Abstract 4367081: Electrocardiogram Abnormalities and Arrhythmias: Analysis of the NHLBI Study on Long-term Outcomes after the Multisystem Inflammatory Syndrome in Children (MUSIC)

Background: Cardiac complications are common in the Multisystem Inflammatory Syndrome in Children (MIS-C); however, data on arrhythmias and other electrocardiogram (ECG) abnormalities are limited. Objective: To characterize the frequency of and risk factors for ECG abnormalities and arrhythmias in patients with MIS-C, and their associated outcomes. Methods: Secondary analysis of ECG and ambulatory monitor data from a 32-center cohort study of patients with MIS-C hospitalized between 03/2020 to 11/2021 with a follow-up period of 2 years. ECG and ambulatory monitor interpretation was performed at each participating site. Greater illness severity was defined as one or more of the following: vasoactive medications, cardiac dysfunction or elevated troponin, intubation or mechanical support. Results: From 1,204 patients in the MUSIC cohort, ECG data were available for 1,104 patients (92%). Overall, ECG was abnormal in 864 (78%) of patients (Figure), most frequently sinus tachycardia (37%), ST-T waves anomalies (30%), prolonged QTc interval (23%), sinus bradycardia (16%), and left ventricular hypertrophy (14%). Arrhythmias were reported in 71/952 (7%) patients with myocarditis and included atrioventricular block (AVB, n=22; 1 st degree in 14, Mobitz 1 in 1, Mobitz 2 or higher in 7), ventricular tachycardia (n=8), supraventricular tachycardia (n=5), junctional tachycardia (n=5) and isolated ectopy (n=5 atrial, n=6 ventricular). Risk factors for ECG abnormalities included older age, White or Hispanic/Latino ethnicity, elevated troponin, myocarditis or cardiac dysfunction, and pericarditis or pericardial effusion (Table). Risk factors for arrhythmias included older age, obesity, elevated troponin and myocarditis or cardiac dysfunction (Table). Patients with arrhythmias and other ECG abnormalities were more likely to have greater illness severity and prolonged length of stay. Ambulatory rhythm monitoring was performed in 156 patients (13%) at median 64 [IQR 22, 164] days after hospital discharge, with normal results in 140 (88%) patients. The most frequent abnormalities were AVB (n=8, 5%) and isolated ectopy (>100 beats/24 hours; n=6, 4%) , with no high-grade AVB or tachyarrhythmias identified. Conclusion: ECG anomalies are frequent in MIS-C and associated with myocarditis, greater illness severity and prolonged hospital length of stay. Arrhythmias and other ECG abnormalities mostly occurred during acute hospitalization, and were very uncommon during outpatient follow-up.