Cardiology: cannon a waves in complete heart block: practice question

A General Medicine 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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General Medicine · Cardiology: cannon a waves in complete heart block

Sample item

A man with syncope has a regular pulse of 36 per minute. Intermittent, very large pulsations are seen in his neck and the intensity of the first heart sound varies from beat to beat. Which jugular venous finding explains the pulsations?

AA steep y descent because of rapid early ventricular fillingBGiant v waves from regurgitation across the tricuspid valveCCannon a waves from atrial contraction against a closed tricuspid valveDAbsent a waves because the atria are fibrillating

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

The answer and the reasoning

C. Cannon a waves from atrial contraction against a closed tricuspid valve

In complete heart block the atria and ventricles beat independently. Occasionally the atrium contracts when the tricuspid valve is shut, sending a large pressure wave up the neck, a cannon a wave, and the first sound varies as the PR interval changes. Treatment is a permanent pacemaker.

Option by option

A. A steep y descent because of rapid early ventricular filling
A steep y descent occurs in constrictive pericarditis and does not cause intermittent cannon waves.
B. Giant v waves from regurgitation across the tricuspid valve
Giant v waves are seen in severe tricuspid regurgitation and the pulse would not be this slow and regular.
C. Cannon a waves from atrial contraction against a closed tricuspid valve (correct)
Correct. AV dissociation makes atrial systole fall on a closed tricuspid valve at irregular intervals.
D. Absent a waves because the atria are fibrillating
Absent a waves occur in atrial fibrillation, which gives an irregularly irregular pulse.

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 General Medicine question

What is the answer to this General Medicine question?

The best answer is C, Cannon a waves from atrial contraction against a closed tricuspid valve. In complete heart block the atria and ventricles beat independently.

Why is "A steep y descent because of rapid early ventricular filling" not the answer?

A steep y descent occurs in constrictive pericarditis and does not cause intermittent cannon waves.

Why is "Giant v waves from regurgitation across the tricuspid valve" not the answer?

Giant v waves are seen in severe tricuspid regurgitation and the pulse would not be this slow and regular.

Why is "Absent a waves because the atria are fibrillating" not the answer?

Absent a waves occur in atrial fibrillation, which gives an irregularly irregular pulse.

What concept does this question test?

It tests Cardiology: cannon a waves in complete heart block in General Medicine. Occasionally the atrium contracts when the tricuspid valve is shut, sending a large pressure wave up the neck, a cannon a wave, and the first sound varies as the PR interval changes. Treatment is a permanent pacemaker.

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 Cardiology: cannon a waves in complete heart block?

For each disease know the classic presentation, the best test, and the first-line treatment. Then use the flashcards and the other General Medicine 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.