Improved diagnosis of COVID-19 vaccine-associated myocarditis with cardiac scarring identified by cardiac magnetic resonance imaging.

Aims Myocarditis is a rare but potentially serious complication of COVID-19 vaccination. Cardiac magnetic resonance (CMR) late gadolinium enhancement (LGE) imaging can identify cardiac scar, which may improve diagnostic accuracy and prognostication. We sought to define the incidence of long-term LGE post COVID-19 vaccine-associated myocarditis (C-VAM) and to establish the additive role of CMR in the diagnostic work up. Methods and Results Patients with Brighton Collaboration Criteria Level 1 (definite) or Level 2 (probable) C-VAM were prospectively recruited from the Surveillance of Adverse Events Following Vaccination In the Community (SAEFVIC) database to undergo CMR at least 6 months after diagnosis. As there were limited patients with access to baseline CMR, prior CMR results were not included in the initial case definition. The presence of LGE at follow-up CMR was then integrated into the diagnostic algorithm and the reclassification rate (definite vs. probable) was calculated. Sixty-seven patients with C-VAM (mean age 30 +/- 13 years, 72% male) underwent CMR evaluation. Median time from vaccination to CMR was 548 (range 398-603) days. Twenty patients (30%) had persistent LGE. At diagnosis, nine patients (13%) were classified as definite and 58 (87%) as probable myocarditis. With integration of CMR LGE data, 16 patients (28%) were reclassified from probable to definite myocarditis. Conclusion Persistent LGE on CMR occurs in one third of patients with C-VAM. Without CMR at the time of diagnosis, almost one third of patients are misclassified as probable rather than definite myocarditis, indicating a diagnostic strategy using echocardiography alone is insufficient. ### Competing Interest Statement The authors have declared no competing interest. ### Funding Statement This study did not receive any funding. ### Author Declarations I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained. Yes The details of the IRB/oversight body that provided approval or exemption for the research described are given below: The ethics committees of the Royal Children's Hospital and Alfred Hospital name gave ethical approval for this work. I confirm that all necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived, and that any patient/participant/sample identifiers included were not known to anyone (e.g., hospital staff, patients or participants themselves) outside the research group so cannot be used to identify individuals. Yes I understand that all clinical trials and any other prospective interventional studies must be registered with an ICMJE-approved registry, such as ClinicalTrials.gov. I confirm that any such study reported in the manuscript has been registered and the trial registration ID is provided (note: if posting a prospective study registered retrospectively, please provide a statement in the trial ID field explaining why the study was not registered in advance). Yes I have followed all appropriate research reporting guidelines, such as any relevant EQUATOR Network research reporting checklist(s) and other pertinent material, if applicable. Yes Data available on reasonable request.