Myocarditis and Inflammatory Cardiomyopathies

Abstract

Myocarditis is an inflammatory disease of the myocardium usually caused by infections, exposure to other pathogens, toxic substances, and immune system activation. Myocarditis may present in acute, fulminant, subacute, and chronic forms. Systolic function is usually preserved in patients with infarct-like presentation, who are considered to have a good prognosis. The clinical presentation of acute myocarditis (AM) is heterogeneous making diagnosis a challenge. Cardiac magnetic resonance (CMR) has significantly improved diagnosis in patients with suspected AM, since its capability in myocardial injury detection, such as myocardial edema, hyperemia, and late gadolinium enhancement (LGE). While CMR is able to detect an inflammatory cardiopathy in vivo easily, it is not able to identify the underlying etiopathogenetic mechanism. In 2009, a consensus group published the original Lake Louise Criteria, which identified three hallmarks of myocardial inflammation with corresponding CMR markers: hyperemia, that is hyperintensity in early gadolinium enhancement images; tissue edema, assessed as an increased myocardial T2 relaxation time or an increased signal intensity in T2-weighted images; and necrosis/fibrosis detected by late gadolinium enhancement (LGE). In recent years, parametric mapping, which allows direct quantification of myocardial tissue magnetic parameters, (primarily T1 and T2) has been increasingly applied in myocarditis with an increase in sensitivity. However, the diagnostic accuracy of CMR might vary according to the clinical presentation and amount of cell necrosis, ranging from a high sensitivity for infarct-like to low for those with chronic presentation. CMR is often repeated after 6 months to assess the evolution of myocardial involvement. Furthermore, in some patients, inflammation may cause extensive scars that triggers left ventricular (LV) remodeling, ventricular arrhythmias, and leading eventually to dilated cardiomyopathy (DCM) or alternatively to a predominant hypokinetic non-dilated phenotype of cardiomyopathy. Endomyocardial biopsy (EMB) is the reference standard for the diagnosis of myocarditis and, mostly, to investigate the underlying etiology. EMB is mandatory in myocarditis in the presence of severe heart failure or ventricular arrhythmias.