Dose-related cardiac electrophysiological effects of intravenous magnesium. A double-blind placebo-controlled dose-response study in patients with paroxysmal supraventricular tachycardia

Aims The role of magnesium as an antiarrhythmic drug is vet not conclusive. Therefore, we performed a double-blind, randomized, placebo-controlled dos e-response study of cardiac electrophysiological effects of intravenous mag nesium. Methods and Results Thirty-six patients undergoing an electrophysiological evaluation for paroxysmal supraventricular tachycardia were randomized to o ne of the following dosages of intravenous magnesium (0, 5, 10 or 30 mmol). Conventional electrophysiological variables for sinus node function, atria l, atrioventricular node and ventricular conduction and refractoriness were measured before and after magnesium administration. Prolongation of the at rial-His interval was found at 5 mmol of magnesium compared with placebo an d no further prolongation was observed at higher doses (-3+/-8, 11+/-9, 7+/ -15, 11+/-16. for the dosages of 0, 5. 10 and 20 mmol of magnesium, respect ively, P<0.05). (Measures of sinus node function, intra-atrial conduction a nd conduction through the Purkinje system were unaffected by magnesium. Mal e gender was associated with prolongation in atrial effective refractory pe riod, in contrast to shortening in females: 2 +/- 43, 35 +/- 44, 36 +/- 33, 13 +/- 12 ms for males and 3 +/- 6, - 12 +/- 11, - 13 +/- 12, 0 +/- 23 ms for females, respectively (P<0.001). Conclusion Atrioventricular node conduction was prolonged by 5 mmol intrave nous magnesium and no further prolongation was observed at higher dosages. At dosages of 5 and 10 mmol magnesium the atrial effective refractoriness w as prolonged in males and shortened in females. (Europace 2000; 2: 320-326) (C) 2000 The European Society of Cardiology.