skip to main content

Torsades de pointes — RCPSC IM MCQ

Instant feedback + full explanation. One question, done properly.

HardCardiologyTorsades de pointesRCPSC IM

A 49-year-old receiving ondansetron has syncope with torsades de pointes. QTc is 570 ms, potassium 2.9 mmol/L and magnesium 0.52 mmol/L; a pulse returns after defibrillation. What is the next targeted treatment?

Educational content. Not a substitute for clinical judgement or local policy.

Reveal the answer and explanation

Correct answer: A — Give intravenous magnesium and correct potassium

The best answer is “Give intravenous magnesium and correct potassium”. Acquired long-QT torsades is treated with intravenous magnesium, withdrawal of precipitating drugs and correction of electrolytes; recurrent pause-dependent episodes may require rate acceleration. Calcium and procainamide do not address the mechanism, and oral-only correction is unsafe after an arrest.

Reference: Ontario Poison Centre, clinical resources and protocols: https://www.ontariopoisoncentre.ca/health-care-professionals/clinical-resources-and-protocols/