Magnesium therapy in acute myocardial infarction when patients are not candidates for thrombolytic therapy

Hypomagnesemia in critically ill patients

BACKGROUND

Magnesium (Mg) is essential for life and plays a crucial role in several biochemical and physiological processes in the human body. Hypomagnesemia is common in all hospitalized patients, especially in critically ill patients with coexisting electrolyte abnormalities. Hypomagnesemia may cause severe and potential fatal complications if not timely diagnosed and properly treated, and associate with increased mortality.

MAIN BODY

Mg deficiency in critically ill patients is mainly caused by gastrointestinal and/or renal disorders and may lead to secondary hypokalemia and hypocalcemia, and severe neuromuscular and cardiovascular clinical manifestations. Because of the physical distribution of Mg, there are no readily or easy methods to assess Mg status. However, serum Mg and the Mg tolerance test are most widely used. There are limited studies to guide intermittent therapy of Mg deficiency in critically ill patients, but some empirical guidelines exist. Further clinical trials and critical evaluation of empiric Mg replacement strategies is needed.

CONCLUSION

Patients at risk of Mg deficiency, with typical biochemical findings or clinical symptoms of hypomagnesemia, should be considered for treatment even with serum Mg within the normal range.

Lack of cardioprotection by single-dose magnesium prophylaxis on isoprenaline-induced myocardial infarction in adult Wistar rats

Aim

Magnesium (Mg²⁺) is effective in treating cardiovascular disorders such as arrhythmias and pre-eclampsia, but its role during myocardial infarction (MI) remains uncertain. In this study, we investigated the effects of Mg²⁺ pre-treatment on isoprenaline (ISO)-induced MI in vivo.

Methods

Rats divided into four groups were each pre-treated with either MgSO₄ (270 mg/kg intraperitoneally) or an equivalent volume of physiological saline, prior to the ISO (67 mg/kg subcutaneously) or saline treatments. One day post-treatment, the electrocardiogram and left ventricular blood pressures were recorded. Infarcts were determined using 2,3,5-triphenyltetrazolium chloride staining, and serum markers of lipid peroxidation were measured with spectrophotometric assays.

Results

Mg²⁺ pre-treatment neither altered the ISO-induced infarct size compared with ISO treatment alone (^p > 0.05), nor reversed the low-voltage electrocardiogram or the prominent Q waves induced by ISO, despite a trend to decreased Q waves. Similarly, Mg²⁺ did not prevent the ISO-induced decrease in peak left ventricular blood pressure or the decrease in minimal rate of pressure change. Mg²⁺ did not reverse the ISO-induced gain in heart weight or loss of body weight. Neither ISO nor Mg²⁺ altered the concentrations of lipid peroxidation markers 24 hours post MI induction.

Conclusion

Although Mg²⁺ had no detrimental effects on electrical or haemodynamic activity in ISO-induced MI, the lack of infarct prevention may detract from its utility in MI therapy.

Magnesium in disease

Although the following text will focus on magnesium in disease, its role in healthy subjects during physical exercise when used as a supplement to enhance performance is also noteworthy. Low serum magnesium levels are associated with metabolic syndrome, Type 2 diabetes mellitus (T2DM) and hypertension; consequently, some individuals benefit from magnesium supplementation: increasing magnesium consumption appears to prevent high blood pressure, and higher serum magnesium levels are associated with a lower risk of developing a metabolic syndrome. There are, however, conflicting study results regarding magnesium administration with myocardial infarction with and without reperfusion therapy. There was a long controversy as to whether or not magnesium should be given as a first-line medication. As the most recent trials have not shown any difference in outcome, intravenous magnesium cannot be recommended in patients with myocardial infarction today. However, magnesium has its indication in patients with torsade de pointes and has been given successfully to patients with digoxin-induced arrhythmia or life-threatening ventricular arrhythmias. Magnesium sulphate as an intravenous infusion also has an important established therapeutic role in pregnant women with pre-eclampsia as it decreases the risk of eclamptic seizures by half compared with placebo.

Magnesium in man: implications for health and disease

Magnesium (Mg(2+)) is an essential ion to the human body, playing an instrumental role in supporting and sustaining health and life. As the second most abundant intracellular cation after potassium, it is involved in over 600 enzymatic reactions including energy metabolism and protein synthesis. Although Mg(2+) availability has been proven to be disturbed during several clinical situations, serum Mg(2+) values are not generally determined in patients. This review aims to provide an overview of the function of Mg(2+) in human health and disease. In short, Mg(2+) plays an important physiological role particularly in the brain, heart, and skeletal muscles. Moreover, Mg(2+) supplementation has been shown to be beneficial in treatment of, among others, preeclampsia, migraine, depression, coronary artery disease, and asthma. Over the last decade, several hereditary forms of hypomagnesemia have been deciphered, including mutations in transient receptor potential melastatin type 6 (TRPM6), claudin 16, and cyclin M2 (CNNM2). Recently, mutations in Mg(2+) transporter 1 (MagT1) were linked to T-cell deficiency underlining the important role of Mg(2+) in cell viability. Moreover, hypomagnesemia can be the consequence of the use of certain types of drugs, such as diuretics, epidermal growth factor receptor inhibitors, calcineurin inhibitors, and proton pump inhibitors. This review provides an extensive and comprehensive overview of Mg(2+) research over the last few decades, focusing on the regulation of Mg(2+) homeostasis in the intestine, kidney, and bone and disturbances which may result in hypomagnesemia.

Pathophysiologic bases for adjunctive therapies in the treatment and secondary prevention of acute myocardial infarction

Postmyocardial infarction (MI) survival has been steadily improving. This improvement has been due, in part, to the actions of the adjunctive medical therapies for the treatment of MI. Aspirin, beta blockers, angiotensin-converting enzyme (ACE) inhibitors, and lipid-lowering agents have been shown to improve survival in the treatment and secondary prevention of MI. Nitrates have beneficial effects as well. These medications complement the reperfusion strategies through different mechanisms. Other adjunctive medical therapies, namely magnesium, antiarrhythmic agents, and calcium-channel blockers, have not been shown to improve mortality with routine post-MI use despite their theoretical benefits.

