Acute Myocarditis

Introduction
Acute myocarditis causes focal or diffuse inflammation of the myocardium. Most cases are infectious, caused by viral, bacterial, rickettsial, spirochetal, fungal, or parasitic agents; but toxins, drugs, and immunologic disorders can also cause myocarditis.

1. Infectious Myocarditis

Introduction Essentials of Diagnosis

• Often follows an upper respiratory infection.
• May present with chest pain (pleuritic or nonspecific) or signs of heart failure.
• ECG may show sinus tachycardia, other arrhythmias, nonspecific repolarization changes, and intraventricular conduction abnormalities.
• Echocardiogram documents cardiomegaly and contractile dysfunction.
• Myocardial biopsy, though not sensitive, may reveal a characteristic inflammatory pattern.

General Considerations
Viral myocarditis is the most common form and is usually caused by coxsackieviruses, but a host of other agents have also been responsible. Rickettsial myocarditis occurs with scrub typhus, Rocky Mountain spotted fever, and Q fever. Diphtheritic myocarditis is caused by the exotoxin and often is manifested by conduction abnormalities as well as heart failure.

Chagas’ disease, caused by the insect-borne protozoan Trypanosoma cruzi, is a common form of myocarditis in Central and South America; the major clinical manifestations appear after a latent period of more than a decade. At this stage, patients present with cardiomyopathy, conduction disturbances, and sudden death. Associated gastrointestinal involvement (megaesophagus and megacolon) is the rule. Toxoplasmosis causes myocarditis that is usually asymptomatic but can lead to heart failure. Among parasitic infections, trichinosis is the most common cause of cardiac involvement. The potential for the HIV virus to cause myocarditis is now well recognized, though the prevalence of this complication is not known. In addition, other infectious myocarditides are more common in patients with AIDS.

Giant cell myocarditis is a rare idiopathic disorder characterized by giant cell and lymphocyte infiltration of the heart muscle. Patients usually die from ventricular arrhythmias or heart failure but occasionally respond to immunosuppressive therapy or early transplantation.

Clinical Findings
A. Symptoms and Signs

Patients may present several days to a few weeks after the onset of an acute febrile illness or a respiratory infection or with heart failure without antecedent symptoms. The onset of heart failure may be gradual or may be abrupt and fulminant. Pleural-pericardial chest pain is common. Examination reveals tachycardia, gallop rhythm, and other evidence of heart failure or conduction defect. It is likely that most myocarditides are subclinical, though they may present later as idiopathic cardiomyopathy or with ventricular arrhythmias.

B. Electrocardiography and Chest X-Ray
Nonspecific ST-T changes and conduction disturbances are common. Ventricular ectopy may be the initial and only clinical finding. Chest x-ray is nonspecific, but cardiomegaly is frequent.

C. Diagnostic Studies
Echocardiography provides the most convenient way of evaluating cardiac function and can exclude many other processes. Gallium-67 scintigraphy has been reported to yield cardiac uptake in acute or subacute myocarditis. Paired serum viral titers and serologic tests for other agents may indicate the cause.

D. Endomyocardial Biopsy
Pathologic examinations may reveal a lymphocytic inflammatory response with necrosis, but the patchy distribution of abnormalities makes the test relatively insensitive. This defines an “active” inflammatory stage and may persist for many months.

Treatment & Prognosis
Specific antimicrobial therapy is indicated when an infecting agent is identified. Immunosuppressive therapy with corticosteroids and other agents has been felt by some to improve the outcome when the process is acute (

< 6 months) and if the biopsy suggests ongoing inflammation. However, controlled trials have not been positive, so the value of routine myocardial biopsies in patients presenting with an acute myocarditic picture is uncertain; immunosuppressive therapy without histologic confirmation is unwise. Otherwise, treatment is directed toward the manifestations of heart failure and arrhythmias.

Many cases resolve spontaneously, but in others cardiac function deteriorates progressively and may lead to dilated cardiomyopathy. Many cases of dilated cardiomyopathy may represent the end stage of viral myocarditis.

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2. Drug-Induced & Toxic Myocarditis

A variety of medications, illicit drugs, and toxic substances can produce acute or chronic myocardial injury; the clinical presentation varies widely. Doxorubicin and other cytotoxic agents, emetine, and catecholamines (especially with pheochromocytoma) can produce a pathologic picture of inflammation and necrosis together with clinical heart failure and arrhythmias; toxicity of the first two is dose related. The phenothiazines, lithium, chloroquine, disopyramide, antimony-containing compounds, and arsenicals can also cause electrocardiographic changes, arrhythmias, or heart failure. Hypersensitivity reactions to sulfonamides, penicillins, and aminosalicylic acid as well as other drugs can result in cardiac dysfunction. Radiation can cause an acute inflammatory reaction as well as a chronic fibrosis of heart muscle, usually in conjunction with pericarditis.

The incidence of cocaine cardiotoxicity has increased markedly. Cocaine can cause Coronary artery spasm, myocardial infarction, arrhythmias, and myocarditis. Because many of these processes are believed to be mediated by cocaine’s inhibitory effect on norepinephrine reuptake by sympathetic nerves, ß-blockers have been used therapeutically. In coronary spasm, calcium channel blockers are more appropriate.

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