The outcome of myocarditis associated with COVID-19 vaccination in adolescents up to one year after diagnosis

Most reported cases of myocarditis and/or pericarditis after COVID-19 vaccination had a clinically mild course, but, some patients required intensive care support or even died of acute heart failure. Symptoms usually occur within the first three days after the second dose of messenger RNA (mRNA) COVID-19 vaccines. BNT162b2 (Pfizer- BioNTech) and mRNA 1273 (Moderna) vaccines were the first mRNA-based vaccines ever approved. In both vaccines (mRNA-1273 and BNT162b2), a mRNA sequence determines the structure and assembly of the immunogen, the SARS-CoV-2 spike (S) glycoprotein. In this study, the authors from Hong Kong, China, investigated the cardiac outcome of myocarditis associated with COVID-19 vaccines in adolescents up to one year after the diagnosis. 

The findings like elevated troponin serum levels, abnormal ST-elevations in the electrocardiogram (ECG), altered ventricle movement in echocardiogram, or late gadolinium enhancement (LGE) in cardiac magnetic resonance imaging (MRI), suggest the development of myocarditis. In most young patients, the short-term clinical trajectory showed a resolution of cardiac symptoms and normalization of the left ventricular ejection fraction. In a small proportion of symptomatic adolescents with COVID-19 vaccine-associated myocarditis, some previous studies demonstrated myocardial tissue sequelae (myocardial inflammation and edema) approximately two months after the vaccination.

About the study

The researchers evaluated the cardiac outcome of myocarditis associated with COVID-19 vaccination in adolescents up to one year after diagnosis. The ECG, echocardiogram, and cardiac MRI at presentation and the latest follow-up were thoroughly examined. 

The study included 40 patients, 33 of whom were males. The median age was 15.1 years, ranging from 12.7 to 17.9 years. The patients were followed for 10.0±1.3 months (ranging from 5.6 to 12.3 months), representing all cases identified in Hong Kong during the study.

During the follow-up period, 73% of included patients (29 patients ) were asymptomatic, 18 (7 patients) reported noncardiac chest pain, 8% (3 patients) reported palpitations, and 3% (one patient) reported fatigue. There were no patients diagnosed with cardiac arrhythmias, angina pectoris, or heart failure.

At presentation, the ECG showed abnormal results in 78% (31 patients) with ST-segment or T-wave abnormalities. At the latest follow-up, the ECG was normalized in all patients.

At presentation, the echocardiogram showed normal left ventricular ejection fraction in all patients. However, 15% (six patients) had mildly increased echogenicity of the pericardium or left ventricular lateral wall, whereas two patients (5%) had minimal (<2 mm) pericardial effusion. At the latest follow-up, the echocardiogram showed normal left ventricular ejection fraction in 95% (38 patients), while two patients (5%) had borderline left ventricular ejection fraction of 51.1% and 53.6%.

Cardiac MRI underwent 39 patients at the presentation, and abnormal findings were detected in 26 patients. These findings included features of myocarditis in 56% (22 patients), abnormal T1 values in 54% (21 patients), abnormal T2 values in 62% (24 patients), LGE in 49% (19 patients), and reduced left ventricular ejection fraction in 18% (7 patients).

At follow-up, cardiac MRI underwent 26 patients with initial abnormal MRI. The findings revealed mild residual LGE in 58% (15 patients), borderline left ventricular ejection fraction in two patients (8%), and normal findings in 42% (11 patients). There were no patients with abnormal T1 values or features of myocarditis. The presence of LGE at diagnosis correlated with the presence of LGE on follow-up. Similar echocardiographic parameters were found in patients with (n=16) or without (n=11) LGE on follow-up cardiac MRI.


According to the authors, this study is, to their knowledge, the longest follow-up study of the cardiac outcome of vaccine-associated myocarditis in adolescents. The results showed that the global systolic ventricular function appears to be preserved, however comprehensive cardiac evaluation and imaging revealed impaired left and right ventricular myocardial deformation and persistence of residual LGE in a significant number of patients ( 58%) up to one year of follow-up. The researchers suggested that the results found in this study are indicators of subclinical myocardial dysfunction and fibrosis with a potential long-term effect on exercise capacity and cardiac functional reserve during stress.

This article was published in Circulation.

Journal Reference

Kwong-man Yu C et al. Cardiovascular Assessment up to One Year After COVID-19 Vaccine–Associated Myocarditis. Circulation. 2023;148:436–439. Published online 2023 Aug 1 (Open Access)

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