Effects of intravenous magnesium sulfate on the QT interval in patients receiving ibutilide.
OBJECTIVE
To determine the effect of intravenous magnesium sulfate on the QT and QTc intervals in patients receiving ibutilide for immediate chemical cardioversion of atrial flutter or fibrillation.


METHODS
Prospective, randomized, double-blind, placebo-controlled trial.


METHODS
Hospital cardiology unit.


METHODS
Twenty patients (mean age 72 +/- 14 yrs) with atrial fibrillation (12 patients) or atrial flutter (8 patients) who were scheduled to receive ibutilide.


METHODS
After determining that the patients' baseline QTc intervals were less than 440 msec and baseline serum magnesium levels were within normal limits (mean 2.1 +/- 0.29 mg/dl), the patients were randomly assigned to receive either a 10-minute infusion of magnesium sulfate 2 g in 50 ml of 0.9% sodium chloride or placebo immediately before ibutilide therapy. An additional 2 g of intravenous magnesium sulfate or placebo was given over 1 hour, 10 minutes after the first dose of ibutilide.


RESULTS
QT interval duration was measured manually in all 12 leads by using a 0.5-mm-scale precision ruler and magnifying lens. The QT interval increased 29% from baseline at 30 minutes after ibutilide therapy in the placebo group (p=0.007), but no significant change from baseline occurred in the magnesium sulfate group. The 30-minute QTc interval in the placebo group was 18% higher than the baseline value (p=0.01) but did not change significantly in the magnesium sulfate group. QTc changes from baseline were greater in the placebo group than in the magnesium sulfate group at 30 minutes (75 vs 19 msec, respectively, p=0.04). Magnesium sulfate reduced the risk of an ibutilide-induced QTc interval increase of greater than 30 msec or greater than 60 msec and reduced the risk of a QTc interval value of more than 500 msec by 65%, 60%, and 68%, respectively (p=0.07, p=0.175, and p=0.160).


CONCLUSIONS
Prophylactic administration of intravenous magnesium sulfate prevents increases in the QT and QTc interval 30 minutes after the last infusion of ibutilide.
Caron
Michael F
MF
Hartford Hospital, Connecticut 06102-5037, USA.
Kluger
Jeffrey
J
Tsikouris
James P
JP
Ritvo
Arnold
A
Kalus
James S
JS
White
C Michael
CM
D000368:Aged; D000889:Anti-Arrhythmia Agents / Q000627:therapeutic use*; D001281:Atrial Fibrillation / Q000188:drug therapy*; D004311:Double-Blind Method; D004562:Electrocardiography / Q000187:drug effects*; D005260:Female; D006801:Humans; D007262:Infusions, Intravenous; D008278:Magnesium Sulfate / Q000008:administration & dosage / Q000494:pharmacology*; D008297:Male; D013449:Sulfonamides / Q000627:therapeutic use*
D000889:Anti-Arrhythmia Agents; D013449:Sulfonamides; C067192:ibutilide; D008278:Magnesium Sulfate