Serum, lymphocyte, and erythrocyte potassium, magnesium, and calcium concentrations and their relation to tachyarrhythmias in patients with acute myocardial infarction

Studies of Element Concentration in the Lymphocytes, Erythrocytes, and Plasma of Healthy Human Donors Using Total Reflection X-ray Fluorescence

In this article, the total reflection X-ray fluorescence (TXRF) analysis was used for determination of element concentrations in three isolated peripheral blood components: lymphocytes, erythrocytes, and plasma, collected from 36 healthy donors (15 men and 21 women) from eastern Poland. The studied blood components were isolated from whole peripheral blood using Histopaque-1077 density gradient centrifugation. In the lymphocytes, the following elements were measured: P, S, Cl, K, Ca, Fe, Zn, Br, Sr, and Pb. In the erythrocytes: P, S, Cl, K, Cr, Mn, Fe, Cu, Zn, Se, Br, Rb, and Pb, while in the plasma samples: P, S, Cl, K, Ti, V, Cr, Fe, Co, Ni, Cu, Zn, Br, Se, Sr, and Pb. The descriptive statistics parameters of concentration such as: mean value, standard deviation, median, first and third quartiles, 10th and 90th percentiles were calculated for all samples of the studied blood components, as well as separately for male and female groups. The measured element concentrations and calculated parameters can be used as the reference values. Element concentration distributions for male and female groups were statistically compared using the non-parametric Mann-Whitney test and statistical significance differences (α = 0.05) were found for: P (in lymphocytes), Se and Rb (in erythrocytes), and V (in plasma). The multigroup statistical comparison of element concentration distribution for different blood components was also done (Mann-Whitney and Kruskal-Wallis tests). The statistical tests show that the concentration levels are usually different, except in the following cases: Zn, Fe (lymphocytes and plasma, Fe only for female group), Cr (erythrocytes and plasma). The obtained concentration ranges were compared with literature-based data available for element concentration in lymphocytes, erythrocytes, and plasma. In this work, the application of the TXRF method allowed additionally for the simultaneous determination of the concentrations of such elements as: P, S, Cl, Br, Sr and Pb in lymphocytes, S, Cl and Br in erythrocytes, and P, S, Cl, K, Ti, Br and Pb in plasma. From an analytical point of view, the article describes in detail the measurement procedure including the isolation of blood components and samples preparation for TXRF measurements, and later the detection limit of the method is discussed.

Low serum calcium is associated with left ventricular systolic dysfunction in a Chinese population with coronary artery disease

Whether serum calcium is associated with heart systolic function in patients with established coronary artery disease (CAD) and acute myocardial infarction (AMI) remains to be elucidated. This study is aimed to assess the association between serum calcium and left ventricular systolic dysfunction in a Chinese population of CAD. The cross-sectional study included 5938 CAD patients with and without AMI in China. The factors associated with AMI and left ventricular ejection fraction (LVEF) were evaluated. The data showed that AMI patients had lower serum calcium levels (2.11 ± 0.13 vs 2.20 ± 0.10 mmol/l, P < 0.001) than those without AMI. Multiple logistic regression analysis exhibited that serum calcium (OR: 0.000, 95% CI: 0.000–0.001) was one of the independent factors correlated with AMI. CAD patients with and without AMI when LVEF <50% had lower serum calcium levels than those when LVEF ≥50% respectively. Serum calcium was independently associated with LVEF and LVEF <50% in CAD patients with and without AMI respectively using multivariate analysis. The independent association between serum calcium and LVEF still existed among CAD patients when LVEF ≥50%. Serum calcium levels are significantly decreased following AMI. Low serum calcium is independently correlated with left ventricular systolic dysfunction in CAD patients with and without AMI.

Congestive heart failure: where homeostasis begets dyshomeostasis

Despite today's standard of care, aimed at preventing homeostatic neurohormonal activation, one in every five patients recently hospitalized with congestive heart failure (CHF) will be readmitted within 30 days of discharge because of a recurrence of their symptoms and signs. In light of recent pathophysiological insights, it is now propitious to revisit CHF with a view toward complementary and evolving management strategies. CHF is a progressive systemic illness. Its features include: oxidative stress in diverse tissues; an immunostimulatory state with circulating proinflammatory cytokines; a wasting of soft tissues; and a resorption of bone. Its origins are rooted in homeostatic mechanisms gone awry to beget dyshomeostasis. For example, marked excretory losses of Ca2+ and Mg2+ accompany renin-angiotensin-aldosterone system activation, causing ionized hypocalcemia and hypomagnesemia that lead to secondary hyperparathyroidism with consequent bone resorption and a propensity to atraumatic fractures. Parathyroid hormone accounts for paradoxical intracellular Ca2+ overloading in diverse tissues and consequent systemic induction of oxidative stress. In cardiac myocytes and mitochondria, these events orchestrate opening of the mitochondrial permeability transition pore with an ensuing osmotic-based destruction of these organelles and resultant cardiomyocyte necrosis with myocardial scarring. Contemporaneous with Ca2+ and Mg2+ dyshomeostasis is hypozincemia and hyposelenemia, which compromise metalloenzyme-based antioxidant defenses, whereas hypovitaminosis D threatens Ca2+ stores needed to prevent secondary hyperparathyroidism. An intrinsically coupled dyshomeostasis of intracellular Ca2+ and Zn2+, representing pro-oxidant and antioxidant, respectively, is integral to regulating the mitochondrial redox state; it can be uncoupled by a Zn2+ supplement in favor of antioxidant defenses. Hence, the complementary use of nutriceuticals to nullify dyshomeostatic responses involving macro- and micronutrients should be considered. Evolving strategies with mitochondria-targeted interventions interfering with their uptake of Ca2+ or serving as selective antioxidant or mitochondrial permeability transition pore inhibitor may also prove efficacious in the overall management of CHF.

A dyshomeostasis of electrolytes and trace elements in acute stressor states: impact on the heart

Acute stressor states are associated with a homeostatic activation of the hypothalamic-pituitary-adrenal axis. A hyperadrenergic state follows and leads to a dyshomeostasis of several intra- and extracellular cations, including K, Mg, and Ca. Prolongation of myocardial repolarization and corrected QT interval (QTc) of the ECG are useful biomarkers of hypokalemia and/or hypomagnesemia and should be monitored to address the adequacy of cation replacement. A dyshomeostasis of several trace elements, including Zn and Se, are also found in critically-ill patients to compromise metalloenzyme-based antioxidant defenses. Collectively, dyshomeostasis of these electrolytes and trace elements have deleterious consequences on the myocardium: atrial and ventricular arrhythmias; induction of oxidative stress with reduced antioxidant defenses; and adverse myocardial remodeling, including cardiomyocytes lost to necrosis and replaced by fibrous tissue. To minimize such consequences during hyperadrenergic states, systematic surveillance of electrolytes and trace elements, together with QTc, are warranted. Plasma K and Mg should be maintained at > or =4.0 mEq/L and > or =2.0 mg/dL, respectively (the 4 and 2 rule).

