Low blood mononuclear cell magnesium in intensive cardiac care unit patients

Effect of Magnesium on Ventricular Extrasystoles in Children

Magnesium (Mg) is a crucial element for cardiovascular system and its deficiency results in a variety of cardiac arrhythmias. The aim of this study is to determine the effect of oral Mg supplementation on the frequency of ventricular extrasystoles (VES) in children. Magnesium supplementation was given to 42 children who had VES without structural heart disease. Clinical, electrocardiographic, and Holter monitoring studies were reviewed. The mean baseline 24 h VES burden on Holter monitoring was 10.26% ± 4.13% and it was decreased to 6.62% ± 3.88% after. There was no significant difference between the pre-treatment serum Mg levels and the decrease in the frequency of VES. In conclusion, oral Mg therapy was found to be effective at suppressing VES in children regardless of serum Mg levels. Large and randomized studies are needed to demonstrate the effect of magnesium on VES suppression.

Magnesium Disorders and Prognosis in Heart Failure: A Systematic Review

Magnesium is an essential mineral for the human body and plays an important role in cardiovascular health. Hypomagnesaemia has been linked with increased cardiovascular mortality in heart failure; however, previous studies have yielded conflicting results. Even fewer studies have addressed the association between hypermagnesemia and prognosis in heart failure. The aim of the present systematic review was to investigate the association of serum magnesium levels with cardiovascular and all-cause mortality in patients with heart failure and reduced ejection fraction (HFrEF). Cardiovascular morbidity, referring to heart failure rehospitalizations and ventricular arrhythmias, was also investigated. Eligible studies were identified by searching PubMed and Scopus. The Quality in Prognosis (QUIPS) tool was used to assess the quality of included studies. Eight studies (total of 13,539 patients with HFrEF) that assessed the effects of serum magnesium levels on cardiovascular mortality, all-cause mortality, and cardiovascular morbidity met inclusion criteria. In half of the studies, hypomagnesemia was found to be an independent risk factor for cardiovascular mortality, including sudden cardiac death. Only 1 study reported that hypermagnesemia (serum magnesium levels above 2.4 mg/dL) is a prognostic factor for noncardiac mortality suggesting that hypermagnesemia is more likely an indicator of comorbidities rather than a true independent prognostic marker. Finally, low serum magnesium levels were not associated with readmissions for heart failure or ventricular arrhythmias in patients with HFrEF.

Preoperative Ionized Magnesium Levels and Risk of Acute Kidney Injury After Cardiac Surgery

RATIONALE & OBJECTIVE

Although postoperative acute kidney injury (AKI) is a serious complication after cardiac surgery, preventive measures are limited. Despite the known association of preoperative low magnesium levels with cardiac surgery-related atrial fibrillation, the association between preoperative magnesium concentration and postoperative AKI has not been fully elucidated. This study evaluated the association between preoperative serum magnesium level and the development of AKI after cardiac surgery.

STUDY DESIGN

Retrospective observational cohort study.

SETTING & PARTICIPANTS

Patients aged≥18 years who underwent cardiac surgery at 2 South Korean tertiary hospitals between 2006 and 2020 were identified from medical records. Patients with missing information, an estimated glomerular filtration rate<15mL/min/1.73m², receiving maintenance dialysis, or a history of AKI treated by dialysis within 1 year before surgery were excluded.

EXPOSURE

Preoperative serum magnesium levels.

OUTCOME

Postoperative AKI within 48 hours after surgery, defined using the Acute Kidney Injury Network (AKIN) criteria, and dialysis-treated AKI within 30 days after surgery.

ANALYTICAL APPROACH

Multivariable logistic regression analysis.

RESULTS

Among the 9,766 patients (median age, 64.0 years; 60.1% male), postoperative AKI and dialysis-treated AKI were observed in 40.1% and 4.3% patients, respectively. Postoperative AKI was more prevalent in patients with lower serum magnesium levels (44.9%, 41.4%, 39.4%, and 34.8% in quartiles 1-4, respectively). Multivariable logistic regression analysis revealed that the odds ratios (ORs) for postoperative AKI were progressively larger across progressively lower quartiles of serum magnesium concentration (adjusted ORs of 1.53 [95% CI, 1.33-1.76], 1.29 [95% CI, 1.12-1.48], 1.15 [95% CI, 1.01-1.31] for quartiles 1-3, respectively, relative to quartile 4, P for trend<0.001). Preoperative hypomagnesemia (serum magnesium level<1.09mg/dL) was also significantly associated with AKI (adjusted OR, 1.39 [95% CI, 1.10-1.77]) and dialysis-treated AKI (adjusted OR, 1.67 [95% CI, 1.02-2.72]).

LIMITATIONS

Causality could not be evaluated in this observational study.

CONCLUSIONS

Lower serum magnesium levels were associated with a higher incidence of AKI in patients undergoing cardiac surgery.

Magnesium Depletion Score (MDS) Predicts Risk of Systemic Inflammation and Cardiovascular Mortality among US Adults

BACKGROUND

Kidney reabsorption of magnesium (Mg) is essential for homeostasis.

OBJECTIVES

We developed and validated models with the kidney reabsorption-related magnesium depletion score (MDS) to predict states of magnesium deficiency and disease outcomes.

METHODS

MDS was validated in predicting body magnesium status among 77 adults (aged 62 ± 8 y, 51% men) at high risk of magnesium deficiency in the Personalized Prevention of Colorectal Cancer Trial (PPCCT) (registered at clinicaltrials.gov as NCT01105169) using the magnesium tolerance test (MTT). We then validated MDS for risk stratification and for associations with inflammation and mortality among >10,000 US adults (weighted: aged 48 ± 0.3 y, 47% men) in the NHANES, a nationally representative study. A proportional hazards regression model was used for associations between magnesium intake and the MDS with risks of total and cardiovascular disease (CVD) mortality.

