Magnesium Administration as a Treatment for Perioperative Atrial Fibrillation following Cardiac Surgery: Safety and Efficacy

Purpose: Atrial fibrillation (AF) is a common complication after cardiac surgery, impacting recovery and outcomes. Magnesium has electrophysiological and rate-controlling effects in AF. This study evaluated the safety and the temporal association between therapeutic intravenous magnesium administration and rhythm outcomes in patients with postoperative atrial fibrillation (POAF) after cardiac surgery. Methods: Between January 2009 and December 2016, 714 patients undergoing cardiac surgery were evaluated. After excluding 49 patients with a history of AF, 130 developed new-onset POAF. Of these, 111 patients (85.4%) received intravenous magnesium according to our institutional protocol, whereas 19 patients (14.6%) did not. Magnesium (20 mEq per dose, 1–3 doses) was administered with other antiarrhythmic agents in 40 patients (36.0%) and as monotherapy in 71 patients (64.0%). The principal efficacy analyses were restricted to the magnesium-monotherapy cohort. Serum magnesium levels after administration were monitored in 35 patients. Results: Among the 71 patients treated with magnesium monotherapy, the heart rate significantly decreased from 114 ± 32.3 bpm to 100 ± 39.7 bpm (P <0.01), with no significant change in blood pressure. Sinus rhythm conversion occurred in 34 patients (47.9%) within 3 hours and in 60 patients (84.5%) within 24 hours. In multivariable logistic regression analysis, a higher preoperative serum magnesium concentration (adjusted OR, 1.31 per 0.1 mg/dL increase; 95% profile-likelihood CI, 1.07–1.65; P = 0.014) and later postoperative onset of POAF (adjusted OR, 1.32 per postoperative day; 95% CI, 1.07–1.68; P = 0.015) were associated with 3-hour conversion. No serious adverse events attributable to magnesium were observed in the monotherapy cohort. However, because no untreated-comparator group was available, spontaneous conversion cannot be distinguished from a treatment effect. Conclusion: Intravenous magnesium monotherapy was associated with heart rate reduction without significant blood pressure deterioration and was followed by early sinus rhythm conversion in a substantial proportion of patients with POAF. These observational findings support the feasibility and apparent safety of this approach, but do not establish a causal antiarrhythmic effect. Prospective controlled studies are required.