Cardiovascular system: Wenckebach conduction: 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: Wenckebach conduction

Sample item

An ECG shows PR interval lengthening on successive beats until a P wave fails to conduct, after which the cycle repeats. What conduction property underlies this pattern?

AComplete dissociation of atria and ventricles with independent rhythmsBProgressively decremental conduction in the AV node, then a dropped beatCEarly ventricular activation through an accessory pathwayDAbrupt block below the bundle of His with a fixed PR interval

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

The answer and the reasoning

B. Progressively decremental conduction in the AV node, then a dropped beat

In Mobitz type I (Wenckebach) block, the AV node becomes less able to conduct with each beat, so the PR interval lengthens progressively until a beat is dropped and the node recovers. It is often vagal or nodal in origin and usually benign. Mobitz II block has a fixed PR interval and sudden dropped beats.

Option by option

A. Complete dissociation of atria and ventricles with independent rhythms
Independent atrial and ventricular rhythms describe complete heart block.
B. Progressively decremental conduction in the AV node, then a dropped beat (correct)
Correct. Decremental AV nodal conduction produces the lengthening PR and the dropped beat.
C. Early ventricular activation through an accessory pathway
Early ventricular activation through an accessory pathway describes pre-excitation, with a short PR interval.
D. Abrupt block below the bundle of His with a fixed PR interval
A fixed PR interval with sudden dropped beats describes Mobitz type II block.

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, Progressively decremental conduction in the AV node, then a dropped beat. In Mobitz type I (Wenckebach) block, the AV node becomes less able to conduct with each beat, so the PR interval lengthens progressively until a beat is dropped and the node recovers.

Why is "Complete dissociation of atria and ventricles with independent rhythms" not the answer?

Independent atrial and ventricular rhythms describe complete heart block.

Why is "Early ventricular activation through an accessory pathway" not the answer?

Early ventricular activation through an accessory pathway describes pre-excitation, with a short PR interval.

Why is "Abrupt block below the bundle of His with a fixed PR interval" not the answer?

A fixed PR interval with sudden dropped beats describes Mobitz type II block.

What concept does this question test?

It tests Cardiovascular system: Wenckebach conduction in Physiology. It is often vagal or nodal in origin and usually benign. Mobitz II block has a fixed PR interval and sudden dropped beats.

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: Wenckebach conduction?

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.