A 22-year-old male presents comatose with QRS duration of 140 ms and rightward axis deviation on ECG after an intentional tricyclic antidepressant overdose. What medication narrows the QRS complex?

Answer and explanation

Correct answer: D. Intravenous sodium bicarbonate bolus

  1. Step 1: Tricyclic antidepressants block myocardial fast sodium channels (phase 0 depolarization), producing QRS prolongation and life-threatening ventricular arrhythmias.
  2. Step 2: Intravenous hypertonic sodium bicarbonate provides a high extracellular sodium load to overcome sodium channel blockade and alkalinizes serum to promote drug unbinding, narrowing the QRS complex.
Answer
Intravenous sodium bicarbonate bolus.
Why not the others: Class IA (procainamide) and Class IC antiarrhythmics block sodium channels further, dramatically worsening QRS widening and precipitating asystole. Class III agents like amiodarone prolong the QT interval and increase torsades de pointes risk. Physostigmine can precipitate asystole and seizures in TCA overdose.

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