Clinical manifestations and diagnosis of myocarditis in adults

●When to suspect myocarditis

Myocarditis should be suspected in patients with or without cardiac signs and symptoms. who present with a rise in cardiac biomarker levels, change in electrocardiogram (ECG) suggestive of acute myocardial injury, arrhythmia, or abnormalities of ventricular systolic function, particularly if these clinical findings are new and unexplained.

●Approach to the diagnosis of myocarditis

The diagnostic evaluation of patients with suspected myocarditis should include the following components:

•Physical examination

History and physical examination to evaluate for symptoms and signs of myocarditis and heart failure (HF) and assess possible causes.

•Initial laboratory testing

Initial laboratory testing, including an ECG, serum troponin levels, and, generally, a chest radiograph. Some clinicians also check erythrocyte sedimentation rate and c-reactive protein levels, although these have nonspecific markers of inflammation. Natriuretic peptide measurement is indicated if the diagnosis of HF is uncertain. 

•Cardiac imaging

Cardiac imaging for myocarditis includes:

–Echocardiography

An echocardiogram is performed in all patients with suspected myocarditis to evaluate regional and global ventricular function, valvular function, and other potential causes of cardiac dysfunction.

–Coronary angiography

Coronary angiography is indicated in selected patients with clinical presentation indistinguishable from an acute coronary syndrome, lifestyle-limiting coronary disease despite medical therapy, or high-risk features for ischemic heart disease on noninvasive testing. 

–Cardiovascular magnetic resonance imaging

Cardiovascular magnetic resonance (CMR) imaging is indicated in patients with suspected myocarditis with elevated troponin level and/or ventricular dysfunction, without a clear cause such as ischemic heart disease. CMR may provide supportive evidence of myocarditis.

•Endomyocardial biopsy

Indications for endomyocardial biopsy (EMB) should be reviewed in patients with clinically suspected myocarditis. The decision on whether to proceed with EMB should be based upon the likelihood that EMB will significantly impact patient management. 

Indications for EMB include unexplained new-onset HF of less than two weeks duration associated with hemodynamic compromise or unexplained new onset HF of two weeks to three months duration associated with a dilated left ventricle and new ventricular arrhythmias, Mobitz type II second-degree atrioventricular (AV) block, third-degree AV block, or refractory HF. Other patient groups who may benefit from EMB are discussed separately.

●Criteria for diagnosis

A definitive diagnosis of myocarditis is based upon EMB, including histology (Dallas criteria) as well as immunohistochemical stains and detection of viral genomes by molecular techniques, mainly polymerase chain reaction.

●Differential diagnosis

When a patient presents with suspected myocarditis, the differential diagnosis includes other conditions with similar symptoms and signs, including other causes of myocardial injury (including ischemic heart disease and stress cardiomyopathy) and other types of cardiomyopathy, as well as valvular heart disease, congenital heart disease, and pulmonary disease. Echocardiography is helpful for distinguishing many of these disorders.

●Causes of myocarditis

The history, physical examination, and clinical evaluation (including cardiac imaging and EMB) may help identify the cause of myocarditis, although the etiology of myocarditis is frequently unknown.