The applications of magnetic resonance imaging in risk assessment of patients with acute myocarditis

Background Cardiac magnetic resonance (cMRI) is commonly employed for the diagnosis of acute myocarditis (AM) and is also conducted six months later to assess ongoing myocardial involvement. Nevertheless, the clinical and prognostic significance of the cMRI performed at the six-month mark remains unclear. Purpose We utilised cMRI to evaluate the morphology and cardiac function in patients with acute myocarditis (AM), examining the relationship between left ventricular remodelling and biomarkers of cardiac dysfunction and myocardial fibrosis. Additionally, we assessed the extent of myocardial fibrosis both at the onset and six months following the acute episode. Results Non-ischemic late gadolinium enhancement (LGE) was observed in 88 patients (97.7%), predominantly affecting the septum and inferior wall. At the 6-month follow-up, cMRI revealed significant reductions in abnormalities related to segmental wall motion (p < 0.001), myocardial edema (p < 0.001), presence of LGE (p < 0.05), LGE mass (p < 0.01), native T1 mapping (p < 0.001), and pericardial effusion (p ≤ 0.001). At 6 months, myocardial edema persisted in 34.4% of patients, while complete resolution (absence of edema and LGE) was observed in 8.8% of cases. LGE resolved in 15.2% of patients, and the average number of affected myocardial segments decreased from 46% to 30%. The most significant independent predictors of major cardiovascular events (MACEs) were LGE mass (adjusted OR = 1.27 [1.11–1.99], p < 0.001), myocardial edema (OR = 1.70 [1.14–209.3], p < 0.001), and prolonged native T1 (OR = 0.97 [0.88–3.06], p < 0.001). The mid-wall pattern of LGE and the presence of edema-free LGE were identified as independent predictors of MACEs. Conclusions LGE, myocardial edema, and prolonged native T1 were predictors of MACEs. LGE does not necessarily mean constituted fibrosis in the presence of edema and may disappear over time. LGE without edema could represent fibrosis, whereas the persistence of edema represents active inflammation and could be associated with the residual chance of complete recovery. cMRI should be performed in all patients with AM at 6 months to evaluate progress and prognosis.