RESULTS

In the PPCCT, the area under the receiver operating characteristic (ROC) curve (AUC) for magnesium deficiency was 0.63 (95% CI: 0.50, 0.76) for the model incorporating the MDS with sex and age compared with 0.53 (95% CI: 0.40, 0.67) for the model with serum magnesium alone. In the NHANES, mean serum C-reactive protein significantly increased with increasing MDS (P-trend < 0.01) after adjusting for age and sex and other covariates, primarily among individuals with magnesium intake less than the Estimated Average Requirement (EAR; P-trend < 0.05). Further, we found that low magnesium intake was longitudinally associated with increased risks of total and CVD mortality only among those with magnesium deficiency predicted by MDS. MDS was associated with increased risks of total and CVD mortality in a dose-response manner only among those with magnesium intake less than the EAR.

CONCLUSIONS

The MDS serves as a promising measure in identifying individuals with magnesium deficiency who may benefit from increased intake of magnesium to reduce risks of systemic inflammation and CVD mortality. This lays a foundation for precision-based nutritional interventions.

Comparison of two methods for the assessment of intra-erythrocyte magnesium and its determinants: Results from the LifeLines cohort study

BACKGROUND

Direct methods for the assessment of intra-erythrocyte magnesium (dIEM) require extensive sample preparation, making them labor intensive. An alternative, less labor intensive method is indirect calculation of intra-erythrocyte magnesium (iIEM). We compared dIEM and iIEM and studied determinants of dIEM and iIEM, plasma magnesium and 24-h urinary magnesium excretion in a large population-based cohort study.

METHODS

dIEM and iIEM were measured using a validated inductively coupled plasma mass spectrometry (ICP-MS) method in 1669 individuals from the second screening from the LifeLines Cohort Study. We used linear regression analyses to study the determinants of IEM, plasma magnesium and 24-h urinary magnesium excretion.

RESULTS

Mean dIEM and iIEM were 0.20 ± 0.04 mmol/10¹² cells and 0.25 ± 0.04 mmol/10¹² cells, respectively. We found a strong correlation between dIEM and iIEM (r = 0.75). Passing-Bablok regression analyses showed an intercept of 0.015 (95% CI: 0.005; 0.023) and a slope of 1.157 (95% CI: 1.109; 1.210). In linear regression analyses, plasma levels of total- and LDL -cholesterol, and triglycerides were positively associated dIEM, iIEM, and plasma magnesium, while glucose and HbA1c were inversely associated with plasma magnesium.

CONCLUSIONS

We observed a strong correlation between dIEM and iIEM, suggesting that iIEM is a reliable alternative for the labor intensive dIEM method.

Magnesium Balance and Measurement

Magnesium is an essential ion in the human body, playing an important role in practically every major metabolic and biochemical process, supporting and maintaining cellular processes critical for human life. Magnesium plays an important physiological role, particularly in the brain, heart, and skeletal muscles. As the second most abundant intracellular cation after potassium, it is involved in over 600 enzymatic reactions including energy metabolism and protein synthesis. Magnesium has been implicated in and used as treatment of several diseases. Although the importance of magnesium is widely acknowledged, routine serum magnesium levels are not routinely evaluated in clinical medicine. This review provides a discussion as to where magnesium is stored, handled, absorbed, and excreted. We discuss approaches for the assessment of magnesium status.

Subclinical magnesium deficiency: a principal driver of cardiovascular disease and a public health crisis

Because serum magnesium does not reflect intracellular magnesium, the latter making up more than 99% of total body magnesium, most cases of magnesium deficiency are undiagnosed. Furthermore, because of chronic diseases, medications, decreases in food crop magnesium contents, and the availability of refined and processed foods, the vast majority of people in modern societies are at risk for magnesium deficiency. Certain individuals will need to supplement with magnesium in order to prevent suboptimal magnesium deficiency, especially if trying to obtain an optimal magnesium status to prevent chronic disease. Subclinical magnesium deficiency increases the risk of numerous types of cardiovascular disease, costs nations around the world an incalculable amount of healthcare costs and suffering, and should be considered a public health crisis. That an easy, cost-effective strategy exists to prevent and treat subclinical magnesium deficiency should provide an urgent call to action.

Temporal changes in circulating P-selectin, plasminogen activator inhibitor-1, magnesium, and creatine kinase after percutaneous coronary intervention

OBJECTIVE

This study aims to determine the mechanisms underlying restenosis and ischemia-reperfusion injury of the myocardium after percutaneous coronary intervention (PCI).

METHODS

The present study examined serial changes (5 min, 30 min, 2 h, 6 h, and 24 h after PCI) in circulating P-selectin, plasminogen activator inhibitor-1 (PAI-1), magnesium (Mg), and creatine kinase-myocardial band fraction (CK-MB) levels, which may be associated with restenosis and myocardial injury in patients undergoing PCI. The occurrence rates of major adverse cardiovascular events were collected over a six-month follow-up.

RESULTS

PCI induced an early elevation of P-selectin, which correlated positively with the inflation pressure used in the PCI procedure. PCI also caused a significant and sustained decrease in serum Mg in PCI patients, without an effect on PAI-1. An increase in CK-MB was observed in PCI patients, although values were within normal reference range. In addition, elevated P-selectin and decreased Mg measured shortly after the coronary angioplasty procedure were associated with recurrent treatment and heart failure, respectively.

CONCLUSIONS

Our study demonstrates that PCI induces temporal changes of P-selectin, Mg, and CK-MB, which may be involved in restenosis and ischemia-reperfusion injury. These findings highlight the need for using antiplatelet therapy and Mg to reduce the risks associated with PCI.

Magnesium administration may improve heart rate variability in patients with heart failure

BACKGROUND AND AIM

Intracellular magnesium (icMg) depletion may coexist with normomagnesemia. Mg deficiency (serum and/or intracellular) and decreased heart rate variability (HRV) are common in heart failure (HF). Since both are predictors of poor prognosis, it was of interest to evaluate the effect of Mg supplementation on HRV in patients with HF.

