From the Guidelines
Magnesium sulfate is not a first-line treatment for most forms of ventricular tachycardia (VT) but has a specific role in certain situations, primarily for torsades de pointes, a polymorphic VT associated with QT prolongation, as recommended by the 2017 AHA/ACC/HRS guideline 1.
Role of Magnesium Sulfate in VT
The use of magnesium sulfate in treating ventricular tachycardia is guided by its efficacy in specific types of VT, such as torsades de pointes. According to the 2010 American Heart Association guidelines for cardiopulmonary resuscitation and emergency cardiovascular care, magnesium sulfate can facilitate the termination of torsades de pointes but is not likely to be effective in terminating irregular/polymorphic VT in patients with a normal QT interval 1.
Administration and Dosage
For torsades de pointes, the administration of 1 to 2 g of magnesium sulfate intravenously is recommended, as stated in the 2010 guidelines 1. The 2017 AHA/ACC/HRS guideline further supports the use of intravenous magnesium sulfate to suppress the arrhythmia in patients with QT prolongation due to a medication, hypokalemia, hypomagnesemia, or other acquired factor and recurrent torsades de pointes 1.
Mechanism and Side Effects
Magnesium works by stabilizing cardiac cell membranes and reducing early afterdepolarizations that trigger torsades. However, its use can be associated with side effects such as flushing, hypotension, respiratory depression, and loss of deep tendon reflexes at high levels. Monitoring of magnesium levels, vital signs, and cardiac rhythm during administration is crucial, especially in patients with renal impairment, where magnesium should be used cautiously and calcium gluconate should be available as an antidote for magnesium toxicity 1.
Other Forms of VT
For other forms of VT, standard treatments include amiodarone, lidocaine, electrical cardioversion, or defibrillation, depending on hemodynamic stability. The choice of treatment is guided by the underlying cause of the VT, the presence of any reversible factors, and the patient's clinical condition.
Key Recommendations
- Magnesium sulfate is recommended for torsades de pointes associated with acquired QT prolongation 1.
- Administration of intravenous magnesium sulfate is beneficial for patients with QT prolongation due to a medication, hypokalemia, hypomagnesemia, or other acquired factor and recurrent torsades de pointes 1.
- Potassium repletion to 4.0 mmol per L or more and magnesium repletion to normal values are beneficial for patients with torsades de pointes associated with acquired QT prolongation 1.
From the Research
Role of Magnesium Sulfate in Treating Ventricular Tachycardia
- Magnesium sulfate has been found to be effective in treating various ventricular tachycardias, including torsade de pointes and polymorphic ventricular tachycardia 2, 3, 4.
- The effectiveness of magnesium therapy in intractable ventricular tachycardia and ventricular fibrillation has been documented in patients with both hypomagnesemia and normomagnesemia 4, 5.
- Magnesium sulfate has been shown to prevent hyperpotassemia in massive digoxin intoxication and tend to produce hypopotassemia in other patients, necessitating concomitant use of potassium chloride 4.
- Intravenous magnesium has diverse electrophysiological actions on the conduction system of the heart, including prolonging sinus node recovery time and reducing automaticity, atrioventricular nodal conduction, and His-ventricular conduction 6.
- However, magnesium injection cannot be recommended for treatment of monomorphic ventricular tachycardia in the emergency setting, as it only controls the arrhythmia in a minority of patients 3.
- The recommended dosage of magnesium sulfate varies, but it has been administered as an infusion of 2-3 grams in one minute, followed by 10 grams over five hours 5.