Effect of acute magnesium administration on the frequency of ventricular arrhythmia in patients with heart failure

How much magnesium sulfate is needed to "keep total serum magnesium above 2.0 mg/dL"?

For patients at increased risk of life-threating ventricular arrythmias, hospitalists often administer intravenous magnesium sulfate to maintain total serum magnesium concentration (TsMg) above 2 mg/dL. How long each dose keeps TsMg above this threshold is not well known, however. We collected TsMg values from 12,618 veterans who were given 24,363 doses of intravenous magnesium sulfate during 14,901 hospitalizations for acute heart failure. Across dose amounts, the average TsMg dropped below 2.0 mg/dL within 24 h of administration. When we limited our analysis to 2 g doses (the most common dose) and adjusted for baseline TsMg, estimated glomerular filtration rate, oral magnesium supplementation, and loop diuretic dosing, we found that less than half of the adjusted TsMg values remained above 2.0 mg/dL just 12 h after dose administration. Hospitalists should expect, on average, to administer 2 g intravenous magnesium sulfate at least twice daily to maintain total serum magnesium above 2 mg/dL.

Hypomagnesemia in critically ill patients

BACKGROUND

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

MAIN BODY

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

CONCLUSION

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

Association of Serum Magnesium on Mortality in Patients Admitted to the Intensive Cardiac Care Unit

BACKGROUND

Although electrolyte disturbances may affect cardiac action potential, little is known about the association between serum magnesium and corrected QT (QTc) interval as well as clinical outcomes.

METHODS

A consecutive 8498 patients admitted to the Mayo Clinic Hospital-Rochester cardiac care unit (CCU) from January 1, 2004 through December 31, 2013 with 2 or more documented serum magnesium levels, were studied to test the hypothesis that serum magnesium levels are associated with in-hospital mortality, sudden cardiac death, and QTc interval.

RESULTS

Patients were 67 ± 15 years; 62.2% were male. The primary diagnoses for CCU admissions were acute myocardial infarction (50.7%) and acute decompensated heart failure (42.5%), respectively. Patients with higher magnesium levels were older, more likely male, and had lower glomerular filtration rates. After multivariate analyses adjusted for clinical characteristics including kidney disease and serum potassium, admission serum magnesium levels were not associated with QTc interval or sudden cardiac death. However, the admission magnesium levels ≥2.4 mg/dL were independently associated with an increase in mortality when compared with the reference level (2.0 to <2.2 mg/dL), having an adjusted odds ratio of 1.80 and a 95% confidence interval of 1.25-2.59. The sensitivity analysis examining the association between postadmission magnesium and analysis that excluded patients with kidney failure and those with abnormal serum potassium yielded similar results.

CONCLUSION

This retrospective study unexpectedly observed no association between serum magnesium levels and QTc interval or sudden cardiac death. However, serum magnesium ≥2.4 mg/dL was an independent predictor of increased hospital morality among CCU patients.

Effects of Oral Administration of CrCl3 on the Contents of Ca, Mg, Mn, Fe, Cu, and Zn in the Liver, Kidney, and Heart of Chicken

This study aimed to investigate the effects of oral administration of trivalent chromium on the contents of Ca, Mg, Mn, Fe, Cu, and Zn in the heart, liver, and kidney. Different levels of 1/8, 1/4, and 1/2 LD50 (LD50 = 5000 mg/kg body mass) CrCl3 milligrams per kilogram body mass daily were added into the water to establish the chronic poisoning model. Ca, Mg, Mn, Fe, Cu, and Zn were detected with the flame atomic absorption spectrometry in the organs exposed 14, 28, and 42 days to CrCl3, respectively. Results showed that Cr was accumulated in the heart, liver, and kidney significantly (P < 0.05) with extended time and dose. The contents of Ca and Fe increased, whereas those of Mg, Mn, Cu, and Zn decreased in the heart, liver, and kidney of each treated group, which had a dose- and time-dependent relationship, but the contents of Mg and Zn in the heart took on a fluctuated change. These particular observations were different from those in the control group. In conclusion, the oral administration of CrCl3 could change the contents of Ca, Mg, Mn, Fe, Cu, and Zn in the heart, liver, and kidney, which may cause disorders in the absorption and metabolism of the metal elements of chickens.

