DOES MAGNESIUM MODIFY LEFT-VENTRICULAR REMODELING AFTER EXPERIMENTAL MYOCARDIAL-INFARCTION

Background: Magnesium therapy has been shown to improve survival and d ecrease the incidence of left ventricular failure when given to patien ts shortly after a myocardial infarction, but the mechanisms are unkno wn. We tested the hypothesis that the benefits of magnesium therapy ar e due to a favorable effect on early left ventricular remodeling, part icularly on infarct shape changes. Methods: Rats were infarcted and ra ndomly allocated to two groups: group 1 (n=8) received intravenous mag nesium sulfate (200 mu mol/kg) over 10 min started 30 min after corona ry ligation, then an intraperitoneal dose (800 mu mol/kg), which was r epeated 6 h later. Group 2 (n = 10) served as a control group, and rec eived normal saline. Using this regimen, the trough level of ionized m agnesium 12 h after the intravenous dose was 33% above the control lev el. 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 analysi s. Results: Infarct size was similar in the magnesium and control grou ps (35+/-4 versus 30+/-2%). infarct thickness, expansion index, and ca vity 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.