Magnesium status and magnesium therapy in cardiac surgery: A systematic review and meta-analysis focusing on arrhythmia prevention

Highlights

• Postoperative magnesium may be effective in the prophylaxis of AF after cardiac surgery

• The optimal timing of magnesium therapy appears to be postoperative with duration > 24 hours, at doses of up to 60mmol and administered as boluses

• Post-operative magnesium administration appears free of significant adverse events

• we found insufficient evidence to support magnesium administration after cardiothoracic surgery for the prevention of other arrhythmias

• These observations suggest that need for appropriately powered, systematic studies of magnesium administration to patients after cardiothoracic surgery

Abstract

Purpose

To investigate magnesium as prophylaxis or treatment of postoperative arrhythmias in cardiac surgery (CS) patients. To assess impact on biochemical and patient-centered outcomes.

Materials and methods

We searched MEDLINE, CENTRAL and EMBASE electronic databases from 1975 to October 2015 using terms related to magnesium and CS. English-Language RCTs were included involving adults undergoing CS with parenterally administered magnesium to treat or prevent arrhythmias, compared to control or standard antiarrythmics. We extracted incidence of postoperative arrhythmias, termination following magnesium administration and secondary outcomes (including mortality, length of stay, hemodynamic parameters, biochemistry).

Results

Thirty-five studies were included, with significant methodological heterogeneity. Atrial fibrillation (AF) was most commonly reported, followed by ventricular, supraventricular and overall arrhythmia frequency. Magnesium appeared to reduce AF (RR 0.69, 95% confidence interval (95%CI) 0.56–0.86, p = 0.002), particularly postoperatively (RR 0.51, 95%CI 0.34–0.77, p = 0.003) for longer than 24 h. Maximal benefit was seen with bolus doses up to 60 mmol. Magnesium appeared to reduce ventricular arrhythmias (RR = 0.46, 95%CI 0.24–0.89, p = 0.004), with a trend to reduced overall arrhythmias (RR = 0.80, 95%CI 0.57–1.12, p = 0.191). We found no mortality effect or significant increase in adverse events.

Conclusions

Magnesium administration post-CS appears to reduce AF without significant adverse events. There is limited evidence to support magnesium administration for prevention of other arrhythmias.

Introduction

Arrhythmias affect up to 50% of patients undergoing cardiothoracic surgery [1], [2], [3] and are associated with increased length of stay, health care costs, morbidity and mortality [2], [4]. Magnesium is commonly used, both to prevent and to treat, such arrhythmias [5]. However, it is unclear how effective magnesium is for either purpose, with recent meta-analyses presenting conflicting results [6], [7]. It is also uncertain whether the amount, mode, duration, and timing of delivery are important in determining the efficacy of such therapy. Moreover, the effects of magnesium levels and the incidence of adverse effects following treatment are poorly understood. Finally, the effects of magnesium administration on patient-centered outcomes such as mortality are uncertain.

Accordingly, we performed a systematic review and meta-analysis of the relevant literature. We aimed to evaluate the efficacy of parenteral magnesium administration as prophylaxis or treatment of post-operative arrhythmias in patients undergoing cardiac surgery, with a focus on atrial fibrillation. Moreover, we aimed to assess the impact of magnesium administration on magnesium levels; the differential effect of bolus versus continuous administration; dose given, and duration of therapy. Finally, we aimed to investigate the association of administration of magnesium with mortality, and other patient-centered outcomes.