Dose-related cardiac electrophysiological effects of intravenous magnesium. A double-blind placebo-controlled dose-response study in patients with paroxysmal supraventricular tachycardia.
OBJECTIVE
The role of magnesium as an antiarrhythmic drug is yet not conclusive. Therefore, we performed a double-blind, randomized, placebo-controlled dose-response study of cardiac electrophysiological effects of intravenous magnesium.


RESULTS
Thirty-six patients undergoing an electrophysiological evaluation for paroxysmal supraventricular tachycardia were randomized to one of the following dosages of intravenous magnesium (0, 5, 10 or 20 mmol). Conventional electrophysiological variables for sinus node function, atrial, atrioventricular node and ventricular conduction and refractoriness were measured before and after magnesium administration. Prolongation of the atrial-His interval was found at 5 mmol of magnesium compared with placebo and 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, respectively, P < 0.05). Measures of sinus node function, intra-atrial conduction and conduction through the Purkinje system were unaffected by magnesium. Male gender was associated with prolongation in atrial effective refractory period, 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).


CONCLUSIONS
Atrioventricular node conduction was prolonged by 5 mmol intravenous magnesium and no further prolongation was observed at higher dosages. At dosages of 5 and 10 mmol magnesium the atrial effective refractoriness was prolonged in males and shortened in females.
Christiansen
E H
EH
Department of Cardiology, Skejby University Hospital, DK-8200 Aarhus N, Denmark.
Frost
L
L
Andreasen
F
F
Mortensen
P
P
Thomsen
P E
PE
Pedersen
A K
AK
D000293:Adolescent; D000328:Adult; D000368:Aged; D000704:Analysis of Variance; D006328:Cardiac Catheterization; D004305:Dose-Response Relationship, Drug; D004311:Double-Blind Method; D004562:Electrocardiography; D004594:Electrophysiology; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D007262:Infusions, Intravenous; D017616:Magnesium Compounds / Q000008:administration & dosage*; D008297:Male; D008875:Middle Aged; D012016:Reference Values; D018709:Statistics, Nonparametric; D013614:Tachycardia, Paroxysmal / Q000175:diagnosis / Q000601:surgery; D013617:Tachycardia, Supraventricular / Q000175:diagnosis* / Q000188:drug therapy*; D016896:Treatment Outcome
D017616:Magnesium Compounds