Transient Sinus Bradycardia in Children with Multisystem Inflammatory Syndrome Associated with COVID-19

Objective: Multisystem inflammatory syndrome in children (MIS-C) may cause cardiovascular involvement and dysrhythmia. Although a variety of arrhythmias may be seen, sinus bradycardia was rarely reported. The aim of this study is to determine the frequency and clinical course of bradycardia in children with MIS-C. Material and Methods: Medical records of patients who were diagnosed with MIS-C between August 2020 and March 2021 were retrospectively evaluated. MIS-C diagnosis was made according to US Centers for Disease Control and Prevention (CDC) criteria. All patients who had sinus bradycardia were included in the study. Results:Transient sinus bradycardia was observed in 7 of 40 (17.5%) patients (2 girls, 5 boys) with MIS-C. The median age was 10.8 years (range, 5.4-13.8 years). All patients were initially treated with intravenous immunoglobulin (IVIG) and six out of the seven patients also received intravenous methylprednisolone (MPZ). Sinus bradycardia developed a median of four days (range, 2-6 days) after MIS-C diagnosis and continued for a median of four days (range, 2-6 days). In six of the seven patients, bradycardia was detected a median of 42 hours (range, 11-74 hours) after MPZ treatment and resolved a median of 36 hours (range, 20-50 hours) after tapering MPZ dosage. Electrocardiogram (ECG) of patients showed sinus bradycardia. All patients were asymptomatic and awake when bradycardia was observed. No patients had any underlying structural heart defect or electrolyte abnormalities. Bradycardia episodes resolved without any specific intervention. Conclusion: Sinus bradycardia may occur due to the cardiac involvement of MIS-C itself or as a possible side effect of MPZ therapy, which can resolve without any specific treatment.