From the Guidelines
Magnesium sulfate is a recommended treatment for torsades de pointes, particularly in patients with acquired QT prolongation, as it can help suppress the arrhythmia [(1, 2)].
Key Points
- Intravenous magnesium sulfate is recommended for patients with QT prolongation due to medication, hypokalemia, hypomagnesemia, or other acquired factors and recurrent torsades de pointes 1.
- Potassium repletion to 4.0 mmol per L or more and magnesium repletion to normal values (e.g., ≥2.0 mmol/L) are beneficial for patients with torsades de pointes associated with acquired QT prolongation 1.
- Dosing: 1 to 2 g of magnesium sulfate intravenously, with repeated doses as needed to suppress ectopy and nonsustained VT episodes [(2, 3)].
- Mechanism: Magnesium can suppress episodes of torsades de pointes without necessarily shortening the QT interval, even when serum magnesium is normal 2.
Important Considerations
- Magnesium toxicity can occur at high serum concentrations, but the risk is small with the usual doses used to treat torsades de pointes 2.
- Temporary pacing or isoproterenol may be needed in some cases, particularly if torsades de pointes is recurrent despite magnesium and potassium supplementation [(1, 2, 4)].
The FDA Drug Labels for magnesium sulfate (IV) do not address this question.
From the Research
Mechanism of Action
- Magnesium sulfate treats torsades de pointes by a direct antagonism of Mg++-K+ and/or Mg++-Ca++ 5
- It increases the ventricular effective refractory period (ERP) without changing the QT interval, resulting in a significant increase in ERP/QT 6
- Magnesium sulfate decreases the dispersion of ERP (dERP), although not significantly 6
Efficacy
- Intravenous magnesium sulfate is extremely effective in treating torsades de pointes, with a success rate of 80-100% in various studies 7, 8, 9
- It is considered the treatment of choice for torsades de pointes due to its simplicity, rapidity of administration, and almost immediate efficacy 7, 5
- Magnesium sulfate is safe to use, even in patients with acute myocardial infarction, angina pectoris, or systemic hypertension, where other treatments like isoproterenol may be contraindicated 8