A 74-year-old woman on sotalol develops recurrent runs of polymorphic ventricular tachycardia with QRS complexes twisting around the baseline. Her QTc is 560 ms. She is conscious with BP 100/65 mmHg. What is the first-line intravenous therapy?
- A IV amiodarone loading
- B IV lidocaine bolus
- C IV magnesium sulfate 2 g ✓
- D IV isoproterenol infusion
Correct answer: C. IV magnesium sulfate 2 g
Explanation
This is torsades de pointes with acquired long QT from a QT-prolonging antiarrhythmic. Intravenous magnesium sulfate suppresses early afterdepolarizations and terminates or prevents recurrences regardless of serum magnesium level, making it first line in the stable patient. Amiodarone further prolongs repolarization and is contraindicated here. Isoproterenol is reserved for bradycardia-dependent torsades when pacing is unavailable, not as initial therapy.
Reference: Katzung's Basic and Clinical Pharmacology, 16th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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