Due to its retrospective design, this study carries inherent limitations. Despite thorough analysis of clinical records and use of different source documents (e.g., discharge notes, nurses’ reports, daily doctors’ documentation) underreporting of arrhythmia events cannot be excluded. Not all arrhythmic events during the clinical course may have been documented in written reports. Asymptomatic arrhythmias in patients without continuous ECG-monitoring may also have been missed. However, clinically relevant arrhythmias leading to medical interventions are documented as part of the participating centers’ standards.