of immunosuppressive drugs, including corticosteroids, may be justified.

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.

Diseases of the Pericardium

As explained in chapter 1, the pericardium consists of two layers of a thin membrane, one lining the outside of the heart (visceral pericardium), the other enveloping the heart and the first portions of the great vessels (parietal pericardium). Between the two layers is space for a small amount of fluid acting as a lubricant to reduce friction between them during cardiac motion. An increase in the amount of pericardial fluid (pericardial effusion) occurs in many conditions affecting the heart and other organs. The parietal pericarduim has enough elasticity to accommodate a fair amount of pericardial fluid, so that pericardial effusion ordinarily does not interfere with the function of the heart.

Diseases of the pericardium may have a significant effect on the function of the heart if they restrict its motion. Restriction can

develop if the amount of pericardial fluid exceeds the elastic capacity of the parietal pericardium or if the pericardium thickens and loses its elasticity.

Pericardial tamponade occurs if pericardial fluid accumulates too rapidly to permit adaptive stretching of the pericardium. The pressure in the pericardial sac rises, and when it exceeds that in the atria, the filling of the heart in diastole is interfered with. Tamponade is a serious condition that may become a life-threatening emergency. Though tamponade may develop in the course of acute pericarditis, its most dangerous cause is the escape of blood from the heart into the pericardial sac, a condition known as hemopericardium. The principal cause of naturally occurring hemopericardium is rupture of the heart during acute myocardial infarction. This complication is usually fatal, although occasionally there is enough time to perform immediate corrective surgery. The commonest cause of pericardial tamponade due to hemopericardium is trauma resulting from one of the many diagnostic or therapeutic intracardiac interventions and, rarely, from cardiac surgery. Tamponade may also develop because of external trauma—stab wounds or gunshot wounds.

The immediate consequence of tamponade is a fall in arterial blood pressure and an increase in venous pressure. When arterial pressure reaches shock level, tamponade becomes a life-threatening emergency and must be recognized immediately. Instant relief follows removal of blood or fluid from the pericardium by means of a needle inserted through the skin and the chest wall into the pericardial sac. It is sometimes necessary to supplement this treatment with surgical drainage of the pericardium.

Acute pericarditis is most often caused by viral infection either as a part of general infection with a virus or as a disease limited to the pericardium. It is usually a self-limiting febrile illness lasting one to two weeks and almost never has immediate aftereffects. The principal feature of acute pericarditis is chest pain, which may resemble the ischemic pain of coronary-artery disease. In rare cases fluid accumulation may be rapid enough to produce tamponade. The diagnosis of pericarditis is commonly made on the basis of characteristic abnormalities in the electrocardiogram. However, the most sensitive and reliable means of demonstrating pericardial fluid is echocardiography.

Acute pericarditis is treated with antiinflammatory drugs to control the pain. Although acute pericarditis is often referred to as benign, in a small number of cases there are late consequences. One or more attacks of recurrent pericarditis may develop at intervals of a few weeks. Late appearance of constrictive pericarditis (see below) may take place particularly in patients who have had more than one attack.

Acute pericarditis similar to the viral variety often develops from one of the systemic diseases characterized by an allergic-type reaction. These diseases include rheumatic fever, systemic lupus erythematosus, and rheumatoid arthritis. Pericarditis can also occur after acute myocardial infarction (Dressler syndrome) and occasionally after cardiac surgery (postcardiotomy syndrome). These attacks are particularly prone to recur periodically.

Chronic pericardial effusion may develop with or without disease of the pericardium. Increased fluid in the pericardial sac is common in cases of general fluid retention due to cardiac or renal disease. As such it produces no symptoms and may be discovered by chest X ray (marked enlargement of the cardiac shadow) or echocardiography. When pericardial disease is present, persistence of fluid is often a precursor of constrictive pericarditis. Tuberculous pericarditis is characterized by pericardial effusion persisting for years and gradually leading to thickening of the pericardium and pericardial constriction, with eventual disappearance of the fluid. Uremic pericarditis is a common complication of chromic kidney failure; tamponade and, rarely, constrictive pericarditis may result. Neoplastic pericarditis may be caused by primary tumors (neoplasms) of the pericarduim or by invasion of tumors from elsewhere, particularly the lungs. Postradiation pericarditis may develop in patients after radiotherapy for cancer in the chest, including breast cancer.

Echocardiography is the principal diagnostic tool in pericardial effusion. Frequently a pericardial needle tap (to remove fluid) is needed to determine the nature of the effusion, particularly if tuberculosis or neoplasm is suspected. Surgical drainage or removal of parts of the pericardium may be indicated even in the absence of fully developed constrictive pericarditis.

Chronic constrictive pericarditis is present when a diseased pericardium becomes so thick and stiff that the filling of the heart is

interfered with. The two layers of the pericardium often adhere to each other, forming a firm, inelastic structure in which the heart is encased. In late stages of constrictive pericarditis calcium deposits may envelop the heart in a bonelike armor. Constrictive pericarditis often resembles congestive heart failure. But because of its chronicity massive edema and enlargement of the liver, which may result in secondary cirrhosis of the liver, are much more common than in congestive heart failure.

At one time, most cases of constrictive pericarditis were caused by tuberculosis, which today is rare. Now constriction may be the end result of acute pericarditis and may sometimes be found in cases of uremic pericarditis and neoplastic pericarditis. It is also a complication of radiation therapy for cancer of the breast or other structures in the chest. The diagnosis of constrictive pericarditis can often be made on the basis of physical examination and X rays. Echocardiography is helpful but may not be as decisive as in pericardial effusion. As mentioned, it is occasionally difficult to distinguish constrictive pericarditis from restrictive cardiomyopathy. Treatment is primarily surgical, although in early stages diuretics can provide considerable relief of symptoms. Surgical removal of the thick pericardium does not require that the heart be opened; nevertheless, the risk in surgery is moderately high.

Purulent pericarditis involves the accumulation of pus in the pericardial space. It frequently is a complication of a purulent process in the chest. This type of pericarditis usually requires prolonged surgical drainage.