Severe electrolyte disorders following cardiac surgery: a prospective controlled observational study

Introduction

Electrolyte disorders are an important cause of ventricular and supraventricular arrhythmias as well as various other complications in the intensive care unit. Patients undergoing cardiac surgery are at risk for development of tachyarrhythmias, especially in the period during and immediately after surgical intervention. Preventing electrolyte disorders is thus an important goal of therapy in such patients. However, although levels of potassium are usually measured regularly in these patients, other electrolytes such as magnesium, phosphate and calcium are measured far less frequently. We hypothesized that patients undergoing cardiac surgical procedures might be at risk for electrolyte depletion, and we therefore conducted the present study to assess electrolyte levels in such patients.

Methods

Levels of magnesium, phosphate, potassium, calcium and sodium were measured in 500 consecutive patients undergoing various cardiac surgical procedures who required extracorporeal circulation (group 1). A total of 250 patients admitted to the intensive care unit following other major surgical procedures served as control individuals (group 2). Urine electrolyte excretion was measured in a subgroup of 50 patients in both groups.

Results

All cardiac patients received 1 l cardioplegia solution containing 16 mmol potassium and 16 mmol magnesium. In addition, intravenous potassium supplementation was greater in cardiac surgery patients (mean ± standard error: 10.2 ± 4.8 mmol/hour in cardiac surgery patients versus 1.3 ± 1.0 in control individuals; P < 0.01), and most (76% versus 2%; P < 0.01) received one or more doses of magnesium (on average 2.1 g) for clinical reasons, mostly intraoperative arrhythmia. Despite these differences in supplementation, electrolyte levels decreased significantly in cardiac surgery patients, most of whom (88% of cardiac surgery patients versus 20% of control individuals; P < 0.001) met criteria for clinical deficiency in one or more electrolytes. Electrolyte levels were as follows (mmol/l [mean ± standard error]; cardiac patients versus control individuals): phosphate 0.43 ± 0.22 versus 0.92 ± 0.32 (P < 0.001); magnesium 0.62 ± 0.24 versus 0.95 ± 0.27 (P < 0.001); calcium 1.96 ± 0.41 versus 2.12 ± 0.33 (P < 0.001); and potassium 3.6 ± 0.70 versus 3.9 ± 0.63 (P < 0.01). Magnesium levels in patients who had not received supplementation were 0.47 ± 0.16 mmol/l in group 1 and 0.95 ± 0.26 mmol/l in group 2 (P < 0.001). Urinary excretion of potassium, magnesium and phosphate was high in group 1 (data not shown), but this alone could not completely account for the observed electrolyte depletion.

Conclusion

Patients undergoing cardiac surgery with extracorporeal circulation are at high risk for electrolyte depletion, despite supplementation of some electrolytes, such as potassium. The probable mechanism is a combination of increased urinary excretion and intracellular shift induced by a combination of extracorporeal circulation and decreased body temperature during surgery (hypothermia induced diuresis). Our findings may partly explain the high risk of tachyarrhythmia in patients who have undergone cardiac surgery. Prophylactic supplementation of potassium, magnesium and phosphate should be seriously considered in all patients undergoing cardiac surgical procedures, both during surgery and in the immediate postoperative period. Levels of these electrolytes should be monitored frequently in such patients.

Admission serum potassium in patients with acute myocardial infarction: its correlates and value as a determinant of in-hospital outcome

STUDY OBJECTIVES

Although controversial, hypokalemia (LK) in patients with acute myocardial infarction (MI) is thought to predict increased in-hospital morbidity, particularly cardiac arrhythmias, and mortality. Also, the mechanism of low serum potassium in the setting of MI has not been delineated. We evaluated the frequency, attributes, and outcome, and speculated on the mechanism of LK in patients with MI.

DESIGN

This was a prospective cross-sectional study of 517 consecutive patients with MI admitted to the coronary care unit (CCU). Serum potassium was measured in the emergency department and repeatedly thereafter throughout hospitalization, and was used in the analysis, along with a large array of clinical and laboratory variables.

RESULTS

The patients were allocated to a LK and a normokalemic (NK) cohort, based on the emergency department serum potassium measurement. The 41 patients with LK (3.16+/-0.24 mEq/L; 7.9% of total) were comparable on admission in their baseline assessment to the 476 patients with normal serum potassium (4.28+/-0.56 mEq/L), except for lower emergency department magnesium (1.48+/-0.15 mg/dL vs. 1.96+/-0.26 mg/dL; p = 0.0005) and earlier presentation after onset of symptoms (3.0+/-4.1 h vs. 4.4+/- 6.2 h; p = 0.05). There was a poor correlation between serum potassium and magnesium on admission (r = 0.14). Peak creatine kinase (CK) and myocardial isomer of CK were higher in the LK patients (3,870+/-3, 840 IU/L vs. 2,359+/-2,653 IU/L [p = 0.018] and 358+/-312 IU/L vs. 228 +/- 258 IU/L [p = 0.013], respectively). Management of the two cohorts was the same, except for a higher rate of use of magnesium (14.6% vs. 4.6%; p = 0.007), serum potassium supplements (90.2% vs 43. 1%; p = 0.000005), and antiarrhythmic drugs (78.0% vs 50.4%; p = 0. 0007) in the LK patients. No difference was detected between the LK and NK patients in total mortality (24.4% vs. 18.3%; p = 0.34), cardiac mortality (17.1% vs. 15.3%; p = 0.52), atrial fibrillation (14.6% vs 13.9%; p = 0.89), and ventricular tachycardia (22.0% vs. 16.0%; p = 0.32), but ventricular fibrillation (VF) occurred more often (24.4% vs 13.0%; p = 0.04) in the LK patients. However, proportions of VF occurring in the emergency department, CCU, or wards in the two cohorts were not different, but they were higher during the time interval prior to emergency department admission in LK patients (17.1% vs 2.1%; p = 0.00001).

CONCLUSIONS

LK is seen in approximately 8% of patients with MI in the emergency department; LK is associated with low emergency department magnesium, and low serum potassium levels in the CCU and throughout hospitalization. LK has no relationship to preadmission use of diuretics, it is associated with early presentation to the emergency department, and it is not a predictor of increased morbidity or mortality.

Magnesium supplementation in the prevention of arrhythmias in pediatric patients undergoing surgery for congenital heart defects

BACKGROUND

The efficacy of magnesium in the prevention of arrhythmias in pediatric patients after heart surgery remains unknown. Therefore we prospectively examined the effect of magnesium treatment on the incidence of postoperative arrhythmias in pediatric patients undergoing surgical repair of congenital heart defects.

