Cardiac Magnetic Resonance Imaging in COVID-19 Vaccine-Associated Myocarditis Compared With Classical Myocarditis

Background: Studies comparing COVID-19 vaccine-associated and classical myocarditis (CM) are lacking. Objectives: The purpose of this study was to compare cardiac magnetic resonance (CMR) imaging findings and short-term clinical outcomes in patients with messenger RNA COVID-19 postvaccination myocarditis (PVM) and CM. Methods: This was a retrospective study of patients with myocarditis: 31 with PVM and 46 with CM. Patients underwent a CMR protocol scan including T1 and T2 sequences. Late gadolinium enhancement (LGE) was expressed as percentage of left ventricular myocardial mass and the extracellular volume was calculated based on precontrast and postcontrast T1 images. Clinical outcomes included heart failure hospitalizations and mortality. Results: Study patients were predominantly male (81% in PVM vs 89% in CM, P = 0.330). Patients with PVM had lower T1 values compared with CM (1,064.2 ± 67.0 ms vs 1,081.6 ± 41.9 ms, P = 0.032), although T2 and extracellular volume values were similar in both groups. Left ventricular ejection fraction and LGE were similar in both groups. The most frequent location of LGE was the basal inferolateral wall. PVM more commonly demonstrated a mid-wall LGE pattern while CM demonstrated a subepicardial LGE pattern. Compared with CM, patients with PVM were more likely to have a pericardial effusion (42% vs 17%, P = 0.018) and pericardial LGE (38% vs 13%, P = 0.009). During short-term follow-up (median 300 days for PVM, 319 days for CM), there were no deaths or heart failure hospitalizations in either group. Conclusions: Our study shows similar CMR imaging findings and short-term outcomes in PVM and CM, although PVM was associated with milder myocardial abnormalities and more frequent pericardial involvement.