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Interact CardioVasc Thorac Surg 2005;4:193-196. doi:10.1510/icvts.2005.106419 © 2005 European Association of Cardio-Thoracic Surgery
Does magnesium offer any additional benefit in patients having anti-arrhythmic treatment for atrial fibrillation following cardiac surgery?Department of Cardiothoracic Surgery, Freeman Hospital, Freeman Road, Newcastle-upon-Tyne NE7 7DN, UK Received 17 January 2005; accepted 20 January 2005
*Corresponding author. Tel.:/fax: +44 780 1548122.
A best evidence topic in cardiac surgery was written according to a structured protocol. The question addressed was whether treatment with magnesium in addition to an anti-arrhythmic is beneficial to patients who have gone into atrial fibrillation after cardiac surgery. Altogether 466 papers were identified using the below mentioned search, of which 8 papers presented the best evidence to answer the clinical question. The author, journal, date and country of publication, patient group, relevant outcomes and weaknesses were tabulated. We conclude that while the literature on magnesium prophylaxis and non-cardiac surgical studies on magnesium therapy for atrial fibrillation suggest that magnesium may be of benefit, there are currently no studies in post-cardiac surgery atrial fibrillation to support the use of magnesium therapy for these patients.
Key Words: Evidence-based medicine; Thoracic surgery; Magnesium; Atrial fibrillation
A best evidence topic was constructed according to the structured protocol. This protocol is fully described in the ICVTS [1].
You are seeing a patient on the ward who is a 65-year-old man 2 days after coronary arterial bypass surgery. He has just gone into atrial fibrillation with a fast ventricular response. He is haemodynamically stable. You prescribe him amiodarone. The SHO sent off blood tests 1 h ago that showed that his plasma potassium was 4.9 and his magnesium was 1.1. The nurse asks you if you want him to have magnesium in addition to the anti-arrhythmic you prescribed. You are not sure if additional magnesium will be of any benefit. Rather than prescribing blind treatment you decide to review the literature before making your decision.
In [patients undergoing cardiac surgery, going into atrial fibrillation] is [the addition of magnesium] more effective than standard therapy alone in [cardioverting or controlling ventricular rate].
Medline 1966 to Oct 2004, Embase 1980 to Oct 2004 and CINAHL 1982 to Oct 2004 using the OVID interface. [exp atrial fibrillation/ OR atrial fibrillation.mp OR AF.mp OR exp atrial flutter OR atrial flutter.mp OR exp supraventricular tachycardia/ OR SVT.mp] AND [exp magnesium/ OR magnesium.mp]. In addition, the 2001 American Heart Association (AHA) guidelines for patients in Atrial Fibrillation and the 2004 AHA guidelines for patients undergoing Coronary Artery Surgery were hand searched.
Two hundred and six papers were found in Medline. Two hundred and fifty-two papers in Embase, and 8 papers in CINAHL were also found using the appropriate MeSH terms. Cochrane reviews were searched using the term Magnesium. Seven papers were found which gave the best evidence to answer the question (Table 1).
Despite searching Medline, Embase, CINAHL, Cochrane, and American Heart Association databases and guidelines, we could find no studies that looked into the effect of using magnesium to treat patients going into atrial fibrillation (AF) after cardiac surgery. We thus extended the search to papers that might aid in a decision as to whether magnesium may potentially aid rate control or cardioversion in cardiac surgical patients. Shiga et al. [2] performed a comprehensive meta-analysis in 2004 looking at the benefit of prophylactic magnesium in the prevention of atrial fibrillation post cardiac surgery. Seventeen randomized controlled trials were identified, comprising of 2069 patients. In the pooled magnesium groups the incidence of SVT was 23%, but in the control group it was 31% (P=0.002). In addition the incidence of ventricular tachycardia was also significantly lower, and the mean serum magnesium was significantly higher than those in the control groups. Magnesium reduced the incidence of atrial fibrillation by 29% across the 17 trials performed. Kalus et al. [3] considered the efficacy of magnesium as an adjunct to ibutilide in medical patients in atrial fibrillation. This was a retrospective multicenter cohort study where the authors reviewed the case notes of patients in atrial flutter/fibrillation in whom cardioversion with ibutilide had been attempted. The rate of conversion was 67.2% vs 58.2% for patients in atrial fibrillation and 78.3% vs 64.4% for those in atrial flutter (ibutilide and magnesium vs ibutilide only) resulting in a 34% reduction in the need for elective DC cardioversion. Brodsky et al. [4] looked at 18 medical outpatients with recent onset fast atrial fibrillation. In all patients, digoxin was given and administered every 6 h up to 3 doses or until the study ended. Patients were then randomised to magnesium or placebo groups. Rate control was achieved in all patients receiving magnesium, in a mean time of 4 h, compared to only 50% of the control patients, who achieved rate control in a mean time of 15 h. Hayes et al. [5] looked at a small number of patients that presented to A&E with fast AF. Patients were randomised to receive MgSO4 or placebo, then at 30 min 500 mcg of digoxin was given and the patients were monitored for the next 3.5 h. Three patients in the placebo group and one in the magnesium group were cardioverted back into SR (P=NS). In the remaining patients at 2.5 h ventricular rates were reduced by 18±10% for the placebo group and 26±7% for the MGSO4 group (P=0.08). Frick et al. [6] performed a small study in patients in chronic AF. They gave 2 doses of Magnesium over 1 h, both with double blinded placebo groups, but could find no differenced in terms of heart rate, heart rate variability or RR interval changes, either in the first few hours after magnesium or at 1 week. Chiladakis et al. [7] performed a trial in 46 medical patients presenting with a new episode of paroxysmal AF less than 12 h in duration. Magnesium cardioverted 57% of the patients within 6 h compared to only 22% of those treated with diltiazem. There was, however, no demonstrated difference in heart rate or time to return to sinus rhythm, due to the small size of the sample. Moran et al. [8] performed a trial in a mixed practice intensive care unit. They compared amiodarone and magnesium treatment in 42 patients going into AF. At 24 h 14 of 21 patients receiving magnesium converted compared to only 7 of 21 patients in the amiodarone group. They concluded that addition of magnesium was superior to Amiodarone alone in conversion of AF in their ICU. Gullestad et al. [9] compared magnesium infusion to verapamil infusion in 57 medical patients who had been in atrial fibrillation for less than one week. Magnesium converted 57% of patients compared to 23% within 4 h, but verapamil reduced the rate to under 100 bpm in 48% compared to 28%. There were no side effects with Magnesium but 6 patients were withdrawn from verapamil treatment due to hypotension or exacerbation of heart failure. Thus in summary, in the cardiac surgical literature, prophylactic magnesium has been well established in the prevention of atrial fibrillation with a reduction of up to 30% in the incidence of atrial fibrillation across 17 trials. However, there have been no studies looking at magnesium therapy in cardiac surgical patients going into AF. In the general medical literature we found 7 papers that looked at either addition of magnesium or magnesium alone in the therapy of AF. Four of these 7 papers demonstrated a significant benefit.
While the literature on magnesium prophylaxis and non-cardiac surgical literature on magnesium therapy for atrial fibrillation suggests that magnesium may be of benefit, there are currently no studies in post-cardiac surgery atrial fibrillation to support the use of magnesium therapy.
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Abstract
1. Introduction