METHODS AND RESULTS

Twenty-eight pediatric patients undergoing heart surgery with cardiopulmonary bypass were prospectively, randomly assigned in a double-blind fashion to receive intravenous magnesium (magnesium group, n = 13; 30 mg/kg) or saline (placebo group, n = 15) immediately after cessation of cardiopulmonary bypass. Magnesium, potassium, and calcium levels were measured at defined intervals during surgery and 24 hours after surgery. Continuous electrocardiographic documentation by Holter monitor was performed for 24 hours after surgery. Magnesium levels were significantly decreased below the normal reference range for patients in the placebo group compared with the magnesium group on arrival in the intensive care unit and for 20 hours after surgery. Magnesium levels remained in the normal range for patients in the magnesium group after magnesium supplementation. In 4 patients in the placebo group (27%), junctional ectopic tachycardia developed within the initial 20 hours in the intensive care unit. No junctional ectopic tachycardia was observed in the magnesium group (P =.026).

CONCLUSIONS

Although this study was originally targeted to include 100 patients, the protocol was terminated because of the unacceptable incidence of hemodynamically significant junctional ectopic tachycardia that was present in the placebo group. Thus low magnesium levels in pediatric patients undergoing heart surgery are associated with an increased incidence of junctional ectopic tachycardia in the immediate postoperative period.

Diuretics and risk of arrhythmic death in patients with left ventricular dysfunction

Background-Treatment with diuretics has been reported to increase the risk of arrhythmic death in patients with hypertension. The effect of diuretic therapy on arrhythmic death in patients with left ventricular dysfunction is unknown. Methods and Results-We conducted a retrospective analysis of 6797 patients with an ejection fraction <0.36 enrolled in the Studies Of Left Ventricular Dysfunction (SOLVD) to assess the relation between diuretic use at baseline and the subsequent risk of arrhythmic death. Participants receiving a diuretic at baseline were more likely to have an arrhythmic death than those not receiving a diuretic (3.1 vs 1.7 arrhythmic deaths per 100 person-years, P=0.001). On univariate analysis, diuretic use was associated with an increased risk of arrhythmic death (relative risk [RR] 1.85, P=0.0001). After controlling for important covariates, diuretic use remained significantly associated with an increased risk of arrhythmic death (RR 1.37, P=0.009). Only non-potassium-sparing diuretic use was independently associated with arrhythmic death (RR 1.33, P=0.02). Use of a potassium-sparing diuretic, alone or in combination with a non-potassium-sparing diuretic, was not independently associated with an increased risk of arrhythmic death (RR 0.90, P=0.6). Conclusions-In SOLVD, baseline use of a non-potassium-sparing diuretic was associated with an increased risk of arrhythmic death, whereas baseline use of a potassium-sparing diuretic was not. These data suggest that diuretic-induced electrolyte disturbances may result in fatal arrhythmias in patients with systolic left ventricular dysfunction.

Is low magnesium concentration a risk factor for coronary heart disease? The Atherosclerosis Risk in Communities (ARIC) Study

BACKGROUND

Hypomagnesemia has been hypothesized to play a role in coronary heart disease (CHD), but few prospective epidemiologic studies have been conducted.

METHODS AND RESULTS

We examined the relation of serum and dietary magnesium with CHD incidence in a sample of middle-aged adults (n=13,922 free of baseline CHD) from 4 US communities. Over 4 to 7 years of follow-up, 223 men and 96 women had CHD develop. After adjustment for sociodemographic characteristics, waist/hip ratio, smoking, alcohol consumption, sports participation, use of diuretics, fibrinogen, total and high-density lipoprotein cholesterol levels, triglyceride levels, and hormone replacement therapy, the relative risk of CHD across quartiles of serum magnesium was 1.00, 0.92, 0.48, and 0.44 (P for trend=0.009) among women and 1.00, 1.32, 0.95, and 0.73 (P for trend=0.07) among men. The adjusted relative risk of CHD for the highest versus the lowest quartile of dietary magnesium was 0.69 in men (95% confidence interval 0.45 to 1.05) and 1.32 in women (0.68 to 2.55).

CONCLUSIONS

These findings suggest that low magnesium concentration may contribute to the pathogenesis of coronary atherosclerosis or acute thrombosis.

[Magnesium deficiency and magnesium substitution. Effect on ventricular cardiac arrhythmias of various etiology]

During recent years there has been an increasing but still controversial discussion on the antiarrhythmic effects and overall benefit of magnesium when directed to patients with various types of ventricular tachyarrhythmias. While magnesium is considered to be a simple, safe and cost-effective approach and many casuistic and empiric reports have indicated antiarrhythmic properties of magnesium in patients with suspected or manifest ventricular arrhythmias, controlled studies proving the antiarrhythmic and overall benefit and justifying a broader use of magnesium in treating various types of ventricular arrhythmias are missing or rare. At present, antiarrhythmic properties and clinical benefit of magnesium application has only been established in patients with torsade de pointes and digitalis-induced ventricular tachyarrhythmias. In perioperative patients at risk for ventricular tachyarrhythmias and in patients suffering from manifest heart failure, data may also indicate some antiarrhythmic properties of magnesium, however, in this case with a wide consensus that the prevention of magnesium deficit is more effective and preferred in most patients over the therapeutic application of magnesium. Another group of patients who may profit from such a therapeutic approach are patients with frequent ventricular arrhythmias and stable underlying heart disease, in whom a recently published double-blind, randomized study documented an antiarrhythmic effect of a 3 week treatment with potassium and magnesium. For all other types of ventricular tachyarrhythmias, the therapeutic use of magnesium can be considered as not harmful, but also as not proven to be effective.

Magnesium--a profibrillatory or antifibrillatory drug depending on plasma concentration, heart rate and myocardial perfusion

BACKGROUND

The opinions on the efficacy of magnesium as an antiarrhythmic drug vary considerably. The action of magnesium on vulnerability to fibrillation was therefore investigated in anaesthetized, open-chest pigs under different conditions as regards plasma concentration, heart rate and myocardial perfusion.

METHODS

Vulnerability to fibrillation was assessed by electrical fibrillation threshold (EFT), measured with 100-ms duration diastolic impulses. These stimuli were delivered to the heart normally perfused, at a usual (90 and 120 beats/min) or accelerated (180 beats/min) rate. Vulnerability to fibrillation was also assessed at the high rate (180 beats/min) in the heart made ischaemic by complete occlusion of the left anterior descending coronary artery near its origin. EFT was then measured at the end of occlusion periods which were of increasing duration (30, 60, 90, 120 s). Monophasic action potential (MAP) duration, intraventricular conduction time, left ventricular dP/dt max (LVdP/dt max) and mean blood pressure were concurrently measured.

