Cardiology: torsades de pointes: 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: torsades de pointes

Sample item

A 55-year-old woman on erythromycin and a diuretic has palpitations and a brief syncope. Her ECG shows a QTc of 570 ms and runs of polymorphic ventricular tachycardia with a twisting axis. She is haemodynamically stable. Which drug should be given first?

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

The answer and the reasoning

B. Intravenous magnesium sulfate

Torsades de pointes is polymorphic VT in the setting of QT prolongation, often precipitated by drugs and hypokalaemia or hypomagnesaemia. Intravenous magnesium suppresses early afterdepolarisations and is first-line even when serum magnesium is normal. Potassium is corrected, offending drugs are stopped, and unstable patients receive defibrillation.

Option by option

  • A. Intravenous adenosine

    Adenosine terminates AV node dependent re-entrant supraventricular tachycardia and has no role in polymorphic VT.

  • B. Intravenous magnesium sulfate (correct)

    Magnesium is the first-line drug that stabilises the myocardium and terminates the arrhythmia.

  • C. Intravenous amiodarone

    Amiodarone prolongs the QT interval and may worsen torsades.

  • D. Intravenous procainamide

    Procainamide is a class IA agent that prolongs repolarisation and is also proarrhythmic here.

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 General Medicine question

What is the answer to this General Medicine question?

The best answer is B, Intravenous magnesium sulfate. Torsades de pointes is polymorphic VT in the setting of QT prolongation, often precipitated by drugs and hypokalaemia or hypomagnesaemia.

Why is "Intravenous adenosine" not the answer?

Adenosine terminates AV node dependent re-entrant supraventricular tachycardia and has no role in polymorphic VT.

Why is "Intravenous amiodarone" not the answer?

Amiodarone prolongs the QT interval and may worsen torsades.

Why is "Intravenous procainamide" not the answer?

Procainamide is a class IA agent that prolongs repolarisation and is also proarrhythmic here.

What concept does this question test?

It tests Cardiology: torsades de pointes in General Medicine. Intravenous magnesium suppresses early afterdepolarisations and is first-line even when serum magnesium is normal. Potassium is corrected, offending drugs are stopped, and unstable patients receive defibrillation.

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: torsades de pointes?

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.