Cardiovascular system: ECG in hypocalcaemia: 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: ECG in hypocalcaemia

Sample item

A woman develops perioral tingling and carpopedal spasm two days after total thyroidectomy. Which ECG finding is expected?

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

The answer and the reasoning

C. Prolonged QT interval from a lengthened ST segment

Low extracellular calcium prolongs phase 2 (the plateau) of the ventricular action potential, which lengthens the ST segment and therefore the QT interval. Hypercalcaemia shortens the plateau and the QT interval.

Option by option

  • A. Prominent U waves with flattened T waves

    Prominent U waves with flat T waves are typical of hypokalaemia.

  • B. Shortened QT interval with a sloping ST segment

    A short QT interval is the pattern of hypercalcaemia, where the plateau shortens.

  • C. Prolonged QT interval from a lengthened ST segment (correct)

    Correct. Hypocalcaemia lengthens the plateau, giving a long ST segment and prolonged QT.

  • D. Tall, narrow, peaked T waves

    Peaked T waves are the early ECG sign of hyperkalaemia.

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, Prolonged QT interval from a lengthened ST segment. Low extracellular calcium prolongs phase 2 (the plateau) of the ventricular action potential, which lengthens the ST segment and therefore the QT interval.

Why is "Prominent U waves with flattened T waves" not the answer?

Prominent U waves with flat T waves are typical of hypokalaemia.

Why is "Shortened QT interval with a sloping ST segment" not the answer?

A short QT interval is the pattern of hypercalcaemia, where the plateau shortens.

Why is "Tall, narrow, peaked T waves" not the answer?

Peaked T waves are the early ECG sign of hyperkalaemia.

What concept does this question test?

It tests Cardiovascular system: ECG in hypocalcaemia in Physiology. Hypercalcaemia shortens the plateau and the QT interval.

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 system: ECG in hypocalcaemia?

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.