Original article: cardiovascular
The efficacy of supplemental magnesium in reducing atrial fibrillation after coronary artery bypass grafting

https://doi.org/10.1016/j.athoracsur.2003.08.027Get rights and content

Abstract

Background

Atrial fibrillation after coronary artery bypass is reported from 17% to 53%. Hypomagnesemia after this surgery is considered a contributing factor.

Methods

Two hundred-two coronary bypass patients were randomized to magnesium (n = 105) or placebo (n = 97). The experimental group received 80-mg magnesium sulfate per kilogram ideal weight in 100 mL dextrose 5% water 30 minutes preoperatively. Postoperatively, patients received 8-mg magnesium sulfate per kilogram ideal weight intravenous per hour more than 48 hours. The control group received dextrose 5% water at these intervals.

Results

After the first bolus serum magnesium was experimental 4.75 mg/dL versus control 1.91 mg/dL, p less than 0.001, and remained different until postoperative day 4 (experimental 2.33 mg/dL vs control 2.26 mg/dL, p = 0.24). Atrial appendage and strap muscle were analyzed after the first bolus and after revascularization. There were no differences between groups in tissue magnesium or calcium. Urinary magnesium was elevated in the experimental (experimental 324.5 mg/24 hours, vs control 45.1 mg/24 hours, p = 0.01). Calcium excretion was higher (experimental 370 mg/24 hours vs control 186 mg/24 hours, p < 0.001) and was associated with lower serum calcium. Serum calcium was higher in the control through the fourth postoperative day. The incidence of atrial fibrillation was experimental 32 of 105 (30.5%) versus control 41 of 97 (42.3%) p = 0.08. Atrial fibrillation was different on the first postoperative day (experimental 3/105, 2.9% vs control 9/97, 9.3%), p = 0.05.

Conclusions

Overall prophylactic magnesium supplementation does not significantly reduce atrial and ventricular arrhythmias. The only significant benefit of magnesium supplementation was on the first postoperative day.

Section snippets

Material and methods

After local institutional review board approval, patients undergoing elective isolated coronary artery bypass grafting (CABG) were approached for consent. The study was conducted over a 5-year period in a midwestern university medical center, which includes a 562-bed and a 606-bed hospital. After consent, 202 patients were randomly assigned to receive either placebo or prophylactic supplemental magnesium. The pharmacy staff assigned patients to study and control groups using a randomization

Results

A total of 202 patients were enrolled in the study. One hundred-five patients were in the Mg group and 97 were assigned as controls. There were no significant differences in preoperative and operative variables except the mean cross-clamp time was about 5 minutes longer in the experimental group (E), 61.11 ± 21.1, versus control group (C) 55 ± 21.89 minutes (p = 0.04). Age, sex, preoperative albumin, preoperative and postoperative renal function, preoperative and postoperative use of

Comment

Magnesium is an important cation in cardiovascular physiology. Supplemental Mg creates a β-adrenergic blocking effect on the myocardial cell by affecting the G proteins; those play a role in the signaling path of the β-adrenergic stimuli in myocytes 14, 15. Mg is also an important cofactor in maintaining the intracellular electrolyte balance and membrane potentials by altering the activity of Na-K-ATP channels and it also acts like a natural Ca antagonist 1, 3, 14, 15.

Low Mg levels are a

Acknowledgements

This work was funded, in part, by Southern Illinois University School of Medicine, Central Research Committee Grant: Efficacy of Magnesium in Reducing Cardiac Dysrhythmias.

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