Seasonal Trends of Cardiac MRI phenotypes in Acute Myocarditis

Background: Registry studies have demonstrated seasonal variations in the incidence of acute myocarditis (AM) in adults, although findings have largely varied^1-3. Cardiovascular magnetic resonance (CMR) is the reference standard for noninvasive diagnosis of myocarditis. Research on how the specific CMR phenotypes might defer across seasons is limited. In this single center study, we investigated seasonal trends in CMR phenotypes, specifically evaluating imaging characteristics and clinical outcomes.

Methods: Consecutive patients with CMR-confirmed AM (referencing the 2018 Lake Louise Criteria) from years 2003–2024 were retrospectively reviewed. Selected patients were placed into two groups: Fall/Winter (September-February), and Spring/Summer (March-August). We evaluated clinical, biomarker, and CMR imaging data. The primary outcome was major adverse cardiovascular events (MACE) defined as a composite of future myocarditis, pericarditis, heart failure admission, atrial and ventricular arrythmia, heart transplantation, or all-cause death. Wilcoxon rank sum and Fisher’s exact test were used for statistical analysis.

Results: 315 patients were evaluated with a median age of 44 years, 69.8% were male. 135 (42.9%) presented in Fall/Winter and 180 (57.1%) in Spring/Summer. Over a mean follow-up of 2.4 years, there was no seasonal variation in MACE (15.2% overall). Advanced cardiac support was required more frequently by patients admitted in Fall/Winter than Spring/Summer (5.5% vs 1.1%, p=0.042) and peak BNP values were higher in the Fall/Winter (324 vs 104 ng/L, p= 0.0091). Patients presenting in Fall/Winter had more impaired left ventricular global longitudinal strain (LVGLS) (-12.8 vs -14.0, p=0.046). Median LVEF was similar between groups (56% vs 57%, p=0.191). Left atrial and right atrial strains and right ventricular strains were no different between the two groups. Variations in distribution across groups were observed: higher rates of subepicardial late gadolinium enhancement (LGE) were observed in the Spring/Summer (68.9% vs 53.3%, p= 0.007), whereas mid-myocardial LGE was observed slightly more frequently in Fall/Winter (55.6% vs 45.0%, p=0.07).

Conclusion: Seasonal variations in CMR phenotypes were observed in this single-center study of patients with CMR confirmed AM. Our study suggests slightly more adverse clinical presentations and more impaired left ventricular strain in Fall/Winter, however, there were no seasonal differences in MACE. Further large-scale research studies are needed in geographically diverse population for further risk stratification in AM.