QTc prolongation and dysrhythmia risk in emergency department patients administered ondansetron

Ondansetron, an anti-emetic with the potential to cause QT-prolongation and dysrhythmia, is commonly used in the emergency department. It is unclear how often ondansetron is given to patients with prolonged QT intervals and if these patients are more likely to have dysrhythmias. We determined the frequency of the use of ondansetron in patients with a corrected QT (QTc) interval ≥500 ms and the rate of dysrhythmias in this population. This study was a retrospective review of adult patients who presented to one of 17 EDs within a large integrated healthcare system between May 1, 2021, and April 30, 2023. Patients were included if they had an electrocardiogram (ECG) and received ondansetron. Patients were categorized by QTc length. Categorical variables were described using frequencies and percentages and p-values obtained from Pearson Chi square or Fisher's exact tests where appropriate. A total of 42,530 patients were included. Of these, 56 developed dysrhythmias. Patients administered ondansetron with a measured QTc ≥500 (n = 2302), compared to patients with a measured QTc <500 (n = 40,228), were not at increased risk for developing a dysrhythmia (p = 1.000). A total of 11 patients with a QTc >475 (n = 6572), developed a dysrhythmia and there was an increased incidence of supraventricular tachycardia (p = 0.002) and cardiac arrest (p = 0.002). This study shows that most patients (95 %) who had an ECG and were administered ondansetron have a QTc <500. The incidence of dysrhythmia in patients with a QTc >500 was 0.09 % and in those with a QTc >475 was 0.17 %.