Intravenous magnesium for acute myocardial infarction

BACKGROUND

Mortality and morbidity from acute myocardial infarction (AMI) remain high. Intravenous magnesium started early after the onset of AMI is thought to be a promising adjuvant treatment. Conflicting results from earlier trials and meta-analyses warrant a systematic review of available evidence.

OBJECTIVES

To examine the effect of intravenous magnesium versus placebo on early mortality and morbidity.

SEARCH STRATEGY

We searched CENTRAL (The Cochrane Library Issue 3, 2006), MEDLINE (January 1966 to June 2006) and EMBASE (January 1980 to June 2006), and the Chinese Biomedical Disk (CBM disk) (January 1978 to June 2006). Some core Chinese medical journals relevant to the cardiovascular field were hand searched from their starting date to the first-half year of 2006.

SELECTION CRITERIA

All randomized controlled trials that compared intravenous magnesium with placebo in the presence or absence of fibrinolytic therapy in addition to routine treatment were eligible if they reported mortality and morbidity within 35 days of AMI onset.

DATA COLLECTION AND ANALYSIS

Two reviewers independently assessed the trial quality and extracted data using a standard form. Odds ratio (OR) were used to pool the effect if appropriate. Where heterogeneity of effects was found, clinical and methodological sources of this were explored.

MAIN RESULTS

For early mortality where there was evidence of heterogeneity, a fixed-effect meta-analysis showed no difference between magnesium and placebo groups (OR 0.99, 95%CI 0.94 to 1.04), while a random-effects meta-analysis showed a significant reduction comparing magnesium with placebo (OR 0.66, 95% CI 0.53 to 0.82). Stratification by timing of treatment (< 6 hrs, 6+ hrs) reduced heterogeneity, and in both fixed-effect and random-effects models no significant effect of magnesium was found. In stratified analyses, early mortality was reduced for patients not treated with thrombolysis (OR=0.73, 95% CI 0.56 to 0.94 by random-effects model) and for those treated with less than 75 mmol of magnesium (OR=0.59, 95% CI 0.49 to 0.70) in the magnesium compared with placebo groups.Meta-analysis for the secondary outcomes where there was no evidence of heterogeneity showed reductions in the odds of ventricular fibrillation (OR=0.88, 95% CI 0.81 to 0.96), but increases in the odds of profound hypotension (OR=1.13, 95% CI 1.09 to 1.19) and bradycardia (OR=1.49, 95% CI 1.26 to 1.77) comparing magnesium with placebo. No difference was observed for heart block (OR=1.05, 95% CI 0.97-1.14). For those outcomes where there was evidence of heterogeneity, meta-analysis with both fixed-effect and random-effects models showed that magnesium could decrease ventricular tachycardia (OR=0.45, 95% CI 0.31 to 0.66 by fixed-effect model; OR=0.40, 95% CI 0.19 to 0.84 by random-effects model) and severe arrhythmia needing treatment or Lown 2-5 (OR=0.72, 95% CI 0.60 to 0.85 by fixed-effect model; OR=0.51, 95% CI 0.33 to 0.79 by random-effects model) compared with placebo. There was no difference on the effect of cardiogenic shock between the two groups.

AUTHORS' CONCLUSIONS

Owing to the likelihood of publication bias and marked heterogeneity of treatment effects, it is essential that the findings are interpreted cautiously. From the evidence reviewed here, we consider that: (1) it is unlikely that magnesium is beneficial in reducing mortality both in patients treated early and in patients treated late, and in patients already receiving thrombolytic therapy; (2) it is unlikely that magnesium will reduce mortality when used at high dose (>=75 mmol); (3) magnesium treatment may reduce the incidence of ventricular fibrillation, ventricular tachycardia, severe arrhythmia needing treatment or Lown 2-5, but it may increase the incidence of profound hypotension, bradycardia and flushing; and (4) the areas of uncertainty regarding the effect of magnesium on mortality remain the effect of low dose treatment (< 75 mmol) and in patients not treated with thrombolysis.

[Acute coronary syndrome in the prehospital phase]

Cardiovascular diseases are the number one cause of death in Germany. In 2002 about 70,000 people died of acute myocardial infarction (AMI) and of these 37% died before arrival at hospital which underlines the relevance of adequate prehospital care. The generic term acute coronary syndrome (ACS) was introduced because a single pathomechanism accounts for the different forms and comprises unstable angina pectoris (iAP), non-ST-elevation myocardial infarction (NSTEMI), ST-elevation myocardial infarction (STEMI) and sudden cardiac death (SCD). Characteristic features are retrosternal pain, vegetative symptoms and radiation of pain into the adjoining regions. Further differentiation can only be achieved by the 12-lead ECG, as cardiac-specific enzymes do not play a role in prehospital decisions. Prehospital delays should be avoided, history and physical examination should be brief but focused, vital parameters should be assessed and monitored. Basic treatment for ACS should comprise inhalative oxygen, nitrates, morphine, aspirin and beta-blockers. If STEMI is diagnosed, patients with symptoms <12 h should undergo fibrinolytic therapy unless there is primary percutaneous coronary intervention (PCI) available within 90 min or if contraindicated. Heparin should be given to patients with STEMI depending on the choice of fibrinolytic agent, it otherwise results in a higher risk of bleeding, but in patients with iAP or NSTEMI it reduces mortality. All patients must be accompanied by the emergency physician during transportation and should be brought to a hospital with primary PCI, especially those with complicated ACS. Treatment of complications depends largely on the type, persistence and severity.

