EFFECT OF INTRAVENOUS MAGNESIUM-SULFATE ON CARDIAC-ARRHYTHMIAS IN CRITICALLY ILL PATIENTS WITH LOW SERUM IONIZED MAGNESIUM

Magnesium affects cardiac function, although until the recent developm ent of a new ion-selective electrode no method existed for measuring t he physiologically active form of magnesium, free ions (iMg(2+)), in t he blood. We investigated the antiarrhythmic effect of magnesium sulfa te administered to critically ill patients with cardiac arrhythmias an d reduced iMg(2+) as determined using the ion-selective electrode. Eig ht patients with a low iMg(2+) level (less than 0.40 mmol/L) were give n intravenous magnesium sulfate (group L). Magnesium sulfate was also administered to patients with a normal iMg(2+) level (more than 0.40 m mol/L) but who did not respond to conventional antiarrhythmic drugs (g roup N). Intravenous magnesium sulfate significantly increased the iMg (2+) 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 effe ct in 7 of the 8 patients (88%). However, in group N patients, intrave nous magnesium sulfate had an antiarrhythmic effect in only 1 of the 6 patients (17%) (p < 0.05 vs group L). These results suggest that intr avenous magnesium sulfate may be effective in the acute management of cardiac arrhythmias in patients with a low serum iMg(2+) level.