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Tricyclic antidepressant and sodium-channel-blocker poisoning
TCA poisoning is a poisoning of cardiac sodium-channel blockade together with anticholinergic effects and coma; the ECG is the key risk tool — a wide QRS and a tall R in aVR — and the treatment is IV sodium bicarbonate.
Why it matters in the exam
The typical question shows a confused or comatose patient with large pupils, tachycardia and an ECG with a wide QRS, sometimes after boxes of amitriptyline were found. The correct answer is sodium bicarbonate 1–2 mEq/kg as a bolus, repeated until the QRS narrows — not a standard antiarrhythmic.
The risk thresholds are also tested: a QRS above 100 ms predicts seizures, above 160 ms predicts ventricular arrhythmias, and an R wave above 3 mm in aVR signals significant sodium blockade. Seizures are treated with benzodiazepines; phenytoin is not recommended, and physostigmine and flumazenil are forbidden in this poisoning because of the risk of cardiac arrest and seizures.
Deterioration in TCA poisoning can be very fast — a patient who talks on arrival can seize and develop shock within an hour — so the airway is prepared early. A patient with no symptoms and a normal ECG over about six hours of monitored observation can move on to psychiatric assessment. The same bicarbonate approach suits other sodium-channel blockers, such as flecainide, high-dose diphenhydramine and cocaine.
Key points
- TCA = sodium blockade + anticholinergic + alpha blockade + seizures.
- QRS above 100 ms — seizures; above 160 — arrhythmias.
- Sodium bicarbonate 1–2 mEq/kg IV until the QRS narrows.
- Seizures — benzodiazepines; no physostigmine and no flumazenil.
- No symptoms and a normal ECG after about six hours — observation can end.
Summary table
| Finding | Value or sign | Meaning | Treatment |
|---|---|---|---|
| QRS | Above 100 ms | Risk of seizures | Sodium bicarbonate |
| QRS | Above 160 ms | Risk of ventricular arrhythmias | Sodium bicarbonate, prepare for resuscitation |
| R in aVR | Above 3 mm | Sodium-channel blockade | Sodium bicarbonate |
| Anticholinergic | Large pupils, dry skin, urinary retention | Associated sign | Support; no physostigmine |
| Seizures | Generalised | Worsen the acidosis | Benzodiazepines |
| Hypotension | Alpha blockade and myocardial depression | Shock | Fluids, noradrenaline |
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Sources
- Goldfrank's Toxicologic Emergencies, 11th edition (2019) — Cyclic antidepressants
- Tintinalli's Emergency Medicine: A Comprehensive Study Guide, 9th edition (2020) — Tricyclic antidepressants
- Boehnert MT, Lovejoy FH, The New England Journal of Medicine, 1985 — QRS duration versus serum level in predicting seizures and ventricular arrhythmias after tricyclic overdose
- Liebelt EL et al., Annals of Emergency Medicine, 1995 — ECG lead aVR versus QRS interval in acute tricyclic antidepressant toxicity
Sources are given for further reading; the text is written afresh and not copied from them.
Reviewed by the Examqo AI Professor · 2026-11-06. The text may contain errors; when in doubt, check the source.