High dose droperidol and QT prolongation: analysis of continuous 12-lead recordings

AimsTo investigate the QT interval after high dose droperidol using continuous 12-lead Holter recordings. MethodsThis was a prospective study of patients given droperidol with a continuous Holter recording. Patients were recruited from the DORM II study which included patients with aggression presenting to the emergency department. Patients initially received 10mg droperidol as part of a standardized sedation protocol. An additional 10mg dose was given after 15min if required and further doses at the clinical toxicologist's discretion. Continuous 12-lead Holter recordings were obtained for 2-24h utilizing high resolution digital recordings with automated QT interval measurement. Electrocardiograms were extracted hourly from Holter recordings. The QT interval was plotted against heart rate (HR) on the QT nomogram to determine if it was abnormal. QT(c)F (Fridericia's HR correction) was calculated and >500ms was defined as abnormal. ResultsForty-six patients had Holter recordings after 10-40mg droperidol and 316 QT-HR pairs were included. There were 32 abnormal QT measurements in four patients, three given 10mg and one 20mg. In three of the four patients QT(c)F >500ms but only in one taking methadone was the timing of QT(c)F >500ms consistent with droperidol dosing. Of the three other patients, one took amphetamines, one still had QT prolongation 24h after droperidol and one took a lamotrigine overdose. No patient given >30mg had a prolonged QT. There were no arrhythmias. ConclusionQT prolongation was observed with high dose droperidol. However, there was little evidence supporting droperidol being the cause and QT prolongation was more likely due to pre-existing conditions or other drugs.