Parenteral magnesium sulfate versus amiodarone in the therapy of atrial tachyarrhythmias: a prospective, randomized study.

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.