Cardiac MRI and Clinical Follow-up in COVID-19 Vaccine-associated Myocarditis.

We previously reported cardiac MRI findings in a cohort of patients with COVID-19 vaccine associated myocarditis (1). The majority of patients had mild imaging abnormalities at the time of acute symptoms. However, little is known about later evolution of the cardiac MRI abnormalities.

The institutional ethics committee approved this retrospective analysis and waived the requirement for written informed consent. Cardiac MRIs were performed at 1.5T or 3T (Siemens, Germany) and were analyzed blinded to all clinical information (Circle cmr42; Canada). Global longitudinal, circumferential and radial strain was analyzed using feature-tracking analysis. Late gadolinium enhancement (LGE) was quantified using a signal-intensity threshold of 4SD. Maximum native T1 and T2 were converted to z-scores using scanner-specific local reference values (1).

Thirteen patients had follow-up cardiac MRI (mean age, 33±14 years, 77% men) (. All patients had chest pain at presentation that followed mRNA-1273 in 9 (69%) and BNT162b2 in 4 (31%). Six patients (46%) required hospitalization. Six were treated with colchicine (46%), three with aspirin (23%), and three with ibuprofen (23%).

At follow-up MRI (median [IQR] 100 [74-237] days after vaccination), myocardial edema had resolved in all patients (. LGE had resolved in 3/13 (23%), decreased in 8/13 (62%), and remained negative in 2/13 (15%). In patients with residual LGE, the extent at follow-up was minimal (range, 1-2 grams). Left ventricular ejection fraction increased and was normal in all at follow-up (56±4% vs. 60±3%, p=.003).

Median [IQR] clinical follow-up duration was 159 [107-232] days. All patients were asymptomatic with normal troponin levels and no adverse cardiac events (death, sustained atrial or ventricular arrhythmia lasting ≥30s, or heart failure hospitalization).

In summary, in our case series of 13 patients with acute myocarditis following COVID-19 vaccination, follow-up MRI demonstrated resolution of myocardial edema, normalization of left ventricular function, and interval decrease in LGE. These findings are consistent with the typical rapid decrease in myocardial inflammation in other causes of myocarditis (2). However, minimal LGE without edema was present in 62% of patients at follow-up, likely reflecting myocardial fibrosis. In conjunction with lack of any adverse events at 5-month follow-up, this raises the likelihood that vaccine-associated myocarditis might have a favorable prognosis despite the persistence of minimal LGE.

Table.

Baseline and Follow-up Findings