A 66-year-old woman on sotalol for atrial fibrillation develops recurrent syncope. Monitor shows polymorphic ventricular tachycardia with QRS complexes twisting around the baseline, initiated after a pause-dependent short-coupled beat. QT interval measures 520 ms. She is haemodynamically stable during episodes. What is the immediate drug of choice?
- A IV magnesium sulphate 2 g ✓
- B IV amiodarone loading
- C IV lidocaine bolus
- D Oral quinidine
Correct answer: A. IV magnesium sulphate 2 g
Explanation
Torsades de pointes is a pause-dependent polymorphic VT occurring with QT prolongation, classically provoked by class IA and class III antiarrhythmics such as sotalol. IV magnesium sulphate suppresses the triggering early afterdepolarisations even when serum magnesium is normal, and is the immediate treatment in the stable patient. Amiodarone prolongs QT further and would worsen torsades, which kills that tempting option. Lidocaine does not shorten QT meaningfully, and if torsades recurs despite magnesium, overdrive pacing to shorten QT is used.
Reference: Harrison's Principles of Internal Medicine, 21st ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.