Myocarditis - Causes, Symptoms and Treatment
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 of Myocarditis
Myocarditis may result from:
1. 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
2. Bacterial Infections: diphtheria, tuberculosis, typhoid fever, tetanus, and staphylococcal, pneumococcal, and gonococcal infections
3. Hypersensitive Immune Reactions: acute rheumatic fever and postcardiotomy syndrome.
4. Radiation Therapy: large doses of radiation to the chest in treating lung or breast cancer.
5. Chemical Poisons: such as chronic alcoholism.
6. Parasitic Infections: especially South American trypanosomiasis (Chagas' disease) in infants and immunosuppressed adults; also, toxoplasmosis.
7. Helminthic Infections: such as trichinosis.
Signs and Symptoms of Myocarditis
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 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 for Myocarditis
The patient history commonly reveals recent febrile upper respiratory tract infection, viral pharyngitis, or tonsillitis. A physical examination shows supraventricular and ventricular arrhythmias, S3 and S4 gallops, a faint S1' possibly a murmur of mitral insufficiency (hom papillary muscle dysfunction) and, if pericarditis is present, a pericardial friction rub.
Electrocardiography typically shows diffuse ST-segment and T-wave abnormalities (as in pericarditis), conduction defects (prolonged PR interval), and other supraventricular arrhythmias. Stool and throat cultures may identify the causative bacteria. An endomyocardial biopsy is used to confirm the diagnosis, but a negative biopsy doesn't exclude the diagnosis. A repeat biopsy may be needed. Laboratory tests can't unequivocally confirm myocarditis, but the following findings support this diagnosis:
1. Cardiac enzyme levels (creatine kinase [CK], the CK-MB isoenzyme, aspartate aminotransferase, and lactate dehydrogenase) are elevated.
2. White blood cell count and erythrocyte sedimentation rate are increased.
3. Antibody titers (such as antistreptolysin titer in rheumatic fever) are elevated.
Endocardial biopsy remains the gold standard for diagnosis of myocarditis, although results remain controversial and the procedure is invasive and costly.
Treatment for Myocarditis
In myocardial infarction, treatment includes antibiotics 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, diuretics to decrease fluid retention, and digitalis glycosides to increase myocardial contractility. Isotropic support of cardiac function with amrinone, dopamine, or dobutamine may be needed. However, digitalis glycosides must be administered cautionsly because some patients with myocarditis show a paradoxical sensitivity to even small doses.
Thromboembolism requires anticoagulation therapy. Treatment with corticosteroids or other immunosuppressants is controversial and therefore limited to combating life-threatening complications such as intractable heart failure .
Special Considerations and Prevention Tips for Myocarditis
1. Assess cardiovascular status frequently, watching for signs of heart failure, such as dyspnea, hypotension, and tachycardia. Check for changes in cardiac rhythm or conduction.
2. Observe for signs of digitalis toxicity (anorexia, nausea, vomiting, blurred vision, cardiac arrhythmias) and for complicating factors that may potentiate toxicity, such as electrolyte imbalances or hypoxia.
3. 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.
4. Offer diversional activities that are physically undemanding.
5. During recovery, recommend that the patient resume normal activities slowly and avoid competitive sports.
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