Myocarditis
Myocarditis: Excerpt from Professional Guide to Diseases (Eighth Edition)
Myocarditis is focal or diffuse inflammation of the cardiac muscle (myocardium). It may be acute or chronic and can occur at any age. In many cases, myocarditis fails to produce specific cardiovascular symptoms or electrocardiogram (ECG) abnormalities, and recovery is usually spontaneous, without residual defects. Occasionally, myocarditis is complicated by heart failure; in rare cases, it leads to cardiomyopathy.
Causes and incidence
Myocarditis may result from:
❑ bacterial infections — diphtheria; tuberculosis; typhoid fever; tetanus; and staphylococcal, pneumococcal, and gonococcal infections
❑ chemical poisons — such as chronic alcoholism
❑ helminthic infections — such as trichinosis
❑ hypersensitive immune reactions — acute rheumatic fever and postcardiotomy syndrome
❑ parasitic infections — especially South American trypanosomiasis (Chagas’ disease) in infants and immunosuppressed adults; also toxoplasmosis
❑ radiation therapy — large doses of radiation to the chest in treating lung or breast cancer
❑ viral infections (most common cause in the United States and western Europe) — coxsackievirus A and B strains and, possibly, poliomyelitis, influenza, rubeola, rubella, and adenoviruses and echoviruses.
Myocarditis occurs in 1 to 10 of every 100,000 people in the United States. The median age for this disorder is 42, and incidence is equal between males and females. Children, especially neonates, and persons who are immunocompromised or pregnant (especially pregnant black women) are at higher risk for developing this disorder.
Signs and symptoms
Myocarditis usually causes nonspecific symptoms — such as fatigue, dyspnea, palpitations, and fever — that reflect the accompanying systemic infection. Occasionally, it may produce mild, continuous pressure or soreness in the chest (unlike the recurring, stress-related pain of angina pectoris). Although myocarditis is usually self-limiting, it may induce myofibril degeneration that results in right- and left-sided heart failure, with cardiomegaly, jugular vein distention, dyspnea, persistent fever with resting or exertional tachycardia disproportionate to the degree of fever, and supraventricular and ventricular arrhythmias. Sometimes myocarditis recurs or produces chronic valvulitis (when it results from rheumatic fever), cardiomyopathy, arrhythmias, and thromboembolism.
Diagnosis
Patient history commonly reveals recent febrile upper respiratory tract infection, viral pharyngitis, or tonsillitis. Physical examination shows supraventricular and ventricular arrhythmias, S3 and S4 gallops, a faint S1, possibly a murmur of mitral insufficiency (from papillary muscle dysfunction) and, if pericarditis is present, a pericardial friction rub.
Laboratory tests can’t unequivocally confirm myocarditis, but the following findings support this diagnosis:
❑ cardiac enzymes: elevated creatine kinase (CK), CK-MB, aspartate aminotransferase, and lactate dehydrogenase levels
❑ increased white blood cell count and erythrocyte sedimentation rate
❑ elevated antibody titers (such as antistreptolysin-O titer in rheumatic fever).
CONFIRMING DIAGNOSIS Endomyocardial biopsy is rarely performed to diagnose myocarditis; the procedure is invasive and costly. A negative biopsy doesn’t exclude the diagnosis, and a repeat biopsy may be needed.
ECG typically shows diffuse ST-segment and T-wave abnormalities as in pericarditis, conduction defects (prolonged PR interval), and other supraventricular arrhythmias. Echocardiography demonstrates some degree of left ventricular dysfunction, and radionuclide scanning may identify inflammatory and necrotic changes characteristic of myocarditis.
Stool and throat cultures may identify bacteria.
Treatment
Treatment includes antibiotics for bacterial infection, modified bed rest to decrease heart workload, and careful management of complications. Inotropic support of cardiac function with amrinone, dopamine, or dobutamine may be needed. Heart failure requires restriction of activity to minimize myocardial oxygen consumption, supplemental oxygen therapy, sodium restriction, diuretics to decrease fluid retention, and cardiac glycosides to increase myocardial contractility. However, cardiac glycosides should be administered cautiously because some patients with myocarditis may show a paradoxical sensitivity to even small doses. Arrhythmias necessitate prompt but cautious administration of antiarrhythmics because these drugs depress myocardial contractility. Thromboembolism requires anticoagulation therapy. Treatment with corticosteroids or other immunosuppressants may be used to reduce inflammation, but they haven’t been shown to change the progression of myocarditis infections. Nonsteroidal anti-inflammatory drugs are contraindicated during the acute phase (first 2 weeks) because they increase myocardial damage.
Surgical treatment may include left ventricular assistive devices and extra corporeal membrane oxygenation for support of cardiogenic shock. Cardiac transplantation has been beneficial for giant cell myocarditis.
Special considerations
❑ Assess cardiovascular status frequently, watching for signs of heart failure, such as dyspnea, hypotension, and tachycardia. Check for changes in cardiac rhythm or conduction.
❑ Observe for signs of digoxin toxicity (anorexia, nausea, vomiting, blurred vision, and cardiac arrhythmias) and for complicating factors that may potentiate toxicity, such as electrolyte imbalance or hypoxia.
❑ Stress the importance of bed rest. Assist with bathing, as necessary; provide a bedside commode because this stresses the heart less than using a bedpan. Reassure the patient that activity limitations are temporary. Offer diversional activities that are physically undemanding.
❑ During recovery, recommend that the patient resume normal activities slowly and avoid competitive sports.
Book Source Details
- Book Title: Professional Guide to Diseases (Eighth Edition)
- Author(s): Springhouse
- Year of Publication: 2005
- Copyright Details: Professional Guide to Diseases (Eighth Edition), Copyright © 2005 Lippincott Williams & Wilkins.
More About Pericarditis
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Medical Books Excerpts
- Myocarditis
- "Professional Guide to Diseases (Eighth Edition)" (2005)
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Copyright notice for book excerpts: Copyright © 2008 Lippincott Williams & Wilkins. All rights reserved.
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