Magnesium Lowers the Incidence of Postoperative Junctional Ectopic Tachycardia in Congenital Heart Surgical Patients: Is There a Relationship to Surgical Procedure Complexity?

Magnesium sulfate was given to pediatric cardiac surgical patients during cardiopulmonary bypass period in an attempt to reduce the occurrence of postoperative junctional ectopic tachycardia (PO JET). We reviewed our data to evaluate the effect of magnesium on the occurrence of JET and assess a possible relationship between PO JET and procedure complexity. A total of 1088 congenital heart surgeries (CHS), performed from 2005 to 2010, were reviewed. A total of 750 cases did not receive magnesium, and 338 cases received magnesium (25 mg/kg). All procedures were classified according to Aristotle score from 1 to 4. Overall, there was a statistically significant decrease in PO JET occurrence between the two groups regardless of the Aristotle score, 15.3 % (115/750) in non-magnesium group versus 7.1 % (24/338) in magnesium group, P < 0.001. In the absence of magnesium, the risk of JET increased with increasing Aristotle score, P = 0.01. Following magnesium administration and controlling for body weight, surgical and aortic cross-clamp times in the analyses, reduction in adjusted risk of JET was significantly greater with increasing Aristotle level of complexity (JET in non-magnesium vs. magnesium group, Aristotle level 1: 9.8 vs. 14.3 %, level 4: 11.5 vs. 3.2 %; odds ratio 0.54, 95 % CI 0.31-0.94, P = 0.028). Our data confirmed that intra-operative usage of magnesium reduced the occurrence of PO JET in a larger number and more diverse group of CHS patients than has previously been reported. Further, our data suggest that magnesium's effect on PO JET occurrence seemed more effective in CHS with higher levels of Aristotle complexity.

Relation of serum magnesium levels and postdischarge outcomes in patients hospitalized for heart failure (from the EVEREST Trial)

Serum magnesium levels may be impacted by neurohormonal activation, renal function, and diuretics. The clinical profile and prognostic significance of serum magnesium level concentration in patients hospitalized for heart failure (HF) with reduced ejection fraction is unclear. In this retrospective analysis of the placebo group of the Efficacy of Vasopressin Antagonism in Heart Failure Outcome Study with Tolvaptan trial, we evaluated 1,982 patients hospitalized for worsening HF with ejection fractions ≤40%. Baseline magnesium levels were measured within 48 hours of admission and analyzed as a continuous variable and in quartiles. The primary end points of all-cause mortality (ACM) and cardiovascular mortality or HF rehospitalization were analyzed using Cox regression models. Mean baseline magnesium level was 2.1 ± 0.3 mg/dl. Compared with the lowest quartile, patients in the highest magnesium level quartile were more likely to be older, men, have lower heart rates and blood pressures, have ischemic HF origin, and have higher creatinine and natriuretic peptide levels (all p <0.003). During a median follow-up of 9.9 months, every 1-mg/dl increase in magnesium level was associated with higher ACM (hazard ratio [HR] 1.77; 95% confidence interval [CI] 1.35 to 2.32; p <0.001) and the composite end point (HR 1.44; 95% CI 1.15 to 1.81; p = 0.002). However, after adjustment for known baseline covariates, serum magnesium level was no longer an independent predictor of either ACM (HR 0.94, 95% CI 0.69 to 1.28; p = 0.7) or the composite end point (HR 1.01, 95% CI 0.79 to 1.30; p = 0.9). In conclusion, despite theoretical concerns, baseline magnesium level was not independently associated with worse outcomes in this cohort. Further research is needed to understand the importance of serum magnesium levels in specific HF patient populations.

Comparison of intravenous and oral magnesium replacement in hospitalized patients with cardiovascular disease

PURPOSE

The results of an investigation of serum magnesium concentrations (SMCs) after i.v. versus oral delivery of magnesium in cardiovascular critical care are presented.