RESULTS

In the absence of ischaemia, 5 mumol.kg-1.min-1 magnesium i.v. infusion, which raised plasma concentration to 1.78 +/- 0.14 mmol/L, lowered EFT, measured at the rate of 116 beats/min, from 14.0 +/- 1.1 to 6.8 +/- 1.0 mA (P < 0.001), without significant variation of the other parameters. Administered as previously or in a markedly higher dose (400 mumol.kg-1 loading dose and 10 mumol.kg-1.min-1 infusion) which raised plasma concentration up to 4.84 +/- 0.52 mmol/L, magnesium significantly influenced neither EFT nor MAP duration, reduced by the high rate (180 beats/min) to 6.2-6.7 mA and 212-220 ms respectively. Under the same conditions, at the same 180 beats/min rate, ischaemia brings about a fall of EFT, from 6.9 down to nearly 0 mA, with occurrence of fibrillation, in approximately 120 s. Magnesium failed to slow this fall and to delay the onset of fibrillation. In contrast, within the minutes following the end of occlusion, magnesium increased EFT to a great extent (from 7.1 +/- 0.4 to 13.5 +/- 0.7 mA, P < 0.001), with a significant prolongation of MAP duration (212 +/- 6 to 234 +/- 8 ms, P < 0.01).

CONCLUSION

Magnesium may develop profibrillatory or antifibrillatory effects depending on plasma concentration, heart rate and myocardial perfusion.

Erythrocyte magnesium in elderly patients: not a reliable guide to magnesium status

To assess body magnesium status in various illness states in older people by measurement of serum magnesium (S Mg) and erythrocyte magnesium (E Mg) and to explore the limitations of E Mg measurement. S Mg and E Mg were measured in 150 consecutive out-patients, mean age 77 years, and in 100 consecutive in-patient admissions, mean age 80 years. Results were analysed for different diagnostic groups S Mg was normally distributed for both in-patients and out-patients, mean values 0.79 mmol/l and 0.77 mmol/l respectively. In-patient E Mg concentrations were often higher but the distribution was considerably skewed, median 2.28 mmol/l, mean 2.35 mmol/l. Out-patient E Mg concentration followed a near normal distribution, median 2.32 mmol/l, mean 2.30 mmol/l. There was a significant correlation between E Mg and S Mg for out-patients, R = 0.29 (p < 0.001). In-patients with infections and pressure sores had significantly raised E Mg concentrations but normal or low S Mg. High E Mg concentrations in illness are likely to be due to alterations in characteristics of the erythrocytes themselves rather than an indication of body magnesium excess. E Mg concentrations in illness should be interpreted with caution.

Blood ionized magnesium concentrations during cardiopulmonary bypass and their correlation with other circulating cations

BACKGROUND AND AIM

The recent introduction of new measurement technology (using ion specific electrodes) makes intraoperative evaluation of blood ionized magnesium (Mg2+, or iMg)--the bioactive fraction of circulation magnesium--possible. The goals of this study were: (1) to examine the longitudinal pattern(s) of change in blood iMg during cardiopulmonary bypass (CPB); and (2) to determine the relationship of iMg to Ca2+ (iCa), K, pH, Na, and hematocrit (Hct) during CPB.

METHODS

Blood was collected serially before, during, and after CPB on 30 patients undergoing elective coronary artery bypass graft procedures and the iMg was measured with an AVL Scientific Corp., model 988-4 instrument.

RESULTS

Overall, 73% of iMg results were abnormally low, 50% during CPB. Some cases had both hypo- and hyperionized magnesemic episodes. There were low iCa during CPB in 97% of cases. Using Spearman's rank order correlations and p < 0.05, iMg and K were directly correlated before, during, and after bypass, suggesting their parallel movement between tissue and blood. iMg and iCa were directly correlated before, and inversely correlated after, CPB, but unassociated during bypass. iMg and Na were inversely correlated after bypass in all cases. iMg was inversely correlated to pH and positively correlated to Hct during CPB only, and only in patients with concurrent association of iMg and iCa.

CONCLUSIONS

Blood iMg depletion occurs frequently in CPB patients. iMg changes are not readily predictable. The association of intraoperative iMg depletion with postsurgical atrial fibrillation--reported to have a hypomagnesemic connection- should be investigated.

Cardiac arrhythmia therapy

Cardiac dysfunction is often manifested as arrhythmia, with disruption of the normal periodicity and regularity of electromechanical activity. The therapy for arrhythmia begins with proper diagnosis, since many pharmacological interventions are themselves arrhythmogenic. Intervention for acute arrhythmia involves correction of underlying systemic conditions by ensuring adequate oxygenation, ventilation, acid-base homeostasis, electrolyte balance, and fluid status. Classification of antiarrhythmic agents assists in a structured treatment approach that utilizes different agents based on the etiology of the arrhythmia and the drug's mechanism of action. A deliberate treatment strategy guided by the morphological criteria of the arrhythmia modified by the rate and duration of complexes, noting symptoms and hemodynamic stability, is desirable.

Electrolyte disturbances in chronic heart failure: metabolic and clinical aspects

The pathophysiology of congestive heart failure (CHF) includes conditions (e.g., activation of the renin-angiotensin-aldosterone system) which, when combined with CHF therapies, make patients afflicted with this syndrome quite susceptible to electrolyte disturbances. The most commonly encountered are hyponatremia, hypokalemia, and hypomagnesemia. These derangements are of vast clinical importance; their development not only represents an immediate threat to the CHF patient (e.g., dysrhythmias secondary to hypokalemia), but are also indicative of underlying pathophysiologic events, an unfavorable clinical course, and occasionally an adverse therapeutic response. The optimal care of CHF patient includes the recognition and management of these electrolyte disturbances.

Magnesium flux caused by coronary artery bypass operation: three patterns of deficiency

We undertook a study to evaluate the patterns of magnesium deficiency that may develop during and following coronary artery bypass operation without cardioplegia. In 18 patients intraoperative measurements of plasma magnesium and potassium concentrations and measurements of cardiac and skeletal muscle content of these ions were taken. The changes in plasma concentrations and excretion were evaluated postoperatively. Hemodilution at initiation of cardiopulmonary bypass caused a 17.3% decrease in plasma magnesium concentration (p < 0.01), which persisted until the first postoperative day. By the fifth postoperative day the level was 19.5% greater than the preoperative value. Urinary excretion of magnesium reflected changes in plasma magnesium concentration. Cardiac muscle content of magnesium decreased by 13.3%. Plasma potassium concentration was elevated by hemodilution (p < 0.01), and muscle potassium was not depleted. We conclude that three patterns of magnesium depletion occur: hemodilution, intraoperative cellular depletion, and postoperative cellular depletion. The findings support the need for magnesium supplementation during and after cardiac operation.

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.

