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Acquired long QT syndrome — RACP Written MCQ

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HardClinical PharmacologyAcquired long QT syndromeRACP Written

A 33-year-old woman has recurrent palpitations and presyncope. ECG shows QTc 520 ms. She recently started clarithromycin for sinusitis and takes citalopram. Serum potassium is 3.0 mmol/L and magnesium is low. What is the most likely cause?

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Correct answer: C — Drug and electrolyte related acquired long QT

Macrolides and SSRIs can prolong QT, and hypokalaemia plus hypomagnesaemia increase torsades risk. The clinical context favours acquired long QT.

Reference: AMH; Therapeutic Guidelines: Toxicology and drug-interaction principles