Myocarditis
Myocarditis: Excerpt from Handbook of Diseases
Myocarditis is focal or diffuse inflammation of the cardiac muscle (myocardium). It may be acute or chronic and can occur at any age. Frequently, 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; rarely, it may lead to cardiomyopathy.
Causes
Myocarditis may result from:
❑ 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
❑ bacterial infections: diphtheria, tuberculosis, typhoid fever, tetanus, and staphylococcal, pneumococcal, and gonococcal infections
❑ hypersensitive immune reactions: acute rheumatic fever and postcardiotomy syndrome
❑ radiation therapy: large doses of radiation to the chest in treating lung or breast cancer
❑ chemical poisons: such as chronic alcoholism
❑ parasitic infections: especially South American trypanosomiasis (Chagas’ disease) in infants and immunosuppressed adults; also, toxoplasmosis
❑ helminthic infections: such as trichinosis
❑ medications: penicillin, ampicillin, hydrochlorothiazide, methyldopa, and sulfonamides (may cause hypersensitivity myocarditis)
❑ autoimmune factors: human immunodeficiency virus (has been shown to directly attack the myocardium)
❑ rejection syndrome: rejection of posttransplant hearts (may cause inflammatory myocarditis).
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, neck 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
The patient history commonly reveals recent febrile upper respiratory tract infection, viral pharyngitis, or tonsillitis. A physical examination shows supraventricular and ventricular arrhythmias, third and fourth heart sounds, a faint first heart sound, possibly a murmur of mitral insufficiency (from papillary muscle dysfunction) and, if pericarditis is present, a pericardial friction rub.
ECG typically shows diffuse STsegment and T-wave abnormalities (as in pericarditis), conduction defects (prolonged PR interval), and other supraventricular arrhythmias.
Echocardiography may show a weak heart muscle, an enlarged heart, or fluid surrounding the heart.
Stool and throat cultures may identify the causative bacteria. An endomyocardial biopsy can confirm the diagnosis, but it’s rarely performed.
Laboratory tests can’t unequivocally confirm myocarditis, but the following findings support this diagnosis:
❑ Cardiac enzyme levels (creatine kinase [CK], the CK-MB isoenzyme, aspartate aminotransferase, and lactate dehydrogenase) are elevated.
❑ White blood cell count and erythrocyte sedimentation rate are increased.
❑ Antibody titers (such as antistreptolysin O titer in rheumatic fever) are
elevated.
❑ Blood cultures may indicate infection.
Treatment
Treatment includes an antibiotic for bacterial infection, modified bed rest to decrease the cardiac workload, and careful management of complications. Heart failure requires restriction of activity to minimize myocardial oxygen consumption, supplemental oxygen therapy, sodium restriction, a diuretic to decrease fluid retention, and a cardiac glycoside to increase myocardial contractility. However, cardiac glycosides must be administered cautiously because some patients with myocarditis show a paradoxical sensitivity to even small doses.
Arrhythmias necessitate prompt but cautious administration of antiarrhythmics, which can depress myocardial contractility. Thromboembolism requires anticoagulation therapy. Treatment with a corticosteroid or other immunosuppressant is controversial and therefore limited to combating life-threatening complications such as intractable heart failure.
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.
❑ Monitor the patient for signs and symptoms of digoxin toxicity (anorexia, nausea, vomiting, blurred vision, and cardiac arrhythmias) and for complicating factors that may potentiate toxicity, such as electrolyte imbalances or hypoxia.
❑ Stress the importance of bed rest. Assist with bathing as necessary; provide a bedside commode, which puts less stress on the heart than using a bedpan. Reassure the patient that activity limitations are temporary.
❑ Instruct the patient on a low-salt diet, if prescribed.
CLINICAL TIP: During recovery, recommend that the patient resume normal activities slowly and avoid competitive sports.
Book Source Details
- Book Title: Handbook of Diseases
- Author(s): Springhouse
- Year of Publication: 2003
- Copyright Details: Handbook of Diseases, Copyright © 2003 Lippincott Williams & Wilkins.
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Copyright notice for book excerpts: Copyright © 2008 Lippincott Williams & Wilkins. All rights reserved.
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More About This Book:
Title: Handbook of Diseases
Authors: Springhouse
Publisher: Lippincott Williams & Wilkins
Copyright: 2003
ISBN: 1-58255-266-5
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» Next page: Pericarditis (Handbook of Diseases)
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