Magnesium for atrial fibrillation after coronary artery bypass graft surgery: its role in aetiology and prevention.

OBJECTIVE To summarise the potential consequences of atrial fibrillation (AF) after coronary artery bypass graft surgery (CABG) and the relationship of the arrhythmia with serum magnesium concentration ([Mg]) and to review the trials of magnesium supplementation as prophylaxis against post-CABG AF. DATA SOURCES Abstracts, articles and published reviews on AF after CABG and magnesium prophylaxis. SUMMARY OF REVIEW AF after CABG occurs in 20-40% of patients. It may cause haemodynamic compromise, stroke, prolongation of hospital stay and an increased use of resources. Effective prophylaxis offers the enticing prospect of reductions in morbidity, hospital stay and resource utilisation. There is circumstantial evidence suggesting that hypomagnesaemia may predispose to cardiac arrhythmias. Serum [Mg] falls after CABG due to haemodilution and beta-adrenergic mediated mechanisms. Several studies have reported an association between hypomagnesaemia and post-CABG AF, but a causal relationship has not been established. Trials have demonstrated that magnesium (Mg) replacement can attenuate the perioperative fall in serum [Mg], but have failed to show efficacy of Mg therapy in AF prevention after CABG. The perioperative changes in serum [Mg] do not seem to reflect changes in intracellular magnesium, including within the atria. CONCLUSIONS AF after CABG is common and a drain on resources through its association with increased morbidity and hospital stay. Previous studies investigating the relationship between serum [Mg] and AF after CABG have produced inconsistent results. The current evidence from randomised, placebo-controlled trials does not support the use of Mg therapy to prevent AF after CABG and strengthens the likelihood of any association between post-CABG AF and hypomagnesaemia being a passive one. That Mg appears ineffective as prophylaxis for postoperative AF may partly be due to limitations in trial methodology, but most probably reflects the poor correlation between serum total [Mg] and intracellular magnesium, specifically the intra-atrial magnesium content.