Correct Answer: A. Intravenous sodium bicarbonate
This is a classic tricyclic antidepressant (TCA) toxicity presentation. TCAs (amitriptyline, imipramine, nortriptyline) block cardiac sodium channels, causing wide QRS complexes (>120 ms) and right axis deviation due to delayed ventricular depolarization. The hypotension results from alpha-adrenergic blockade and myocardial depression. Intravenous sodium bicarbonate is the cornerstone of TCA cardiotoxicity management because it works through two mechanisms: (1) alkalinization increases the ionized fraction of TCA, reducing cardiac binding, and (2) sodium loading directly antagonizes the sodium channel blockade. A serum pH of 7.45–7.55 is the target. Sodium bicarbonate rapidly reverses the QRS widening and hypotension, making it the first-line agent in TCA overdose with cardiac manifestations. This is the Indian standard of care per Harrison and poison management guidelines used in Indian ICUs.
Why the other options are wrong
B. Phenytoin — Phenytoin was historically used for TCA-induced arrhythmias but is now contraindicated because it can worsen hypotension and does not address the underlying sodium channel blockade. Modern toxicology (including Indian poison control protocols) has abandoned phenytoin in favor of sodium bicarbonate, which directly reverses the pathophysiology. Phenytoin may be a trap for students recalling outdated teaching. C. Antiarrhythmics — Class I antiarrhythmics (quinidine, procainamide) are contraindicated in TCA toxicity because they further block sodium channels and worsen the QRS widening and hypotension. This is a critical safety principle: do not use sodium channel blockers in sodium channel blocker toxicity. NBE may include this to test whether students understand that antiarrhythmics can be harmful in this context. D. Propranolol — Beta-blockers like propranolol are contraindicated in TCA overdose because they worsen hypotension and may precipitate cardiogenic shock. TCAs already cause alpha-blockade and myocardial depression; adding beta-blockade removes compensatory tachycardia and further depresses contractility. Supportive care with fluids and vasopressors (noradrenaline) is preferred if hypotension persists despite sodium bicarbonate.
High-Yield Facts
- Wide QRS (>120 ms) + hypotension + antidepressant use = TCA toxicity until proven otherwise; sodium bicarbonate is first-line.
- Sodium bicarbonate mechanism in TCA toxicity: alkalinization + sodium loading both reverse sodium channel blockade and restore cardiac conduction.
- Target serum pH in TCA overdose: 7.45–7.55 (mild alkalosis); monitor QRS width as clinical endpoint.
- Contraindicated in TCA toxicity: Class I antiarrhythmics, phenytoin, and beta-blockers (all worsen outcomes).
- Supportive measures: IV fluids, noradrenaline for refractory hypotension, continuous cardiac monitoring; avoid hypoxia and acidosis.
Mnemonics
TCA Toxicity = WIDE QRS** Wide QRS → IV sodium bicarb, Don't use antiarrhythmics, Elevate pH to 7.45–7.55. Use when you see wide QRS + TCA history. AVOID in TCA OD: Class I, Phenytoin, Beta-blockers Remember: Antiarrhythmics, Phenytoin, B**eta-blockers all worsen TCA toxicity. Sodium bicarb is the antidote.
NBE Trap
NBE pairs TCA toxicity with antiarrhythmics to trap students who think "arrhythmia = antiarrhythmic drug" without considering that Class I agents worsen sodium channel blockade. The phenytoin option exploits outdated knowledge from older textbooks.
Clinical Pearl
In Indian emergency departments, TCA overdose (often accidental in children or intentional in psychiatric patients) is a common ICU admission. The triad of wide QRS, hypotension, and altered mental status should immediately trigger sodium bicarbonate infusion—do not wait for serum TCA levels. Monitoring QRS width on continuous ECG is the bedside guide to therapy adequacy.
_Reference: Harrison Ch. 395 (Drug Poisoning); KD Tripathi Ch. 30 (Antidepressants & Toxicology)_