[Value of magnesium in acute myocardial infarct].

Experiments in animal models of myocardial infarction have provided evidence that early magnesium infusion can limit the infarct size. One mechanism that has been postulated to be of importance is a protection of the cardiomyocyte against a calcium overload during or after ischemia. We had shown that in isolated human myocytes from patient with ischemic cardiomyopathy an increase of the extracellular magnesium concentration could block the L-type-calcium current in a dose dependent manner. Until recently only small, uncontrolled studies have indicated there may be a reduction of mortality due to myocardial infarction when intravenous magnesium infusion was added to standard therapy. However, two recently published randomized studies showed different results, although similar doses of magnesium were used (70-80 mmol magnesium over 24 h). The LIMIT-2-study was a double-blind, placebo controlled investigation of over 2300 patients with suspected myocardial infarction. Magnesium infusion was associated with a reduction of the 28 day mortality by 24%. The ISIS-4-study on over 50,000 patients with suspected myocardial infarction did not show any positive effect of magnesium on mortality. Major differences between both studies were differences in thrombolysis (LIMIT-2:1/3, ISIS-4: 70%). Furthermore, in LIMIT-2 magnesium infusion was started as early as possible, whereas in ISIS-4 magnesium was given after the end of thrombolytic therapy. In can be concluded that magnesium therapy in acute myocardial infarction after thrombolytic therapy is not useful. However, in patients where thrombolytic therapy is not feasable, early infusion of magnesium may be beneficial. As side effects are minor and costs are low, a therapeutic trial may be warranted, although a final decision on the effects of magnesium cannot be made.