Magnesium deficiency in critical illness

Magnesium (Mg) deficiency commonly occurs in critical illness and correlates with a higher mortality and worse clinical outcome in the intensive care unit (ICU). Magnesium has been directly implicated in hypokalemia, hypocalcemia, tetany, and dysrhythmia. Moreover, Mg may play a role in acute coronary syndromes, acute cerebral ischemia, and asthma. Magnesium regulates hundreds of enzyme systems. By regulating enzymes controlling intracellular calcium, Mg affects smooth muscle vasoconstriction, important to the underlying pathophysiology of several critical illnesses. The principle causes of Mg deficiency are gastrointestinal and renal losses; however, the diagnosis is difficult to make because of the limitations of serum Mg levels, the most common assessment of Mg status. Magnesium tolerance testing and ionized Mg2+ are alternative laboratory assessments; however, each has its own difficulties in the ICU setting. The use of Mg therapy is supported by clinical trials in the treatment of symptomatic hypomagnesemia and preeclampsia and is recommended for torsade de pointes. Magnesium therapy is not supported in the treatment of acute myocardial infarction and is presently undergoing evaluation for the treatment of severe asthma exacerbation, for the prevention of post-coronary bypass grafting dysrhythmias, and as a neuroprotective agent in acute cerebral ischemia.

Vitamins, Supplements, Herbal Medicines, and Arrhythmias

Nutritional and herbal supplements may have harmful or beneficial effects on arrhythmias. Potential supplements that may have antiarrhythmic activity include omega-3 polyunsaturated fatty acids (N-3 PUFA), coenzyme Q10, and carnitine. Clinical studies show that N-3 PUFA or fish oil supplementation appears to reduce mortality and sudden death. Coenzyme Q10, used in treatment of heart failure, and carnitine and its derivatives may have beneficial effects on arrhythmias, although clinical studies have been limited. Antioxidant supplements may be beneficial, but large studies with vitamin E have been disappointing in that it does not reduce mortality. Correction of electrolyte disturbances has been long advised and magnesium supplementation has been beneficial in the treatment of torsades de pointes and in some studies after cardiac surgery. However, routine electrolyte supplementation with empiric potassium or magnesium in non-deficient patients has not been convincingly beneficial. Several herbal supplements have also been promoted to have antiarrhythmic activity. However, clinical studies are lacking to support routine use of these herbal medications. In addition, some herbal supplements may cause serious proarrhythmia, and many supplements significantly interact with warfarin and digoxin.

When the MAGIC stops: magnesium in acute coronary syndromes — a lesson in medical humility

There has been much debate as to whether magnesium, a well-tolerated, readily available and cheap therapy, should be used to treat patients with suspected myocardial infarction. Despite promising results from animal studies and small clinical trials conducted in the 1980s, two large recent trials have concluded that the once phenomenal treatment is ineffective. The story of magnesium for acute myocardial infarction is a lesson in medical humility.

Involvement of the antiplatelet activity of magnesium sulfate in suppression of protein kinase C and the Na+/H+ exchanger

Magnesium sulfate is widely used to prevent seizures in pregnant women with hypertension. The aim of this study was to examine the inhibitory mechanisms of magnesium sulfate in platelet aggregation in vitro. In this study, magnesium sulfate concentration-dependently (0.6-3.0 mM) inhibited platelet aggregation in human platelets stimulated by agonists. Magnesium sulfate (1.5 and 3.0 mM) also concentration-dependently inhibited phosphoinositide breakdown and intracellular Ca+2 mobilization in human platelets stimulated by thrombin. Rapid phosphorylation of a platelet protein of M(r) 47,000 (P47), a marker of protein kinase C activation, was triggered by phorbol-12-13-dibutyrate (PDBu, 50 nM). This phosphorylation was markedly inhibited by magnesium sulfate (3.0 mM). Magnesium sulfate (1.5 and 3.0 mM) further inhibited PDBu-stimulated platelet aggregation in human platelets. The thrombin-evoked increase in pHi was markedly inhibited in the presence of magnesium sulfate (3.0 mM). In conclusion, these results indicate that the antiplatelet activity of magnesium sulfate may be involved in the following two pathways: (1) Magnesium sulfate may inhibit the activation of protein kinase C, followed by inhibition of phosphoinositide breakdown and intracellular Ca+2 mobilization, thereby leading to inhibition of the phosphorylation of P47. (2) On the other hand, magnesium sulfate inhibits the Na+/H+ exchanger, leading to reduced intracellular Ca+2 mobilization, and ultimately to inhibition of platelet aggregation and the ATP-release reaction.

Comparison Between Nicorandil and Magnesium as an Adjunct Cardioprotective Agent to Percutaneous Coronary Intervention in Acute Anterior Myocardial Infarction

BACKGROUND

It has been reported that both nicorandil and magnesium have a cardioprotective effect in experimental ischemia - reperfusion models. In the present study, the cardioprotective effects of nicorandil and magnesium as an adjunct to reperfusion therapy in patients with acute myocardial infarction (AMI) were compared.

METHODS AND RESULTS

Forty consecutive patients with AMI caused by occlusion of anterior descending coronary artery were randomized into 3 groups: (1) Group N: nicorandil was given as 4 mg iv and 4 mg ic before reperfusion, followed by continuous infusion at 4 mg/h for 24 h; (2) Group M: magnesium was administered at 10 mmol iv before reperfusion, followed by continuous infusion at 0.4 mmol/h for 24 h; and (3) Group C: neither nicorandil nor magnesium was given. Left ventriculography was performed immediately after reperfusion and 3 months later. There was no significant change in regional wall motion (RWM) in either Group C or M, whereas that of group N improved significantly. The change in RWM in Group N was significantly greater than in Group C (Group N: 0.92+/-0.92, Group M: 0.44+/-0.80, Group C: -0.01+/-0.65, p<0.05).

CONCLUSIONS

The early administration of nicorandil as an adjunct to reperfusion is useful for cardioprotection in AMI, but magnesium is not.