METHODS AND RESULTS

We investigated the effect of Mg administration on HRV in normomagnesemic patients with systolic HF. HRV, serum Mg and icMg were determined before and after 5-week 300 mg/day Mg citrate treatment in 16 patients (group 1). The control group included 16 Mg-non-treated HF patients (group 2). HRV was determined by a non-linear dynamics analysis, derived from the chaos theory, which calculates HRV-correlation dimension (HRV-CD). After 5 weeks, serum Mg (mmol/l) increased more significantly in group 1 (from 0.78+/-0.04 to 0.89+/-0.06, p<0.001), than in group 2 (from 0.79+/-0.07 to 0.84+/-0.06, p=0.042). IcMg and HRV-CD increased significantly only in group 1 (from 59+/-7 to 66+/-9 mmol/g cell protein, p=0.025, and from 3.47+/-0.42 to 3.94+/-0.36, p<0.001, respectively). In group 2, the differences in the respective parameters were 63+/-12 to 66+/-9 mmol/g cell protein (p=0.7) and 3.59+/-0.42 to 3.55+/-0.4 (p=0.8).

CONCLUSION

Mg administration to normomagnesemic patients with systolic HF increases serum Mg, icMg and HRV-CD. Increasing of HRV by Mg supplementation may prove beneficial to HF patients.

Cellular magnesium acquisition: an anomaly in embryonic cation homeostasis

The intracellular dominance of magnesium ion makes clinical assessment difficult despite the critical role of Mg(++) in many key functions of cells and enzymes. There is general consensus that serum Mg(++) levels are not representative of the growing number of conditions for which magnesium is known to be important. There is no consensus method or sample source for testing for clinical purposes. High intracellular Mg(++) in vertebrate embryos results in part from interactions of cations which influence cell membrane transport systems. These are functionally competent from the earliest stages, at least transiently held over from the unfertilized ovum. Kinetic studies with radiotracer cations, osmolar variations, media lacking one or more of the four biological cations, Na(+), Mg(++), K(+), and Ca(++), and metabolic poison 0.05 mEq/L NaF, demonstrated that: (1) all four cations influence the behavior of the others, and (2) energy is required for uptake and efflux on different time scales, some against gradient. Na(+) uptake is energy dependent against an efflux gradient. The rate of K(+) loss is equal with or without fluoride, suggesting a lack of an energy requirement at these stages. Ca(++) efflux took twice as long in the presence of fluoride, likely due in part to intracellular binding. Mg(++) is anomalous in that early teleost vertebrate embryos have an intracellular content exceeding the surrounding sea water, an isolated unaffected yolk compartment, and a clear requirement for energy for both uptake and efflux. The physiological, pathological, and therapeutic roles of magnesium are poorly understood. This will change: (1) when (28)Mg is once again generally available at a reasonable cost for both basic research and clinical assessment, and (2) when serum or plasma levels are determined simultaneously with intracellular values, preferably as part of complete four cation profiles. Atomic absorption spectrophotometry, energy-dispersive x-ray analysis, and inductively coupled plasma emission spectroscopy on sublingual mucosal and peripheral blood samples are potential methods of value for coordinated assessments.

Effect of various clinical variables on total intracellular magnesium in hospitalized normomagnesemic diabetic patients before discharge

Deficiency of intracellular magnesium (icMg) may coexist with normal serum Mg levels. Little is known about clinical and pharmacological factors affecting icMg in normomagnesemic patients with diabetes mellitus (DM). Moreover, no information exists regarding the icMg state in diabetic patients after acute illness and before hospital discharge. We have evaluated the effect of antihyperglycemic medications and other relevant clinical variables on icMg in 119 such patients. Total icMg was measured in peripheral blood mononuclear cells. Twenty healthy volunteers served as controls. IcMg content (microg/mg cell protein) was lower in DM compared to controls (1.74 +/- 0.44 vs 2.4 +/- 0.39, p < 0.001). It was also significantly lower in patients treated with insulin (1.57 +/- 0.31 vs 1.8 +/- 0.46, p = 0.01), while metformin treatment was associated with higher icMg (1.86 +/- 0.49 vs 1.63 +/- 0.35, p = 0.003). After adjustment for age, gender, and concomitant use of other hypoglycemic drugs, only treatment with metformin was independently associated with increased icMg (p = 0.03). No statistically significant association or correlation was found between icMg content and age, causes of hospitalization, comorbid conditions, treatment with other drugs, concentrations of HbA1c, serum glucose, Mg, or creatinine. In conclusion, icMg is depleted in normomagnesemic DM patients. Insulin treatment is associated with worsening of icMg status, while metformin treatment may confer protective effect.

Intracellular magnesium in elderly patients with heart failure: effects of diabetes and renal dysfunction

Hypomagnesemia is frequent in diabetes mellitus (DM), while renal dysfunction (RD) may be associated with hypermagnesemia. Severe cardiac arrhythmias and other adverse clinical manifestations are frequent in heart failure (HF), in DM and in RD. Depletion of intracellular magnesium (icMg), which may coexist with normal serum Mg, might contribute to these deleterious effects. However, icMg content in normomagnesemic HF patients with RD or DM has not been studied. We assessed total icMg in peripheral blood mononuclear cells (PBMC) from 80 normomagnesemic furosemide-treated HF patients who were divided as follows: subgroups A (DM), B (RD), C (DM and RD), and D (free of DM or RD). PBMC from 18 healthy volunteers served as controls. IcMg content (microg/mg cell protein) in HF was lower compared to controls (1.68+/-0.2 vs. 2.4+/-0.39, p<0.001). In the entire HF group, a significant inverse correlation was evident between icMg and serum creatinine (r=-0.37) and daily furosemide dosages (r=-0.121). IcMg in the HF subgroups A, B, C, and D was 1.79+/-0.23, 1.57+/-0.23, 1.61+/-0.25, and 1.79+/-0.39, respectively (p=0.04 between A and B, p=0.08 between B and D, and non-significant in the remaining comparisons). Serum Mg, potassium, calcium, furosemide dosages and left ventricular ejection fraction were comparable in all subgroups. In conclusion, icMg depletion was demonstrable in PBMC, which may be responsible for some of the adverse clinical manifestations in HF patients. In particular, icMg depletion in RD might contribute to cardiac arrhythmias in this patient group. Mg supplementation to normomagnesemic HF patients might therefore prove beneficial.

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.

A Randomized Controlled Trial of Magnesium Sulfate, in Addition to Usual Care, for Rate Control in Atrial Fibrillation

STUDY OBJECTIVES

We examine the safety and efficacy of magnesium sulfate infusion, in addition to usual care, for acute rate reduction in patients with atrial fibrillation and a rapid ventricular response rate.

