Relationship of serum magnesium level and supplemental magnesium dosage with post coronary artery bypass graft surgery arrhythmias

Atrial and ventricular arrhythmias are among the most common complications after coronary artery bypass graft (CABG) surgery. Previous studies demonstrated that cardiopulmonary bypass itself results in reduced serum magnesium levels. In this study, we evaluated the effect of total blood magnesium level (TMG) on the prevention of perioperative arrhythmias with routine regimens of 2-4 grams supplemental magnesium (SMG).

TMG was measured in patients who were scheduled for CABG on three occasions: just before anesthesia, just after entering the intensive care unit (ICU) after completion of the sugery, and on the first morning after the operation. Patients were evaluated for primary cardiac rhythm and other variables that could have an influence on the magnesium level, including serum creatinine, urine output in the operating room and diuretic therapy. The SMG dosage was also recorded in the operating room and ICU. Patients were then evaluated for the rate and type of arrhythmia for the next three days.

The mean TMG levels in 174 cases were 2.2 (0.5), 2.6 (0.6) and 2.4 (0.6) mg/dl for the three occasions, respectively. The mean SMG was 2.5 (1.2) grams. Of 164 patients, 51 (31%) developed the following post-operative arrhythmias: AF (7.3%), non- AF SVA (15.2%) and ventricular (16.5%). The mean serum creatinine level and urine output were 1.2 mg/dl and 1800 ml, respectively. Although there was a significant difference between the TMG levels on the three different occasions (P<0.001), all values were within normal range. When we stratified the TMG levels of the patients based on administered SMG, the Mentel-Haenszel test revealed no significant difference between the first and third TMG (P=0.6). Although the TMG levels were higher in arrhythmic patients compared to those without arrhythmia (2.25 vs. 2.14 mg/dl), both values were within the normal range and there was no significant difference between the two groups. Serum creatinine levels and urine volume were not related to TMG levels.

This study indicates that routine magnesium administration has no significant effect on SMG levels. Also, serum creatinine and urine output are not determinant factors for SMG administration. There was no correlation between TMG levels and perioperative arrhythmia. We conclude that the routine regimen of magnesium administration has no effect on the incidence of perioperative arrhythmia, though it is necessary for maintaining normal magnesium levels.