Should magnesium be part of the routine therapy for acute myocardial infarction?

Role of magnesium sulfate in neuroprotection in acute ischemic stroke

AIMS

To study the effect of intravenous magnesium sulfate infusion on clinical outcome of patients of acute stroke.

MATERIALS AND METHODS

Sixty consecutive cases of acute ischemic stroke hospitalised within 24 h of an episode of stroke were taken as subjects. All subjects underwent a computed tomography head, and those found to have evidence of bleed/space-occupying lesions were excluded from the study. The subjects taken up for the study were divided into two groups of 30 subjects each. Both the groups received the standard protocol management for acute ischemic stroke. Subjects of Group 1 additionally received intravenous magnesium sulfate as initial 4 g bolus dose over 15 min followed by 16 g as slow infusion over the next 24 h. In all the subjects of the two study groups, serum magnesium levels were estimated at the time of admission (Day 0), Day 1 and Day 2 of hospitalization using an atomic absorption spectrometer.

STATISTICAL ANALYSIS USED

Scandinavian stroke scores were calculated on Day 3, day of discharge and Day 28. Paired t-test was employed for comparison of stroke scores on Day 3, day of discharge and Day 28 within the same group and the unpaired t-test was used for the intergroup comparison, i.e. comparison of stroke scores of control group with corresponding stroke scores of magnesium group.

RESULTS

Comparison of stroke scores on Day 3 and day of discharge, on the day of discharge and Day 28 and on Day 3 and Day 28 in the magnesium group produced a t-value of 5.000 and P <0.001, which was highly significant. However, the comparison of the mean stroke scores between the magnesium and the control groups on Day 3, day of discharge and Day 28 yielded a P-value of >0.05, which was not significant.

CONCLUSIONS

The study failed to document a statistical significant stroke recovery in spite of achieving a significant rise in serum magnesium level, more than that necessary for neuroprotection, with an intravenous magnesium sulfate regime.

Is there a place for magnesium in the treatment of acute myocardial infarction?

Infusions of solutions of magnesium sulfate for patients with acute myocardial infarction were shown by a meta-analysis of seven small studies and a larger study of 2316 patients (LIMIT-2) to have clinical efficacy. However, the ISIS-4 study of 58,050 patients found no improvement in short-term mortality rates with magnesium therapy in patients with acute myocardial infarction. In this article we explore the following four differences between the ISIS-4 study and the earlier studies: (1) Time of initiation of magnesium treatment after acute myocardial infarction and thrombolytic therapy; (2) dosage of magnesium in the first 24 hours after acute myocardial infarction; (3) duration of magnesium infusion after acute myocardial infarction; and (4) differences in patient risks in control and treatment groups. These four differences may explain the different outcomes among these studies and indicate the type of additional studies that are needed to define the clinical utility of magnesium infusion in the treatment of patients with acute myocardial infarction.

The important role of modifiable dietary and behavioral characteristics in the causation and prevention of coronary heart disease hospitalization and mortality: the prospective NHANES I follow-up study

OBJECTIVE

Our specific aim in the prospective, longitudinal assessment of 8,251 subjects in the National Health and Nutrition Examination Survey, NHANES I, followup study was to assess the important roles of modifiable dietary and behavioral characteristics in the causation and prevention of coronary heart disease (CHD).

METHODS

Using NHANES I prospective 10 year followup data, we studied 8,251 subjects; 492 with cardiovascular events and 7,759 without events during the followup period (1971-75 to 1982-84). Using general linear models and logistic regression, we assessed the relationships of CHD risk factors to CHD morbidity and mortality.

RESULTS

By logistic regression, the following factors were independently, significantly, and inversely associated with coronary heart and vascular disease deaths and hospitalizations: alcohol intake, dietary riboflavin, dietary iron, serum magnesium, leisure time exercise, habitual physical activity, and female gender. Positive significant independent determinants of CHD events included cigarette smoking, sedimentation rate, Quetelet index, maximum body weight, and age.

CONCLUSIONS

These associations emphasize the important role of modifiable dietary and behavioral characteristics in the causation and prevention of CHD.

