Canada: Cardiac MRI shows the presence of a similar pattern of myocardial injury in myocarditis associated with the COVID-19 vaccine compared to myocarditis caused by other factors, says a recent study in the journal Radiology. Abnormalities although were found to be less severe, with no adverse events, and less frequent septal involvement over short-term follow-up.
Myocarditis is a non-ischemic inflammatory disease of the heart muscle (myocardium), with diverse causes, clinical patterns, and outcomes. Myocarditis after immunization is a rare occurrence that recently has received increased attention recently due to reports of myocardial injury in a minority of patients who received messenger RNA (mRNA) based COVID-19 vaccines. However, there is not much data on the pattern and severity of myocardial injury in patients with COVID-19 vaccination-associated myocarditis.

Against the above background, Matteo Fronza, Department of Medical Imaging, Women's College Hospital, University of Toronto, Toronto, and colleagues aimed to describe myocardial injury following COVID-19 vaccination compared these findings to other causes of myocarditis in a retrospective cohort study.
The study included consecutive adult patients with myocarditis with at least one T1-based and at least one T2-based abnormality on cardiac MRI performed at a tertiary referral hospital between 2019-2021. Patients were categorized into three groups: myocarditis following COVID-19 vaccination, myocarditis following COVID-19 illness, and other myocarditis not associated with COVID-19 vaccination or illness.
The study yielded the following findings:
· Of the 92 included patients, 21 (22%) had myocarditis following COVID-19 vaccination (mean age 31 years ±14; 17 men; mRNA-1273 in 12 [57%] and BNT162b2 in 9 [43%]).
· Ten patients (11%) had myocarditis following COVID-19 illness (mean age 51 years ±14; 3 men), and 61 (66%) had other myocarditis (mean age 44 years ±18; 36 men).
· MRI findings in vaccine-associated myocarditis included late gadolinium enhancement (LGE) in 17 (81%) and left ventricular dysfunction in 6 (29%).
· Compared with other causes of myocarditis, patients with vaccine-associated myocarditis had higher left ventricular ejection fraction and less extensive LGE, even after controlling for age, sex, and duration between symptom onset and MRI.
· The most frequent location of LGE in all groups was subepicardial at the basal inferolateral wall, although septal involvement was less common in vaccine-associated myocarditis.
· At short-term follow-up (median 22 days), all patients with vaccine-associated myocarditis were asymptomatic with no adverse events.
To conclude, the study demonstrates that the pattern of MRI abnormalities in vaccine-associated myocarditis is similar to other causes although patient demographics differ and MRI findings tend to be less severe.
Reference:
The study titled, Myocardial Injury Pattern at MRI in COVID-19 Vaccine–associated Myocarditis," was published in the journal Radiology.
DOI: https://doi.org/10.1148/radiol.212559