Incidences, risk factors, and clinical correlates of severe QT prolongation after the use of quetiapine or haloperidol

Background: Case reports suggest that quetiapine or haloperidol use is associated with severe QT prolongation (SQTP) and torsades de pointes. Objective: The purpose of this study was to examine the incidences, risk factors, and outcomes of SQTP in quetiapine and haloperidol users. Methods: This study accessed electronic medical records from a multicenter health-care hospital system in Taiwan and included patients who received quetiapine or haloperidol therapy and had both baseline and follow-up electrocardiograms. SQTP was defined as a posttreatment corrected QT (QTc) interval exceeding 500 ms or an increase in QTc interval of >60 ms compared with the baseline value. We analyzed the risk factors and outcomes of SQTP using multivariate logistic regression. Results: Mean increases in QTc interval were +8.3 ± 51.8 and +8.9 ± 44.0 ms after the administration of quetiapine (n = 8832) and haloperidol (n = 2341). Among these users, 1149 (13.0%) and 333 (14.2%) developed SQTP, respectively. Common risk factors for SQTP included old age, heart failure, hypokalemia, amiodarone use, and baseline QTc interval. SQTP in quetiapine users was significantly associated with ventricular arrhythmias (odds ratio 2.84; 95% confidence interval 1.95–4.13) and sudden cardiac death (odds ratio 2.29; 95% confidence interval 1.44–3.66). Conclusion: More than 10% of patients receiving quetiapine or haloperidol therapy developed SQTP, and many of them were exposed to risk factors for SQTP. SQTP in quetiapine users was significantly associated with increased risks of ventricular arrhythmias and sudden cardiac death. Clinicians should be vigilant for ventricular arrhythmias in quetiapine users who have risk factors for SQTP.