Diagnostic value of CMR in young patients with clinically suspected acute myocarditis is determined by cardiac enzymes.

AIMS: Cardiovascular magnetic resonance (CMR) has become a valuable diagnostic tool for non-invasive diagnosis of acute myocarditis. However, since CMR studies are time- and cost-intensive and its diagnostic accuracy still not perfect, additional parameters are warranted to preselect and identify those individuals in whom a CMR study is likely to add crucial information regarding correct and timely diagnosis of acute myocarditis. The diagnostic value of CMR was evaluated in a population of young patients with clinically suspected acute myocarditis in relation to ECG and serum cardiac enzyme findings. METHODS AND
RESULTS: Only young patients aged ≤ 40 years in whom acute myocarditis was highly suspected based on their clinical symptoms, resting ECG findings and/or levels of cardiac enzymes (at presentation) were included to this study. After ruling out obstructive coronary artery disease, a multi-parametric CMR study was performed as part of the diagnostic work-up. The CMR protocol comprised cine sequences, T2-weighted edema imaging and late gadolinium enhancement (LGE) imaging on a 1.5-T MR scanner. 89 patients (28 ± 7 years, 89 % male) were included to this study presenting with symptoms of chest pain (85 %), dyspnea (26 %), fatigue (23 %) and/or palpitations (18 %). Pathological ECG changes were present in 72 patients (81 %). An elevated serum troponin level was measured in 45 patients (51 %). Pathological CMR findings (presence of edema and/or LGE) were detected in 35 patients (39 %). In detail, pathological CMR findings were detected in 36 % of patients with resting ECG changes and in 73 % of patients with troponin rise. In contrast, normal CMR results were obtained in 95 % of patients with negative troponin at presentation, but only in 41 % of patients with normal ECG. On multivariable analysis, a positive serum troponin was the only independent predictor for a pathological CMR finding (OR = 33.26, 95 % CI = 3.04-363.35, p = 0.004).
CONCLUSIONS: The clinical use of non-invasive CMR in the work-up of clinically suspected "acute" myocarditis in young patients is only helpful and appropriately indicated in those ones with elevated cardiac enzymes. A pre-selection of such patients for CMR based on serum cardiac enzymes--but not on ECG recordings--may prevent a meaningless overuse of CMR.