ECG changes in drug toxicity
A toxicology read of the ECG, covering sodium channel blockade (QRS and aVR), potassium channel blockade (QT and the QT nomogram), AV nodal blockers, digoxin and drug-induced hyperkalaemia, with worked examples and the findings that change treatment.
Tier 1Medical sciences concept
Written with AI assistance and fact-checked against the sources below. For exam study, not clinical decisions. How notes are made
At a glance
- Drug toxicity changes the ECG through a few channels. Name the channel and you have the treatment.
- Sodium channel blockade: wide QRS, terminal R in aVR. Treat with sodium bicarbonate.
- Potassium (hERG) channel blockade: long QT, torsades. Assess on the QT nomogram; treat with magnesium, potassium and faster heart rate.
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Sources
- Therapeutic Guidelines: Toxicology & Toxinology (December 2024 update)AU/NZTherapeutic Guidelines Limited, 2024
- Isbister GK, Page CB. Drug induced QT prolongation: the measurement and assessment of the QT interval in clinical practice. Br J Clin Pharmacol 2013;76:48-57AU/NZBritish Journal of Clinical Pharmacology, 2013
- Chan A, Isbister GK, Kirkpatrick CM, Duffull SB. Drug-induced QT prolongation and torsades de pointes: evaluation of a QT nomogram. QJM 2007;100:609-15AU/NZQJM, 2007
- Boehnert MT, Lovejoy FH. Value of the QRS duration versus the serum drug level in predicting seizures and ventricular arrhythmias after an acute overdose of tricyclic antidepressants. N Engl J Med 1985;313:474-9New England Journal of Medicine, 1985
- CredibleMeds QTdrugs List and List of Drugs to Avoid in Congenital Long QT SyndromeAZCERT, 2026
- Tisdale JE, Chung MK, Campbell KB et al. Drug-induced arrhythmias: a scientific statement from the American Heart Association. Circulation 2020;142:e214-e233American Heart Association, 2020
- 2017 AHA/ACC/HRS guideline for management of patients with ventricular arrhythmias and the prevention of sudden cardiac death. Circulation 2018;138:e272-e391American Heart Association, American College of Cardiology, Heart Rhythm Society, 2017
- 2022 ESC Guidelines for the management of patients with ventricular arrhythmias and the prevention of sudden cardiac death. Eur Heart J 2022;43:3997-4126European Society of Cardiology, 2022
- Last updated
- 14 November 2026
What changed
- 14 November 2026 Personal emails, About story and Australian-style copy