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(Circulation. 2009;120:S163-S169.)
© 2009 American Heart Association, Inc.

Arrhythmia Surgery

Prophylactic Intravenous Magnesium Sulphate in Addition to Oral β-Blockade Does Not Prevent Atrial Arrhythmias After Coronary Artery or Valvular Heart Surgery

A Randomized, Controlled Trial

Richard C. Cook, MD, MSc; Karin H. Humphries, DSc; Kenneth Gin, MD; Michael T. Janusz, MD; Richard S. Slavik, PharmD; Victoria Bernstein, MD; Mats Tholin, MD; May K. Lee, MSc

From Division of Cardiovascular Surgery (R.C.C., M.T.J.), Division of Cardiology (K.H.H., K.G., V.B.), Department of Anaesthesiology, Pharmacology & Therapeutics (M.T.), University of British Columbia, Vancouver, British Columbia, Canada; Provincial Health Services Authority of British Columbia (K.H.H., M.K.L.), Vancouver, British Columbia, Canada; Pharmacy Department (R.S.S.), Interior Health Authority of British Columbia, Vancouver, British Columbia, Canada.

Correspondence to Richard C. Cook, MD, St. Paul’s Hospital, 1081 Burrard Street, Vancouver, British Columbia, Canada V6Z 1Y6. E-mail richard.cook{at}vch.ca

Background— Atrial arrhythmias (AA) are an important cause of morbidity after cardiac surgery. Efforts at prevention of postoperative AA have been suboptimal. Perioperative beta-blocker administration is the standard of care at many centers. Although prophylactic administration of magnesium sulfate (MgSO₄) has been recommended, review of all previously published trials of MgSO₄ reveals conflicting results. This study was designed to address methodological shortcomings from previous studies and is the largest randomized, placebo-controlled trial of intravenous (IV) MgSO₄ for the prevention of AA after coronary artery bypass grafting or cardiac valvular surgery.

Methods and Results— A total of 927 nonemergent cardiac surgery patients were stratified into 2 groups: isolated coronary artery bypass grafting (n=694), or valve surgery with or without coronary artery bypass grafting (n=233), and randomized to receive either 5g IV MgSO₄ or placebo on removal of the cross-clamp, followed by daily 4-hour infusions, from postoperative day 1 until postoperative day 4. All patients were treated according to an established oral β-blocker protocol. Postoperative serum Mg levels were checked and standard of care was to administer IV MgSO₄ for low serum levels. The primary end point was AA lasting 30 minutes or requiring treatment for hemodynamic compromise. There were no differences in the incidence of AA between patients who received IV MgSO₄ or placebo (26.4% versus 24.3%, respectively). The results were similar when broken down according to stratified groups.

Conclusions— In patients treated with a protocol for postoperative oral β-blocker after nonemergent cardiac surgery, the addition of prophylactic IV MgSO₄ did not reduce the incidence of AA.

Key Words: atrial fibrillation • coronary artery bypass surgery • magnesium • prevention • tachyarrhythmias