METHODS

This was a prospective, randomized, double-blind, placebo-controlled trial of intravenous magnesium sulfate in adult emergency department patients with rapid atrial fibrillation. Study solutions were given in addition to any therapy the treating physician would normally consider appropriate, including the use of standard rate-reduction agents. Patients received either 20 mEq (2.5 g, 10 mmol) magnesium sulfate over a 20-minute period, followed by 20 mEq (2.5 g, 10 mmol) over a 2-hour period intravenously, or placebo.

RESULTS

One hundred ninety-nine patients were randomized, 102 to receive magnesium sulfate and 97 to receive placebo. The antiarrhythmic drug most commonly used by treating physicians was digoxin. Magnesium sulfate was more likely than placebo to achieve a pulse rate of less than 100 beats/min (63 [65%] of 97 versus 32 [34%] of 93, relative risk [RR] 1.89; 95% confidence interval [CI] 1.38 to 2.59; P <.0001) and more likely to convert to sinus rhythm (25 [27%] of 94 patients versus 11 [12%] of 91 patients; RR 2.20; 95% CI 1.15 to 4.21; P =.01). Comparative mean pulse rate reductions in the magnesium sulfate group did not reach predetermined clinical significance levels (> or =15 beats/min reduction) at any of the measured time points. Magnesium sulfate was more likely to be associated with an adverse event (14 [15%] of 95 patients versus 5 [5%] of 92 patients; RR 2.71; 95% CI 1.02 to 7.23; P =.04).

CONCLUSION

Magnesium sulfate, when used to supplement other standard rate-reduction therapies, enhances rate reduction and conversion to sinus rhythm in patients with rapid atrial fibrillation.

Do intracellular, extracellular or urinary magnesium concentrations predict renal retention of magnesium in critically ill patients?

BACKGROUND AND OBJECTIVE

Magnesium disorders are common in hospitalized patients. In patients with low or normal magnesium, the intravenous magnesium loading test has been demonstrated to be a sensitive test to assess magnesium deficiency in critically ill patients. However, it is more time consuming and more difficult than the measurement of intracellular or extracellular magnesium concentrations. This study evaluated whether erythrocyte, plasma and urinary magnesium concentrations predict renal magnesium retention measured by th magnesium loading test.

METHODS

One-hundred-and-three intensive care patients (36 females, 67 males) in a tertiary care centre and 41 healthy subjects (13 females, 28 males) took part in this prospective study. Intracellular, total plasma, ionize extracellular and urinary magnesium concentrations were measured and also magnesium retention by intravenous magnesium loading test.

RESULTS

Total plasma magnesium concentration was poorly correlated with magnesium retention (r = 0.36 r2 = 0.13) and was the only parameter that significantly predicted magnesium retention in intensive care patients (P < 0.01). However, only 10% of the magnesium retention data were linked to the total plasma magnesium concentration.

CONCLUSIONS

Total plasma magnesium concentration predicts magnesium retention in critically ill intensive care patients but not intracellular and urinary magnesium concentrations. Only a small proportion of the magnesium retention was due to the total plasma magnesium concentration.

Reduced intracellular Mg concentrations in patients with acute asthma

STUDY OBJECTIVES

To determine the intracellular and extracellular Mg concentrations in patients with acute asthma and their correlation with parameters expressing the disease severity.

PATIENTS

Thirty patients with acute asthma (FEV(1), 56% predicted [SD, 14.5]), 20 patients with stable asthma (FEV(1), 97% predicted [SD, 10]), and 20 healthy subjects (FEV(1), 97% predicted [SD, 8]).

METHODS

Mg concentrations in erythrocytes and plasma were measured four times: at hospital admission, after 2 days, after 5 days, and at hospital discharge. Percentage of predicted FEV(1) and peak expiratory flow rate variability were recorded simultaneously. Similar measurements were carried in all study groups.

RESULTS

Mg concentrations of healthy subjects and patients with stable asthma remained unchanged in both plasma and erythrocytes. Initial Mg content in erythrocytes was significantly lower in patients with acute asthma (1.77 fmmol per cell; 95% confidence interval [CI], 1.71 to 1.83) compared to normal subjects (1.94 fmmol per cell; 95% CI, 1.82 to 2.00) and patients with stable asthma (1.92 fmmol per cell; 95% CI, 1.87 to 1.96) [p < 0.0001], and it increased significantly after the resolution of the exacerbation (from 1.77 fmmol per cell [95% CI, 1.71 to 1.83] at hospital admission to 1.90 fmmol per cell [95% CI, 1.83 to 1.98] at hospital discharge; p < 0.0001). No correlation was observed between parameters of disease severity and the initial values of Mg concentrations in erythrocytes and plasma.

CONCLUSIONS

Acute asthma is associated with lower erythrocyte Mg content while plasma levels remain unchanged. This decrease in intracellular Mg content occurs regardless of the severity of the exacerbation and returns to normal values after control has been achieved.

Hypomagnesemia in acute and chronic illness

Magnesium deficit is associated with several acute and chronic illnesses. Of major concern is the association between cardiovascular problems, such as myocardial infarction, hypertension, congestive heart failure, and hypomagnesemia. In addition, evidence is mounting regarding the relationship between Type II Diabetes Mellitus, and magnesium deficit. The American diet is low in magnesium, and with modern water systems, very little is ingested in the drinking water. A review of the state of the science in relation to literature on magnesium follows, as well as nursing interventions crucial to managing magnesium deficit.

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.

Blood glucose and platelet-dependent thrombosis in patients with coronary artery disease

OBJECTIVES

To investigate the influence of blood glucose on platelet-dependent thrombosis (PDT).

BACKGROUND

Elevated blood glucose is a predictor of adverse cardiovascular risk independent of a diagnosis of diabetes, possibly due to adverse effects promoting thrombosis. The effects of blood glucose on PDT have not been characterized.

METHODS

An ex vivo extracorporeal perfusion protocol was used to measure PDT in 42 patients with stable coronary artery disease (CAD). The Badimon chamber was perfused with unanticoagulated venous blood and PDT evaluated using computerized morphometry. Whole blood impedance aggregometry and flow cytometry evaluated platelet aggregation and P-selectin expression, respectively.

