Inclusion of both tertiary and secondary-level hospitals may lead to treatment bias due to different standards of care or available facilities. Importantly, in our study, all contributing centers provide intermediate and intensive care units and operate according to national and international guidelines. Cardiorespiratory monitoring, non-invasive and mechanical ventilation are carried out according to guidelines in all participating centers. All centers treated both moderate and severe cases of COVID-19. Patients requiring extracorporeal life support were primarily treated at tertiary centers but constituted a minority of subjects in this study cohort. Therefore, we do not expect significant bias due to differences in center size. However, due to the limited number of patients in the respective subgroups a comprehensive analysis of this aspect was not feasible. In order to provide further insight, we present an overview into the types and individual contribution of participating centers (Table S1). Additionally, individual specific therapy attemps with respect to COVID-19, e.g., hydroxochloroquine administration, were specified (Table 1). Left ventricular ejection fraction (LVEF) may have constituted an additional predictor for arrhythmia, however, the value was not provided in a relevant number of patients in this cohorts. In order to account for this limitation, we attempted imputation of these values (Supplementary Materials) hinting at a potential role of reduced LVEF as a risk factor for arrhythmia during hospitalization for COVID-19. However, these results are exploratory and have to be interpreted with caution due to the high number of missing values. Further efforts should be made to study this specific aspect in COVID-19 patients.