A 19-year-old woman is brought in comatose after ingesting her mother's amitriptyline tablets. ECG shows sinus tachycardia, a QRS duration of 140 ms, and hypotension. The single most appropriate immediate treatment for the ECG abnormality is:

• A Intravenous amiodarone infusion
• B Intravenous calcium gluconate
• C Oral activated charcoal followed by gastric lavage
• D Intravenous sodium bicarbonate boluses ✓

Explanation

Tricyclic antidepressants block cardiac fast sodium channels, widening the QRS and predisposing to ventricular arrhythmias. Alkalinisation with intravenous sodium bicarbonate dissociates the drug from sodium channels and corrects the conduction abnormality; a QRS wider than 100 ms is the classic indication. Amiodarone is avoided because of additive sodium channel blockade, and charcoal does not reverse established cardiotoxicity.

Reference: Harrison's Principles of Internal Medicine, 21st ed.

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Written and medically reviewed by the StethoPrep medical team.