RESULTS

Using a multivariate stepwise regression model, blood glucose was the best independent predictor of PDT (R2 = 0.19, p < 0.008), followed by apolipoprotein B (R2 = 0.18, p = 0.002) and intracellular magnesium levels (R2 = 0.12, p = 0.02). Platelet-dependent thrombosis was significantly greater in patients with blood glucose >, compared with <, the median value of 4.9 mmol/l (159 +/- 141 vs. 67 +/- 69 microm2/mm, p < 0.01). Neither platelet aggregation nor P-selectin expression was significantly different between the two groups. Insulin levels correlated with blood glucose (r = 0.56, p = 0.0003), but were not independently associated with either PDT, platelet aggregation or P-selectin expression. A two-way analysis of variance demonstrated an interaction between insulin (>126 pmol/l) and blood glucose (>4.9 mmol/l) in modulating PDT (F [1,38] = 8.5, p < 0.006).

CONCLUSIONS

Blood glucose is an independent predictor of PDT in stable CAD patients. The relationship is evident even in the range of blood glucose levels considered normal, indicating that the risk associated with blood glucose may be continuous and graded. These findings suggest that the increased CAD risk associated with elevated blood glucose may be, in part, related to enhanced platelet-mediated thrombogenesis.

Magnesium in disease: a review with special emphasis on the serum ionized magnesium

This review deals with the six main clinical situations related to magnesium or one of its fractions, including ionized magnesium: renal disease, hypertension, pre-eclampsia, diabetes mellitus, cardiac disease, and the administration of therapeutic drugs. Issues addressed are the physiological role of magnesium, eventual changes in its levels, and how these best can be monitored. In renal disease mostly moderate hypermagnesemia is seen; measuring ionized magnesium offers minimal advantage. In hypertension magnesium might be lowered but its measurement does not seem relevant. In the prediction of severe pre-eclampsia, elevated ionized magnesium concentration may play a role, but no unequivocal picture emerges. Low magnesium in blood may be cause for, or consequence of, diabetes mellitus. No special fraction clearly indicates magnesium deficiency leading to insulin resistance. Cardiac diseases are related to diminished magnesium levels. During myocardial infarction, serum magnesium drops. Total magnesium concentration in cardiac cells can be predicted from levels in sublingual or skeletal muscle cells. Most therapeutic drugs (diuretics, chemotherapeutics, immunosuppressive agents, antibiotics) cause hypomagnesemia due to increased urinary loss. It is concluded that most of the clinical situations studied show hypomagnesemia due to renal loss, with exception of renal disease. Keeping in mind that only 1% of the total body magnesium pool is extracellular, no simple measurement of the real intracellular situation has emerged; measuring ionized magnesium in serum has little added value at present.

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.

Ventricular Arrhythmia Suppression by Magnesium Treatment after Coronary Artery Bypass Surgery

Ventricular arrhythmias occur frequently shortly after coronary artery bypass grafting (CABG), and their occurrence coincides with the postoperative decline in serum magnesium (Mg) levels. To examine if this decline causes ventricular arrhythmias and if their appearance could be reduced by intravenous Mg administration, 140 consecutive CABG patients were randomized to receive 70 mmol of Mg sulphate (N = 69) or placebo (N = 71) over two days. Serum Mg concentration fell to 0.77 mmol/l in the control group but rose to 1.09 mmol/l in the Mg group (p < 0.001). On 48 h Holter, the number of ventricular premature complexes (VPC) on the third postoperative day was reduced in the Mg group (4 +/- 5 vs 12 +/- 21 VPCs/h; p < 0.05) and the incidence of complex ventricular arrhythmias (Lown grade 2-5) was significantly diminished (19% vs 41% of the patients; p < 0.05). In multivariate analysis, high risk ventricular arrhythmias (repetitive polymorphic ventricular complexes, couplets, R-on-T complexes or operative tachycardia) were independently predicted by high number of bypassed vessels (p = 0.01), poor NYHA functional class (p = 0.06), preoperative diuretic use (p = 0.07), and low postoperative Mg levels (p = 0.08). In conclusion, correction of the postoperative decline in serum Mg concentration decreases the occurrence of early VPCs and complex ventricular arrhythmias. Patients with extensive underlying coronary artery disease and prior diuretic therapy appear to benefit greatest from Mg treatment.http://link.springer-ny.com/link/service/journals/00547/bibs/8n3p165.html

Optimal nutrition: calcium, magnesium and phosphorus

In the past, a major challenge for nutrition research was in defining indicators of nutritional adequacy. More recently, the research base related to the role of nutrition in chronic disease has expanded sufficiently to permit moving beyond deficiency indicators to other indicators with broader functional significance. Thus, nutrition research is faced with the new challenge of defining 'optimal nutrition'. One definition of optimal nutrition with respect to any particular nutrient could be when a functional marker reaches an 'optimal value' or plateau beyond which it is not longer affected by intake or stores of the nutrient. A functional marker of nutrient status could be defined as a physiological or biochemical factor which (1) is related to function or effect of the nutrient in target tissue(s) and (2) is affected by dietary intake or stores of the nutrient (which may include markers of disease risk). Examples of such indicators or markers are those related to risk of chronic diseases such as osteoporosis, CHD, or hypertension. The present review focuses on the concept of optimal nutrition with respect to three nutrients, Ca, Mg and P. However, for P and Mg there are as yet no functional indicators which respond to dietary intake, and in such cases nutrient requirements are established using more traditional approaches, e.g. balance data. For Ca, there has been interest in using maximal Ca retention, which is based on balance data, bone mass measurements and biomarkers of bone turnover as useful functional indicators of the adequacy of Ca intake.

