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 plus minus 15 yrs and mean Acute Physiology and Chronic Health Evaluation II score of 22 plus minus 6, with atrial tachyarrhythmias (ventricular response rate of more than equals 120 beats/min) sustained for more than equals 1 hr.
Interventions
After correction of the plasma potassium concentration to more than equals 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 plus minus 16 (SD) beats/min and 127 plus minus 30 mm Hg in the magnesium sulfate group vs. 153 plus minus 23 beats/min and 123 plus minus 23 mm Hg in the amiodarone group, respectively (p equals .8 and.65). Plasma magnesium (time 0) was 0.84 plus minus 0.20 vs. 1.02 plus minus 0.22 mmol/L in the magnesium and amiodarone group, respectively (p equals .1). Eight patients had chronic dysrhythmias (magnesium 3, amiodarone 5). Excluding the two patient deaths (amiodarone group, time 0 plus 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 plus minus 0.36, 1.82 plus minus 0.41, 2.16 plus minus 0.45, and 1.92 plus minus 0.49 mmol/L at time 0 plus 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 plus 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 plus to 0.5 hrs (mean decrease 19 beats/min, p equals .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.
(Crit Care Med 1995; 23:1816-1824)
