Cardiac magnetic resonance imaging (CMR), including T1 and T2 mapping, are effective tools for confirming or rejecting a diagnosis of myocarditis in patients with acute symptoms, and are superior to Lake Louise criteria, according to data published in the Journal of the American College of Cardiology.
The data also suggest that T2 mapping has acceptable diagnostic performance for patients with chronic symptoms.
Endomyocardial biopsy (EMB) is the current standard for diagnosing myocarditis, however this procedure is invasive and not widely available. Previous research has suggested that T1 and T2 mapping have excellent diagnostic accuracy in patients with suspected myocarditis. Therefore, researchers sought to assess the performance of CMR imaging compared with EMB in an unselected, consecutive patient cohort.
Patients were divided into 2 groups based on symptom duration (acute: ≤14 days vs chronic: >14 days). They underwent biventricular EMB, cardiac catheterization (for coronary artery disease exclusion), and CMR imaging on 1.5-T and 3-T scanners. The CMR protocol included the Lake Louise criteria for myocarditis and native T1. Researchers also calculated the extracellular volume fraction (ECV) and performed T2 mapping for the 1.5-T scanners.
“Our results suggested that duration of symptoms is crucial when using CMR techniques to confirm or reject myocarditis,” the authors wrote. “This seemed to be a consequence of the shift in inflammatory pathology over the disease course.”
“Although a variety of CMR techniques are useful in patients with recent onset of symptoms, for those with heart failure in the chronic phase of myocarditis, T2-weighted edema imaging has greater diagnostic sensitivity.”
Researchers selected 129 patients who underwent 1.5-T imaging. For patients with acute symptoms, native T1 resulted in the best diagnostic performance, defined by area under the curve (AUC) of receiver-operating curves (0.82). The AUC was 0.81 for T2, 0.75 for ECV, and 0.56 for Lake Louise criteria.
However, in patients with chronic symptoms, onlyT2 yielded an acceptable AUC of 0.77.
Among the patients who underwent 1.5-T imaging, 111 underwent subsequent 3-T imaging. Among patients with acute and chronic symptoms, the AUCs of the 3-T group for native T1, ECV, and Lake Louise criteria were similar to the 1.5-T group with no significant differences.
The T2 mapping for 3-T imaging was excluded from this study for technical reasons. “The lack of T2 mapping results on 3-T markedly limits comparison of 1.5-T and 3-T results in our study,” researchers wrote. Further studies will be necessary before drawing any definite conclusions about the effect of CMR field strength in patients with suspected myocarditis.”
They also noted that specific CMR acquisition protocols are needed to define the inflammatory, edematous, and fibrotic stages of myocarditis and guide clinical management.
Lurz P, Luecke C, Eitel I, et al. Comprehensive cardiac magnetic resonance imaging in patients with suspected myocarditis: the Myo-Racer trial. J Am Coll Cardiol. 2016;67(15):1800-1811. doi:10.1016/j.jacc.2016.02.013.