Long-term outcome of intravenous magnesium therapy in thrombolysis-ineligible acute myocardial infarction patients

The aim of our study was to analyze the long-term survival and cardiac function in 194 consecutive, thrombolysis-ineligible acute myocardial infarction (AMI) patients receiving 48-hour intravenous magnesium sulfate (22 g) - 96 patients, compared with placebo - 98 patients. After a mean 4.8-year follow-up, all-cause mortality and cardiac mortality were significantly lower in the magnesium compared to the placebo group [(18 vs. 33 patients, p < 0.01) and (12 vs. 30 patients, p < 0.001), respectively]. Rest radionuclide ventriculography tests for left-ventricular ejection fraction (LVEF) were assessed in surviving patients up to completion of follow-up. Magnesium-treated patients had a significantly higher LVEF (0.51 +/- 0.10 vs. 0.44 +/- 0.14, p < 0.05) and a lower incidence of heart failure compared to placebo-treated patients (12 vs. 3 patients, p = 0.02). Beneficial effects of intravenous magnesium therapy in thrombolysis-ineligible AMI patients appeared to last for at least 4.8 years, concomitant with preserved LVEF, suggesting a favorable role for acute magnesium treatment in these patients.

Antithrombotic effects of magnesium sulfate in in vivo experiments

In this study, magnesium sulfate was effective in reducing the mortality of adenosine diphosphate-induced acute pulmonary thromboembolism in mice, when it was administered intravenously at doses of 100 and 200 microg/g body weight. In addition, intravenous injections of magnesium sulfate (100 and 200 microg/g) significantly prolonged bleeding time in the severed mesenteric arteries of rats by approximately 1.7- and 1.9-fold, respectively, compared with normal saline. Continuous infusion of magnesium sulfate (20 microg/g per minute) for 10 minutes also significantly increased the bleeding time by approximately 1.7-fold, and the bleeding time returned to baseline within 60 minutes of cessation of magnesium sulfate infusion. On the other hand, platelet thrombi formation was induced by irradiating mesenteric venules with filtered light in mice pretreated with intravenous fluorescein sodium. When magnesium sulfate was administered at 300 microg/g during induction of platelet plug formation with 10 microg/kg fluorescein sodium, occlusion time was not significantly prolonged, but a dose of 600 microg/g did significantly prolong the occlusion time. Furthermore, aspirin (250 microg/g) also showed a similar activity in this experiment in prolonging the occlusion time. In conclusion, these results suggest that magnesium sulfate has an effective antithrombotic activity in vivo, and treatment with magnesium sulfate may lower the risk of thromboembolic-related disorders.

Does magnesium have a role in the treatment of patients with coronary artery disease?

Hypomagnesemia is common in hospitalized patients, especially in elderly patients with coronary artery disease (CAD) and/or those with chronic heart failure. Hypomagnesemia is associated with increased all cause mortality and mortality from CAD. Magnesium supplementation improves myocardial metabolism, inhibits calcium accumulation and myocardial cell death; it improves vascular tone, peripheral vascular resistance, afterload and cardiac output, reduces cardiac arrhythmias and improves lipid metabolism. Magnesium also reduces vulnerability to oxygen-derived free radicals, improves endothelial function and inhibits platelet function, including platelet aggregation and adhesion, which potentially confers upon magnesium physiologic and natural effects similar to adenosine-diphosphate inhibitors such as clopidogrel. However, data regarding the use of magnesium in patients with acute myocardial infarction (AMI) are conflicting. Although some previous relatively small randomized clinical trials demonstrated a remarkable reduction in mortality when intravenous magnesium was administered to relatively high risk AMI patients, two recently published large-scale randomized clinical trials (the Fourth International Study of Infarct Survival [ISIS 4] and Magnesium in Coronaries [MAGIC]) were unable to demonstrate any advantage of intravenous magnesium over placebo. Nevertheless, the theoretical benefits of magnesium supplementation as a cardio-protective agent in CAD patients, promising results from animal and human studies, its relatively low-cost and ease of handling requiring no special expertise, together with its excellent tolerability, gives magnesium a place in treating CAD patients, especially in those at high risk, such as CAD patients with heart failure, the elderly and hospitalized patients with hypomagnesemia. Furthermore, magnesium therapy is indicated in life-threatening ventricular arrhythmias such as torsades de pointes and intractable ventricular tachycardia.

Magnesium in stroke treatment

Magnesium is involved in multiple physiological processes that may be relevant to cerebral ischaemia, including antagonism of glutamate release, NMDA receptor blockade, calcium channel antagonism, and maintenance of cerebral blood flow. Systemically administered magnesium at doses that double physiological serum concentration significantly reduces infarct volume in animal models of stroke, with a window of up to six hours after onset and favourable dose-response characteristics when compared with previously tested neuroprotective agents. Small clinical trials have reported benefit, but results are not statistically significant in systematic review. A large ongoing trial (IMAGES) will report in 2003-4 and further trials are planned.

Early administration of intravenous magnesium to high-risk patients with acute myocardial infarction in the Magnesium in Coronaries (MAGIC) Trial: a randomised controlled trial

BACKGROUND

The benefits of supplemental administration of intravenous magnesium in patients with ST-elevation myocardial infarction (STEMI) are controversial. Despite promising results from work in animals and the ready availability of this simple, inexpensive treatment, conflicting results have been reported in clinical trials. Our aim was to compare short-term mortality in patients with STEMI who received either intravenous magnesium sulphate or placebo.

METHODS

We did a randomised, double-blind trial in 6213 patients with acute STEMI who were assigned a 2 g intravenous bolus of magnesium sulphate administered over 15 min, followed by a 17 g infusion of magnesium sulphate over 24 h (n=3113), or matching placebo (n=3100). Our primary endpoint was 30-day all-cause mortality. At randomisation, patients were stratified by their eligibility for reperfusion therapy. The first stratum included patients who were aged 65 years or older and eligible for reperfusion therapy, and the second stratum included patients of any age who were not eligible for reperfusion therapy. Analysis was by intention-to-treat.

