Effects of Intravenous Magnesium Sulfate on the QT Interval in Patients Receiving Ibutilide

20 patients with atrial fibrillation (n=12) or atrial flutter (n=8) scheduled to receive ibutilide for immediate chemical cardioversion, mean age 72 +/- 14 years. Key inclusion: baseline QTc interval <440 msec and baseline serum magnesium levels within normal limits.

Intravenous magnesium sulfate (2 g in 50 ml of 0.9% sodium chloride infused over 10 minutes immediately before ibutilide therapy, followed by an additional 2 g over 1 hour starting 10 minutes after the first dose of ibutilide).

Placebo infusions administered immediately before and after ibutilide therapy.

Change in QT and QTc intervals from baseline at 30 minutes after ibutilide therapy.surrogate