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Magnesium Sulfate in ACLS

Magnesium Sulfate in ACLS

Pharmacotherapy is an important method of treatment in advanced cardiac life support (ACLS), aimed at increasing cardiac contractility, increasing or decreasing cardiac chronotropy, and treating cardiac arrhythmias. Magnesium sulfate plays a crucial role in the treatment of polymorphic ventricular tachycardia (also known as torsades de pointes) with associated prolonged QT interval, for both patients with a pulse and patients who are in cardiac arrest from polymorphic VT.

Magnesium sulfate is also indicated in patients with acute coronary syndrome with hypomagnesemia and atrial fibrillation with rapid ventricular response. Therefore, it is crucial that ACLS practitioners are familiar with the indications and use of magnesium sulfate, as it could save lives.

Magnesium Sulfate: An Overview

Magnesium sulfate is a naturally occurring element in nature and in the human body. Among its many functions, magnesium is required to transport potassium and calcium across the cell membrane. It works by inhibiting the release of calcium in the muscle cells causing smooth muscle relaxation. In some cases, it can even be used to treat asthma or eclampsia.

The first reported clinical trial of magnesium sulfate in cardiac arrest was conducted in 1997.  Several randomized trials showed no difference in outcomes among patients with ventricular fibrillation. However, several case series showed a potential benefit of magnesium sulfate in ventricular tachycardia associated with a long QT interval, which led to its official use in the ACLS algorithm.

Today in ACLS, magnesium sulfate is indicated for the treatment of polymorphic ventricular tachycardia (torsades de pointes) associated with a long QT interval. Magnesium sulfate may also be given in the treatment of acute coronary syndrome to prevent arrhythmias if hypomagnesemia is present. The main side effect of magnesium sulfate is vasodilation resulting in flushing and hypotension.

While magnesium sulfate is used for the treatment of polymorphic ventricular tachycardia (torsades de pointes) with associated long QT interval, it should not be given for monomorphic ventricular tachycardia, ventricular fibrillation, or pulseless electrical activity.


Magnesium sulfate is the second most common intracellular cation after potassium. In fact, magnesium levels typically rise and fall in the same way as potassium levels, which is why hypokalemia is typically associated with hypomagnesemia and vice versa. Therefore, if correction of hypomagnesemia is needed, hypokalemia should be corrected as well.

The use of magnesium is thought to shorten the QT interval thereby making the heart less susceptible to ventricular tachycardia. It causes smooth muscle relaxation by reducing intracellular calcium binding. At the same time, magnesium sulfate slows conduction through the AV node, thus reducing the heart rate (in the treatment of Polymorphic VT with long QT interval).

Magnesium Sulfate in Cardiac Care

In patients with acute coronary symptoms (ACS), magnesium sulfate should not be routinely administered. However, it is recommended to keep magnesium level >2 mg/dl in patients with cardiac arrhythmias or ACS. Therefore, magnesium sulfate should only be administered in ACS if the magnesium level is known to be low.

Magnesium sulfate can also be used as an adjunctive medicine for atrial fibrillation with rapid ventricular response, as it slows conduction through the atrioventricular node. However, magnesium should typically be given with an atrioventricular nodal blocker such as a calcium channel blocker or beta blocker.

Magnesium Sulfate in the ACLS Algorithm

Magnesium is indicated for Polymorphic VT (torsades de pointes) associated with a long QT interval, both with and without a pulse.

Of course, ACLS care should always begin with basic life support addressing airway, breathing, and circulation prior to ACLS interventions. If a patient is noted to have ventricular tachycardia and is in cardiac arrest, the ACLS provider should immediately defibrillate the patient.

If a patient has ventricular tachycardia with a pulse and is hemodynamically unstable, this calls for immediate synchronized cardioversion. However, polymorphic ventricular tachycardia is often a difficult cardiac rhythm on which to perform synchronized cardioversion, as the defibrillator will often have difficulty identifying the QRS complex. Because of this, magnesium sulfate is an important treatment in VT with associated long QT interval.

Magnesium sulfate may be administered with other antidysrhythmic medications such as procainamide or amiodarone. However, it’s important to note that antidysrhythmics have poor efficacy treating Polymorphic VT. What’s more, magnesium sulfate may only be administered through the intravenous (IV) or intraosseous (IO) route. Oral preparations of magnesium are available but do not increase magnesium levels quickly enough in critically ill patients.

