Cardiac conduction: escape pacemaker: 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 · Cardiac conduction: escape pacemaker

Sample item

A 70-year-old man has complete heart block with a regular ventricular rate of 44 per minute and a narrow QRS complex. Where is the escape pacemaker most likely located?

APurkinje fibres in the distal ventriclesBAV junction above the bifurcation of the bundle of HisCAtrial muscle near the coronary sinusDSinoatrial node

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

The answer and the reasoning

B. AV junction above the bifurcation of the bundle of His

When the AV node fails to conduct, the next fastest pacemaker takes over. The AV junction fires at about 40 to 60 per minute and activates the ventricles through the normal His-Purkinje system, giving a narrow QRS. Ventricular escape from Purkinje fibres is slower, about 20 to 40 per minute, with a wide QRS.

Option by option

A. Purkinje fibres in the distal ventricles
Purkinje fibres would give a wide QRS at a slower rate of 20 to 40 per minute.
B. AV junction above the bifurcation of the bundle of His (correct)
Correct. A junctional escape gives a narrow QRS at about 40 to 60 per minute.
C. Atrial muscle near the coronary sinus
Atrial escape would not be disconnected from the ventricles in a block and would not set the ventricular rate.
D. Sinoatrial node
The sinoatrial node is the primary pacemaker and is blocked from the ventricles in this condition.

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.

Questions about this Physiology question

What is the answer to this Physiology question?

The best answer is B, AV junction above the bifurcation of the bundle of His. When the AV node fails to conduct, the next fastest pacemaker takes over.

Why is "Purkinje fibres in the distal ventricles" not the answer?

Purkinje fibres would give a wide QRS at a slower rate of 20 to 40 per minute.

Why is "Atrial muscle near the coronary sinus" not the answer?

Atrial escape would not be disconnected from the ventricles in a block and would not set the ventricular rate.

Why is "Sinoatrial node" not the answer?

The sinoatrial node is the primary pacemaker and is blocked from the ventricles in this condition.

What concept does this question test?

It tests Cardiac conduction: escape pacemaker in Physiology. The AV junction fires at about 40 to 60 per minute and activates the ventricles through the normal His-Purkinje system, giving a narrow QRS. Ventricular escape from Purkinje fibres is slower, about 20 to 40 per minute, with a wide QRS.

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 Cardiac conduction: escape pacemaker?

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.