[Clinical electrophysiologic properties of magnesium and correlations with its anti-arrhythmia efficacy in acquired torsade de pointes].

Recently, intravenous administration of low doses of magnesium has proved remarkably effective in the treatment of acquired torsade de pointe, but its electrophysiologic effects remain poorly understood. Three clinical cases are reported in three distinct situations (quinidine treatment, hypokalemia, bradycardia with complete atrioventricular block). These cases confirm the efficacy of magnesium, which acts without notable modification of ventricular cycles or the duration of repolarization. In ten patients undergoing intracavitary exploration, the electrophysiologic parameters were analyzed before and after injection of magnesium sulfate (35 mg/kg). Only three parameters were significantly altered; the corrected sinusal recovery time (increase from 245 +/- 92 ms to 296 +/- 96 ms), the effective nodal refractory period (increase from 333 +/- 98 ms to 346 +/- 93 ms), and the Wenckebache period (decrease from 157 +/- 28/min to 144 +/- 21/min). No changes were noted in other parameters, notably ventricular (QT interval, QRS duration, HV interval, and effective ventricular refractory period). The arrhythmic action on the ventricle is therefore remarkable and is not accompanied by patent electrophysiologic effects. The efficacy of magnesium in torsade de pointe may suggest action on calcium currents.