METHODS

A retrospective case review was conducted to compare the net gain of magnesium after i.v. (n = 188) or oral (n = 164) magnesium therapy for the prevention of ventricular fibrillation and arrhythmias in patients hospitalized for serious cardiovascular disorders, as determined by assessing SMCs. The primary study outcome was the change from baseline SMC values 6-24 hours after the completion of magnesium courses; secondary outcomes included the impact of renal impairment, concomitant medication use, and other clinical variables on SMC changes.

RESULTS

Although consistent elevations in SMC were produced by oral magnesium delivery, i.v. administration resulted in greater and more rapid elevations relative to baseline SMC. The degree of change in SMC was significantly influenced by the timing of SMC measurement after a magnesium course, by renal function, and by concomitant use of i.v. loop diuretics.

CONCLUSION

A comparison of 24-hour courses of magnesium replacement therapy showed that magnesium sulfate 2 g i.v. was associated with larger changes in SMC than magnesium oxide 800, 1200, or 1600 mg orally when the baseline SMC was 1.4-1.8 mg/dL. At baseline SMCs of 1.4-1.8 mg/dL, oral magnesium oxide provided a consistent median increase in SMC of 0.1 mg/dL. The change in the number of bowel movements did not differ significantly between courses of i.v. magnesium sulfate and oral magnesium oxide.

Spironolactone Reduced Arrhythmia and Maintained Magnesium Homeostasis in Patients With Congestive Heart Failure

BACKGROUND

Patients with congestive heart failure (CHF) often have increased aldosterone activity that leads to hypomagnesemia. Hypomagnesemia can induce arrhythmias, an important cause of death in patients with CHF. We determined whether the aldosterone receptor antagonist spironolactone improved magnesium homeostasis and reduced arrhythmias in patients with CHF.

METHODS AND RESULTS

We randomized 116 consecutive patients with CHF into placebo control group (n = 58) and spironolactone group (20 mg daily, n = 58) in addition to conventional therapy. Plasma magnesium concentration (PMC), erythrocyte magnesium concentration (EMC), and erythrocyte magnesium efflux were not different between the 2 groups of patients before treatment. Compared with control patients, patients treated with spironolactone for 6 months had increased PMC and EMC and decreased erythrocyte magnesium efflux. Patients on spironolactone therapy also had a marked decrease of 24-hour mean heart rate, ventricular and atrial premature beats, and the risk of atrial fibrillation/flutter. Pooled data from the 116 patients showed that patients with a higher EMC or a lower sodium-dependent erythrocyte magnesium efflux had a slower heart rate, fewer ventricular premature beats, and a lower risk of atrial fibrillation/flutter.

CONCLUSIONS

Our results suggest that reducing cellular magnesium efflux and loss may contribute to the spironolactone-reduced arrhythmias in patients with CHF.

Use of nonantiarrhythmic drugs for prevention of sudden cardiac death

It is of interest that the drugs having the most significant impact on total and sudden death mortality are those without direct electrophysiologic actions on myocardial excitable tissue. This observation may provide insight into mechanisms responsible for ventricular tachyarrhythmias causing cardiac arrest. One way to think about ventricular fibrillation is that it is the final common pathway of an electrically unstable heart. After all, the heart can "die" in only three major ways: electromechanical dissociation, asystole and heart block, and ventricular fibrillation, with the latter most common. It is the "upstream" events provoking the electrical instability that these drugs probably act upon (i.e., ischemia, fibrosis). Although we unquestionably need to pursue investigations into the electrophysiology of these ventricular tachyarrhythmias, more studies need to investigate the drugs affecting upstream events, because these agents appear to yield the greatest dividends, at least for the present. This article reviews these drugs and how they may be effective.

Body Weight-Related ionized hypomagnesemia in pediatric patients undergoing cardiopulmonary bypass for surgical repair of congenital cardiac defects

STUDY OBJECTIVES

To examine the serial time course of perioperative plasma ionized magnesium (iMg(2+)) concentrations and to analyze the plasma iMg(2+) concentrations in children with different body mass who were undergoing open-heart surgery.

