Objective: To compare the efficacy of parenteral magnesium sulfate vs. amiodarone in the therapy of atrial tachyarrhythmias in critically ill patients.
Design: Prospective, randomized study.
Setting: Multidisciplinary intensive care unit (ICU) at a university teaching hospital.
Patients: Forty-two patients, 21 medical and 21 surgical, of mean (SD) age 67 +/- 15 yrs and mean Acute Physiology and Chronic Health Evaluation II score of 22 +/- 6, with atrial tachyarrhythmias (ventricular response rate of > or = 120 beats/min) sustained for > or = 1 hr.
Interventions: After correction of the plasma potassium concentration to > or = 4.0 mmol/L, patients were randomly allocated to treatment with either a) magnesium sulfate 0.037 g/kg (37 mg/kg) bolus followed by 0.025 g/kg/hr (25 mg/kg/hr); or b) amiodarone 5 mg/kg bolus and 10 mg/kg/24-hr infusion. Therapeutic plasma magnesium concentration in the magnesium sulfate group was 1.4 to 2.0 mmol/L. Therapeutic end point was conversion to sinus rhythm over 24 hrs.
Measurements and main results: At study entry (time 0), initial mean ventricular response rate and systolic blood pressure were 151 +/- 16 (SD) beats/min and 127 +/- 30 mm Hg in the magnesium sulfate group vs. 153 +/- 23 beats/min and 123 +/- 23 mm Hg in the amiodarone group, respectively (p = .8 and .65). Plasma magnesium (time 0) was 0.84 +/- 0.20 vs. 1.02 +/- 0.22 mmol/L in the magnesium and amiodarone group, respectively (p = .1). Eight patients had chronic dysrhythmias (magnesium 3, amiodarone 5). Excluding the two patient deaths (amiodarone group, time 0 + 12 to 24 hrs), no significant change in systolic blood pressure subsequently occurred in either group. In the magnesium group, mean plasma magnesium concentrations were 1.48 +/- 0.36, 1.82 +/- 0.41, 2.16 +/- 0.45, and 1.92 +/- 0.49 mmol/L at time 0 + 1, 4, 12 and 24 hrs, respectively. By logistic regression, the probability of conversion to sinus rhythm was significantly better for magnesium than for amiodarone at time 0 + 4 (0.6 vs. 0.44), 12 (0.72 vs. 0.5), and 24 (0.78 vs. 0.5) hrs. In patients not converting to sinus rhythm, a significant decrease in ventricular response rate occurred at time 0 + to 0.5 hrs (mean decrease 19 beats/min, p = .0001), but there was no specific treatment effect between the magnesium and the amiodarone groups; thereafter, there was no significant reduction in ventricular response rate over time in either group.
Conclusions: Intravenous magnesium sulfate is superior to amiodarone in the conversion of acute atrial tachyarrhythmias, while initial slowing of ventricular response rate in nonconverters appears equally efficacious with both agents.