Shunji Kasaoka, M.D., Ryosuke Tsuruta, M.D., Ken Nakashima, M.D., Yoshiyuki Soejima, M.D., Toshiro Miura, M.D., Daikai Sadamitsu, M.D., Akio Tateishi, M.D. and Tsuyoshi Maekawa, M.D.

Abstract
Magnesium affects cardiac function, although until the recent development of a new ion-selective electrode no method existed for measuring the physiologically active form of magnesium, free ions (iMg²⁺), in the blood. We investigated the antiarrhythmic effect of magnesium sulfate administered to critically ill patients with cardiac arrhythmias and reduced iMg²⁺ as determined using the ion-selective electrode. Eight patients with a low iMg²⁺ level (less than 0.40 mmol/L) were given intravenous magnesium sulfate (group L). Magnesium sulfate was also administered to patients with a normal iMg²⁺ level (more than 0.40 mmol/L) but who did not respond to conventional antiarrhythmic drugs (group N). Intravenous magnesium sulfate significantly increased the iMg²⁺ level in patients in group L from 0.35±0.06 mmol/L (mean±SD) to 0.54±0.09 mmol/L (p<0.01), and had an antiarrhythmic effect in 7 of the 8 patients (88%). However, in group N patients, intravenous magnesium sulfate had an antiarrhythmic effect in only 1 of the 6 patients (17%) (p<0.05 vs group L). These results suggest that intravenous magnesium sulfate may be effective in the acute management of cardiac arrhythmias in patients with a low serum iMg²⁺ level.
(Jpn Circ J 1996; 60: 871-875)

Key Words: Cardiac arrhythmia, Critically ill patient, Intravenous magnesium sulfate, Ionized magnesium, Ion-selective electrode

Mailing address: Shunji Kasaoka, M.D., Critical Care Medical Center, Yamaguchi University Hospital, 1144 Kogushi, Ube, Yamaguchi 755, Japan