DESIGN

Randomized, single-blinded study.

SETTING

University-affiliated hospital of an academic medical institution.

PATIENTS

38 children undergoing open-heart surgery.

INTERVENTIONS

Patients were divided into three groups according to their body mass: Group 1 (n = 12) <10 kg, Group 2 (n = 13) 10 kg to 20 kg, and Group 3 (n = 13) >20 kg.

MEASUREMENTS

The relationship of iMg(2+) among the three groups of different body mass were analyzed at five different time intervals during the operation: induction of anesthesia, 5 minutes and 30 minutes after the onset of cardiopulmonary bypass (CPB), the beginning of rewarming, and the end of surgery.

MAIN RESULTS

iMg(2+) levels at 5 minutes after onset of CPB in patients weighing less than 20 kg (Groups 1 and 2) differed with those weighing more than 20 kg (Group 3) (p = 0.007 and 0.013). However, there was no difference in the iMg(2+) levels between Groups 1 and 2 (p = 0.993). In addition, iMg(2+) levels at 5 minutes after onset of bypass correlated well (r(2) = 0.66) in children with body mass less than 20 kg.

CONCLUSIONS

Low levels of ionized magnesium is an important finding in patients at the onset of CPB, which correlates well with the body mass of patients weighing less than 20 kg, and could be predicted by the regression curve. Based on these findings, hypomagnesemia can be prevented during CPB.

The role of magnesium in the emergency department

Magnesium has been advocated for the treatment of a variety of conditions seen in emergency medicine. The authors present a systematic review and advice on appropriate indications for its use. Evidence supports its use in severe asthma, eclampsia, and torsade de pointes. There is insufficient evidence to justify its routine use in other emergencies.

Digoxin

After 200 years of use, digitalis still appears to have a place in our armamentarium for heart failure and atrial fibrillation despite the proven survival benefits with ACE inhibitors and beta-blockers. Digoxin therapy is inexpensive and well tolerated and may result in considerable savings. Digoxin is the only oral inotrope that does not increase mortality in heart failure patients, particularly if low doses are being used. Digoxin therapy should be used in patients with systolic heart failure who continue to have signs and symptoms despite therapeutic doses of ACE inhibitors or diuretics or in patients with atrial fibrillation with or without heart failure for rate control.

Cardiovascular actions of magnesium

Intracellular magnesium is an important modulator of calcium and potassium channels in cardiac myocytes. Hypomagnesemia is common in hospitalized patients and may contribute significantly to cardiac morbidity and mortality, particularly in states associated with myocardial ischemia. Therefore, it is important to maintain the plasma magnesium concentration within the normal range in asymptomatic patients and in patients with cardiac disease as prophylaxis against the occurrence of significant arrhythmias.

Postoperative atrial tachyarrhythmias in patients undergoing coronary artery bypass graft surgery without cardiopulmonary bypass: a role for intraoperative magnesium supplementation

OBJECTIVE

To determine if intraoperative magnesium supplementation would be associated with a reduction in postoperative atrial tachyarrhythmias (POAT) in patients undergoing coronary artery bypass grafting (CABG) surgery without cardiopulmonary bypass (off-pump CABG surgery).

DESIGN

Retrospective study.

SETTING

University Medical Center.

PARTICIPANTS

Patients who had undergone off-pump CABG surgery (n = 124).

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

The charts of 124 patients who had undergone off-pump CABG surgery (64 by anterior thoracotomy and 60 by median sternotomy) were retrospectively reviewed. Demographic data and perioperative care were recorded and compared among patients who did and did not experience POAT and among patients who did and did not receive intraoperative magnesium supplementation. Logistic regression analysis was used to assess the association between magnesium supplementation and incidence of POAT, controlling for other covariables. Of the 124 patients, 16 had a prior history of atrial or ventricular arrhythmias and/or were receiving antiarrhythmic medications. Medical records of the remaining 108 patients were reviewed. Twenty-four patients (22%) had POAT. Forty-two patients (39%) received intraoperative magnesium. In patients receiving intraoperative magnesium, the incidence of POAT was significantly decreased (12% v 29%; p = 0.03). In these patients, initial postoperative serum magnesium was significantly higher (2.37 mEq/L v 1.86 mEq/L; p < 0.01). In patients not receiving intraoperative magnesium, 35% had hypomagnesemia (serum magnesium < 1.8 mEq/L) compared with 9% of patients receiving magnesium (p < 0.01). Patients who received intraoperative magnesium and beta-adrenergic blockers had a lower incidence of POAT (5%) than patients who received only one (19%) or neither (33%) (p < 0.05).

