[Antiarrhythmic effects of intravenous magnesium sulfate in torsade de pointes. Apropos of 6 cases].

The antiarrhythmic properties of magnesium salts, known for many years, are periodically recalled but rarely used in daily clinical practice. They are usually used in digitalis-induced arrhythmias and are rarely indicated in other conditions; they are often reserved for cases in which a magnesium deficiency is suspected. In 6 cases of torsades de pointes, magnesium sulphate was administered at a dose 1 to 3 g by direct intravenous injection. Although hypokalaemia was a common finding, a low magnesium concentration was only found in one case. The ventricular arrhythmia regressed completely at the end of the injection in 4 cases (one after two injections). One positive but incomplete response was observed in the only case of magnesium deficiency, probably due in retrospect to inadequate dosage. Finally, one patient with very poor ventricular function had recurrence after a good initial response. The diversity of the clinical and biological findings in this series suggests a specific antiarrhythmic action of the magnesium ion, apparently independant of the correction of magnesium deficiency; experimental studies suggest that the mode of action is a direct antagonism of Mg++-K+ and/or Mg++-Ca++. Compared to usual means of treatment of torsades de pointes (isoprenaline infusion or pacing) the advantages of intravenous magnesium sulphate are clear-cut: innocuity, simplicity and rapidity of administration, and almost immediate efficacy.