The associations of levels of serum potassium and magnesium with ventricular premature complexes (the Framingham Heart Study)

There are conflicting data regarding the impact of serum potassium and magnesium levels on susceptibility to ventricular premature complexes (VPCs) in the clinical setting. The associations of serum potassium and magnesium levels with the prevalence of complex or frequent (> 30/hour, multiform or repetitive) VPCs were examined after adjusting for age, sex, smoking, caffeinated coffee consumption, alcohol consumption, and left ventricular mass in Framingham Offspring Study subjects who were free of clinically apparent heart disease. There were 3,327 eligible subjects (mean age 44 years). Complex or frequent VPCs were present in 183 subjects (5.5%). When age-adjusted prevalences of complex or frequent VPCs were compared among quartiles of serum potassium and magnesium using a trend test, lower potassium (p = 0.002) and lower magnesium (p = 0.010) levels were associated with higher prevalence rates of arrhythmia. In logistic regression analyses that included potassium and magnesium simultaneously, potassium (p = 0.0021) and magnesium (p = 0.0311) levels were inversely associated with the occurrence of complex or frequent VPCs after adjustment for age, sex, smoking, coffee and alcohol consumption, diuretic use, and systolic blood pressure. These associations remained significant after accounting for left ventricular mass. A 1 SD decrement in potassium (0.48 mEq/liter) or magnesium (0.16 mEq/liter) level was associated with a 27% (95% confidence interval 6% to 51%) and a 20% (95% confidence interval 3% to 41%) greater odds of complex or frequent VPCs, respectively. Lower levels of serum potassium and magnesium were concurrently associated with higher prevalence rates of ventricular arrhythmias.

Glucose and insulin levels during diuretic therapy in hypertensive men

We investigated serum glucose and insulin levels resulting from thiazide or thiazide-like diuretic administration and determined whether they were associated with serum or intracellular potassium or magnesium values. We also explored the role of obesity both alone and with thiazides on serum insulin and glucose. Hypertensive men were withdrawn from diuretics and repleted with oral potassium and magnesium and then randomized to 2 months of treatment with (1) hydrochlorothiazide, (2) hydrochlorothiazide with oral potassium, (3) hydrochlorothiazide with oral potassium and magnesium (4) hydrochlorothiazide and triamterene, (5) chlorthalidone, or (6) placebo. Serum was available from 202 participants for insulin and glucose determinations. Mean fasting serum glucose and insulin did not change significantly after 2 months of randomized therapy with the exception of participants randomized to chlorthalidone, who had significant increases in both serum insulin and glucose (P < .05 and P < .01, respectively). As body mass index increased, there was a corresponding increase in serum insulin and to a lesser degree in serum glucose. Also, as body mass index increased, participants taking hydrochlorothiazide had a corresponding increase of serum insulin (P < .05). After treatment, intracellular potassium and magnesium were both associated with higher serum insulin (P < .001 for each), and serum potassium was associated with higher and serum magnesium with lower serum glucose (P < .01 for each). In most hypertensive men, treatment with 50 mg chlorthalidone increases glucose and insulin levels, whereas administration of 50 mg hydrochlorothiazide, with or without potassium and/or magnesium conserving strategies, does not.(ABSTRACT TRUNCATED AT 250 WORDS)

Dietary and serum magnesium levels in patients with acute myocardial infarction, coronary artery disease and noncardiac diagnoses

OBJECTIVE

To study the relation of dietary and serum levels of magnesium (Mg) in acute myocardial infarction (AMI) and its complications in relation to noncardiac diagnoses.

METHODOLOGY

Case control study in a primary and secondary care center for AMI patients. The study included 460 subjects with definite AMI (n = 335, group A), possible AMI (n = 64, group B), unstable angina (n = 19, group C) and controls with noncardiac chest pain (n = 42, group D). Demographic variables, dietary intake, and clinical and biochemical data were compared. Mean age, sex, body weight, and body mass index were comparable in all the groups.

RESULTS

Dietary fat and cholesterol intakes were significantly higher and carbohydrate intakes were lower in group A, B and C patients with coronary artery disease compared to control group D. Dietary consumption of Mg was comparable in all groups; however, in 85 patients in group A (272.5 mg/day) and 17 in group B (280.4 mg/day) in whom ventricular arrhythmias were present, Mg intake was relatively lower compared to control group D (316.6 mg/day). Serum Mg levels in group A (1.66 mEq/L), B (1.65 mEq/L), and C (1.66 mEq/L) were within normal (1.74 mEq/L) limits, but were significantly lower than in control group D.

CONCLUSIONS

Lower serum Mg in group A, B and C patients was attributed to increased demand during AMI, although in patients with complications (ventricular arrhythmias), Mg deficiency may in part result from relatively lower Mg intake, a hypothesis which requires further study.

Intravenous magnesium therapy in acute myocardial infarction

OBJECTIVE

To review the methods and summarize the findings of clinical trials evaluating the use of intravenous magnesium (Mg2+) in acute myocardial infarction (AMI); to discuss serum Mg2+ in AMI and the potential mechanisms by which intravenous Mg2+ may be effective. Tables are used extensively to provide detailed information about the various trials.

DATA SOURCES

A MEDLINE search was used to identify pertinent literature. Additional references were obtained from the articles retrieved from that search.

STUDY SELECTION

Studies randomized and/or placebo-controlled were selected for review. Additional relevant citations were used in the introductory material and discussion.

DATA EXTRACTION

There were surprisingly few large, placebo-controlled trials. All clinical trials available at the time of publication were reviewed. Only eight trials enrolled sufficient numbers of patients and/or were of adequate design to make meaningful interpretations. The description of the methods and results of these articles are the basis of this review. Although additional controlled studies with more subjects are needed, the results to date form a foundation from which to make inferences regarding the utility of this therapeutic modality.

DATA SYNTHESIS

Intravenous Mg2+ has been demonstrated, albeit inconclusively, to reduce immediate and long-term morbidity and mortality when given in the immediate postinfarction period. Six of the eight controlled trials discussed report a decrease in the overall incidence of arrhythmia or in the frequency of arrhythmia requiring treatment. Four of the eight reported statistical significance. Five of the six trials evaluating mortality reported a decrease in the mortality rate from intravenous Mg2+ administered post-MI. Four of the five reported statistical significance. The favorable effect of intravenous Mg2+ on the mortality rate appears to occur in the first 30 days post-MI and is maintained through at least one year. The effects appear to be independent of concurrent therapy and do not appear to relate to baseline serum Mg2+ concentrations. Intravenous Mg2+ appears to be safe and well tolerated. Flushing, hypotension, and atrioventricular (AV) node conduction abnormalities occur on occasion and seem related to the rate of administration. The exact dosage in this setting remains to be determined.

CONCLUSIONS

Additional, well-designed, multicenter, controlled trials evaluating intravenous Mg2+ in AMI are needed. The pending Fourth International Study of Infarct Survival, with an anticipated 400,000 subjects, should clarify a number of unresolved issues regarding this therapy. Based on the information available to date, however, intravenous Mg2+ as a significant therapeutic modality for AMI shows promise. Pending further investigation, however, it should be avoided in patients with significant sinoatrial or AV conduction disturbances.

Magnesium homeostasis and clinical disorders of magnesium deficiency

OBJECTIVE

To survey the causes of clinical hypomagnesemia and Mg deficiency. The relationship of hypomagnesemia to digitalis toxicity, congestive heart failure, arrhythmias, and acute myocardial infarction is discussed, as is the clinical interrelationship of Mg and K concentrations, the principal intracellular cations.

DATA SOURCES

A MEDLINE search and retrieval was used to identify relevant references.

STUDY SELECTION

Clinical reports, as well as studies, were selected for this review.

