Does magnesium modify left ventricular remodeling after experimental myocardial infarction?

BACKGROUND

Magnesium therapy has been shown to improve survival and decrease the incidence of left ventricular failure when given to patients shortly after a myocardial infarction, but the mechanisms are unknown. We tested the hypothesis that the benefits of magnesium therapy are due to a favorable effect on early left ventricular remodeling, particularly on infarct shape changes.

METHODS

Rats were infarcted and randomly allocated to two groups: group 1 (n = 8) received intravenous magnesium sulfate (200 mumol/kg) over 10 min started 30 min after coronary ligation, then an intraperitoneal dose (800 mumol/kg), which was repeated 6 h later. Group 2 (n = 10) served as a control group, and received normal saline. Using this regimen, the trough level of ionized magnesium 12 h after the intravenous dose was 33% above the control level. Three weeks after infarction, the hearts of the rats were arrested with saturated potassium chloride and fixed in formalin at 7.5 mmHg. The hearts were cut transversely into four slices. Photographs of both sides of each slice were taken and projected for morphometric analysis.

RESULTS

Infarct size was similar in the magnesium and control groups (35 +/- 4 versus 30 +/- 2%). Infarct thickness, expansion index, and cavity area were also similar in both groups.

CONCLUSIONS

Magnesium has no effect on early left ventricular remodeling or infarct expansion. The mechanism of its clinical benefits remains unexplained.