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

Background: Myocarditis is a rare but potentially serious complication of COVID-19 vaccination. Cardiac magnetic resonance (CMR) with 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 workup of this condition.

Methods: 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 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.

Results: 67 patients with C-VAM (mean age 30±13 years, 72% male) underwent CMR evaluation. The median time from vaccination to CMR was 548 (range 398-603) days. 20 patients (30%) had LGE. At diagnosis, nine patients (13%) were classified as definite and 58 (87%) as probable myocarditis. With the integration of CMR-LGE data, 16 patients (28%) were reclassified from probable to definite myocarditis.

Conclusion: LGE on CMR occurred 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.