DATA EXTRACTION

There were very few placebo-controlled clinical studies. Clinical observations were related primarily to compilation of series in which Mg was administered and clinical results reported. In addition, conclusions derived from review articles on the subject of clinical Mg depletion were used.

DATA SYNTHESIS

Clinical diagnosis of Mg deficiency is ascertained most expeditiously by estimating serum Mg concentrations. Although available on order by physicians, the lack of routine serum Mg analysis as part of the "electrolyte panel" impedes the diagnosis of clinical Mg deficiency. Renal loss of Mg resulting from the widespread use of loop diuretics is responsible for significant numbers of patients with Mg deficiency and hypomagnesemia. Life-threatening cardiac arrhythmias and seizures represent the most serious manifestations of clinical hypomagnesemia and Mg depletion. In the most critically ill patients, treatment with intravenous Mg is recommended. Oral repletion of Mg is reserved for the less critically ill hospitalized patients and ambulatory patients. Close attention must be paid to optimizing K replenishment in hypokalemic patients by concurrent treatment of any accompanying hypomagnesemia to avoid the problem of refractory K repletion.

CONCLUSIONS

Hypomagnesemia is one of the most frequent serum electrolyte abnormalities in current clinical practice. Routine inclusion of serum Mg analysis in the electrolyte panel will enhance the clinical recognition and treatment of hypomagnesemic Mg-depleted patients. Failure to respond to treatment of recurrent ventricular tachycardia/fibrillation to usual antiarrhythmic therapy in patients with acute myocardial infarction, idiopathic dilated cardiomyopathy, and congestive heart failure should alert the clinician to consider administering intravenous Mg. Repair of coexisting hypomagnesemia in hypokalemic patients is essential to avoid the problem of refractory K repletion caused by coexisting Mg depletion. More controlled clinical studies of Mg deficiency are necessary to ascertain the cost-effectiveness of Mg replacement therapy.

Do diuretics cause magnesium deficiency?

1. Controlled trials, of which there are few, do not substantiate claims that diuretics play a role in causing magnesium deficiency. Consequently, the vast majority of patients taking conventional doses of thiazide diuretics (i.e. bendrofluazide 2.5 mg day-1 or equivalent) do not need magnesium supplements. On balance, potassium-sparing diuretics tend to increase serum and intracellular magnesium content; this should not be taken as evidence of prior magnesium deficiency. It remains theoretically possible that large doses of loop diuretics given more than once daily for long periods could induce negative magnesium balance and magnesium deficiency. However, it has been difficult to run appropriately controlled trials in conditions where such therapy is needed (i.e. heart failure) and until more reliable information becomes available no absolute recommendation can be made. 2. Methods for the measurement of intracellular free magnesium levels are now available and are more relevant to the assessment of magnesium deficiency than total intracellular magnesium content; the complex relationship between intracellular free and total magnesium content remains to be defined. Future work involving the effect of diuretics on intracellular free magnesium measurements should make every attempt to avoid the errors of trial design and multiple publication that litter current and past literature.

Clinical and electrophysiologic effects of magnesium sulfate on paroxysmal supraventricular tachycardia and comparison with adenosine triphosphate

Electrophysiologic studies have shown that intravenous magnesium sulfate prolongs atrioventricular (AV) nodal conduction and refractoriness and thus could play a role in the management of patients with paroxysmal AV reentrant supraventricular tachycardia (SVT). The present study evaluates the clinical and electrophysiologic effects of intravenous magnesium sulfate in patients with SVT and compares them with those of adenosine triphosphate (ATP), one of the most potent drugs in the treatment of this arrhythmia. Patients with inducible sustained SVT were treated with ATP (10 or 20 mg) and magnesium sulfate (2 g over 15 seconds) during electrophysiologic study. If the tachycardia failed to terminate by the sixth minute, an additional 2 g dose of magnesium was given. ATP (10 or 20 mg) was significantly better than magnesium for terminating induced tachycardias (14 of 14 vs 6 of 14, p less than 0.0001). Arrhythmia termination with ATP was due to anterograde AV nodal blockade in all but 1 patient who developed retrograde block over an accessory pathway with decremental conduction. Arrhythmia termination by magnesium was due to retrograde block over an accessory pathway in 3 patients (including the patient with accessory pathway exhibiting decremental conduction), anterograde AV nodal conduction block in 2 patients and premature ventricular complexes in 1 patient. During induced tachycardias, only AH intervals were prolonged by ATP, whereas magnesium significantly prolonged AH and QRS intervals. Short-lasting side effects (chest pain, flushing, nausea) occurred after both drugs were administered but were more severe after magnesium.(ABSTRACT TRUNCATED AT 250 WORDS)

Electrophysiologic effects of magnesium sulfate infusion in patients with cardiac conduction defects

We report the electrocardiographic and electrophysiologic effects of magnesium (Mg) sulfate infusion in 25 normomagnesemic patients (16 men and 9 women, aged 22-74 years; mean +/- SD, 60.4 +/- 11.9) with different cardiac conduction impairments. Ten patients had chronic ischemic heart disease, two had idiopathic dilated cardiomyopathy, two had hypertensive heart disease, three had valvular heart disease, five had sclerodegenerative heart disease and three had no clinical evidence of cardiac disease. Five patients had trifascicular block [first degree atrioventricular (A-V) block+right bundle branch block (RBBB)+left anterior hemiblock (LAH)], eight had bifascicular block (6 RBBB+LAH, 2 first degree A-V block+RBBB), four had isolated first degree A-V block and eight had bundle branch block [5 RBBB, 3 left bundle branch block (LBBB)]. Before and during Mg infusion (50 mg/min/60 min) we evaluated the A-V (P-R), intraatrial (P-A), suprahisian (A-H), infrahisian (H-V) conduction times, electrical ventricular systole (Q-T), Q-T index (Q-Tc) intraventricular conduction time (QRS) and heart rate. At the end of infusion the P-R, P-A, A-H, H-V increased from 215.4 +/- 36.6, 33.6 +/- 9.1, 112.8 +/- 37.3, 69.0 +/- 12.8 ms to 217.6 +/- 37.1 (p less than 0.002), 33.8 +/- 9.4 (NS), 114.2 +/- 38.1 (p less than 0.005), 69.6 +/- 13.3 (NS) ms. QRS complex did not change (125 +/- 16.9 ms).(ABSTRACT TRUNCATED AT 250 WORDS)

Changes in calcium homoeostasis and bone formation in patients recovering from acute myocardial infarction: effect of verapamil treatment. Danish Study Group on Verapamil in Myocardial Infarction

The effect of the calcium antagonist verapamil on calcium homoeostasis and bone metabolism has been investigated in a double-blind randomized placebo-controlled study. Ten patients randomized to verapamil 120 mg t.i.d. and 9 patients randomized to placebo in The Danish Verapamil Infarction Trial II took part in the study. Bone formation, estimated by 24-h whole body retention of diphosphonate (WBR), osteocalcin, alkaline phosphatase and calcium metabolic indices, was recorded before the start of medication and after 1 and 6 months of treatment. Baseline calcium metabolic variables were not significantly different between the two study groups. There were no significant differences in WBR (0.38 vs 0.37), osteocalcin level (8.2 vs 8.0 micrograms/l) or alkaline phosphatase (218 vs 200 U/l) after treatment for 6 months with verapamil compared to placebo. Serum PTH, calcium and phosphate levels were also not affected by verapamil. The results suggest that prolonged treatment with clinical doses of verapamil does not affect indices of calcium and bone metabolism in humans.

