Cardiac electrophysiology: hyperkalaemia: 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 electrophysiology: hyperkalaemia

Sample item

A patient with acute kidney injury has serum potassium 7.2 mmol/L, and the ECG shows tall, narrow, peaked T waves. Which change in the ventricular action potential best explains this finding?

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

The answer and the reasoning

C. Increased potassium conductance causing faster phase 3 repolarisation

A high extracellular potassium concentration partially depolarises the resting membrane and increases potassium channel conductance. Repolarisation in phase 3 becomes faster and more synchronous, which produces tall, tented T waves. With further rises the cell becomes inactivated and the P wave flattens and QRS widens.

Option by option

  • A. Failure of phase 0 from fast sodium channel activation

    Phase 0 slows with more severe hyperkalaemia because of sodium channel inactivation, which widens the QRS, not peaks the T wave.

  • B. Prolonged plateau from increased calcium entry

    The plateau is shortened, not prolonged, in hyperkalaemia.

  • C. Increased potassium conductance causing faster phase 3 repolarisation (correct)

    Correct. Faster repolarisation from higher potassium conductance causes peaked T waves.

  • D. Delayed repolarisation from reduced potassium conductance

    Reduced conductance would delay repolarisation and prolong the QT interval, as in hypokalaemia.

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, Increased potassium conductance causing faster phase 3 repolarisation. A high extracellular potassium concentration partially depolarises the resting membrane and increases potassium channel conductance.

Why is "Failure of phase 0 from fast sodium channel activation" not the answer?

Phase 0 slows with more severe hyperkalaemia because of sodium channel inactivation, which widens the QRS, not peaks the T wave.

Why is "Prolonged plateau from increased calcium entry" not the answer?

The plateau is shortened, not prolonged, in hyperkalaemia.

Why is "Delayed repolarisation from reduced potassium conductance" not the answer?

Reduced conductance would delay repolarisation and prolong the QT interval, as in hypokalaemia.

What concept does this question test?

It tests Cardiac electrophysiology: hyperkalaemia in Physiology. Repolarisation in phase 3 becomes faster and more synchronous, which produces tall, tented T waves. With further rises the cell becomes inactivated and the P wave flattens and QRS widens.

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 electrophysiology: hyperkalaemia?

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.