[Treatment of torsade des pointes by intravenous magnesium]

A 72 year old woman was admitted with decompensation of a hypertensive cardiopathy and treated with diuretics. She developed recurrent syncopal torsades de pointes during the 24th hour which were reduced by a bolus intravenous injection of 3 g of magnesium sulphate (Mg SO4). There was a recurrence 30 minutes later which regressed after a second injection of 3 g of Mg SO4. A continuous intravenous infusion of 18 g/day of Mg SO4 prevented further recurrences of the arrhythmia. Biochemical analysis showed intra and extracellular magnesium deficiency at the time of the torsades de pointes but the intracellular potassium was normal. The QT interval was prolonged but this parameter did not change after the bolus of Mg SO4. It returned to normal progressively afterwards. The clinical course was uncomplicated with no recurrences. Metabolic correction was obtained in 3 days. This observation raises the question of the mechanisms relating diuretic therapy, magnesium and torsades de pointes.