Serum magnesium and potassium in acute myocardial infarction: relationship to existing beta-blockade and infarct size

Serum potassium levels and mortality of patients with acute myocardial infarction: A systematic review and meta-analysis of cohort studies

BACKGROUND

The evidence of current epidemiological studies investigating the association between serum potassium levels and mortality of acute myocardial infarction (AMI) patients is controversial and inadequate.

DESIGN

Systematic review and meta-analysis.

METHODS

Two researchers independently searched the PubMed, EMBASE and Web of Science databases to identify observational studies published prior to 31 October 2017. Similarly, two researchers separately extracted data and any differences were resolved by discussion. Pooled relative risks and 95% confidence intervals (CIs) were computed with an inverse variance-weighted random-effects model. Heterogeneity among studies was assessed with the I² statistic.

RESULTS

Seven cohort studies were included for analysis. Compared with the reference group (3.5 to <4.0 mEq/L), the pooled relative risks of mortality were 1.15 (95% CI = 1.00-1.32), 1.09 (95% CI = 0.97-1.24), 1.42 (95% CI = 1.19-1.70) and 1.85 (95% CI = 1.39-2.47) for AMI patients with a potassium level of<3.5, 4.0 to <4.5, 4.5 to <5.0, and ≥5.0 mEq/L, respectively. For admission and post-admission potassium, although J-shaped associations were also indicated, non-significant results were observed for AMI patients with potassium levels of <3.5 mEq/L when compared with the reference group. Notably, in subgroup analyses of study characteristics, stratified by study quality, geographic location, type of outcome, number of cases, type of AMI, and adjustment for potential confounders, the findings were broadly consistent across strata.

CONCLUSIONS

These findings indicate that both lower (<3.5 mEq/L) and higher (≥4.5 mEq/L) serum potassium levels are associated with an increased risk of mortality of patients with AMI.

Serum Potassium Levels and Short-Term Outcomes in Patients With ST-Segment Elevation Myocardial Infarction

Current guidelines recommend maintaining serum potassium levels between 4.0 and 5.0 mEq/L (1 mEq/L = mmol/L) in patients with acute myocardial infarction. However, these guidelines are based on studies conducted before the β blocker and reperfusion era. We retrospectively analyzed 6613 patients diagnosed with ST-segment elevation myocardial infarction (STEMI) who presented without renal insufficiency. Patients were categorized into 5 groups according to mean serum potassium levels: <3.5, 3.5 to <4.0, 4.0 to <4.5, 4.5 to <5.0, and ≥5.0 mEq/L. Patients with potassium levels of 4.0 to <4.5 mEq/L had the lowest predefined event rates, which were 6.4% for 7-day malignant arrhythmia, 3.7% for 7-day mortality, and 5.3% for 30-day mortality. Compared with the reference group (4.0 to <4.5 mEq/L), multivariate regression analysis revealed significantly higher 30-day mortality risk in patients with potassium level of 4.5 to <5.0 (hazard ratio [HR]: 1.52, 95% confidence interval [CI]: 1.17-1.98; P = .002) and even higher risk in patients with potassium level of ≥5.0 mEq/L (HR: 1.80, 95% CI: 1.22-2.66; P = .002). The lowest 30-day mortality was observed in patients with STEMI having potassium levels between 4.0 and 4.5 mEq/L, and a level >4.5 mEq/L significantly increased mortality risk.

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.

[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.