Late enhancement detected by cardiac magnetic resonance imaging in acute myocarditis mimicking acute myocardial infarction: location patterns and lack of correlation with systolic function.

OBJECTIVE: Clinical recognition of acute myocarditis is difficult. Late enhancement (LE) detected by magnetic resonance imaging appears to be a valuable tool for evaluating and monitoring inflammatory myocardial diseases. However, patterns of myocardial enhancement and its correlation with systolic function are not yet well defined. The aim of this study was to assess the extent and location of LE during the acute phase of active myocarditis mimicking acute myocardial infarction and at follow-up, in order to correlate LE with systolic function and to monitor disease progression.

METHODS: Magnetic resonance imaging was performed in 13 patients with clinical symptoms and signs of acute myocarditis.

RESULTS: All patients showed LE, which was located in the lateral free wall in 11 (85%) patients, at the basal level in eight (61%), at the mid level in nine (69%), and at the distal level in 10 (77%). Moreover, six (46%) patients showed LE in the posterior and inferior wall (P = 0.099 versus lateral wall), four (31%) patients in the septum and inferior wall (P = 0.017 versus lateral wall) and three (23%) patients in the anterior wall (P = 0.006 versus lateral wall). Left ventricular ejection fraction was 0.50 +/- 10 and it was severely reduced only in one patient (0.20). Conversely, in the remaining patients, left ventricular ejection fraction was preserved (> or =0.45) (P < 0.001). Multifocal LE was detected in eight (61%) patients, whereas pericardial effusion was observed only in two (15%) patients (P = 0.002). Twelve patients showed ST-segment elevation and chest pain, as it occurs in acute myocardial infarction, whereas one patient showed non-ST-segment elevation with dyspnoea, as it occurs in non-ST-elevation myocardial infarction. The mean follow-up duration was 4 +/- 12 months, and follow-up was complete for all but one patient who died. LE extent decreased in 11 (92%) patients, whereas new areas of LE were detected in one (8%) patient (P < 0.001).

CONCLUSIONS: Contrast enhancement is a frequent finding in the clinical setting of suspected myocarditis and is associated with active and/or persistent myocardial inflammation. Myocarditis detected by magnetic resonance imaging predominantly occurs in the lateral free wall and very rarely affects systolic function.