Andersons pediatric cardiology 1707

Viral Myocarditis The majority of the cases of myocarditis seen in the developed world are of viral origin.5 Biopsy specimens from patients with dilated cardiomyopathy can contain viral particles even when the histologic criterion for myocarditis is not evident Enteroviruses, particularly coxsackie group B, have been found most frequently, but polymerase chain reaction (PCR) studies have shown that adenoviruses are also common.6 Parvovirus B19, cytomegalovirus, echovirus, hepatitis C, respiratory syncytial virus, influenza, mumps, and rubella have also been implicated.7,8 Human immunodeficiency virus can cause myocarditis and pericarditis, often presenting with the picture of a dilated cardiomyopathy.9–12 The mechanisms involved in producing the myocardial injury are complex Invasion of the myocardial cells by viruses and elaboration of toxins both play important roles Cellular immune mechanisms and circulating autoantibodies may also be important in the overall pathogenesis of the disease Indeed, a combination, which may vary considerably between individual patients, of viral infection and subsequent abnormal immune response, causing either ineffective viral clearance or autoimmune myocyte damage, seems to underlie the clinical manifestation of the disease Persistence of the virus, or continuing immune reactions after the viral infection has cleared, may produce chronic myocardial damage and present as chronic myocarditis or dilated cardiomyopathy Clinical Features Myocarditis may be acquired prenatally or postnatally In older children it often includes pericarditis as a dominant feature Its clinical onset is usually seen after a latent period following the onset of a systemic viral infection The signs and symptoms of myocarditis are highly variable, and the patient may be asymptomatic Nonspecific symptoms include fever, dyspnea, fatigue, diarrhea, abdominal pain, problems with feeding, pallor, mild jaundice, and lethargy The most easily recognized signs include congestive heart failure or arrhythmias Older children will often complain of chest pain from pericarditis Occasionally the clinical picture may be dominated by severe respiratory distress secondary to left ventricular failure that has been mistaken for reactive airway disease or pneumonitis The important symptoms to recognize for myocarditis are cardiomegaly, tachycardia out of proportion to fever, a gallop rhythm, hepatomegaly, or an apical murmur indicating mitral insufficiency The clinical picture of cardiac failure in a previously well child with often a minor, preceding viral infection is typical Laboratory Findings The laboratory findings in myocarditis are nonspecific and generally consistent with an increased inflammatory state (Box 63.1) The white blood cell count may be elevated The presence of eosinophilia raises the suspicion of a parasitic etiology Cardiac troponin I and other cardiac enzymes are frequently elevated but may also be normal The erythrocyte sedimentation rate is usually elevated but may be normal The level of C-reactive protein may also be elevated, and this may be of prognostic significance.13 Although the diagnosis of viral myocarditis is generally based on history of a recent viral infection, viral cultures and PCR testing should be attempted However, the diagnosis of a viral origin is often based on the exclusion of other possible etiologies rather than positive identification of an etiologic agent Box 63.1 Laboratory Evaluation in Myocarditis Complete blood count Serum electrolytes Blood urea nitrogen/creatinine Alanine aminotransferase/aspartate aminotransferase Erythrocyte sedimentation rate C-reactive protein Troponin I Brain natriuretic peptide Bacterial blood culture Viral polymerase chain reaction/serologies