Rationale and design of the Magnesium in Coronaries (MAGIC) study: A clinical trial to reevaluate the efficacy of early administration of magnesium in acute myocardial infarction

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 ST-segment elevation myocardial infarction and prior stroke: an analysis from the Magnesium in Coronaries (MAGIC) trial

BACKGROUND

Patients with prior stroke represent a substantial proportion of patients presenting with acute ST-segment elevation myocardial infarction (STEMI). However, the impact of prior stroke on prognosis has not been rigorously examined in the reperfusion era.

METHODS

The baseline characteristics, treatments, and clinical outcomes of patients with prior stroke enrolled in the Magnesium in Coronaries (MAGIC) trial were evaluated and compared to those of patients without prior stroke.

RESULTS

MAGIC enrolled 6213 patients with STEMI, of whom 558 (9.0%) had prior stroke. Patients with prior stroke were more likely to have a history of hypertension (88.0% vs 70.3%), diabetes (19.9% vs 14.5%), myocardial infarction (38.2% vs 25.1%), and congestive heart failure (15.6% vs 9.7%). The mean Thrombolysis in Myocardial Infarction Risk Score was higher in patients with prior stroke compared to those without prior stroke (4.37 vs 3.93, P < .0001). Patients with prior stroke were less likely to receive reperfusion therapy, even among those considered eligible at presentation (66.3% vs 80.6%, P < .0001). Compared to patients without prior stroke, inhospital stroke (3.0% vs 1.0%, P < .0001), severe congestive heart failure (23.3% vs 18.2%, P = .003), and 30-day mortality (21.0% vs 14.7%, P < .0001) were higher among patients with prior stroke. On multivariable analysis, prior stroke was independently associated with a significantly higher risk of death at 30 days (odds ratio 1.44, P = .0023).

CONCLUSIONS

Patients with prior stroke who present with STEMI are at very high risk for short-term morbidity and mortality. Aggressive treatment of these patients appears warranted.

Magnesium decreases cardiac injury in patients undergoing coronary artery bypass surgery

BACKGROUND

The calcium-channel blocking effect of magnesium might have protective effects in patients undergoing cardiopulmonary bypass surgery. We assessed the effects of magnesium on hearts undergoing coronary artery bypass surgery with intermittent warm blood hyperkalemic cardioplegia in the antegrade fashion.

PATIENTS AND METHODS

Twenty patients undergoing coronary bypass surgery were randomly divided into two groups, a control group who received intermittent antegrade warm blood hyperkalemic cardioplegia for myocardial protection, and a study group who received the same solution with the addition of magnesium to the cardioplegia. Extracellular substrates (creatinine phosphokinase, creatinine phosphokinase-MB group, lactate dehydrogenase, c-reactive protein, and cardiac troponin I were measured preoperatively and postoperatively.

RESULTS

There were significant differences in the post-operative concentrations of creatinine phosphokinase, creatinine phosphokinase-MB group, c-reactive protein, and lactate dehydrogenase after cardiopulmonary bypass (P<0.001) in the study group compared with the control subjects. Cardiac troponin I levels were also significantly lower in the study group after cardiopulmonary bypass (P<0.005).

CONCLUSIONS

Our study indicates that if magnesium is added to intermittent antegrade warm blood hyperkalemic cardioplegia, blood levels of many markers of cardiac myocardial injury after cardiopulmonary bypass are lowered. This finding may have implications for myocardial protection.

Realism in evidence based medicine: interpreting the randomised controlled trial

Realism is emerging as a paradigm for research and explanation in the natural and social sciences. A realist framework is elaborated and applied to the four possible situations that may generate the observations of randomised, controlled trials. It is demonstrated that by using two realist concepts "mechanism" and "context" a number of misinterpretations of such trials from within the dominant empiricist paradigm may be rectified. Evidence based medicine should adopt realism to temper a misleading empiricism, this will involve relegating statistical arguments to their proper subsidiary place and adopting an adequate theory of causation.

The therapeutic use of magnesium in anesthesiology, intensive care and emergency medicine: a review

PURPOSE

To review current knowledge concerning the use of magnesium in anesthesiology, intensive care and emergency medicine.

METHODS

References were obtained from Medline(R) (1995 to 2002). All categories of articles (clinical trials, reviews, or meta-analyses) on this topic were selected. The key words used were magnesium, anesthesia, analgesia, emergency medicine, intensive care, surgery, physiology, pharmacology, eclampsia, pheochromocytoma, asthma, and acute myocardial infarction.

