Myocarditis

Myocarditis refers to inflammation, necrosis, or myocytolysis and may be caused by many infectious, connective tissue, granulomatous, toxic, or idiopathic processes affecting the myocardium with or without associated systemic manifestations of the disease process or involvement of the endocardium or pericardium.

Etiology:
The most common causative agents in children are adenovirus, coxsackievirus B, and other enteroviruses, although most known viral agents have been implicated.

Pathophysiology:
Acute viral myocarditis may produce a fulminant inflammatory process characterized by cellular infiltrates, cell degeneration and necrosis, and subsequent fibrosis. Viral myocarditis may also become a chronic process with persistence of viral RNA or DNA (but not infectious virus particles) in the myocardium.In addition, some viral proteins may share antigenic epitopes with host cells, which results in autoimmune damage to the antigenically related myocyte.

The net final result of chronic viral-associated inflammation is often dilated cardiomyopathy.

Clinical Manifestations:
Signs and symptoms depend on the patient’s age and the acute or chronic nature of the infection. A neonate may initially have fever, severe heart failure, respiratory distress, cyanosis, distant heart sounds, weak pulses, tachycardia out of proportion to the fever, mitral insufficiency caused by dilatation of the valve annulus, a gallop rhythm, acidosis, and shock. Evidence of viral hepatitis, aseptic meningitis, and an associated rash may be present. In the most fulminant form, death may occur within 1–7 days of the onset of symptoms.

An older patient with acute myocarditis may also initially be seen with acute congestive heart failure; however, more commonly, patients have a gradual onset of congestive heart failure or a sudden onset of ventricular arrhythmias. In these patients, the acute infectious phase has usually passed and an idiopathic dilated cardiomyopathy is present.

Diagnosis:
The sedimentation rate, heart enzymes (creatine phosphokinase, lactate dehydrogenase), and brain natriuretic peptide (BNP) may be elevated in acute or chronic myocarditis. If positive, serum viral titers are helpful; negative titers do not eliminate the diagnosis.

Echocardiography demonstrates poor ventricular function and often a pericardial effusion, mitral valve regurgitation, and the absence of coronary artery or other congenital heart lesions.

Treatment:
The approach to treating acute myocarditis involves supportive measures for severe congestive heart failure or cardiogenic shock .

Dopamine, epinephrine, and milrinone may be helpful in those with poor cardiac output and systemic hypoperfusion.

All inotropic agents, including digoxin, should be used with caution because patients with myocarditis are susceptible to the arrhythmogenic properties of these agents. When used, digoxin is often started at half the normal dosage.

Arrhythmias should be treated aggressively and may require the use of intravenous amiodarone to achieve adequate control.

For infants and children in cardiogenic shock, extracorporeal membrane oxygenation (ECMO) may be indicated.

The role of specific treatments of viral myocarditis is controversial. Intravenous immunoglobulin (IVIG) has been used at 2 g/kg. Corticosteroids have also been utilized and, in several small series of pediatric patients, treatment with prednisone (2 mg/kg daily, tapered to 0.3 mg/kg daily over a period of 3 mo) was effective in reducing myocardial inflammation and improving cardiac function. Relapse has been noted to occur when immunosuppression is discontinued in some patients