From the Guidelines
Magnesium can slow heart rate in individuals with certain types of tachycardia, particularly in cases of torsades de pointes and some supraventricular tachycardias. For acute treatment, magnesium sulfate is typically administered intravenously at a dose of 1-2 grams diluted in 50-100 mL of fluid over 5-20 minutes, with careful monitoring, as recommended by the 2017 AHA/ACC/HRS guideline for management of patients with ventricular arrhythmias and the prevention of sudden cardiac death 1.
Key Points
- Magnesium works by stabilizing cardiac cell membranes, regulating calcium channels, and modulating the sodium-potassium pump, which collectively help normalize electrical conduction in the heart.
- It's particularly effective when tachycardia is associated with magnesium deficiency or certain electrolyte imbalances.
- However, magnesium is not effective for all types of tachycardia and should be used under medical supervision as excessive magnesium can cause hypotension, respiratory depression, and cardiac conduction abnormalities.
- Patients with kidney disease should use magnesium with caution as they may have impaired ability to excrete excess magnesium, as noted in the 2010 American Heart Association guidelines for cardiopulmonary resuscitation and emergency cardiovascular care 1.
Administration and Monitoring
- For maintenance therapy, oral magnesium supplements (magnesium oxide, citrate, or glycinate) at doses of 200-400 mg daily may be used.
- The dose and administration of magnesium should be individualized based on the patient's condition and response to treatment, with careful monitoring of serum magnesium levels and cardiac function, as recommended by the 2015 ACC/AHA/HRS guideline for the management of adult patients with supraventricular tachycardia 1.
Special Considerations
- Magnesium can be used in combination with other treatments, such as beta blockers or calcium channel blockers, to control heart rate and rhythm in patients with supraventricular tachycardia.
- The use of magnesium in patients with torsades de pointes or other life-threatening arrhythmias should be guided by the recommendations of the 2017 AHA/ACC/HRS guideline for management of patients with ventricular arrhythmias and the prevention of sudden cardiac death 1.
From the FDA Drug Label
Magnesium acts peripherally to produce vasodilation With low doses only flushing and sweating occur, but larger doses cause lowering of blood pressure. Heart block also may occur at this or lower serum levels of magnesium.
The answer to whether magnesium slows heart rate in individuals with tachycardia is not directly stated. However, heart block is mentioned as a possible effect of high serum levels of magnesium, which could be interpreted as a slowing of the heart rate.
- Key points:
- Magnesium can cause heart block at high serum levels.
- Magnesium has a peripheral effect of producing vasodilation, which can lead to lowering of blood pressure.
- The relationship between magnesium and heart rate is not explicitly stated in the context of tachycardia. 2
From the Research
Magnesium's Effect on Heart Rate
- Magnesium has been shown to have a positive effect on cardiac arrhythmias, including those that cause an increased heart rate 3, 4, 5, 6, 7.
- Studies have demonstrated that intravenous magnesium can reduce the frequency of ventricular arrhythmias in patients with heart failure 6.
- Magnesium sulfate has been found to be effective in treating supraventricular tachyarrhythmias, including paroxysmal supraventricular tachycardia, chaotic atrial tachycardia, and atrial fibrillation with rapid heart rate 4.
- The administration of intravenous magnesium chloride has been shown to decrease total ventricular ectopy, couplets, and episodes of ventricular tachycardia in patients with symptomatic heart failure 6.
Mechanism of Action
- Magnesium's electrophysiological actions on the heart include prolonging sinus node recovery time, reducing automaticity, and slowing atrioventricular nodal conduction 3.
- Magnesium can also homogenize transmural ventricular repolarization, which may help to prevent arrhythmias 3.
- The mechanism of magnesium's effect on cardiac arrhythmias is thought to be related to its ability to increase the ventricular threshold for fibrillation and prolong sinus node refractoriness and conduction in the AV node 5.
Clinical Applications
- Magnesium has been used to prevent and treat various types of cardiac arrhythmias, including those caused by digitalis toxicity, neuroleptic overdose, and tricyclic antidepressant overdose 5, 7.
- Intravenous magnesium has been shown to be effective in reducing the ventricular response in acute onset atrial fibrillation and in treating multifocal atrial tachycardia 3, 7.
- Oral magnesium has been used to reduce the incidence of extrasystoles and symptoms in patients with symptomatic extrasystoles 5.