Magnesium dynamics and sympathetic nervous system activity in patients with chronic heart failure

This study was undertaken in patients with heart failure to investigate the relation between plasma norepinephrine (NE) concentration and Mg dynamics. The study subjects comprised 16 patients with chronic heart failure (mean age 64.9+/-10.0 years). Cardiopulmonary exercise testing was performed on all patients, and anaerobic threshold (AT), peak oxygen uptake (peak VO2) and peak exercise time were measured. Resting and peak values of plasma NE concentration and serum and erythrocyte magnesium concentration were also measured. The results were as follows: the serum Mg concentration was increased significantly immediately after exercise (p<0.01), and the erythrocyte Mg concentration showed a tendency to decrease (p<0.1). The resting plasma NE level was inversely correlated with AT (p<0.05, r=-0.57), peak VO2 (p<0.05, r=-0.55) and peak exercise time (p<0.01, r=-0.62). When the plasma NE concentration at rest was analyzed in 2 groups of patients, ie, those with higher than average and those with lower than average concentrations, the resting erythrocyte Mg concentration was significantly lower in the high-NE group (2.2+/-0.3 mg/dl) than in the low-NE group (2.7+/-0.5 mg/dl) (p<0.05). The data indicate that patients with chronic heart failure associated with high NE levels at rest who showed low exercise tolerance have intracellular hypomagnesemia, which may be caused by Mg migration from intracellular to extracellular spaces.

Serum and intracellular magnesium concentrations in intoxicated chronic alcoholic and control subjects

Serum magnesium levels may not accurately reflect overall magnesium homeostasis. To clarify the relationship between serum and intracellular magnesium concentrations in chronic alcoholism, we determined intralymphocytic magnesium levels and serum magnesium, sodium and potassium concentrations in ten chronic alcoholic subjects admitted to the emergency room during acute ethanol intoxication, and compared the results to those of 14 healthy nonalcoholic controls. Serum magnesium, sodium and potassium concentrations were within the normal range in both groups of subjects and determination of intralymphocytic magnesium levels revealed a nonsignificant decrease in alcoholic subjects compared to controls. In conclusion, serum and intralymphocytic magnesium concentrations did not differ between chronic alcoholics and controls in our population; the results of the present study do not support the practice of routine magnesium administration to chronic alcoholics in the emergency room setting.

Magnesium supplementation in patients with congestive heart failure

OBJECTIVE

To evaluate several potential clinical indicators of magnesium status (diet, blood, urine, 24-hour load retention) in patients with congestive heart failure before, during, and after oral magnesium supplementation.

METHODS

Twelve patients with New York Heart Association class II-III heart failure and 12 age and sex matched healthy control subjects were supplemented with 10.4 mmol oral magnesium lactate for 3 months. For the determination of magnesium status, samples of whole blood, serum, plasma, red blood cells, and urine (24-hour) were collected. Four-day dietary intake records were reviewed. A 4-hour IV magnesium load retention study was performed before and 3 months after magnesium supplementation. A non-supplemented control group was similarly studied.

RESULTS

At baseline, magnesium intakes for all groups were below the RDA. No significant differences were seen in serum, plasma, ultrafiltrates of serum or plasma or red cell magnesium concentrations among groups over time. At baseline 5/27 subjects (19%) compared to 11/27 subjects (41%) after supplementation demonstrated normal magnesium retentions (< 25%). Magnesium excretions among groups were significantly different during supplementation. Percent magnesium retentions among groups were not different.

CONCLUSIONS

Supplementation with 10.4 mmol oral magnesium daily for 3 months did not significantly alter blood levels or magnesium retention; however, patients demonstrated lower retention of magnesium after supplementation. Differences in magnesium retention was not related to basal magnesium intake, blood levels or excretion. Unfortunately, even an intensive effort at characterizing magnesium status did not identify a clinical indicator of utility for differentiating patients with congestive heart failure before, during, and after 3 months of magnesium supplementation.

Significance of magnesium in congestive heart failure

Electrolyte balance has been regarded as a factor important to cardiovascular stability, particularly in congestive heart failure. Among the common electrolytes, the significance of magnesium has been debated because of difficulty in accurate measurement and other associated factors, including other electrolyte abnormalities. The serum magnesium level represents < 1% of total body stores and does not reflect total-body magnesium concentration, a clinical situation very similar to that of serum potassium. Magnesium is important as a cofactor in several enzymatic reactions contributing to stable cardiovascular hemodynamics and electrophysiologic functioning. Its deficiency is common and can be associated with risk factors and complications of heart failure. Typical therapy for heart failure (digoxin, diuretic agents, and ACE inhibitors) are influenced by or associated with significant alteration in magnesium balance. Magnesium therapy, both for deficiency replacement and in higher pharmacologic doses, has been beneficial in improving hemodynamics and in treating arrhythmias. Magnesium toxicity rarely occurs except in patients with renal dysfunction. In conclusion, the intricate role of magnesium on a biochemical and cellular level in cardiac cells is crucial in maintaining stable cardiovascular hemodynamics and electrophysiologic function. In patients with congestive heart failure, the presence of adequate total-body magnesium stores serve as an important prognostic indicator because of an amelioration of arrhythmias, digitalis toxicity, and hemodynamic abnormalities.

Serum and erythrocyte magnesium in critically ill patients

OBJECTIVES

To evaluate the prevalence of serum and erythrocyte magnesium (Mg) abnormalities in patients on admission to the intensive care unit (ICU) and to test the hypothesis that low levels of Mg are associated with a higher mortality.

DESIGN

Prospective study.

SETTING

14-bed ICU in a 1000-bed teaching hospital.

PATIENTS

179 consecutive patients admitted over a 4-month period.

MEASUREMENTS

Total serum Mg (Mgs) and erythrocyte Mg (Mge) were determined on admission by atomic absorption spectrophotometry. Severity of illness was assessed by Acute Physiology and Chronic Health Evaluation (APACHE) II and the number of organ system failures (OSF) during the first 24 h. The patients were followed up until discharge from hospital.

MAIN RESULTS

On admission, 79 patients (44%) were hypomagnesemic and 10 (6%) were hypermagnesemic. A low level of Mge was observed in 119 patients (66%). In patients with similar APACHE II scores and OSF numbers, more of those with hyperMgs died during their ICU stay. However, the Mge value on admission did not correlate with patient outcome.

CONCLUSIONS

We confirm the high prevalence of Mgs abnormalities as well as Mg deficiency on admission to a medical ICU. Low levels of Mgs and Mge are not associated with higher fatality. HyperMgs was associated with patient death.

