Magnesium substitution and postoperative arrhythmias in patients undergoing coronary artery bypass grafting.

Sixty coronary artery bypass grafting patients were randomized to receive either magnesium sulphate or placebo for 4 days postoperatively. The magnesium substitution reduced the duration of atrial fibrillation or flutter (p < 0.05), but not the number of patients developing these arrhythmias. The number of ventricular ectopic beats was also reduced among patients receiving magnesium sulphate compared to placebo (p < 0.05). To evaluate whether the anti-arrhythmic effect of magnesium sulphate was explained by a faster resumption of cellular potassium postoperatively, skeletal muscle electrolyte concentrations were measured pre-operatively and on the third day postoperatively. No significant difference was found in skeletal muscle potassium or magnesium contents on the third day postoperatively when comparing the two groups. The serum magnesium level declined postoperatively in the placebo group, whereas an increase was found in patients receiving magnesium sulphate. We suggest magnesium substitution as a routine postoperatively, because this treatment seems to reduce the severity of postoperative arrhythmias.

Postoperative arrhythmias and myocardial electrolytes in patients undergoing coronary artery bypass grafting.

Electrolyte changes in right atrial and skeletal muscle pre- intra- and postoperatively, and their relationship to the development of postoperative atrial fibrillation or flutter were evaluated in 31 patients with coronary artery bypass grafting (CABG). Such postoperative arrhythmias occurred in 14 patients (45%). Before CABG the skeletal muscle potassium concentration was lower in these patients than in the others: median 261.4 (range 148.2-329.5) vs 298.6 (167.1-416.4) mumol/g dry weight, p = 0.017. The right atrial potassium concentration was normal, but sodium levels were higher in the patients with, than in those without postoperative arrhythmias: median 340.3 (263.7-454.9) vs 296.3 (203.9-355.0) mumol/g dry weight, p = 0.008, indicating disturbed transmembrane electrolyte transfer. During CABG the potassium levels fell and sodium increased in both right atrium and skeletal muscle, and on postoperative day 2 the potassium content in skeletal muscle was not yet restored. Magnesium levels showed no changes in right atrium or skeletal muscle, but serum magnesium declined postoperatively. As the observed electrolyte derangements may be important in the development of postoperative arrhythmias, concomitant potassium and magnesium supplement postoperatively may be beneficial in restoring cellular potassium concentration.

Magnesium content of the human heart.

Although changes in the body's magnesium status have been linked to ischemic heart disease, sudden death and arrhythmia, there is as yet no recommended, established procedure for evaluation of magnesium homeostasis. We therefore explored the relationship between the magnesium content of the heart and that of serum, lymphocytes and skeletal muscle in 50 men undergoing cardiac surgery, using biopsies from the right auricula, right atrium and skeletal muscle and simultaneously drawn venous blood for measurement of lymphocyte and serum electrolyte concentration. Median magnesium values (mumol/g wet weight) were 7.42 (3.98-8.89) in skeletal muscle, 5.49 (3.44-7.66) in right auricula and 5.80 (2.60-7.53) in right atrium. The magnesium concentration in skeletal muscle was found to correlate with that in right auricula (r = 0.46, p less than 0.01) and right atrium (r = 0.43, p less than 0.01), whereas values in serum and lymphocytes showed no correlation with the heart's magnesium content. When myocardial biopsy is not available, skeletal muscle magnesium concentration seems to be the best predictor of the human myocardium's magnesium status.