Continuous QTc Monitoring for Patients Intoxicated with QTc Prolonging Medication in the Emergency Department: A Proof of Principle Study

Background It can be challenging to determine when patients presenting with an overdose of QT interval prolonging drugs can be discharged safely, especially when the moment of intoxication or the substance ingested is unknown. Objective In a proof of principle study, we aimed to determine whether continuous corrected QT interval (QTc) analysis can be used to establish optimal observation duration of patients intoxicated with QTc prolonging medication. Methods For patients presenting with an intoxication with QT interval prolonging drugs in the emergency department, electrocardiography signals sampled at 500 Hz were preprocessed and the mean heart rate QTc per 5 min was calculated and plotted against time. A third order polynomial was fitted to visualize when the QTc would be highest (i.e., electrophysiological time to maximum concentration [T max ]). This point in time was compared with the estimated T max based on pharmacokinetic properties of the ingested substance. Results In a retrospective biobank-based study, a total of 22 emergency department visits (of 15 patients) were analyzed. An electrophysiological T max could be calculated for 17 of 22 visits. The remaining 5 patients presented either long after the electrophysiological T max (n = 4) or were admitted to the ward before reaching the T max (n = 1). The mean (SD) difference between the estimated T max based on drug properties and the calculated electrophysiological T max was 18 (133) min (range –158 to 296 min). Despite the wide range, there was a significant correlation between recorded electrophysiological T max and estimated T max ( r = 0.67, p = 0.012). Conclusions Continuous electrophysiological monitoring can be used as an adjunct to determine the toxicokinetic T max for patients presenting with an intoxication, especially when the time of ingestion or the substance ingested is unknown.