Ibutilide is a class III antiarrhythmic agent indicated for
cardioversion of
atrial fibrillation and
atrial flutter to sinus rhythm (SR). The most serious complication of
ibutilide is
torsades de pointes (TdP).
Magnesium has been successfully used for the treatment of TdP, but its use as a prophylactic agent for this
arrhythmia has not yet been established. The present study investigated whether high dose of
magnesium would increase the safety and efficacy of
ibutilide administration. A total of 476 patients with
atrial fibrillation or
atrial flutter who were candidates for conversion to SR were divided into 2 groups. Group A consisted of 229 patients who received
ibutilide to convert
atrial fibrillation or
atrial flutter to SR. Group B consisted of 247 patients who received an
intravenous infusion of 5 g of
magnesium sulfate for 1 hour followed by the administration of
ibutilide. Then, another 5 g of
magnesium were infused for 2 additional hours. Of the patients in groups A and B, 154 (67.3%) and 189 (76.5%), respectively, were converted to SR (p = 0.033). Ventricular arrhythmias (sustained,
nonsustained ventricular tachycardia, and TdP) occurred significantly more often in group A than in group B (7.4% vs 1.2%, respectively, p = 0.002). TdP developed in 8 patients (3.5%) in group A and in none (0%) in group B (p = 0.009). The administration of
magnesium (despite the high doses used) was well tolerated. In conclusion, the administration of high doses of
magnesium probably makes
ibutilide a much safer agent, and
magnesium increased the conversion efficacy of
ibutilide.