By Michael Crawford, MD

Professor of Medicine, Chief of Clinical Cardiology, University of California, San Francisco

Dr. Crawford reports no financial relationships relevant to this field of study.

SYNOPSIS: New quantitative MRI technique performs better than the older Lake Louise criteria for diagnosing myocarditis as compared to the standard of endomyocardial biopsy.

SOURCES: Lurz P, Luecke C, Eitel I, et al. Comprehensive cardiac magnetic resonance imaging in patients with suspected myocarditis: The MyoRacer-Trial. J Am Coll Cardiol 2016;67:1800-1111.

Dec GW. How should we diagnose myocarditis, and is its recognition really clinically relevant? J Am Coll Cardiol 2016;67:1812-1814.

The current gold standard for diagnosing myocarditis is endomyocardial biopsy (EMB). However, it is a highly invasive test and suffers from low sensitivity. Recently, novel quantitative MRI techniques have been shown to demonstrate diagnostic utility vs. EMB in small studies. Thus, investigators from Germany utilized a comprehensive MRI protocol and compared it to biventricular EMB on a large group of patients suspected of suffering from myocarditis on clinical grounds. Inclusion criteria were: 1) symptoms consistent with myocarditis; 2) evidence of myocardial damage; 3) history of a systemic viral illness; and 4) absence of coronary artery disease on angiography. Patients were divided into two symptom groups: acute (≤ 14 days) and chronic (> 14 days). The MRI protocol included assessment of late enhancement and extra cellular fluid volume (ECV). Over a three-year period, 138 patients were enrolled, but nine did not have complete data, leaving 129 patients — 61 acute and 68 chronic. Left ventricular ejection fraction (LVEF) was lower in chronics vs. acutes (27% vs. 48%). Biventricular EMB was performed in 93%; the rest had only specimens from one ventricle. In both groups, 70-71% had myocarditis by EMB. Evidence of fibrosis was more common in the chronic group (14% vs. 10%). In acute patients, T1 mapping yielded the best diagnostic area under the curve (AUC) at 0.82, followed by T2 mapping (0.81), ECV (0.75), and the so-called Lake Louise criteria (0.56). In chronic patients, only T2 mapping exhibited a reasonable AUC (0.77). There was no difference in results using the 1.5 T or the 3.0 T MRI scanners. The authors concluded that in patients with acute symptoms, new MRI techniques are superior to the previous Lake Louise criteria for the diagnosis of myocarditis. In chronic patients, only T2 mapping demonstrates an acceptable diagnostic performance.

COMMENTARY

It would be very useful to utilize an accurate non-invasive technique for the diagnosis of myocarditis. This study shows reasonable diagnostic performance against EMB for certain newer cardiac MRI findings. The previous MRI criteria, referred to as the Lake Louise criteria, were: 1) T1 weighted early enhancement; 2) late enhancement; and 3) T2 weighted edema detection. Previous studies have shown that the presence of two of these three criteria has a 67% sensitivity, a 91% specificity, and a negative predictive value of 69%. These findings occur in other myocardial diseases, especially late enhancement. For example, I examined a young woman with an acute chest pain syndrome who had the characteristic patchy mid-wall late enhancement on MRI. Contrast angiography showed an acute coronary syndrome. Thus, new techniques and measurements that are more specific and sensitive are welcomed.

This study shows that in patients with very recent symptoms, T1 weighted mapping showed the best AUC, followed closely by T2 weighted mapping. ECV and the Lake Louise criteria were less useful. These T1 criteria indicate intracellular and extracellular edema and hyperemia, which is sensitive for acute inflammation. T2 mapping demonstrates edema, which is present in acute and chronic inflammation, but not in chronic dilated cardiomyopathy. The detection of fibrosis (late enhancement) is not particularly discriminatory, especially in more chronic inflammation.

Although these new MRI criteria seem to be an improvement over the Lake Louise criteria, there are several caveats to this study. Most patients studied had heart failure symptoms and reduced LVEF. There were relatively few patients who presented with acute chest pain and segmental myocardial dysfunction resembling acute coronary syndrome. In these patients, the Lake Louise Criteria have performed relatively well. The patients in this study represent more of a challenge in distinguishing dilated cardiomyopathies with or without inflammation. In dilated cardiomyopathies with inflammation, T2 weighted detection of edema performed well. Unfortunately, cardiac MRI cannot distinguish the cause of myocarditis. Most are lymphocytic, but a few are giant cell or eosinophilic. The latter conditions come with a very different prognosis and treatment. In the accompanying editorial by William Dec, he raised the issue that there is no specific therapy for the most common type of myocarditis (lymphocytic), so the diagnosis may not be clinically relevant unless the treatable subtypes can be identified. This leaves clinicians with the need to perform EMB. Perhaps the best role for cardiac MRI in suspected myocarditis is to identify those who may benefit from a biopsy, but this concept must be proven before clinicians use MRI to deny biopsies.