Atlas of pathophysiology, 2 Edition

Part II - Disorders

Cardiovascular disorders

Myocarditis

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 causes neither specific cardiovascular symptoms nor electrocardiogram abnormalities, and recovery is usually spontaneous without residual defects. Occasionally, myocarditis is complicated by heart failure; in rare cases, it leads to cardiomyopathy.

Causes

·         Infections: viral, bacterial, parasitic-protozoan, fungal, or helminthic (such as trichinosis)

·         Hypersensitive immune reactions, such as acute rheumatic fever or postcardiotomy syndrome

·         Radiation therapy or chemotherapeutic agents

·         Toxins, such as lead, chemicals, or cocaine

·         Chronic alcoholism

·         Systemic autoimmune disorders, such as systemic lupus erythematosus and sarcoidosis

Pathophysiology

Damage to the myocardium occurs when an infectious organism triggers an autoimmune, cellular, or humoral reaction; noninfectious causes can lead to toxic inflammation. In either case, the resulting inflammation may lead to hypertrophy, fibrosis, and inflammatory changes of the myocardium and conduction system. The heart muscle weakens, and contractility is reduced. The heart muscle becomes flabby and dilated, and pinpoint hemorrhages may develop.

Signs and symptoms

·         Fatigue, dyspnea, palpitations

·         Fever

·         Chest pain or mild, continuous pressure or soreness in the chest

·         Tachycardia, S3 and S4 gallops

·         Murmur of mitral insufficiency, pericardial friction rub

·         Right-sided and left-sided heart failure (jugular vein distention, dyspnea, edema, pulmonary congestion, persistent fever with resting or exertional tachycardia disproportionate to the degree of fever, and supraventricular and ventricular arrhythmias)

Clinical Tip

To auscultate for a pericardial friction rub, have the patient sit upright, lean forward, and exhale. Listen over the third intercostal space on the left side of the chest. A pericardial rub has a scratchy, rubbing quality. If you suspect a rub and have difficulty hearing one, have the patient hold his breath.

Diagnostic test results

·         Blood testing shows elevated levels of creatine kinase (CK), CK-MB, troponin I, troponin T, aspartate aminotransferase, and lactate dehydrogenase. Also, inflammation and infection cause elevated white blood cell count and erythrocyte sedimentation rate.

·         Antibody titers are elevated, such as antistreptolysin-O titer, in rheumatic fever.

·         Electrocardiogram illustrates diffuse ST-segment and T-wave abnormalities, conduction defects (prolonged PR interval, bundle-branch block, or complete heart block), supraventricular arrhythmias, and ventricular extrasystoles.

·         Chest X-rays show an enlarged heart and pulmonary vascular congestion.

·         Echocardiography demonstrates some left ventricular dysfunction.

·         Radionuclide scanning identifies inflammatory and necrotic changes characteristic of myocarditis.

·         Laboratory cultures of stool, throat, and other body fluids identify bacterial or viral causes of infection.

·         Endomyocardial biopsy shows damaged myocardial tissue and inflammation.

Treatment

·         No treatment for benign self-limiting disease

·         Antibiotics

·         Antipyretics

·         Restricted activity

·         Supplemental oxygen therapy

·         Sodium restriction and diuretics

·         Angiotensin-converting enzyme inhibitors

·         Beta-adrenergic blockers

·         Digoxin

·         Antiarrhythmic drugs, such as quinidine or procainamide

·         Temporary pacemaker

·         Anticoagulants

·         Corticosteroids and immunosuppressants

·         Cardiac assist devices or heart transplantation

P.65

TISSUE CHANGES IN MYOCARDITIS

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