[Electrophysiological effects of intravenous magnesium sulfate in man]

Magnesium salts have been used for many years to correct a wide variety of arrhythmias. A few experimental studies have been devoted to their electrophysiological effects, but these remain poorly documented in man, hence this study. An electrophysiological investigation was conducted in 24 patients before, and immediately after a bolus intravenous injection of magnesium sulphate in doses of 1.5 g to 12 patients (group I) and 3 g to 12 other patients (group II), followed by a continuous infusion at the rate of 1 mg/min. The drug had no influence on heart rate, duration of QRS, QT and QTc intervals and ventricular refractory period. A small, but statistically significant prolongation of HV (from 57 to 59 ms, p less than 0.05) was observed in group II. Analysis of the results in group I revealed a moderate but significant prolongation of the PR and AH intervals. The electrophysiological effects were distinctly more pronounced in group II patients, with significant prolongation of: PR and AH intervals, effective refractory period of the right atrium and AV node, Wenckebach's point, corrected sinus node recovery time and sinoatrial conduction time. These results demonstrate that magnesium sulphate principally acts on the sinus node, the AV node and the atrium, suggesting a blocking effect on calcium channels.