Magnesium deficiency in critically ill patients

A study was performed to assess the value of estimation of intracellular magnesium in peripheral blood cells (red and mononuclear blood cells) in critically ill patients as an index of tissue magnesium content. A magnesium loading test was used to diagnose magnesium depletion in 16 critically ill patients. Patients were divided into magnesium depleted and non-depleted groups according to their response to the loading test. Pre-infusion plasma and intracellular (blood cell) magnesium levels were measured. There were no significant difference between the magnesium depleted (mean plasma magnesium 0.81 mmol.l-1, red blood cell magnesium 2.34 mmol.l-1, mononuclear blood cell magnesium 25.16 mmol.kg-1 dry weight) and non-depleted groups (mean plasma magnesium 0.90 mmol.l-1, red blood cell magnesium 2.18 mmol.l-1, mononuclear blood cell magnesium 18.1 mmol.kg-1 dry weight). We conclude that the diagnosis of magnesium depletion cannot be excluded in the face of normal plasma, red blood cell or mononuclear blood cell concentrations of magnesium.

Clinical relevance and management of the major electrolyte abnormalities in congestive heart failure: hyponatremia, hypokalemia, and hypomagnesemia

Electrolyte disturbances are a common complication of CHF. CHF provides a perfect milieu for the development of these disturbances; renal dysfunction, elevation of neurohormonal substances, activation of the renin-angiotensin-aldosterone axis, and diuretic therapy represent the major contributory factors. Hyponatremia is closely aligned with an unfavorable clinical course. Hypokalemia is associated with increased ventricular dysrhythmias. Hypomagnesemia noted in advanced CHF can be accompanied by arrhythmias and refractory hypokalemia. CHF also offers the ideal milieu (diseased, ischemic, and arrhythmogenic myocardium; elevated catecholamines; and arrhythmogenic drugs) for the threatening clinical consequences (clinical deterioration, dysrhythmias, or death) of these disturbances. These consequences underscore the importance of the recognition, appreciation, and management of these electrolyte abnormalities.

Influence of oral magnesium supplementation on cardiac events among survivors of an acute myocardial infarction

OBJECTIVE

To investigate the effect of long term oral magnesium treatment on incidence of cardiac events among survivors of an acute myocardial infarction.

DESIGN

Double blind, placebo controlled parallel study in which patients were randomised to treatment or placebo.

SETTING

Two coronary care units and corresponding outpatient clinics.

SUBJECTS

468 survivors of an acute myocardial infarction (289 men and 178 women) aged 31-92.

INTERVENTIONS

One tablet of 15 mmol magnesium hydroxide or placebo daily for one year.

MAIN OUTCOME MEASURES

Incidences of reinfarction, sudden death, and coronary artery bypass grafting in one year.

RESULTS

There was no significant difference between treatment and placebo groups in the incidence of each of the three cardiac events, but when the events were combined and drop outs were excluded from calculations there was a significantly higher incidence of events in the treatment group (56/167 v 33/153; relative risk 1.55 (95% confidence interval 1.07 to 2.25); p = 0.02). When the timing of events was incorporated by means of a Kaplan-Meier plot the treatment group showed a significantly higher incidence of events whether drop outs were included or excluded (p < 0.025).

CONCLUSION

Long term oral treatment with 15 mmol magnesium daily doses not reduce the incidence of cardiac events in survivors of an acute myocardial infarction and, indeed, seems to increase the risk of developing a cardiac event. Consequently, this treatment cannot be recommended as secondary prophylaxis for such patients.

Mononuclear blood cell magnesium in older subjects: evaluation of its use in clinical practice

Serum and mononuclear blood cell (MBC) magnesium were measured in 24 healthy community subjects, average age 76 years (67-93), and in 21 ill hospitalized subjects, average age 79 years (65-90). MBC magnesium, expressed as mumol/mg protein, was significantly lower in the in-patient group (P < 0.001), but tended to be higher in the same group when expressed as fmol/cell (not significant). Further samples from community subjects on the same day, and again at 7 days, revealed coefficients of variation for intrasubject analysis of 12% and 22%, respectively (fmol/cell). The equivalent intrasubject values for serum were 2.8% on the same day and 4% at 1 week. MBC magnesium values for inpatients were probably distorted by changes in cell size and cell protein content caused by illness. Biological variability and the effects of illness on the composition and size of cells seem to limit the usefulness of MBC magnesium measurement as a clinical tool for assessment of body magnesium status.

Mononuclear cell magnesium and retention of magnesium after intravenous loading in patients with acute myocardial infarction

A magnesium (Mg++) retention test was performed in 19 patients with acute myocardial infarction (AMI) 4-11 days after admission to the coronary care unit. The retention of Mg++ was 45 +/- 23% of the 30 mmol given intravenously. It has been proposed that a retention of more than 20% represents Mg++ deficiency. The mononuclear cell Mg++ concentration before the retention test was on an average slightly higher in the AMI patients than in 25 healthy volunteers (72.5 +/- 24.2 vs. 62.9 +/- 9.2 mumol g-1 protein) indicating no Mg++ depletion in the first group. The reason why patients during the phase of AMI show an increased retention of Mg++ is unknown, but changes in concentrations of several hormones and a reduction in blood glucose could be of importance. Serum concentrations of Mg++ were lower on admission than after 4-11 days. These initial reductions are probably due to increased concentrations of circulating catecholamines during the early hours of AMI.

Magnesium: clinical considerations

Magnesium is gaining recognition as a clinically important electrolyte. Hypomagnesemia has been associated with a variety of disorders including seizures, malignant ventricular dysrhythmias, and sudden death. The emergency department patients who are most likely to be magnesium deficient include alcoholics, patients who take diuretics, and those in diabetic ketoacidosis. Hypokalemia and hypocalcemia may represent unrecognized hypomagnesemia. Clinical trials and case reports also document increasing interest in magnesium as an effective therapeutic agent for potentially life-threatening problems such as torsade de pointes, digitalis toxicity, bronchospasm, and alcohol withdrawal. We present an overview of hypomagnesemia, review the current literature, and focus on the role of magnesium in the acute care setting and the implications for the emergency physician.

