## Why Intravenous magnesium sulfate is right The patient presents with Torsades de Pointes (polymorphic VT with "twisting of the points"), a life-threatening arrhythmia directly caused by prolongation of the interval marked **D** (QT interval). His corrected QTc of 480 ms exceeds the upper limit of normal (450 ms in men), and he has two major risk factors: haloperidol (an antipsychotic that prolongs QT) and hypokalemia (K+ 3.2 mEq/L). According to Harrison 21e Ch 248 and standard ACLS protocols, IV magnesium sulfate 2 g bolus is the first-line treatment for Torsades de Pointes, regardless of serum magnesium level. Magnesium stabilizes the cardiac membrane and suppresses the triggered activity underlying the arrhythmia. ## Why each distractor is wrong - **Intravenous potassium chloride 40 mEq over 1 hour**: While hypokalemia is a contributing cause and must be corrected, potassium replacement alone does not acutely terminate Torsades de Pointes. Magnesium is the immediate antiarrhythmic of choice. Potassium should be given after magnesium and cautiously to avoid hyperkalemia. - **Immediate DC cardioversion followed by amiodarone infusion**: Although DC cardioversion may be considered if the patient is hemodynamically unstable and unresponsive to magnesium, amiodarone (a Class III antiarrhythmic) further prolongs the QT interval and is contraindicated in long QT–related Torsades. It may paradoxically worsen the arrhythmia. - **Temporary pacemaker insertion for overdrive pacing**: Overdrive pacing is reserved for recurrent or refractory Torsades de Pointes after magnesium and correction of electrolyte abnormalities. It is not the first-line acute intervention. **High-Yield:** Torsades de Pointes = prolonged QT interval + triggered activity; IV Mg²⁺ is first-line regardless of serum Mg level; avoid Class III antiarrhythmics (they prolong QT further). [cite: Harrison 21e Ch 248; KD Tripathi 9e Ch 38]
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