Low serum magnesium level predicts major adverse cardiac events after coronary artery bypass graft surgery

Background: Despite improved myocardial protection strategies and enhanced surgical techniques, mortality after coronary artery bypass graft surgery (CABG) remains essentially unchanged. This may be because of the increasing age of patients who undergo primary CABG. Magnesium is an important regulator of vascular tone, reperfusion injury, and thrombosis. Therefore, we decided to investigate the relationship between serum magnesium levels and major adverse cardiac events (MACE) after CABG. Methods: A total of 957 patients undergoing primary CABG were prospectively recruited into the Duke Cardiovascular database and had daily serum magnesium levels measured. Low magnesium was defined as < 1.8 mmol/L^-1 at any point during the first 8 days after surgery. Adverse events were defined as Q-wave infarction or death measured 1 year after surgery. A Kaplan-Meier survival analysis was performed, followed by a Cox proportional hazards model, to account for other known predictors of adverse events. Results: In the low magnesium group, 12.3% of patients had adverse events, compared with 9.2% of patients in the normal magnesium group. A serum magnesium level < 1.8 mmol/L^-1 decreased the event-free survival rate (2-fold increased risk of death or myocardial infarction at 1 year; hazard ratio 2.0, 95% CI 1.19-3.37). Conclusions: We demonstrated a robust relationship between low serum magnesium levels after CABG and a 2-fold increased incidence of Q-wave infarction and all-cause mortality rate as long as 1 year after surgery. This relationship is independent of known preoperative and intraoperative predictors of adverse outcomes. This study provides a rationale for a randomized controlled trial of magnesium therapy during CABG.