FINDINGS

At 30 days, 475 (15.3%) patients in the magnesium group and 472 (15.2%) in the placebo group had died (odds ratio 1.0, 95% CI 0.9-1.2, p=0.96). No benefit or harm of magnesium was observed in eight prespecified subgroup analyses of patients and in 15 additional exploratory subgroup analyses. After adjustment for factors shown to effect mortality risk in a multivariate regression model, no benefit of magnesium was observed (1.0, 0.8-1.1, p=0.53).

INTERPRETATION

Early administration of magnesium in high-risk patients with STEMI has no effect on 30-day mortality. In view of the totality of the available evidence, in current coronary care practice there is no indication for the routine administration of intravenous magnesium in patients with STEMI.

Magnesium reduces myocardial infarct size via enhancement of adenosine mechanism in rabbits

OBJECTIVES

Clinical impact of magnesium (Mg) therapy remains controversial in acute myocardial infarction. We investigated the infarct size limiting effects of Mg and its mechanism in rabbits.

METHODS

Anesthetized rabbits underwent 30 min coronary occlusion and 3 h reperfusion in ten groups: (1) Control, (2) Low Mg, (3) Mg, (4) High Mg, (5) calcium (Ca), (6) Mg+Ca, (7) 8-phenyltheophylline (8PT), an adenosine receptor blockade, (8) 8PT+Mg, (9) alpha, beta-methylene-adenosine diphosphate (AOPCP), a selective inhibitor of ecto-5'-nucleotidase, and (10) AOPCP+Mg groups. Infract size (IS) to area at risk (AR) was measured by triphenyltetrazorium chloride method.

RESULTS

The IS/AR ratio was significantly smaller in Mg, 27+/-3% (P<0.05) and High Mg, 24+/-2% (P<0.05) compared to Control, 50+/-3% and Low Mg, 42+/-4%. The IS limiting effects of Mg were abolished in 8PT+Mg, AOPCP+Mg and Mg+Ca. The IS/AR ratio correlated with neither rate-pressure products nor incidence of arrhythmia.

CONCLUSION

Magnesium administration has an infarct size limiting effect independent of its effects on myocardial oxygen consumption and incidence of arrhythmia in rabbits. The infarct size limiting effect of magnesium is attributable, at least in part, to augmentation of adenosine mechanism.

The importance of effect mechanism in the design and interpretation of clinical trials: the role of magnesium in acute myocardial infarction

The design and interpretation of randomized clinical trials and of meta-analyses of trials should be informed by a biologically plausible hypothesis of treatment effect. Without some insight on likely mechanism, trial conditions may not be optimum to allow a true treatment effect to be detected. Judgments on mechanism underpin decisions on the appropriateness of pooling studies in meta-analysis. Where statistical heterogeneity of trial results is found, the possibility of true biological effect modification can only be assessed by considering potential treatment mechanisms. These can then be tested in carefully designed laboratory models. Meta-analysis of 12 randomized controlled trials of intravenous Mg(2+) in acute myocardial infarction gives a null effect (odds ratio 1.02, 95% CI 0.96 to 1.08) with a fixed effects model, but with strong evidence of heterogeneity (P <.0001) due to a single large study in which Mg(2+) was generally given late and after fibrinolytic treatment. A random effects model gives a pooled odds ratio 0.61 (95% CI 0.43 to 0.87, P = 0.006). Laboratory models show that timing of Mg(2+) administration before or after reperfusion critically determines whether myocardial protection occurs.

GENERAL PHARMACOLOGIC TREATMENT OF ACUTE MYOCARDIAL INFARCTION

The general pharmacotherapeutic issues surrounding AMI are complex and expanding, especially with regard to treatment aimed at the [table: see text] culprit, coronary atherosclerotic thrombus. Basic, well-established therapy includes the routine administration of oxygen, nitroglycerin, aspirin, and at times morphine, with selected cases invoking caution with respect to these agents (e.g., nitroglycerin and the risk of hypotension in right ventricular infarction; contraindication to nitrolycerin in patients on sildenafil). Cardioprotective agents, especially beta-adrenergic antagonists, should be considered early in light of their demonstrated benefit; others, such as ACE inhibitors, need not be administered in the ED. Heparin, both UFH and the newer LMWHs, have well-established roles in acute coronary syndromes. The GP IIb/IIIa inhibitors are the most recent addition to the pharmacologic armamentarium; their role is evolving rapidly as research on this frontier continues. Table 2 reviews recommended dosing of selected agents in acute coronary syndromes.

Hypomagnesemic disorders

Adequate magnesium stores are vitally important for life. Critically ill patients will almost always have diminished levels of circulating magnesium, and this predisposes them to a variety of adverse effects, some life threatening. The causes of hypomagnesemia are many and varied, but in the critically ill, losses from the kidneys, often secondary to medications and from the gastrointestinal (GI) tract, predominate. The measurement of magnesium is not straightforward, although many clinicians are now switching to the use of ionized magnesium from ion selective electrodes. The use of supplemental magnesium in acute flares of asthma has some support in medical literature, especially for those patients with severe disease who fail traditional therapy. Magnesium holds the preeminent position in the treatment of pre-eclampsia and eclampsia in the minds of most obstetricians, who have decades of experience showing it to be both effective and safe. Magnesium is clearly useful for certain types of ventricular tachycardia, and probably assists in the treatment of several types of supraventricular tachycardia. Its role in acute myocardial ischemia is less certain, although there is no benefit once reperfusion therapy has already been carried out. Finally, the role of magnesium in the treatment of acute cerebral insults is an exciting area of active investigation with initial studies suggesting much promise.

