What is the recommended magnesium infusion regimen for treating torsades de pointes?

Magnesium Infusion Regimen for Torsades de Pointes

For torsades de pointes, administer intravenous magnesium sulfate 1-2 g over 1-2 minutes as initial therapy, followed by continuous infusion of 0.5-1.0 mg/kg/hr if needed for recurrent episodes. 1

Initial Management Algorithm

• Immediately recognize torsades de pointes by its distinctive polymorphic ventricular tachycardia pattern with QT prolongation and "twisting of the points" morphology 1
• For hemodynamically unstable patients, perform immediate direct current cardioversion with appropriate sedation 2, 1
• Withdraw any QT-prolonging medications that may be contributing to the arrhythmia 1
• Correct electrolyte abnormalities, particularly hypokalemia 2, 1

Magnesium Administration Protocol

Initial Bolus

• Administer 1-2 g of magnesium sulfate IV over 1-2 minutes 1, 3
• This dose is effective even when serum magnesium levels are normal 1, 3
• In clinical studies, a single bolus completely abolished torsades de pointes within 1-5 minutes in most patients 3

For Recurrent Episodes

• If torsades recurs after initial bolus, administer a second bolus of 1-2 g 3
• Follow with continuous infusion at 0.5-1.0 mg/kg/hr (approximately 3-20 mg/min) for 7-48 hours until QT interval normalizes (below 0.50 seconds) 1, 3
• Target serum magnesium concentration of 3-5 mg/dL 4

Additional Management Considerations

• Target serum potassium levels between 4.5-5 mEq/L to shorten the QT interval and reduce recurrence of torsades 1
• If magnesium therapy is inadequate:
  • Consider temporary cardiac pacing, which is highly effective for recurrent torsades after magnesium and potassium supplementation 1, 5
  • Isoproterenol infusion (2-10 mcg/min IV) may be considered for pause-dependent torsades in patients without congenital LQTS 1, 5

Special Considerations

• For torsades associated with acute myocardial ischemia, consider urgent coronary angiography with view to revascularization and intravenous beta blockers 2, 1
• For LQT3 patients with torsades, consider intravenous lidocaine or oral mexiletine 2, 1
• Magnesium is specifically effective for torsades de pointes but not for polymorphic VT with normal QT intervals 3

Clinical Pearls and Pitfalls

• Magnesium works by preventing reinitiation of torsades rather than pharmacologically converting polymorphic VT 2
• There may not be immediate shortening in the QT interval after magnesium administration, despite clinical efficacy 6
• Magnesium can be safely administered even in patients with acute myocardial infarction, angina pectoris, or systemic hypertension, conditions in which isoproterenol is contraindicated 6
• For pediatric patients with torsades, the optimal bolus dosage is 3-12 mg/kg, with infusion rates of 0.5-1.0 mg/kg/hr 4