Post-intubation ECG of a young adult presenting with coma following a 6g quetiapine overdose. Describe the ECG.


Describe and interpret this ECG


Main Abnormalities

This ECG displays the characteristic electrocardiographic features of quetiapine toxicity:

A similar pattern would be seen with other atypical antipsychotic agents such as olanzapine or clozapine.

Significance of QT prolongation

  • QT prolongation is a common source of concern in patients with antipsychotic toxicity, because of the theoretical risk of Torsades de Pointes
  • A QTc interval > 500 ms is commonly cited as a marker of increased risk of TdP
  • However, tachycardia (which is almost ubiquitous in significant poisoning with quetiapine, olanzapine or clozapine) is actually protective against TdP
  • For this reason, TdP rarely occurs with quetiapine toxicity


QT interval nomogram

  • Many Australian toxicologists use the QT interval nomogram to assess risk of TdP
  • The absolute QT interval is measured manually in multiple leads and the median QT interval plotted on the nomogram (read how to do this here)
  • Plots above the line indicate significant QT prolongation and consequent risk of TdP
QT nomogram risk stratification for torsades de pointes

By my measurements, our patient has an absolute QT of ~320 ms with HR 120 so plots below the line — i.e. not at significant risk of TdP.

TOP 100 ECG Series

Emergency Physician in Prehospital and Retrieval Medicine in Sydney, Australia. He has a passion for ECG interpretation and medical education | ECG Library |

MBBS (UWA) CCPU (RCE, Biliary, DVT, E-FAST, AAA) Adult/Paediatric Emergency Medicine Advanced Trainee in Melbourne, Australia. Special interests in diagnostic and procedural ultrasound, medical education, and ECG interpretation. Editor-in-chief of the LITFL ECG Library. Twitter: @rob_buttner

One comment

  1. Hi. It would be very helpful if you to marked the point where it is easier to determine the qt interval of in this example

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