[Indications for the use of magnesium in anesthesia and intensive care]

Magnesium (Mg), a cofactor in numerous enzymatic reactions, is often ignored by clinicians, as the symptomatology of Mg depletion is not specific and usually associated with that of the cause of the depletion. Furthermore, the plasma Mg concentration (0.8 to 1.1 mmol.L-1) is only equivalent to one percent of the total body content. A Mg deficit may exist while plasma Mg concentration is normal. Therefore other techniques for Mg assessment, such as the repletion test, as well as red blood cell and lymphocyte concentrations have been used. A renewed interest for Mg occurred as numerous studies have shown the therapeutic efficiency of Mg and as the mechanisms of its haemodynamic effects have been recognized. Mg regulates Na-K-ATPase activity, K channels activity and, most of all, it is a natural calcium channel blocking agent. These properties explain its important place in electrophysiology of myocardial cells and the effects on the tension of smooth muscles, resulting in a vasodilation and a bronchodilation respectively. The antagonistic effect of Mg on calcium decreases the presynaptic release of acetylcholine at the neuromuscular junction and the release of epinephrine at the peripheral sympathetic nerves and the adrenals. Mg potentiates the effect of non-depolarizing muscle relaxants. A Mg deficiency occurs often in ICU patients, in alcoholics and during use of diuretics. Simultaneous administration of Mg is often required for treatment of potassium deficiency. Mg has an anti-arrhythmic effect towards digoxin-mediated dysrhythmias and torsades de pointes, and can be efficient in other arrhythmias. Systematic use of Mg seems to decrease mortality of acute myocardial infarction and is justified during cardiac surgery, often associated with hypomagnesemia, because of vasodilation of coronary arteries and in order to prevent occurrence of arrhythmias. Mg, because of its calcium channel blocking properties and as it lowers the release of epinephrine, is indicated for surgery of pheochromocytoma. In eclamptic and pre-eclamptic patients, the use of Mg is valuable, but not as an anti-epileptic agent. Other clinical uses of Mg have been proposed, but they are either anecdotal or of uncertain efficiency.

Magnesium in acute myocardial infarction

Clinical studies on the use of magnesium in acute myocardial infarction have yielded contradictory results. While the exact reasons for these discrepancies are unclear, it appears that the timing of magnesium administration is crucial to the success or failure of therapy. Although some studies have shown a significant reduction in the odds of death with this agent, the exact reasons underlying this possible benefit are not yet fully understood. A reduction in arrhythmias, inhibition of thrombus generation, changes in coronary and peripheral hemodynamics, and the limitation of ischemic damage and reperfusion injury have been inferred as possible mechanisms. IV magnesium is inexpensive and easy to administer, and has minimal side effects. While further research on magnesium therapy in ischemic states is warranted, the early use of IV magnesium should be considered in selected patients with suspected acute myocardial infarction.

Magnesium and its therapeutic uses: a review

Magnesium has been reported as an effective medical therapy in an expanding array of conditions. Evidence investigating magnesium's use is presented, with a number of studies suggesting it should be seriously considered in such conditions as ischemic heart disease, cardiac arrhythmias, and asthma. Magnesium balance and metabolism are briefly reviewed, and then various hypotheses are presented that may explain magnesium's physiologic mechanisms of action, most likely involving calcium and potassium flux across cellular membranes in smooth muscle. In a number of the conditions to be discussed, it has been uncertain whether magnesium administration serves the purpose of merely correcting an underlying deficiency state or of utilizing a specific pharmacologic effect of magnesium. Magnesium deficiency is a relatively common condition, and predisposing factors as well as recent methods for assessing total body stores of magnesium are discussed. Physicians should be familiar with the numerous conditions and therapeutics that are risk factors for an underlying magnesium deficiency and in which empiric magnesium replacement should be considered. Guidelines for administration of parenteral magnesium are presented with specific focus on the low risk of adverse effects, as suggested by the large and rapid dosing regimens used in many of the clinical studies discussed here.