Purpose: Case reports of the development of perimyocarditis in adolescents and young adults after BNT162b2 messenger RNA (mRNA) COVID-19 vaccination have raised concerns about the cardiac side effects of the vaccine. The aim of the study was to evaluate clinical follow-up and subclinical myocardial function after mRNA COVID-19 vaccine in adolescents with chronic heart disease.

Methods: Forty-one adolescents aged 12-18 who were followed up at paediatric cardiology clinic between December 2021 and May 2022, and who had received two doses of the Pfizer-BioNTech COVID-19 mRNA vaccine were included in the study. The patients were evaluated five times in total - before the vaccination, one week after receiving the first dose, one month after receiving the first dose, one week after receiving the second dose, and one month after receiving the second dose. Cardiac assessment for all patients included an electrocardiogram, transthoracic echocardiography, and two-dimensional speckle-tracking strain echocardiography for left ventricular subclinical myocardial function.

Results: The mean age of the adolescents was 16.2 ± 1.5 years, and 56% (n = 23) were male. There was no statistically significant difference in patients' echocardiographic measurements including left ventricular global longitudinal strain and electrocardiogram parameters including PR, QRS, and QTc intervals through the follow-up. Seven patients reported cardiac complaints at post-vaccination follow-up visits, but laboratory and echocardiographic evidence of cardiac involvement was not observed.

Conclusions: Based on the results of our study, the mRNA COVID-19 vaccine did not cause impairment in subclinical myocardial function assessed by speckle-tracking echocardiography in adolescents with chronic heart disease.