Cardiac physiology: splitting of S2: 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 physiology: splitting of S2

Sample item

A 65-year-old man with complete left bundle branch block has a second heart sound whose split is widest during expiration and narrows on inspiration. What explains this paradoxical splitting?

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

The answer and the reasoning

C. Delayed left ventricular activation makes aortic valve closure follow pulmonary valve closure

In left bundle branch block the left ventricle is activated late, so aortic closure (A2) is delayed beyond pulmonary closure (P2). The order becomes P2 then A2. On inspiration P2 is delayed and moves closer to A2, so the split narrows, and on expiration the split widens, the reverse of normal.

Option by option

  • A. Increased inspiratory venous return fixing the split

    Fixed splitting occurs in atrial septal defect because of a constant right ventricular volume load.

  • B. Delayed right ventricular emptying makes pulmonary valve closure late

    Delayed P2 from right bundle branch block produces a wide, normally varying split.

  • C. Delayed left ventricular activation makes aortic valve closure follow pulmonary valve closure (correct)

    Correct. Late A2 reverses the normal order and produces paradoxical splitting.

  • D. Early aortic valve closure from reduced stroke volume

    Early A2 would widen the normal split, not reverse it.

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 C, Delayed left ventricular activation makes aortic valve closure follow pulmonary valve closure. In left bundle branch block the left ventricle is activated late, so aortic closure (A2) is delayed beyond pulmonary closure (P2).

Why is "Increased inspiratory venous return fixing the split" not the answer?

Fixed splitting occurs in atrial septal defect because of a constant right ventricular volume load.

Why is "Delayed right ventricular emptying makes pulmonary valve closure late" not the answer?

Delayed P2 from right bundle branch block produces a wide, normally varying split.

Why is "Early aortic valve closure from reduced stroke volume" not the answer?

Early A2 would widen the normal split, not reverse it.

What concept does this question test?

It tests Cardiac physiology: splitting of S2 in Physiology. The order becomes P2 then A2. On inspiration P2 is delayed and moves closer to A2, so the split narrows, and on expiration the split widens, the reverse of normal.

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 Cardiac physiology: splitting of S2?

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.