Myocarditis can mimic myocardial infarction but a unique biomarker provides clinicians an opportunity to distinguish the two conditions.
Acute myocarditis (aMC) has many different causes but the prevalence is unclear because the condition has similar clinical symptoms to an acute myocardial infarction (aMI). Although the diagnosis of myocarditis can be confirmed with cardiac magnetic resonance imaging, this technique is not always available. However, one approach to resolve the diagnosis involves the use of microRNAs (miRNAs), which are small, non-coding RNAs that play an important role in gene expression. Several miRNAs have been identified in the infarcted heart and this led a team from the Vascular Pathophysiology Area, Madrid, to try and identify a unique miRNA which could be used to distinguish between myocarditis and myocardial infarction. The team focused on circulating T cells, in particular T helper 17 (Th17) cells, which were confirmed as being a characteristic of myocardial injury in the acute phase of myocarditis. They performed a miRNA microarray analysis and quantitative polymerase chain reaction (qPCR) assays in Th17 cells after experimentally inducing myocarditis and myocardial infarction in mice to identify unique biomarkers.
The researchers identified the miRNA, mmu-miR-721, produced by Th17 cells in mice which was only produced in response to either autoimmune or viral myocarditis and which was absent from those with aMI. Using four patient cohorts with myocarditis, they subsequently identified a human homologue to mmu-miR-721, termed has-miR-Chr8:96. The researchers found that plasma levels of has-miR-Chr8:96 were considerably higher among myocarditis patients compared to both those with a myocardial infarction and in healthy controls. The area under the receiver-operating characteristics curve for has-miR-Chr8:96 was 0.927 (i.e., 92.7%) for distinguishing between aMC and aMI and this diagnostic value was retained even after adjusting for age, ejection fraction, and serum troponin levels.
Although the authors accepted that more work is needed to validate this biomarker in other cardiac disorders such as dilated cardiomyopathy, their preliminary findings suggest that raised plasma levels of has-miR-Chr8:96 are unique to those with myocarditis and have sufficient discriminatory power from myocardial infarction.
Blanco-Dominguez R et al. A Novel Circulating MicroRNA for the Detection of Acute Myocarditis. N Engl J Med 2021;384:2014-27