Drug treatment of elderly patients with acute myocardial infarction: practical recommendations

Aspirin (acetylsalicylic acid) should be administered to patients on day 1 of an acute myocardial infarction (MI) and continued indefinitely. Early intravenous beta-blockade should be used during acute MI. beta-blockers should be continued indefinitely. Angiotensin-converting enzyme (ACE) inhibitors should be used in patients with acute MI with ST-segment elevation in two or more anterior precordial leads. ACE inhibitors should be used during and after acute MI in patients with chronic heart failure (CHF) or with a left ventricular ejection fraction < or =40%. There are no class I indications for using calcium channel antagonists during and after acute MI. Intravenous heparin should be used in patients with acute MI undergoing coronary revascularisation and in patients at high risk for systemic embolisation. Enoxaparin should be used in patients with non-Q-wave MI. Thrombolytic therapy should be considered in patients with acute MI with ST-segment elevation in contiguous leads of a 12-lead electrocardiogram or with left bundle branch block. Platelet glycoprotein IIb/IIIa inhibitors should be administered intravenously as an adjunct to heparin and aspirin in patients with non-Q-wave MI. Intravenous nitroglycerin should be used: (i) for the first 24 to 48 hours in patients with acute MI and CHF, large anterior MI, persistent ischaemia or hypertension; and (ii) continued beyond 48 hours in patients with recurrent angina pectoris or persistent pulmonary congestion. Long-acting nitrates should be given after MI, along with beta-blockers, to patients with angina pectoris. There are no class I indications for using intravenous magnesium during acute MI. The routine use of antiarrhythmic drugs other than beta-blockers during and after acute MI is not recommended.

A randomized study of intravenous magnesium in acute myocardial infarction treated with direct coronary angioplasty

BACKGROUND

Notwithstanding the negative result of the International Study of Infarct Survival-4 (ISIS-4), the controversy about the role of magnesium in acute myocardial infarction is still open because, according to experimental data, magnesium could decrease myocardial damage and mortality only if infusion is started before reperfusion. This randomized placebo-controlled trial was designed to evaluate the effect of intravenous magnesium, delivered before, during, and after direct coronary angioplasty, in patients with acute myocardial infarction.

METHODS

One-hundred fifty patients were randomized to intravenous magnesium sulfate or placebo. The primary end point was an infarct zone wall motion score index at 30 days, as a measure of infarct size. The secondary end points included creatine kinase peak, ventricular fibrillation/tachycardia within the first 24 hours, death and congestive heart failure within the 30-day follow-up, and 30-day left ventricular ejection fraction. Analysis was by intention to treat.

RESULTS

There were no significant differences between the magnesium and placebo groups in the 30-day infarct zone wall motion score index (1.93 +/- 0.61 vs 1.85 +/- 0.51, P =.39), ventricular arrhythmias (24% vs 15%, P =.15), death (0 vs 1%, P =.32), heart failure (8% vs 7%, P =.75), and 30-day left ventricular ejection fraction (49% +/- 11% vs 50% +/- 9%, P = 0.55). There was a trend toward a higher creatine kinase peak in the magnesium group (3059 +/- 2359 vs 2404 +/- 1673,P =.052).

CONCLUSIONS

Intravenous magnesium delivered before, during, and after reperfusion did not decrease myocardial damage and did not improve the short-term clinical outcome in patients with acute myocardial infarction treated with direct angioplasty.

Low intracellular magnesium levels promote platelet-dependent thrombosis in patients with coronary artery disease

BACKGROUND

Although reduced intracellular levels of magnesium have been described in patients with acute myocardial infarction, its significance as a regulator of thrombosis remains unknown.

METHODS AND RESULTS

To determine whether reduced intracellular levels of magnesium enhance platelet-dependent thrombosis, we evaluated 42 patients with coronary artery disease (CAD) by exposing porcine aortic media to their flowing unanticoagulated venous blood for 5 minutes by using an ex vivo perfusion (Badimon) chamber. Baseline analysis demonstrated significant associations between intracellular levels of magnesium, platelet-dependent thrombosis (P =.02), and platelet P-selectin (CD62P) expression (P <.05). Patients were divided into 2 groups: below (n = 22) and above (n = 20) the median intracellular levels of magnesium (1.12 microg/mg protein). There were no significant differences in age, body mass index, serum lipids, fibrinogen, platelet count, or serum magnesium levels between the two groups. Platelet-dependent thrombosis was significantly higher in patients with intracellular levels of magnesium below compared with above median (150 +/- 128 vs 45 +/- 28 microm(2)/mm, P <.004). Neither platelet aggregation nor CD62P expression was significantly different between the two groups.

CONCLUSIONS

Platelet-dependent thrombosis was significantly increased in patients with stable CAD with low intracellular levels of magnesium, suggesting a potential role for magnesium supplementation in CAD.

Mg(2+)-induced vasodilation in human forearm vasculature is inhibited by N(G)-monomethyl-L-arginine but not by indometacin

We have investigated the mechanism of the vasodilator action of Mg(2+) in human forearm resistance vasculature. Venous occlusion plethysmography was used to measure vasodilator responses to Mg(2+) infused via the brachial artery in healthy men, and to determine effects on Mg(2+) responses of indometacin (an inhibitor of cyclo-oxygenase) and of N(G)-monomethyl-L-arginine (L-NMMA, an inhibitor of the L-arginine/nitric oxide, L-arg/NO, pathway). Magnesium sulphate infusion (0.05, 0.1, 0.2 mmol x min(-1)) increased plasma Mg(2+) concentration to 1.57+/-0.16 mmol x l(-1) in venous blood from the infused arm at the highest dose. There was a dose-related increase in forearm blood flow in the infused arm to a maximum of 6.37+/-1.37 ml x min(-1) x dl forearm(-1) at the highest dose corresponding to an increase of 159+/-25% in blood flow relative to the non-infused arm. There was no tachyphylaxis during a second infusion following a 21-min recovery period. Indometacin had no effect on vasodilator responses to Mg(2+), whereas L-NMMA inhibited Mg(2+) responses (area under the dose-response curve) by 43+/-6% (p = 0.0003 by repeated-measures ANOVA). Therefore the L-arg/NO pathway is responsible, in part, for the vasodilator action of Mg(2+) in human forearm resistance vasculature.

