Magnesium and Heart Surgery in Children

By Hans R. Larsen MSc ChE

CHARLESTON, SOUTH CAROLINA. Administration of magnesium has been shown to reduce the incidence of heart surgery related arrhythmias in adults. It has also been observed that the magnesium level in the right atrial tissue is lower in adult patients with postoperative cardiac arrhythmias compared to patients without arrhythmias after heart surgery. Researchers at the Department of Pediatric Cardiology at the Medical University of South Carolina now report that children undergoing surgery for congenital heart defects develop a severe magnesium deficiency immediately after surgery. This deficiency is associated with a greater incidence of a serious arrhythmia (junctional ectopic tachycardia) and can be prevented by an infusion of magnesium sulfate immediately after completion of the surgery.

The study involved 28 pediatric patients (average age of five years) who were scheduled to undergo heart surgery with cardiopulmonary bypass (CPB). The patients were randomly assigned to receive an infusion of magnesium (30 mg/kg body weight of a five per cent saline solution administered over a period of 10 minutes) or an infusion of saline solution immediately after cessation of CPB. Blood levels of magnesium were measured in all patients before surgery, before CPB, after CPB, upon arrival in the intensive care unit (ICU), and then every four hours for 24 hours. Each patient was also monitored for arrhythmias for 24 hours with a Holter monitor.

Comparison of the results for the two treatment groups revealed that the magnesium level was significantly below normal in patients who had received saline solution (placebo) when they arrived in the ICU and for the following 20 hours. Patients who had received the magnesium infusion, on the other hand, had magnesium levels that were well within the normal range (1.6 to 2.3 mg/dL) when tested in the ICU and for the following 20 hours. There were no incidences of junctional ectopic tachycardia in the magnesium group, but four (27 per cent) of the patients in the placebo group experienced this serious arrhythmia. It stopped after a magnesium infusion. The researchers “recommend routine measurement of magnesium levels after CPB in children undergoing heart surgery, with timely magnesium supplementation in the postoperative period.” [49 references]

Dorman, B. Hugh, et al. Magnesium supplementation in the prevention of arrhythmias in pediatric patients undergoing surgery for congenital heart defects. American Heart Journal, Vol. 139, No. 3, 2000, pp. 522- 28