Effect of magnesium on the monophasic action potential during early ischemia in the in vivo human heart.
OBJECTIVE
This study sought to examine the effects of magnesium on epicardial action potential duration in patients during early myocardial ischemia.


BACKGROUND
Magnesium has been shown to reduce arrhythmias in experimental models of myocardial ischemia. Experimental and clinical observations suggest an effect on repolarization.


METHODS
Patients undergoing elective coronary artery bypass surgery were randomized (double blind) to receive intravenous magnesium (n = 10) or placebo (n = 10). Patients were placed on cardiopulmonary bypass and paced at 600 ms, and stable monophasic action potentials were obtained. Ischemia was achieved by aortic cross-clamping for 2 min while normothermia was maintained.


RESULTS
Serum magnesium levels increased from 0.60 +/- 0.03 to 1.69 +/- 0.07 mmol/liter (mean +/- SEM) in the magnesium group, with no change in the placebo group. Epicardial temperature was identical in the two groups and did not alter during ischemia. At 90% repolarization, initial action potential prolongation was observed in the placebo group over the first minute of ischemia (282.0 +/- 6.0 to 294.0 +/- 4.8 ms) but not in the magnesium group (278.3 +/- 5.9 to 274.5 +/- 7.4 ms). At 2 min of ischemia, action potential duration was shorter in the magnesium group than in the placebo group (258.1 +/- 5.5 vs. 281.3 +/- 5.9 ms, respectively, p < 0.05).


CONCLUSIONS
Intravenous magnesium infusion altered the epicardial action potential response to ischemia in patients. These findings may have important implications in the pathogenesis of arrhythmias in ischemic myocardium.
Redwood
S R
SR
Department of Cardiological Sciences, St. George's Hospital Medical School, London, England, United Kingdom.
Taggart
P I
PI
Sutton
P M
PM
Bygrave
A
A
Bashir
Y
Y
Purkayastha
D D
DD
Camm
A J
AJ
Treasure
T
T
D000200:Action Potentials / Q000187:drug effects; D004311:Double-Blind Method; D005260:Female; D006801:Humans; D007262:Infusions, Intravenous; D008278:Magnesium Sulfate / Q000008:administration & dosage / Q000494:pharmacology*; D008297:Male; D008875:Middle Aged; D017202:Myocardial Ischemia / Q000503:physiopathology*; D010496:Pericardium / Q000187:drug effects* / Q000503:physiopathology
D008278:Magnesium Sulfate