Emerging research suggests the development of myocarditis after COVID-19 vaccination has a similar pattern to other causes of myocarditis on cardiac MRI but has less severe abnormalities.
In a recent retrospective study published in Radiology, researchers assessed the cardiac MRI findings of 92 patients with myocarditis who had at least one T1-based abnormality and one T2-based abnormality. According to the study, 10 patients (with a mean age of 51 years) developed myocarditis after a COVID-19 related illness, 61 patients (with a mean age of 44 years) had myocarditis from non-COVID-related causes and 21 patients ( with a mean age of 31 years) developed myocarditis after receiving COVID-19 vaccination.
After controlling for factors such as sex, age and duration between symptom onset and MRI, the researchers found that patients with vaccine-associated myocarditis had a higher left ventricular ejection fraction, less extensive late gadolinium enhancement (LGE) and less septal involvement. The patients with vaccine-associated myocarditis had no adverse events at a short-term follow-up (median of 22 days), according to the study.
“Milder MRI abnormalities in patients with vaccine-associated myocarditis compared to other causes raises the possibility that this group may have a lower future adverse event rate,” wrote Kate Hanneman, MD, MPH, FRCPC, a cardiothoracic radiologist affiliated with the Women’s College Hospital and associate professor at the University of Toronto, and colleagues. “Lack of any adverse events in our patients with vaccine-associated myocarditis over short-term follow-up is reassuring. However, longer-term follow-up is needed, particularly given the association between LGE with adverse cardiac events in non-vaccine associated myocarditis.”
In the group with vaccine-associated myocarditis, all 21 patients (12 patients who had the Moderna vaccine and 9 patients who had the Pfizer-BioNTech vaccine) had chest pain, which started at a median of three days with a duration between one to six days, according to the study. While 14 of these patients were admitted to the hospital with high troponin levels, Hanneman and colleagues noted that none of the patients went to the intensive care unit and, after treatment with medication, had significantly decreases in troponin levels at the time of hospital discharge.
While acknowledging in an accompanying editorial that larger studies with long-term follow-up are necessary, Betty Raman, MBBS, DPhil and Stefan Neubauer, MD, who are affiliated with the Division of Cardiovascular Medicine in the Radcliffe Department of Medicine at the University of Oxford, maintained that “numerous epidemiological studies have confirmed that myocarditis following mRNA vaccines is rare.”
They also pointed out that the study by Hannemann and colleagues showed no major adverse events in a short-term follow-up for patients who had vaccine-associated myocarditis, which contrasted with three major adverse cardiovascular events (MACE) at a median of 211 days in the group with COVID-19-related myocarditis and five MACE at a median of 195 days among patients with non-COVID-19-related myocarditis.
The study authors conceded limitations to the study including a small sample size as well as significant differences in sex and patient age between the study groups. In regard to the timing of symptom onset after vaccine administration or diagnosis of COVID-19, the authors acknowledged there is no standard definition in the current literature when it comes to vaccine-associated myocarditis or COVID-19 related myocardial injury.
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