What is the utility of magnesium in AFib with RVR?
Bottom line up top
Intravenous magnesium is a reasonable adjunct to standard rate control therapy in hemodynamically stable patients with atrial fibrillation with rapid ventricular response. Although it should not replace first line agents such as calcium channel blockers or beta blockers, current evidence suggests it may improve rate control with minimal added risk.
Clinical scenario
A 68 year old man with hypertension and paroxysmal atrial fibrillation presents to the ED with palpitations and mild dyspnea. His heart rate is 145, blood pressure is 128/76, oxygen saturation is normal, and he is mentating appropriately. EKG shows atrial fibrillation with rapid ventricular response. You plan to give IV diltiazem, but a colleague suggests adding IV magnesium. You wonder, does magnesium actually improve rate control or is it unnecessary?
What your gut says
No reason to complicate the situation: skip the magnesium and just order the diltiazem.
What the evidence says
The 2023 ACC/AHA/ACCP/HRS atrial fibrillation guideline place beta blockers and nondihydropyridine calcium channel blockers as first line agents for acute rate control in hemodynamically stable AFib with RVR (so called “lone AFib”). However, the guideline specifically states that adding IV magnesium to standard rate control measures is reasonable to achieve and maintain rate control, with a Class 2a recommendation and Level A evidence (ACC/AHA/ACCP/HRS Joglar 2023). This is important because magnesium is not framed as primary therapy, but as an adjunct when standard agents are being used.
2022 systematic review and meta-analysis
Recent emergency medicine literature generally supports that recommendation with some caveats. A 2022 systematic review and meta analysis (SRMA) focused on ED patients included five randomized trials with 815 patients. It found that magnesium was associated with a significant reduction in heart rate, without a significant increase in hypotension or bradycardia when compared to placebo. However, it did not significantly increase conversion to sinus rhythm (Hoffer 2022).
2021 systematic review and meta-analysis
A 2021 SRMA included six randomized trials with 745 patients and found that IV magnesium added to standard care improved rate control with an odds ratio of 2.49 and an absolute risk difference of 23 percent (Ramesh 2021, Tchouapi 2023). This resulted in an NNT of 4; rate control was improved in 1 patient out of every 4 patients receiving magnesium in addition to standard treatment. This SRMA also demonstrated a modest increase in conversion to sinus rhythm, with an NNT of 14. The main adverse effect was flushing, while bradycardia and hypotension were not significantly increased.
Limitations and precautions
Both reviews agree that magnesium appears safe and may improve rate control. The major limitation is that many of the included trials were older, had variable magnesium doses, used different outcome definitions, and often paired magnesium with digoxin rather than modern ED first line agents such as diltiazem or metoprolol (Tchouapi 2023). Intravenous magnesium should be avoided in patients with hypotension, renal impairment, and those with Myasthenia Gravis, as it can significantly worsen neuromuscular weakness.
Clinical bottom line
For hemodynamically stable Afib with RVR, IV magnesium should not be used alone and should not delay standard rate control with diltiazem, verapamil, or a beta blocker. However, adding IV magnesium is reasonable, guideline supported, and likely beneficial for rate control with minimal downside.
References
Hoffer, M., Tran, Q. K., Hodgson, R., Atwater, M., & Pourmand, A. (2022). Utility of magnesium sulfate in the treatment of rapid atrial fibrillation in the emergency department: A systematic review and meta analysis. European Journal of Emergency Medicine, 29(4), 253 to 261. PMID: 35503562.
Joglar, J. A., Chung, M. K., Armbruster, A. L., et al. (2023). 2023 ACC/AHA/ACCP/HRS guideline for the diagnosis and management of atrial fibrillation. Pages 61-62. PMID: 38033089.
Ramesh, T., Lee, P. Y. K., Mitta, M., & Allencherril, J. (2021). Intravenous magnesium in the management of rapid atrial fibrillation: A systematic review and meta analysis. Journal of Cardiology, 78(5), 375 to 381. PMID: 34162502.
Tchouapi, P., Anderson, K. E., & Hein, P. N. (2023). Intravenous magnesium as an adjunct to standard of care for treatment of atrial fibrillation with rapid ventricular response. Academic Emergency Medicine. PMID: 37021611
