Clinical Characteristics and Mechanisms of Acute Myocarditis

Myocarditis is defined by an immune response to infection or injury, most commonly identified after a viral infection or recent exposure to cardiotoxins or drugs. Classic myocarditis may also result from the activation of the immune system by self-antigens without an exogenous trigger. Pathogenic variants of genes encoding sarcolemmal and desmosomal proteins are present in 4% to 44% of myocarditis patients and may relate to persistent cardiac dysfunction and arrhythmias. The most common clinical presentation is acute chest pain resembling an ischemic infarction or pericarditis. Heart failure and syncope
from tachy- or brady-arrhythmias are features of a complicated clinical course with substantial risk of future cardiovascular events and death. High-sensitivity troponin, ECG, and echocardiograms are useful but lack sufficient sensitivity and specificity to confirm the diagnosis. Cardiovascular magnetic resonance is indicated to confirm myocarditis in low-risk, uncomplicated cases. Endomyocardial biopsy is indicated to guide therapy in high-risk scenarios. In this review, we discuss the clinical aspects, pathogenesis, genetic susceptibility, and management of uncomplicated, complicated, and fulminant myocarditis related to viral injury. We identify gaps in understanding and suggest prime research questions in the pathogenesis, diagnosis, and treatment of acute myocarditis.