PRINCIPLE FINDINGS

Hypomagnesemia is frequent postoperatively and in the intensive care and needs to be detected and corrected to prevent increased morbidity and mortality. Magnesium reduces catecholamine release and thus allows better control of adrenergic response during intubation or pheochromocytoma surgery. It also decreases the frequency of postoperative rhythm disorders in cardiac surgery as well as convulsive seizures in preeclampsia and their recurrence in eclampsia. The use of adjuvant magnesium during perioperative analgesia may be beneficial for its antagonist effects on N-methyl-D-aspartate receptors. The precise role of magnesium in the treatment of asthmatic attacks and myocardial infarction in emergency conditions needs to be determined.

CONCLUSIONS

Magnesium has many known indications in anesthesiology and intensive care, and others have been suggested by recent publications. Because of its interactions with drugs used in anesthesia, anesthesiologists and intensive care specialists need to have a clear understanding of the role of this important cation.

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.

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.

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.

Being sceptical about meta-analyses: a Bayesian perspective on magnesium trials in myocardial infarction

BACKGROUND

There has been extensive discussion of the apparent conflict between meta-analyses and a mega-trial investigating the benefits of intravenous magnesium following myocardial infarction, in which the early trial results have been said to be 'too good to be true'.

METHODS

We apply Bayesian methods of meta-analysis to the trials available before and after the publication of the ISIS-4 results. We show how scepticism can be formally incorporated into an analysis as a Bayesian prior distribution, and how Bayesian meta-analysis models allow appropriate exploration of hypotheses that the treatment effect depends on the size of the trial or the risk in the control group.

RESULTS

Adoption of a sceptical prior would have led early enthusiasm for magnesium to be suitably tempered, but only if combined with a random effects meta-analysis, rather than the fixed effect analysis that was actually conducted.

CONCLUSIONS

We argue that neither a fixed effect nor a random effects analysis is appropriate when the mega-trial is included. The Bayesian framework provides many possibilities for flexible exploration of clinical hypotheses, but there can be considerable sensitivity to apparently innocuous assumptions.

The reperfusion era. Strategies for establishing or maintaining coronary patency

Only 3 decades ago, controversy existed over the origin of the thrombus that occluded coronary arteries during myocardial infarction (MI). Then, the acute clinical angiographic studies of DeWood butterssed new pathological and experimental evidence that the thrombus was the proximate cause of MI and unstable angina. The remaining years of the 20th century saw an explosion of knowledge delineating a spectrum of related disorders now collectively called acute coronary syndromes (ACS). The clinician managing patients is confronted with an array of evidence as more than 75,000 patients worldwide have been randomized to clinical trials in ACS. This article reviews key pathophysiological concepts, presents an initial strategy for triage of patients, and summarizes evidence-based medicine guiding therapy for acute coronary lesions.

Acute ischemic syndromes. Adjunctive therapy

The acute coronary syndromes (ACS) represent a heterogeneous group of patients along a continuum of risk from unstable angina to non-ST-segment elevation myocardial infarction. ACS is a term that has been used to describe the constellation of clinical symptoms that represent acute myocardial ischemia. This article reviews the adjunctive medications that are used during emergency cardiovasculare care for the early management of patients experiencing the ACS. The adjunctive therapies are divided into early immediate treatment and then subsequent management in the acute care setting.

Statistical significance versus clinical relevance in cardiovascular medicine

Evidence-based medicine is the foundation of everyday clinical practices and large clinical trials investigating the effects of various interventions on morbidity and survival and generally provide the most robust evidence. Cardiovascular medicine is considered one of the most evidence-based disciplines of medicine. However, there are a number of limitations to the general applicability of clinical trial results in cardiovascular medicine. Although generally useful to the clinician, clinical trials have often been suboptimally designed from 1 or several points of view. As a consequence of flaws in the design and the execution of the trials, statistical significance is quite often not equal to clinical relevance. This article outlines some of the shortcomings of designing and carrying out clinical trials, as well as inadequacies concerning the publication, interpretation, and implementation of the trial results. Evidence-based medicine is obviously not always as solid as one might think.

Using Bayesian inference to perform meta-analysis

Bayesian modeling offers an elegant approach to meta-analysis that efficiently incorporates all sources of variability and relevant quantifiable external information. It provides a more informative summary of the likely value of parameters after observing the data than do non-Bayesian approaches. This leads to direct probabilistic inference about model parameters such as the average treatment effect, the between-study variance, and individual study treatment effects. The latter are weighted averages of the common mean and individual study means with weights reflecting the amount of information provided by each study relative to the others. Homogeneity among these posterior study estimates indicates that pooling these studies is appropriate; heterogeneity suggests that some cause of between-study variation should be explored. The author describes the construction of such models and shows how to use them to estimate a common mean and regression slopes. Two examples illustrate the additional inferences available with the Bayesian methodology.