LOWMAGHI – Magnesium for Afib Rate Control

Written by Thomas Davis

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Among patients with atrial fibrillation with rapid ventricular response (RVR), low-dose magnesium (4.5g over 30 minutes) was an effective adjunct to standard therapy* compared to placebo and caused far fewer side effects than high-dose magnesium. 

Why does this matter?
Magnesium seems to be indicated for almost everything: pre-eclampsia, hypokalemia, torsades, migraine, and asthma exacerbations. In atrial fibrillation, magnesium has been considered a potential therapy given it decreases automaticity and increases the refractory period of the AV node.  Prior studies have shown benefit of magnesium in addition to standard therapy, but the dose of magnesium administered varies considerably among studies.

MAGic Medicine for the Heart
This is a double blind RCT performed in three tertiary centers in Tunisia that enrolled 450 consecutive patients with rapid atrial fibrillation (HR > 120 beats/min). In addition to standard rate control therapy, patients received either low-dose magnesium (4.5g in 100cc NS), high-dose magnesium (9g in 100cc NS), or placebo (100cc NS) administered over 30 minutes. The primary endpoint was HR < 90 or drop in HR by 20% at 4 hours. Low-dose magnesium had a higher percentage of patients that achieved rate control compared to placebo (64% vs 43%, respectively, p < 0.05). There was no statistical difference in primary outcome between low dose (64%) and high dose (60%) magnesium although both statistically outperformed placebo. High dose placebo had significantly more adverse events, namely flushing, compared to both placebo and low dose magnesium.

*The big caveat to this study is that digoxin was the most used rate control agent (47.5%). A secondary analysis looking exclusively at magnesium as an adjunct to calcium channel blockers and beta blockers found outcomes consistent with the overall results although the study author states the secondary analysis was not statistically significant.

Source
LOw dose MAGnesium sulfate versus HIgh dose in the early management of rapid atrial fibrillation: randomised controlled double blind study.  Acad Emerg Med. 2018 Jul 19. doi: 10.1111/acem.13522. [Epub ahead of print]
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Another Spoonful
ALiEM posted a review of the literature a couple years back.

Reviewed by Clay Smith