Abstract
Ventricular arrhythmias occur frequently shortly after coronary artery bypass grafting
(CABG), and their occurrence coincides with the postoperative decline in serum magnesium
(Mg) levels. To examine if this decline causes ventricular arrhythmias and if their
appearance could be reduced by intravenous Mg administration, 140 consecutive CABG
patients were randomized to receive 70 mmol of Mg sulphate (N=69) or placebo (N=71)
over two days. Serum Mg concentration fell to 0.77 mmol/l in the control group but
rose to 1.09 mmol/l in the Mg group (p < 0.001). On 48 h Holter, the number of ventricular premature complexes (VPC) on
the third postoperative day was reduced in the Mg group (4 ± 5 vs 12 ± 21 VPCs/h;
p < 0.05) and the incidence of complex ventricular arrhythmias (Lown grade 2–5) was
significantly diminished (19% vs 41% of the patients; p < 0.05). In multivariate analysis, high risk ventricular arrhythmias (repetitive
polymorphic ventricular complexes, couplets, R-on-T complexes or operative tachycardia)
were independently predicted by high number of bypassed vessels (p = 0.01), poor NYHA functional class (p = 0.06), preoperative diuretic use (p = 0.07), and low postoperative Mg levels (p = 0.08). In conclusion, correction of the postoperative decline in serum Mg concentration
decreases the occurrence of early VPCs and complex ventricular arrhythmias. Patients
with extensive underlying coronary artery disease and prior diuretic therapy appear
to benefit greatest from Mg treatment.