Metabolic, hemodynamic, and electrocardiographic responses to increased circulating adrenaline: effects of pretreatment with class 1 antiarrhythmics

In order to study the effects of treatment with class 1 antiarrhythmics on the metabolic, hemodynamic, and electrocardiographic responses to adrenaline, 12 healthy volunteers were infused on four occasions, after pretreatment with placebo, disopyramide, mexiletine, and flecainide, respectively, with adrenaline at a rate producing serum adrenaline concentrations comparable with those seen in acute myocardial infarction. After pretreatment with placebo adrenaline caused significant falls in serum potassium, serum magnesium, serum calcium, and serum phosphate and a significant increase in blood glucose. Adrenaline also caused a significant increase in heart rate and systolic blood pressure and a significant fall in diastolic blood pressure. On the electrocardiogram a significant prolongation of QTc duration and a flattening of the T-wave amplitude were seen. Pretreatment with disopyramide had no effect on the hemodynamic response to adrenaline but caused a significant prolongation of Qtc duration before the adrenaline infusion. Pretreatment with mexiletine was associated with a significantly greater fall in serum potassium during adrenaline infusion, and pretreatment with flecainide with a greater fall in serum magnesium, as compared with placebo pretreatment Flecainide also caused a significant prolongation of the QRS duration before adrenalin infusion, and after all the active pretreatments a prolongation of QRS duration was seen during adrenaline infusion. The metabolic and hemodynamic changes during adrenaline infusion may not only reduce the antiarrhythmic efficacy of antiarrhythmics but may also increase the risk of proarrhythmic effects in a clinical setting. These results may help to explain why treatment with antiarrhythmics seems to be without beneficial effect on mortality in post-myocardial infarction patients.

The rise of serum creatinine levels during labor

Serum creatinine, blood urea nitrogen and creatine phosphokinase were measured in 32 women during the last 3 weeks of pregnancy and, in a further 39 women, during and after labor. The serum creatinine increased from 61.9 +/- 0.9 to 69.8 +/- 1.8 mumol/l (mean +/- SEM) (P less than 0.05) in the third stage of labor and returned to normal by 72 h after delivery. The muscle creatine phosphokinase increased from 54 +/- 7 to 77 +/- 9.9 units (P less than 0.05) during the third stage and remained high (87 +/- 13.3 units) 72 h later. We conclude that these changes are due to muscle contraction and injury during delivery.

Clinical correlates of the molecular and cellular actions of magnesium on the cardiovascular system

Magnesium is a ubiquitous element that participates in metabolic processes essential for life. Magnesium acts as a metallic cofactor in more than 300 enzymatic reactions; notably it is essential for all reactions requiring ATP. Magnesium also functions as a transmembrane and intracellular modulator of other ions. Altered magnesium homeostasis, particularly a deficiency, can cause alterations in metabolic functions that result in clinically recognizable events. Recognition of magnesium deficiency is problematic, since there is no test that will reliably and consistently detect this condition. A high index of suspicion for magnesium deficiency is necessary and treatment should be given when indicated. This article reviews the molecular and cellular actions of magnesium and correlates these basic scientific findings with clinically recognized cardiovascular events in humans. In addition, management guidelines are delineated.

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.

Magnesium therapy in ventricular arrhythmias

Magnesium (Mg) is the known activator of 300 enzymes which govern energy utilization, cell permeability, and ionic membrane currents in the cardiac conducting cells. This may explain the antiarrhythmic efficacy of Mg in specific clinical settings, despite its only modest electrophysiological effects. This review summarizes the effect of Mg administration in four clinical conditions: in digitalis toxicity; in drug-induced torsade de pointes; in patients with chronic diuretic therapy; and in acute myocardial infarction. Mg effectively abolished ventricular tachyarrhythmias associated with digitalis intoxication. This effect of Mg is related to the activation of sodium-potassium ATP-ase, which is inhibited by digitalis. Drug-induced torsade de pointes was promptly abolished by Mg sulfate in the clinical setting. Experimental studies showed that Mg suppresses the early afterdepolarizations and the triggered activity responsible for occurrence of the arrhythmia. In diuretic-treated hypertensives, potassium depletion has been associated with increased ventricular ectopy and sudden death. Mg has been found to be an important adjuvant for intracellular repletion of potassium in these patients. Several randomized, double-blind studies in patients with acute infarction showed that Mg administered on admission improved survival or reduced the incidence of complex ventricular arrhythmias. Thus, Mg should be employed as first-line therapy in digitalis intoxication and drug-related torsade de pointes, and should be considered an important adjuvant therapy in hypertensives treated with diuretics and patients with acute myocardial infarction.

Potential role of potassium as a determinant of morbidity and mortality in patients with systemic hypertension and congestive heart failure

Prehistoric animals and humans consumed a diet low in sodium but high in potassium, and thus, evolutionary forces fostered the development of physiologic systems that conserved sodium and excreted potassium. With the advent of civilized societies, food cooking and processing have greatly increased the sodium but decreased the potassium content of the diet. However, there has been little time for physiologic systems to adapt. The resulting excess of sodium has been implicated as an important factor in the development of hypertension and congestive heart failure. This traditional focus on sodium has ignored the potential role that an inadequate dietary intake of potassium might play in the degenerative diseases of the heart, brain and kidney. Yet dietary potassium may be as powerful a determinant of cardiovascular morbidity and mortality as dietary sodium. In experimental and clinical hypertension, an increased intake of potassium (without a change in dietary sodium) can reduce blood pressure, may suppress the activity of the sympathetic nervous and renin-angiotensin systems, and can prevent the development of vascular injury; conversely, potassium depletion has been associated with an increase in stroke and sudden death. In patients with chronic heart failure, potassium can modify both the mechanical and electrical properties of the heart, it can exert diuretic effects, and it can reduce the frequency and complexity of potentially lethal ventricular tachyarrhythmias. Given this central role, the effects of many pharmacologic interventions on the morbidity and mortality of patients with hypertension or chronic heart failure can be enhanced or diminished by the effect that these treatments might have on potassium homeostasis.(ABSTRACT TRUNCATED AT 250 WORDS)

Serum magnesium increases following severe hemorrhage in dogs blocked by verapamil treatment

The opening of voltage sensitive calcium channels is an important event in the progression of irreversible shock, allowing the entry of toxic amounts of calcium (Ca2+) into the cells. Because intracellular magnesium (Mg2+) can efflux through these same channels, changes in serum Mg2+ may reflect the patency of these channels. In this study, electrolytes and selected serum enzymes were monitored in chronically instrumented conscious dogs to follow the progression of shock following a fixed volume hemorrhage. Plasma enzymes indicative of liver damage were elevated only in the terminal phase of hemorrhagic decompensation. A significant increase in serum Mg2+ was evident 60 min following hemorrhage, even though arterial pressure was still recovering. Serum Mg2+ continued to rise throughout the recovery and decompensating phases of shock. Verapamil treatment, which increased survival time and survival rate, significantly attenuated the changes in serum Mg2+ which normally followed hemorrhage. These results indicate that serum Mg2+ may be a useful indicator of the severity and the progression of hemorrhagic shock.

