Quetiapine Toxicity Overview
- Brisk sinus tachycardia (HR = 120 bpm)
- Prolonged QTc interval (QTc = 560ms; the absolute QT interval is more than half the R-R interval)
- Quetiapine (a second-generation atypical antipsychotic) is a leading cause of toxic coma in Australia.
- Main toxic effects in overdose include coma, anticholinergic delirium, prolonged QTc and a brisk sinus tachycardia.
- Doses > 3g are associated with coma.
- Despite the prolonged QTc, Torsades de Pointes does not occur (see below).
- A similar pattern of clinical and ECG features is seen with other atypical antipsychotics, such as olanzapine or clozapine.
Drug-Induced QT-Prolongation And Torsades
- In the context of acute poisoning with QT-prolonging agents, the risk of TdP is better described by the absolute rather than corrected QT.
- More precisely, the risk of TdP is determined by considering both the absolute QT interval and the simultaneous heart rate (i.e. on the same ECG tracing).
- These values are then plotted on the QT nomogram (below) to determine whether the patient is at risk of TdP.
- A QT interval-heart rate pair that plots above the line indicates that the patient is at risk of TdP.
- From the nomogram, you can see that QTc-prolonging drugs that are associated with a relative tachycardia (e.g. quetiapine) are much less likely to cause TdP than those that are associated with a relative bradycardia (e.g. amisulpride).
This ECG (taken following a 6g quetiapine overdose) with characteristic features of quetiapine toxicity
- Beta-blocker toxicity
- Calcium-channel blocker toxicity
- Carbamazepine cardiotoxicity
- Tricyclic overdose (sodium-channel blocker toxicity)
LITFL Further Reading
- ECG Library Basics – Waves, Intervals, Segments and Clinical Interpretation
- ECG A to Z by diagnosis – ECG interpretation in clinical context
- ECG Exigency and Cardiovascular Curveball – ECG Clinical Cases
- 100 ECG Quiz – Self-assessment tool for examination practice
- ECG Reference SITES and BOOKS – the best of the rest
- Brady WJ, Truwit JD. Critical Decisions in Emergency and Acute Care Electrocardiography
- Surawicz B, Knilans T. Chou’s Electrocardiography in Clinical Practice: Adult and Pediatric
- Wagner GS. Marriott’s Practical Electrocardiography 12e
- Chan TC. ECG in Emergency Medicine and Acute Care
- Rawshani A. Clinical ECG Interpretation
- Mattu A. ECG’s for the Emergency Physician
- Hampton JR. The ECG In Practice, 6e