Management of cardiopulmonary resuscitation

Since cardiopulmonary resuscitation was first described in 1960, it has become a standardized medical intervention. Separate guidelines have been developed for the neonatal and pediatric population, but none exist for the elderly population. This review will discuss recent available outcome data on resuscitation of the elderly and the known physiologic changes with aging that may affect decisions made during resuscitation.

Magnesium Therapy for Acute Myocardial Infarction

The use of magnesium therapy for acute myocardial infarction remains controversial despite recent clinical trials such as ISIS-4. Magnesium has numerous beneficial effects in the setting of myocardial infarction, including inhibitory effects on platelet aggregation. Clinical trials of magnesium therapy for myocardial infarction have yielded conflicting results that may be related to the difference in the timing of magnesium administration. Moreover, magnesium may have salutary effects in patients who are ineligible for thrombolytic therapy. Further clinical trials are still needed to elucidate definitively the role of magnesium therapy for myocardial infarction.

Protective effect of intravenous magnesium in acute myocardial infarction following thrombolytic therapy

The role of intravenous magnesium therapy in patients with acute myocardial infarction (AMI) who received thrombolytic therapy is controversial. The results from previous clinical trials were not in consonance. We therefore conducted a prospective, randomized, double-blind, placebo controlled study in 350 patients with confirmed AMI during the period January 1994 to December 1996. The role of intravenous magnesium sulphate therapy (2 g over 5 min followed by 16 g over 24 h) was evaluated in patients with AMI who received thrombolytic therapy. Study group consisted of 169 patients who were administered magnesium sulphate. Control group comprised of 181 patients who were given isotonic saline. Among those in the magnesium group, 70% received magnesium within 6 h after the onset of symptoms. All patients received magnesium immediately after the completion of thrombolytic therapy. Patients were followed up for 30 days after AMI. The number of deaths in the study group was 6 (3.5%) compared with control arm in which 18 patients (9.9%) died (P value <0.01 95% Confidence intervals [CI] 1.2 to 11.6). Ventricular arrhythmias were also less in the magnesium arm; 27 patients (13%) compared with 83 patients (48.6%) in the control arm (P value 0.00001 95% Cl 26.7 to 44.5). In the magnesium group 15 patients (8.8%) had re-infarction compared with 23 patients (12.7%) in the placebo arm (P value not significant). Post myocardial infarction angina was observed in 47 patients (27.8%) in the magnesium arm compared with 60 patients (33.1%) in the placebo arm (P value not significant). The main side effect of intravenous magnesium was transient flushing observed in 152 (90%) patients. Intravenous magnesium sulphate in patients with AMI is a safe and useful adjunct to thrombolytic therapy in reducing the short-term mortality and ventricular arrhythmias after AMI.

Oral magnesium supplementation inhibits platelet-dependent thrombosis in patients with coronary artery disease

The use of magnesium in the treatment of acute myocardial infarction remains controversial despite preliminary experimental evidence that magnesium plays a beneficial role as a regulator of thrombosis. This study examines whether oral magnesium treatment inhibits platelet-dependent thrombosis (PDT) in patients with coronary artery disease (CAD). In a randomized prospective, double-blind, crossover, and placebo-controlled study, 42 patients with CAD (37 men, 5 women, mean age 68 +/- 9 years) on aspirin received either magnesium oxide tablets (800 to 1,200 mg/day) or placebo for 3 months (phase 1) followed by a 4-week wash-out period, and the crossover treatment for 3 months (phase 2). PDT, platelet aggregation, platelet P-selectin flow cytometry, monocyte tissue factor procoagulant activity (TF-PCA), and adhesion molecule density were assessed before and after each phase. PDT was evaluated by an ex vivo perfusion model using the Badimon chamber. Median PDT was significantly reduced by 35% in patients who received magnesium versus placebo (delta change from baseline -24 vs 26 mm2/mm; p = 0.02, respectively). There was no significant effect of magnesium treatment on platelet aggregation, P-selectin expression, monocyte TF-PCA, or adhesion molecules. Oral magnesium treatment inhibited PDT in patients with stable CAD. This effect appears to be independent of platelet aggregation or P-selectin expression, and is evident despite aspirin therapy. These findings suggest a potential mechanism whereby magnesium may beneficially alter outcomes in patients with CAD.

Therapy for acute myocardial infarction in older persons

OBJECTIVE

To review the early management of acute myocardial infarction (AMI) in older adults.

METHODS

Recently published studies relevant to the early management of AMI were systematically reviewed. When possible, the impact of older age on complication rates and clinical outcomes was evaluated.

RESULTS

In general, AMI therapies that are effective in younger patients are also effective in older patients. Conversely, older age is associated with an increased risk of complications from therapy, implying that careful patient selection is required to optimize outcomes while minimizing risks. The principal limitation of currently available data is that relatively few patients older than the age of 80 have been enrolled in prospective randomized clinical trials.

CONCLUSIONS

Thrombolysis and primary angioplasty are effective in establishing reperfusion and improving clinical outcomes in older patients with AMI. In the absence of contraindications, aspirin and beta blockers should be considered standard therapy in AMI patients of all ages, whereas heparin, nitrates, and angiotensin converting enzyme inhibitors are indicated in selected subgroups. At the present time, calcium channel blockers, magnesium, and antiarrhythmic agents are not recommended for routine use in the AMI setting, and the role of glycoprotein IIb/IIIa inhibitors, low molecular weight heparin, and other newer agents await the results of ongoing clinical trials.

