Magnesium Substitution in Elective Coronary Artery Surgery

Abstract

Magnesium may be beneficial in the control of ventricular ectopy and supraventricular tachyarrhythmias after coronary artery bypass graft (CABG) surgery, but it is not known whether a high-dose magnesium regimen is superior to a regimen keeping the patient normomagnesemic. A prospective randomized and double-blind clinical comparison was performed in 81 elective CABG patients in order to assess the effects of two different magnesium infusion regimens on electrolyte balance and postoperative arrhythmias. Forty-one patients (high-dose group, H) received 4.2 ± 0.7 g (mean ± SD), of magnesium sulfate before cardiopulmonary bypass, followed by an infusion of 11.9 ± 2.8 g of magnesium chloride until the first postoperative (PO) morning, and a further 5.5 ± 1.0 g until the second PO morning. Forty patients (low-dose group, L) received magnesium sulfate only after bypass to a total of 2.9 ± 0.5 g at the first, and 1.4 ± 0.1 g at the second PO morning. A blood cardioplegia technique was used in both groups, including bolus doses of magnesium chloride to a total of 2.4 ± 0.6 g and 2.3 ± 0.6 g to H and L patients, respectively. Continuous Holter tape-recording was used for 12 to 15 hours preoperatively, and for 48 hours postoperatively. Serum magnesium peaked in H patients on the first PO morning at 1.60 ± 0.25 mmol/L, whereafter it declined to the normal level on the third PO morning. Patients in the L group were normomagnesemic, except after the start of bypass. Recovery to spontaneous rhythm after declamping of the aorta was better in the H patients; only one patient had ventricular fibrillation (VF), whereas in the L group, four patients had VF and five patients needed a temporary pacemaker ( p = 0.016). Atrial fibrillation (AF) was detected in 3 H (7.3%), and 10 L patients (25%) within the first 48 PO hours ( p = 0.037). Ten H (24.3%) and 18 L patients (45.0%) had a total of 19 and 41 episodes of AF during the first PO week ( p p = 0.013).