Electrolyte balance in heart failure and the role for magnesium ions

It is well established that clinically significant changes in a number of electrolytes occur in patients with congestive heart failure (CHF). Magnesium ions are an essential requirement for many enzyme systems, and evidence is rapidly emerging that magnesium deficiency is a major risk factor for survival of CHF patients. In animal experiments, magnesium has been shown to be involved in several steps of the atherosclerotic process and, although in humans the situation is somewhat more complex, magnesium ions play an extremely important role in CHF and various cardiac arrhythmias. A number of drugs commonly used to treat CHF can significantly affect not only cellular magnesium ion homeostasis, but potassium as well. These include mercurial, thiazide, and loop diuretics. It has also been reported that hypomagnesemia is common in digitalis intoxication. In contrast, a number of agents have been shown to have either a magnesium-conserving effect (potassium-sparing diuretics) or not to affect magnesium ion balance (angiotensin-converting enzyme inhibitors). The clinical consequences of magnesium deficiency include the development of various cardiac arrhythmias, all of which respond well to magnesium treatment. Thus, it is more than apparent that magnesium ion homeostasis is of major importance in CHF. Future studies should address the complex role of magnesium ions in electrolyte imbalance, particularly in relation to heart failure.

Successful resuscitation and neurologic recovery from refractory ventricular fibrillation after magnesium sulfate administration

A 46-year-old man suffered a witnessed cardiac arrest. Ventricular fibrillation persisted despite 62 minutes of basic and advanced cardiac life support measures in the field. On arrival in the emergency department, he received 4 g magnesium sulfate IV and was defibrillated successfully to normal sinus rhythm with the next countershock. The patient was discharged neurologically intact. We discuss the possible mechanisms of action and clinical use of IV magnesium sulfate in cardiac arrest.

An evaluation of plasma and erythrocyte magnesium concentration and the activities of alkaline phosphatase and creatine kinase as indicators of magnesium status

Rats were fed diets containing magnesium at concentrations ranging from 3.3 to 26.7 mmol/kg of diet (80 to 650 mg/kg). The magnesium concentration of their plasma and erythrocytes, and the activities of plasma alkaline phosphatase and creatine kinase were investigated to determine their usefulness as indices of magnesium status. All the indices increased with increasing dietary magnesium levels. The best correlations were observed between dietary intake and plasma concentration of magnesium (r = 0.846, p less than 0.001) and between intake and femur concentration (r = 0.811, p less than 0.001). There was an extremely high correlation between plasma concentration and femur concentration (r = 0.930, p less than 0.001). Although significant, the correlations between intake and the enzyme activities were not strong. It is concluded that plasma magnesium concentration is the most useful indicator of magnesium status and that the activities of the two magnesium-requiring enzymes can only be used for the purpose of diagnosing severely deficient magnesium status.

Myocardial magnesium: relation to laboratory and clinical variables in patients undergoing cardiac surgery

Magnesium concentration was measured in the right atrial appendage of 100 patients undergoing cardiac surgery and associations with serum and mononuclear blood cell magnesium, other laboratory values and patient clinical variables were studied. In addition, magnesium was measured in the right atrial appendage and left ventricular free wall in 23 autopsy subjects to determine whether there was a proportional relation between right atrial appendage and left ventricular free wall magnesium. The mean left ventricular free wall/right atrial appendage magnesium ratio was 2.13 +/- 0.39 (r = 0.67, p = 0.0009). In the group with cardiac surgery, the right atrial appendage magnesium concentration correlated inversely with age (r = -0.54, p = 0.001). The mean right atrial appendage magnesium concentration (micrograms/g wet weight tissue) was lower in patients with postoperative cardiac arrhythmia than in those without arrhythmia (103 +/- 13 versus 111 +/- 10, p = 0.009) and in diabetic than in nondiabetic patients (103 +/- 13 versus 109 +/- 12, p = 0.02). The right atrial appendage magnesium concentration also tended to be lower in patients receiving potassium/magnesium-losing diuretics, although this difference did not achieve statistical significance (105 +/- 14 versus 109 +/- 11, p = 0.16). Right atrial appendage magnesium concentration correlated positively with serum creatinine concentration (r = 0.31, p = 0.002) and negatively with serum calcium concentration (r = -0.29, p = 0.013). Serum magnesium did not correlate with right atrial appendage or mononuclear blood cell magnesium concentration or clinical variables. There was a statistically significant correlation between mononuclear blood cell and right atrial appendage magnesium concentrations in some subgroups of patients.

Blood magnesium parameters do not differ with age

The relationship between age and blood magnesium (Mg) parameters has not been defined. Mg measurements in plasma, red blood cells (RBCs), and mononuclear blood cells (MBCs) were made in 104 normal volunteers (43 males and 61 females, ages 11-75 years). MBCs were separated from blood using a discontinuous Ficoll-Hypaque gradient. The mean values (+/- SEM) were as follows: plasma Mg 1.63 +/- 0.01 mEq/L, RBC Mg 4.55 +/- 0.06 mEq/L, MBC Mg content 72.8 +/- 1.0 fg/cell, and MBC Mg concentration 19.6 +/- 0.3 mEq/L. We compared these parameters with age (intervals of 10 years) using analysis of variance (ANOVA) and found no significant differences (p greater than 0.05). Thus, plasma, RBC, and MBC Mg parameters do not vary significantly between the ages of 11 and 75 years.

Beneficial effect of magnesium sulfate in acute myocardial infarction

The effects of magnesium on the incidence of arrhythmias and on mortality were evaluated in 103 patients with documented acute myocardial infarction (AMI) in a randomized, double-blind, placebo-controlled study. Fifty patients received a magnesium infusion for 48 hours and 53 received only the vehicle (isotonic glucose) as placebo. The baseline characteristics of the population were similar in the 2 groups. Tachyarrhythmias requiring drug therapy were recorded in 32% of the patients in the magnesium group and in 45% of the placebo group. Conduction disturbances were found in 23% of the placebo group as compared to 14% in the magnesium group. The intrahospital mortality was 2% (1 patient) in the magnesium group, compared to 17% (9 patients) in the placebo group (p less than 0.01). No adverse effects were observed during and after the magnesium infusion. These data support a possible protective role of magnesium in patients with AMI.