Muscle relaxants: succinylcholine and bradycardia: practice question

A Anaesthesia question in the style of the NEET PG paper. Answer it first, then read why the right option is right and why each of the others is wrong.

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Anaesthesia · Muscle relaxants: succinylcholine and bradycardia

Sample item

A 6-year-old receives two doses of succinylcholine five minutes apart for persistent laryngospasm, and the ECG shows sinus bradycardia. What is the mechanism?

Original practice item, not a recalled exam question. Nothing here is recorded.

The answer and the reasoning

D. Stimulation of cardiac muscarinic receptors in the sinus node

Succinylcholine stimulates muscarinic receptors in the sinus node, causing bradycardia that is more marked in children and after a second dose. Atropine given beforehand or treated afterwards prevents or corrects it. Hyperkalaemia causes peaked T waves and arrhythmias, not typically isolated sinus slowing.

Option by option

  • A. Release of histamine from mast cells

    Histamine release causes hypotension and flushing, not this bradycardia.

  • B. Blockade of beta-1 receptors

    Succinylcholine has no beta-1 blocking action.

  • C. Hyperkalaemia from muscle depolarisation

    Hyperkalaemia would show peaked T waves and widened QRS before bradycardia.

  • D. Stimulation of cardiac muscarinic receptors in the sinus node (correct)

    Correct. Muscarinic stimulation of the sinus node explains the slowing.

Source note: Original NextPrep sample item — pending expert review. This item is original practice material awaiting independent expert review, so confirm important facts in a standard textbook.

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Questions about this Anaesthesia question

What is the answer to this Anaesthesia question?

The best answer is D, Stimulation of cardiac muscarinic receptors in the sinus node. Succinylcholine stimulates muscarinic receptors in the sinus node, causing bradycardia that is more marked in children and after a second dose.

Why is "Release of histamine from mast cells" not the answer?

Histamine release causes hypotension and flushing, not this bradycardia.

Why is "Blockade of beta-1 receptors" not the answer?

Succinylcholine has no beta-1 blocking action.

Why is "Hyperkalaemia from muscle depolarisation" not the answer?

Hyperkalaemia would show peaked T waves and widened QRS before bradycardia.

What concept does this question test?

It tests Muscle relaxants: succinylcholine and bradycardia in Anaesthesia. Atropine given beforehand or treated afterwards prevents or corrects it. Hyperkalaemia causes peaked T waves and arrhythmias, not typically isolated sinus slowing.

How hard is this question?

We tag it as a multi-step question: it asks you to combine more than one idea. The tag is our own editorial judgement, not an official difficulty rating, so read the reason for every option, not only the answer.

How should I study Muscle relaxants: succinylcholine and bradycardia?

Make a table of each agent, its key advantage and its main side effect. Then use the flashcards and the other Anaesthesia questions on this site to test what stuck.

Is this a real NEET PG question?

No. It is an original practice item (editorial status: sample, version 1). NextPrep does not publish recalled or leaked questions, and independent faculty review of this item has not been completed yet, so confirm important facts in a standard textbook.