Cardiovascular: ECG in pre-excitation: 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: ECG in pre-excitation

Sample item

A 19-year-old with palpitations has an ECG showing a PR interval of 0.09 s with a slurred upstroke at the start of a broad QRS complex. Which mechanism explains the short PR interval?

AEarly repolarisation of the atriaBFaster conduction through the AV node because of high sympathetic tone aloneCAn accessory pathway bypasses the AV node, so the ventricle is activated early without the nodal delayDDelayed conduction in the His-Purkinje system

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

The answer and the reasoning

C. An accessory pathway bypasses the AV node, so the ventricle is activated early without the nodal delay

Normally the AV node delays conduction and gives a PR interval of 0.12 to 0.20 s. In Wolff-Parkinson-White syndrome an accessory pathway conducts to the ventricle without delay, producing a short PR and a slurred delta wave from early ventricular activation. The QRS widens because part of the ventricle is activated slowly through muscle.

Option by option

A. Early repolarisation of the atria
Atrial repolarisation is not a determinant of the PR interval.
B. Faster conduction through the AV node because of high sympathetic tone alone
Sympathetic tone shortens the PR slightly but does not give a delta wave.
C. An accessory pathway bypasses the AV node, so the ventricle is activated early without the nodal delay (correct)
Correct. Bypass of the nodal delay shortens the PR and produces the delta wave.
D. Delayed conduction in the His-Purkinje system
His-Purkinje delay would widen the QRS and not shorten the PR.

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 C, An accessory pathway bypasses the AV node, so the ventricle is activated early without the nodal delay. Normally the AV node delays conduction and gives a PR interval of 0.

Why is "Early repolarisation of the atria" not the answer?

Atrial repolarisation is not a determinant of the PR interval.

Why is "Faster conduction through the AV node because of high sympathetic ton…" not the answer?

Sympathetic tone shortens the PR slightly but does not give a delta wave.

Why is "Delayed conduction in the His-Purkinje system" not the answer?

His-Purkinje delay would widen the QRS and not shorten the PR.

What concept does this question test?

It tests Cardiovascular: ECG in pre-excitation in Physiology. 12 to 0.20 s. In Wolff-Parkinson-White syndrome an accessory pathway conducts to the ventricle without delay, producing a short PR and a slurred delta wave from early ventricular activation. The QRS widens because part of the ventricle is activated slowly through muscle.

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: ECG in pre-excitation?

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.