Cardiovascular system: subendocardial ischaemia in aortic stenosis: 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: subendocardial ischaemia in aortic stenosis

Sample item

A 66-year-old man with severe aortic stenosis and a thick left ventricle has exertional angina, although coronary angiography is normal. Which mechanism makes the inner layers of the ventricular wall most vulnerable?

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

The answer and the reasoning

B. High wall tension and diastolic pressure reduce the perfusion gradient while oxygen demand rises

Left ventricular coronary flow occurs mainly in diastole, driven by the gap between aortic diastolic pressure and the pressure in the ventricular wall. In aortic stenosis with hypertrophy, systolic wall tension and diastolic filling pressure are high, so the subendocardial layer has the lowest perfusion gradient and the highest oxygen demand. Ischaemia can therefore occur with angiographically normal epicardial arteries.

Option by option

  • A. Myocytes lose the ability to extract oxygen from coronary blood

    Myocardium already extracts a very large share of delivered oxygen, and extraction is not the limiting defect here.

  • B. High wall tension and diastolic pressure reduce the perfusion gradient while oxygen demand rises (correct)

    Correct. The subendocardium has the smallest perfusion gradient and the greatest demand, so it fails first.

  • C. Haemoglobin affinity for oxygen rises during exertion

    Oxygen affinity does not rise during exertion; exercise acidosis and heat shift the curve to the right.

  • D. Coronary flow occurs mainly in systole and is cut off by tachycardia

    Left ventricular coronary flow is mainly diastolic, so this timing is the wrong way round.

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 B, High wall tension and diastolic pressure reduce the perfusion gradient while oxygen demand rises. Left ventricular coronary flow occurs mainly in diastole, driven by the gap between aortic diastolic pressure and the pressure in the ventricular wall.

Why is "Myocytes lose the ability to extract oxygen from coronary blood" not the answer?

Myocardium already extracts a very large share of delivered oxygen, and extraction is not the limiting defect here.

Why is "Haemoglobin affinity for oxygen rises during exertion" not the answer?

Oxygen affinity does not rise during exertion; exercise acidosis and heat shift the curve to the right.

Why is "Coronary flow occurs mainly in systole and is cut off by tachycardia" not the answer?

Left ventricular coronary flow is mainly diastolic, so this timing is the wrong way round.

What concept does this question test?

It tests Cardiovascular system: subendocardial ischaemia in aortic stenosis in Physiology. In aortic stenosis with hypertrophy, systolic wall tension and diastolic filling pressure are high, so the subendocardial layer has the lowest perfusion gradient and the highest oxygen demand. Ischaemia can therefore occur with angiographically normal epicardial arteries.

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 Cardiovascular system: subendocardial ischaemia in aortic stenosis?

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.