Cardiovascular system: vasovagal syncope: practice question

A Physiology 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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Physiology · Cardiovascular system: vasovagal syncope

Sample item

A 19-year-old student becomes pale and sweaty at the sight of blood, then faints. Heart rate is 44 per minute and blood pressure 80/45 mmHg. What is the mechanism?

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

The answer and the reasoning

B. Sudden sympathetic withdrawal with vagal surge, causing vasodilatation and bradycardia

In vasovagal (neurally mediated) syncope, emotional or orthostatic triggers cause abrupt withdrawal of sympathetic vasomotor tone and an increase in vagal outflow. Vasodilatation and bradycardia lower cardiac output and cerebral perfusion, and consciousness returns once the patient is supine.

Option by option

  • A. Primary pump failure from atrioventricular conduction block

    Conduction block would not explain the pallor and vasodilatation that follow an emotional trigger.

  • B. Sudden sympathetic withdrawal with vagal surge, causing vasodilatation and bradycardia (correct)

    Correct. Falling vasomotor tone together with vagal slowing of the sinus node produces the faint.

  • C. Reflex sympathetic surge causing tachyarrhythmia and a fall in stroke volume

    This would give tachycardia, whereas this patient is bradycardic and vasodilated.

  • D. Loss of carotid sinus afferents causing unopposed vasoconstriction

    Loss of baroreceptor afferents causes labile hypertension rather than a faint with bradycardia.

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 Physiology question

What is the answer to this Physiology question?

The best answer is B, Sudden sympathetic withdrawal with vagal surge, causing vasodilatation and bradycardia. In vasovagal (neurally mediated) syncope, emotional or orthostatic triggers cause abrupt withdrawal of sympathetic vasomotor tone and an increase in vagal outflow.

Why is "Primary pump failure from atrioventricular conduction block" not the answer?

Conduction block would not explain the pallor and vasodilatation that follow an emotional trigger.

Why is "Reflex sympathetic surge causing tachyarrhythmia and a fall in stroke…" not the answer?

This would give tachycardia, whereas this patient is bradycardic and vasodilated.

Why is "Loss of carotid sinus afferents causing unopposed vasoconstriction" not the answer?

Loss of baroreceptor afferents causes labile hypertension rather than a faint with bradycardia.

What concept does this question test?

It tests Cardiovascular system: vasovagal syncope in Physiology. Vasodilatation and bradycardia lower cardiac output and cerebral perfusion, and consciousness returns once the patient is supine.

How hard is this question?

We tag it as an application question: it asks you to use a fact on a patient or a finding. 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 Cardiovascular system: vasovagal syncope?

For each system, sketch the key graph (pressure–volume loop, oxygen dissociation curve, nephron handling) and explain it aloud. Then use the flashcards and the other Physiology 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.