Cardiovascular consequences of magnesium deficiency and loss: pathogenesis, prevalence and manifestations--magnesium and chloride loss in refractory potassium repletion

Dietary magnesium (Mg) deficiency is more prevalent than generally suspected and can cause cardiovascular lesions leading to disease at all stages of life. The average American diet is deficient in Mg, especially in the young, in alcoholic persons, and in those under stress or with diseases or receiving certain drug therapies, who have increased Mg needs. Otherwise normal, Mg-deficient diets cause arterial and myocardial lesions in all animals studied, and diets that are atherogenic, thrombogenic and cardiovasopathic, as well as Mg-deficient, intensify the cardiovascular lesions, whereas Mg supplementation prevents them. Diuretics and digitalis can intensify an underlying Mg deficiency, leading to cardiac arrhythmias that are refractory unless Mg is added to the regimen. Potassium (K) depletion in diuretic-treated hypertensive patients has been linked to an increased incidence of ventricular ectopy and sudden death. K supplementation alone is not the answer. Mg has been found to be necessary to intracellular K repletion in these patients. Because patients with congestive heart failure and others receiving diuretic therapy are also prone to chloride loss leading to metabolic alkalosis that also interferes with K repletion, the addition of Mg and chloride supplements in addition to the K seems prudent.

Hypomagnesemia in patients in postoperative intensive care

In order to study the clinical consequences of postoperative hypomagnesemia, the serum magnesium (Mg) concentration was measured in samples of blood collected from 193 patients admitted to two postoperative ICUs. On admission to the ICU, 117 patients (61 percent) had hypomagnesemia (serum Mg less than 1.5 mEq/dl), 66 patients (34 percent) had normomagnesemia (1.5 to 2.0 mEq/dl), and ten patients (5 percent) had hypermagnesemia (greater than 2.0 mEq/dl). There were no correlations between the severity of illness score (r = 0.145) or the degree of hypoproteinemia (r = 0.01) and the postoperative serum Mg level. Patients with severe hypomagnesemia (serum Mg less than or equal to 1.0 mEq/dl) experienced hypokalemia more often (p less than 0.02) than the others in the study. Furthermore, those with severe hypomagnesemia had a higher mortality rate (7/17 or 41 percent) than the remainder of the population studied (22/176 or 13 percent) (p less than 0.02). Those with severe hypomagnesemia had received aminoglycosides more often (p less than 0.001) than those with normal serum Mg concentrations. The serum Mg level was not a sensitive (68 percent) or specific (37 percent) predictor of survival. Our conclusions were as follows: (1) hypomagnesemia is common in postoperative ICU patients; and (2) patients in the postoperative ICU who have severe hypomagnesemia have a higher mortality and more hypokalemia than similarly ill patients with normomagnesemia. Because of the association between aminoglycoside therapy and severe hypomagnesemia, we recommend measurement of this variable in those patients receiving aminoglycosides. Furthermore, Mg replacement therapy is recommended for those patients with serum Mg values of 1 mEq/dl or less.

Effects of magnesium on ischemic and reperfusion arrhythmias in the rat heart and electrophysiologic effects of hypermagnesemia in the anesthetized dog

Magnesium sulfate, reportedly clinically effective against some ventricular arrhythmias, has not been extensively studied for its effects on experimental ischemic and reperfusion arrhythmias. We evaluated the effects of three high extracellular concentrations of magnesium (Mg2+) 1.19, 2.38, and 4.76 mM in 70 isolated perfused rat hearts following coronary artery ligation and reperfusion, at each of three different perfusate ionized calcium (Ca2+) concentrations (0.9, 1.25, and, 2.5 mM), where 1.25 mM is close to physiologic. At 0.9 mM Ca2+, higher concentrations of Mg2+ increased the sinus node cycle length (p less than 0.02) and virtually abolished ischemic ventricular tachycardia (VT) and reperfusion ventricular fibrillation (VF) (p less than 0.01), otherwise consistently found in this model. At 1.25 and 2.5 mM Ca2+ increasing Mg2+ had no effect on the incidence of ischemic or reperfusion arrhythmias, although at 1.25 mM Ca2+ ischemic VT had longer cycle lengths and VT appeared after a longer delay (p less than 0.01). In the nonischemic dog heart, marked increases of serum Mg2+ progressively prolonged the A-H, H-V, and QR S intervals, the ventricular effective refractory period, and the sinus cycle length, while the arterial blood pressure fell. Because of its relatively modest electrophysiologic and hemodynamic effects, it is inferred that intravenous magnesium may be given therapeutically with relative safety.

Magnesium metabolism in health and disease

Magnesium is an important element for health and disease. Magnesium, the second most abundant intracellular cation, has been identified as a cofactor in over 300 enzymatic reactions involving energy metabolism and protein and nucleic acid synthesis. Approximately half of the total magnesium in the body is present in soft tissue, and the other half in bone. Less than 1% of the total body magnesium is present in blood. Nonetheless, the majority of our experimental information comes from determination of magnesium in serum and red blood cells. At present, we have little information about equilibrium among and state of magnesium within body pools. Magnesium is absorbed uniformly from the small intestine and the serum concentration controlled by excretion from the kidney. The clinical laboratory evaluation of magnesium status is primarily limited to the serum magnesium concentration, 24-hour urinary excretion, and percent retention following parenteral magnesium. However, results for these tests do not necessarily correlate with intracellular magnesium. Thus, there is no readily available test to determine intracellular/total body magnesium status. Magnesium deficiency may cause weakness, tremors, seizures, cardiac arrhythmias, hypokalemia, and hypocalcemia. The causes of hypomagnesemia are reduced intake (poor nutrition or IV fluids without magnesium), reduced absorption (chronic diarrhea, malabsorption, or bypass/resection of bowel), redistribution (exchange transfusion or acute pancreatitis), and increased excretion (medication, alcoholism, diabetes mellitus, renal tubular disorders, hypercalcemia, hyperthyroidism, aldosteronism, stress, or excessive lactation). A large segment of the U.S. population may have an inadequate intake of magnesium and may have a chronic latent magnesium deficiency that has been linked to atherosclerosis, myocardial infarction, hypertension, cancer, kidney stones, premenstrual syndrome, and psychiatric disorders. Hypermagnesemia is primarily seen in acute and chronic renal failure, and is treated effectively by dialysis.