Question

A patient ingested some unknown substance and presented with myoclonic jerks, seizures, tachycardia and hypotension. The ECG showed a heart rate of 120/minute with QRS interval of 0.16 seconds. The arterial blood gas revealed a pH of 7.25, PCO2 of 30 mmHg and HCO3 of 15 mmol/L. The most likely cause of poisoning is ingestion of:

• A. Amanita phalloides
• B. Ethylene glycol
• C. Imipramine
• D. Phencyclidine

Hint:

A widened QRS complex after an overdose is the classic clue for tricyclic antidepressant poisoning.

Answer 1

The Correct Option is C

Step 1: Understanding the Question:
A patient who has taken an unknown substance now has myoclonic jerks, seizures, a fast heart rate and low blood pressure. The ECG shows a wide QRS of 0.16 seconds (160 milliseconds) at a rate of 120 per minute, and the blood gas shows a high anion gap type metabolic acidosis (pH 7.25, PCO2 30, HCO3 15). We need to identify the poison responsible.

Step 2: Key Concept:
A markedly widened QRS complex after an overdose is a classic sign of sodium channel blockade in the heart. Tricyclic antidepressants such as imipramine block fast sodium channels in the myocardium, and the degree of QRS widening correlates directly with the risk of seizures, arrhythmia and death, which is why it is used to judge severity in tricyclic overdose. Tricyclics also block muscarinic, alpha-adrenergic and histamine receptors, which explains the mixed picture of seizures, hypotension and tachycardia.

Step 3: Detailed Explanation:
Amanita phalloides poisoning (death cap mushroom) causes severe gastrointestinal symptoms first, followed by liver failure over one to several days; it does not cause an acutely wide QRS or seizures within a short time frame, so it does not fit. Ethylene glycol poisoning causes a high anion gap metabolic acidosis too, but through its toxic metabolites (glycolic and oxalic acid), and it typically presents with drunkenness, oxalate crystals in urine and later kidney injury, not a wide QRS complex, so this is a distractor built around the acidosis alone. Phencyclidine causes agitation, nystagmus and hypertension more than a wide QRS and severe hypotension. Imipramine, a tricyclic antidepressant, fits every part of this picture: sodium channel blockade widens the QRS to 0.16 seconds, anticholinergic and membrane effects provoke seizures and myoclonus, alpha blockade causes hypotension, and the resulting seizures and poor perfusion drive the high anion gap metabolic acidosis seen on the blood gas.

Step 4: Final Answer:
The most likely cause of this poisoning is ingestion of imipramine, option (3).