Impact of intravenous magnesium on post-cardiothoracic surgery atrial fibrillation and length of hospital stay: a meta-analysis

Henyan NN, Gillespie EL, White CM, Kluger J, Coleman CI. Ann Thorac Surg 80:2402-2406, 2005.

Reviewer: Mark A. Chaney, MD
University of Chicago
Chicago, IL

Abstract: Postoperative atrial fibrillation (POAF) occurs in 25% to 40% of patients undergoing cardiothoracic surgery. Although the majority of POAF is benign, it has been associated with prolonged hospital length of stay. Magnesium prophylaxis against POAF has been evaluated in several clinical trials; however, these trials were small in size and therefore conveyed mixed or inconclusive results. In an attempt to better understand magnesium's role in this setting, the authors conducted a meta-analysis. A systematic literature search was conducted from January 1999 through August 2004 to identify trials of prophylactic magnesium in the setting of cardiothoracic surgery. The primary outcome measure was the incidence of POAF. Trials were further analyzed based on cumulative doses of magnesium and perioperative time of initiation of prophylaxis, as well as length of stay. Seven randomized trials were identified. Upon meta-analysis, magnesium was found to prevent POAF. The incidence of POAF was also significantly reduced in the low dose and in the preoperative groups. Prophylactic magnesium reduced length of stay by a weighted mean difference of 0.29 days. The authors conclude that prophylactic magnesium reduced cardiothoracic surgery patients' risk in POAF and length of stay and administering lower doses and initiating prophylaxis in the preoperative period achieved the greatest reduction in POAF.

Comments: POAF remains a common complication following cardiothoracic surgery, occurring in 25% to 40% of patients. While most episodes of POAF are benign and self-limited, some can increase morbidity/mortality (thromboembolism fatal arrhythmia, etc.). Furthermore, POAF has been associated with increased hospital length of stay and increased total hospital costs. Magnesium (second most abundant intracellular cation) plays a vital role in many physiologic processes. Hypomagnesemia is common in patients undergoing cardiothoracic surgery and is associated with many cardiovascular disease states, including atrial arrhythmias. However, the exact role of magnesium in the pathogenesis of POAF remains to be determined. The several studies conducted using magnesium for POAF prophylaxis in the setting of cardiothoracic surgery have used relatively small sample sizes, various dosing regimens, and have conveyed mixed results. Thus, in order to hopefully shed light on this topic, the authors conducted a meta-analysis of recent relevant clinical trials. Seven trials (n = 1,234 patients) satisfying inclusion criteria were identified. Their analysis illustrated that prophylactic intravenous magnesium significantly decreased the incidence of POAF and length of hospital stay. Interestingly, this represents the first such meta-analysis to evaluate the impact of magnesium dose and the time of initiation of therapy to efficacy. Regimens utilizing lower doses of magnesium showed a significant reduction in POAF whereas those that used moderate to high doses did not. "Low" cumulative dose of magnesium was considered less than 10 grams whereas "moderate to high" cumulative dose was considered greater than or equal to 10 grams. Furthermore, initiating magnesium during the preoperative period was associated with a significant reduction in POAF whereas initiation of prophylaxis during the intraoperative/postoperative periods was not. The authors postulate that it is possible that lower doses of intravenous magnesium administered over a longer period of time may be optimal to correct intracellular deficiencies without precipitating intracellular or serum hypermagnesemia.As with any meta-analysis, substantial and definitive conclusions will not be generated for a wide variety of reasons (publication bias, etc.) However, such analysis oftentimes yields ideas for fruitful clinical research. The results of this meta-analysis indicates that the use of lower dosages of magnesium (initiated during the preoperative period) should be evaluated for reducing the incidence of POAF and length of hospital stay in patients undergoing cardiothoracic surgery.

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  • Improving the Quality of Coronary Bypass Surgery With Intraoperative Angiography: Validation of a New Technique
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  • Impact of intravenous magnesium on post-cardiothoracic surgery atrial fibrillation and length of hospital stay: a meta-analysis
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