In Polymorphic VT associated with long QT intervals without a pulse, magnesium sulfate should be administered as a slow bolus. In Polymorphic VT associated with a long QT interval with a pulse, magnesium sulfate should be administered as an infusion.

For more information on magnesium’s recommended use in ACLS situations, always consult the most recent version of the ACLS guidelines and algorithms.

Dosage of Magnesium Sulfate in ACLS

Pulseless polymorphic ventricular tachycardia (torsades de pointes) associated with long QT interval IV or IO 1-2 grams Over 1-2 minutes
Polymorphic ventricular tachycardia with a pulse (torsades de pointes) associated with long QT interval IV or IO 1-2 grams Over 5-60 minutes, then 0.5-1 grams/hour titrated to control the arrhythmia
Acute coronary syndrome with hypomagnesemia IV or IO 2 grams Over 5-60 minutes, followed by 0.5-1 grams/hour titrated to keep serum magnesium over >2 mg/dl

Magnesium Sulfate Overdose and Toxicity

It is extremely unlikely that ACLS practitioners will ever encounter a patient with intentional or accidental magnesium overdose. Magnesium toxicity is associated with renal impairment or when large doses of magnesium are improperly administered for treatment of an emergent medical condition. Therefore, it is crucial that ACLS practitioners provide close cardiorespiratory monitoring on patients receiving magnesium.

There is no specific antidote for magnesium sulfate toxicity. If any side effects occur such as bradycardia or hypotension, the infusion should be stopped immediately. Hypotension should be managed with crystalloid fluids and vasopressors medications (such as norepinephrine) as needed. In combination with beta blockers or calcium channel blockers, administration of magnesium can lead to severe bradycardia or heart block resulting in hemodynamic instability.

As magnesium sulfate inhibits release of calcium inside muscle cells, hypotension may be treated with intravenous calcium chloride or calcium gluconate. If hyperkalemia is suspected to be co-occurring with hypermagnesemia, it should be treated with standard medications such as calcium gluconate or calcium chloride, insulin and glucose, albuterol, and sodium bicarbonate.

Issues to Keep in Mind Before Using Magnesium Sulfate

There are no absolute contraindications to the administration of magnesium sulfate in Polymorphic VT associated with a long QT interval. When administering this drug, patients should have continuous cardiac monitoring and frequent blood pressure monitoring. That said, patients with renal failure have a high incidence of adverse events from magnesium as they have difficulty excreting the magnesium.

What Are the Side Effects of Magnesium Sulfate?

Possible Drug Interactions

As magnesium sulfate can cause bradycardia by slowing conduction through the atrioventricular node, it can accentuate the effects of beta blockers and calcium channel blockers resulting in profound bradycardia. Magnesium can also interact with central nervous system depressants to increase sedation.

Frequently Asked Questions (FAQs)

Q: Why is magnesium given for torsades de pointes?
A:  In some cases, Polymorphic VT (torsades de pointes) may be caused by a prolonged QT interval. Magnesium sulfate slows cardiac conduction through the atrioventricular node and decreases the QT interval, thereby increasing the refractory period and decreasing cardiac excitability.
Q: What is the protocol for magnesium sulfate?
A: Magnesium sulfate should be given for Polymorphic VT (torsades de pointes) without a pulse as a 1-2g IV or IO over 1-2 minutes. For Polymorphic VT (torsades de pointes) with a pulse, clinicians should administer 2 grams infused over 5-60 minutes and 0.5-1 gram/hour IV titrated to control ventricular arrhythmia.
Q: How fast can I give IV magnesium?
A: For cardiac arrest, give a slow IV bolus over 1-2 minutes. For polymorphic ventricular tachycardia (torsades de pointes), administer the drug over 5-60 minutes.

Final Thoughts

Magnesium sulfate is a crucial medication to treat polymorphic ventricular tachycardia (torsades) associated with a long QT interval, with or without a pulse. It is an extremely safe medication and should be administered liberally if there is any concern for this specific manifestation of Polymorphic VT.

Polymorphic VT is possible in several different clinical scenarios, and it happens more than some might think. To remain ready to administer the proper treatment at the proper time, ACLS clinicians need to be trained and informed about the drugs, clinical scenarios, and ECG rhythms associated with ACLS. Magnesium sulfate is one such drug that is crucial in treating conditions like this.

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