[Effect of magnesium on infarct size after coronary occlusion. Animal experiment studies]

In addition to its antiarrhythmic and antithrombotic effects magnesium is said to have a beneficial effect in patients with acute myocardial infarction. Magnesium can protect myocardial tissue after coronary occlusion and reduces infarct size in experimental models of ischaemia and reperfusion, though the given doses of magnesium are relatively high and differ from clinically reachable serum concentrations. We tested 2 hypotheses in a dog model of ischaemia-reperfusion: 1. The protective effect may be due to a direct, local influence of magnesium on myocardial reperfusion injury. 2. Systemic magnesium treatment with low doses comparable to clinical study regiments may reduce myocardial infarct size. Anaesthetized open chest dogs underwent 1 h of left anterior descending artery occlusion followed by 6 h of reperfusion. 1. Ten animals received intracoronary magnesium aspartate (Mg i.c.) or vehicle infusion (control i.c.) for the first hour of reperfusion to increase regional Mg-concentration by 2 mmol/l. 2. Fourteen animals received intravenous infusion with magnesium potassium aspartate (Mg-K i.v.) or vehicle infusion (control i.v.), beginning 1 h before occlusion until the end of the 6 h reperfusion period. Regional magnesium concentration in the Mg i.c.-group increased to 2.7 +/- 1.00 mmol/l at 45 min of reperfusion. Intravenous infusion raised serum magnesium from 0.71 +/- 0.03 mmol/l to 1.29 +/- 0.14 mmol/l in the Mg-K i.v. group (5 min of reperfusion, p < 0.01 vs. baseline). Infarct size after 6 h reperfusion (TTC staining) was similar in both groups of intracoronary treatment (Mg i.c., 20.6 +/- 5.0; control, 24.4 +/- 8.7% of area at risk; p = n.s.) and intravenous treatment (Mg-K i.v. 18.1 +/- 14.8; control 14.1 +/- 12.2% of area at risk; p = n.s.). Neither regional nor systemic magnesium leads to a clinically relevant reduction of infarct size in the regional ischaemic-reperfused dog heart when it is given in clinically usable doses. The beneficial action of systemic Mg is probably not due to an early direct protective effect on ischaemic-reperfused myocardium but to its antiarrhythmic and antithrombotic effects. Possibly only to high doses of Mg applied under experimental conditions can reduce infarct size.

[Value of K+ and Mg2+ in treatment of acute myocardial infarct]

A critical role analysis of literature concerning the effects of intravenous magnesium on arrhythmias and mortality in acute myocardial infarction shows discrepant results and often inappropriate methods. So far neither an antiarrhythmic efficacy nor prophylactic effects with respect to mortality could be demonstrated. In contrast, potassium substitution should be performed in the setting of acute myocardial infarction with documented hypokalemia (K+ < 3.5 mmol/l) because of increased risk of ventricular arrhythmias. According to the documented results of the trials reviewed in this article no recommendations for the routine use of magnesium in myocardial infarction can be given.

Antiarrhythmic effects of increasing the daily intake of magnesium and potassium in patients with frequent ventricular arrhythmias. Magnesium in Cardiac Arrhythmias (MAGICA) Investigators

OBJECTIVES

This study sought to assess potential antiarrhythmic effects of an increase in the daily oral intake of magnesium and potassium in patients with frequent ventricular arrhythmias.

BACKGROUND

Magnesium and potassium contribute essentially to the electrical stability of the heart. Despite experimental and clinical evidence for the antiarrhythmic properties of the two minerals, controlled data in patients with stable ventricular arrhythmias are lacking.

METHODS

In a randomized, double-blind study, 232 patients with frequent ventricular arrhythmias (> 720 ventricular premature beats [VPBs]/24 h) confirmed at baseline and after 1 week of placebo therapy were subsequently treated over 3 weeks with either 6 mmol of magnesium/12 mmol of potassium-DL-hydrogenaspartate daily or placebo.

RESULTS

Compared with placebo pretreatment, active therapy resulted in a median reduction of VPBs by -17.4% (p = 0.001); the suppression rate was 2.4 times greater than that in patients randomized to 3 weeks of placebo therapy (-7.4%, p = 0.038). The likelihood of a > or = 60% (predefined criterion) or > or = 70% suppression rate (calculated from the placebo-controlled run-in period) was 1.7 (25% vs. 15%, p = 0.044) and 1.5 times greater in the active than in the placebo group (20% vs. 13%, p = 0.085), respectively. No effect of magnesium and potassium administration was observed on the incidence of repetitive and supraventricular arrhythmias and clinical symptoms of the patients.

CONCLUSIONS

To our knowledge, this study is the first to provide controlled data on the antiarrhythmic effect of oral administration of magnesium and potassium salts when directed to patients with frequent and stable ventricular tachyarrhythmias. A 50% increase in the recommended minimum daily dietary intake of the two minerals for 3 weeks results in a moderate but significant antiarrhythmic effect. However, with the given therapeutic regimen, repetitive tachyarrhythmias and patient symptoms remain unchanged.

The role of magnesium therapy in acute myocardial infarction

Magnesium possesses numerous salutary effects for the treatment of acute myocardial infarction (AMI). It is a coronary vasodilator, calcium antagonist, afterload reducer, antiarrhythmic, and antiplatelet drug that modulates autonomic function and limits reperfusion injury when administered early in infarction. Various clinical trials of magnesium therapy for AMI have proffered conflicting results as to the efficacy of magnesium therapy because of significant differences in the timing of magnesium administration. Additional clinical trials that focus on early administration of magnesium are warranted to delineate the role of magnesium therapy for AMI.

Safety, tolerability, and efficacy of a glucose-insulin-potassium-magnesium-carnitine solution in acute myocardial infarction

Fifty-four patients with AMI were treated with a front-loaded 15-hour infusion of hypertonic glucose, insulin, potassium, magnesium, and L-carnitine in addition to usual therapy. This metabolic solution was well tolerated, free of serious side effects, and reduced the incidence of morbid events.

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.