What is the role of Magnesium (Mg) in Cardiology?

From the Guidelines

Magnesium plays a crucial role in the management of cardiac arrhythmias, particularly torsades de pointes, and its administration is recommended in patients with recurrent torsades de pointes associated with acquired QT prolongation and bradycardia. For acute management of cardiac arrhythmias, particularly torsades de pointes or ventricular arrhythmias, IV magnesium sulfate at 1-2g (8-16 mEq) administered over 5-20 minutes is recommended, followed by an infusion of 0.5-1g/hour if needed, as suggested by the 2017 AHA/ACC/HRS guideline for management of patients with ventricular arrhythmias and the prevention of sudden cardiac death 1.

Key Recommendations

• Intravenous magnesium sulfate is recommended 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.
• 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.
• For maintenance therapy in patients with hypomagnesemia or those at risk, oral magnesium supplements such as magnesium oxide 400-800mg daily or magnesium citrate 200-400mg daily are typically prescribed.

Rationale

Magnesium is essential for proper cardiac electrical conduction, stabilizes cell membranes, regulates calcium channels, and supports normal cardiac contractility. It also helps maintain normal blood pressure by promoting vasodilation and has anti-inflammatory properties that protect against atherosclerosis. Magnesium deficiency is common in heart failure patients and those taking diuretics, and correction of low magnesium levels can improve outcomes in various cardiac conditions including arrhythmias, coronary artery disease, and heart failure. Monitoring serum magnesium levels is important, with normal ranges between 1.7-2.2 mg/dL, though intracellular levels may be low even with normal serum levels.

Clinical Considerations

While the evidence from the 2010 American Heart Association guidelines for cardiopulmonary resuscitation and emergency cardiovascular care suggests that routine administration of magnesium sulfate in cardiac arrest is not recommended unless torsades de pointes is present 1, the more recent and higher-quality evidence from the 2017 AHA/ACC/HRS guideline takes precedence in guiding clinical practice 1. Therefore, the administration of intravenous magnesium sulfate is a crucial component of the management of patients with torsades de pointes and acquired QT prolongation.

From the FDA Drug Label

Magnesium is an important cofactor for enzymatic reactions and plays an important role in neurochemical transmission and muscular excitability. Magnesium prevents or controls convulsions by blocking neuromuscular transmission and decreasing the amount of acetylcholine liberated at the end-plate by the motor nerve impulse. Magnesium acts peripherally to produce vasodilation With low doses only flushing and sweating occur, but larger doses cause lowering of blood pressure. In paroxysmal atrial tachycardia, magnesium should be used only if simpler measures have failed and there is no evidence of myocardial damage.

Magnesium in Cardiology:

• Magnesium plays a crucial role in muscular excitability and neurochemical transmission.
• It is used to prevent or control convulsions by blocking neuromuscular transmission.
• Magnesium has a vasodilatory effect, which can lead to lowering of blood pressure.
• In paroxysmal atrial tachycardia, magnesium should be used with caution, only if simpler measures have failed and there is no evidence of myocardial damage 2.
• The usual dose for paroxysmal atrial tachycardia is 3 to 4 g administered IV over 30 seconds with extreme caution 2.

From the Research

Importance of Magnesium in Cardiology

• Magnesium plays a crucial role in maintaining a normal heart rhythm and is implicated in various cardiac arrhythmias 3, 4.
• It is essential for the proper functioning of the heart, and its deficiency can lead to disturbances in energy metabolism, ion channel exchanges, and action potential alteration, resulting in ventricular arrhythmia 4.

Antiarrhythmic Effects of Magnesium

• Magnesium has been shown to have antiarrhythmic effects, particularly in the treatment of torsade de pointes, digitalis-induced tachyarrhythmias, and multifocal atrial tachycardias 3, 5, 6.
• Intravenous magnesium sulfate has been found to be effective in controlling ventricular arrhythmias, including torsades de pointes, with a specific antiarrhythmic action independent of magnesium deficiency correction 5.

Clinical Applications of Magnesium

• Magnesium therapy is recommended for various cardiac arrhythmias, including intractable ventricular tachycardia and fibrillation, torsades de pointes, digitalis-toxic ventricular tachyarrhythmia, and multifocal atrial tachycardia 7.
• The administration of magnesium can be done through intravenous infusion, with a recommended dose of 10-15 ml of 20% MgSO4 over 1 min, followed by 500 ml of 2% MgSO4 over 5 h 7.

Benefits and Limitations of Magnesium Therapy

• Magnesium therapy has been found to be effective in reducing the incidence of arrhythmic events, including atrial and ventricular arrhythmias 3, 4.
• However, the use of magnesium therapy is not without limitations, and its effectiveness can be influenced by various factors, including renal function, serum potassium levels, and the presence of underlying heart disease 7.