Magnesium and arrhythmias after coronary artery bypass surgery

Arrhythmias are very common after cardiac surgery and are multifactorial. Magnesium is receiving increased consideration in the management of supraventricular and ventricular arrhythmias. This study was designed to evaluate the role of magnesium in preventing arrhythmias in hypokalemic (K < 3.5 mEq/L) and normokalemic (K > 3.5 mEq/L) patients with normal renal and ventricular function after coronary artery bypass grafting (CABG). One hundred forty patients ranging from 32 to 71 years of age who were scheduled for CABG were studied. They were divided into four groups: group I (control) received no magnesium; group II received 10 mg/kg of magnesium sulfate intravenously before cardiopulmonary bypass (CPB); group III received 10 mg/kg of magnesium soon after CPB; group IV received 10 mg/kg of magnesium before and after CPB. Serum potassium and catecholamine levels, as well as serum and urine magnesium levels, were measured and the incidence and type of arrhythmias were determined. There was a statistically significant difference in the occurrence of arrhythmias between the groups studied. The incidence of arrhythmias was highest in groups I and II and lowest in group IV (12 patients in group I, 14 in group II, 5 in group III; and 1 in group IV). Magnesium levels were higher in group IV than any other group studied after completion of surgery. There was no difference in serum and urine magnesium levels between the hypokalemic and normokalemic patients within each group. Serum magnesium returned to normal in all patients after 48 hours. Therefore, it appears that administration of magnesium during and after cardiac surgery reduces the incidence of arrhythmias in hypokalemic and normokalemic patients.