CONCLUSIONS

Intraoperative magnesium supplementation is associated with a decrease in POAT after off-pump CABG surgery. The combination of a beta-blocker and magnesium may reduce POAT further. It is recommended that intraoperative magnesium supplementation be part of the care of patients undergoing off-pump CABG surgery.

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.

Hypomagnesemia in heart failure with ventricular arrhythmias. Beneficial effects of magnesium supplementation

OBJECTIVE

To assess the role of electrolyte imbalance in cardiac arrhythmias associated with congestive heart failure.

DESIGN

Serum magnesium and potassium levels, urine magnesium excretion and the incidence of ventricular arrhythmias were assessed throughout the study. The patients who displayed complex arrhythmias after the first week of hospital medication were randomized 2:1 to double-blind magnesium supplementation or placebo.

SETTING

The study was carried out in one municipal hospital, providing primary care.

SUBJECTS

A total of 588 consecutive patients were screened for eligibility (clinical heart failure >/=6 months; NYHA class II-IV; left ventricular ejection fraction </=40%; sinus rhythm; serum creatinine </=2 mg dL-1). A total of 78 patients entered and 68 patients completed the study.

INTERVENTIONS

Intravenous administration of magnesium (magnesium sulphate 8 g in 250 mL of 5% glucose) or placebo (250 mL of 5% glucose) over 12 h.

MAIN OUTCOME MEASURES

(i) Incidence of ventricular arrhythmias in patients with hypomagnesemia; (ii) effects of magnesium supplementation on ventricular arrhythmias.

RESULTS

On admission, hypomagnesemia was found in 38% and excessive magnesium loss in 72% of patients. Serum magnesium levels were lower and urine magnesium excretion was greater in patients with complex ventricular arrhythmias, both on admission and after treatment for heart failure. Intravenous administration of magnesium caused a significant decrease in the number of ventricular ectopic beats (P < 0.0001), couplets (P < 0.003) and episodes of nonsustained ventricular tachycardia (P < 0.01).

CONCLUSIONS

Hypomagnesemia, probably related to increased urine magnesium excretion, is an essential feature of heart failure associated with complex ventricular arrhythmias. These arrhythmias can be alleviated/abolished by magnesium supplementation.

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

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.

Randomised trial of magnesium in in-hospital cardiac arrest. Duke Internal Medicine Housestaff

BACKGROUND

The apparent benefit of magnesium in acute myocardial infarction, and the persistently poor outcome after cardiac arrest, have led to use of magnesium in cardiopulmonary resuscitation. Because few data on its use in cardiac arrest were available, we undertook a randomised placebo-controlled trial (MAGIC trial).

METHODS

Patients treated for cardiac arrest by the Duke Hospital code team were randomly assigned intravenous magnesium (2 g [8 mmoles] bolus, followed by 8 g [32 mmoles] over 24 h; 76 patients) or placebo (80 patients). Only patients in intensive care or general wards were eligible; those whose cardiac arrest occurred in emergency, operating, or recovery rooms were excluded. The primary endpoint was return of spontaneous circulation, defined as attainment of any measurable blood pressure or palpable pulse for at least 1 h after cardiac arrest. The secondary endpoints were survival to 24 h, survival to hospital discharge, and neurological outcome. Analysis was by intention to treat.

FINDINGS

There were no significant differences between the magnesium and placebo groups in the proportion with return of spontaneous circulation (41 [54%] vs 48 [60%], p = 0.44), survival to 24 h (33 [43%] vs 40 [50%], p = 0.41), survival to hospital discharge (16 [21%] vs 17 [21%], p = 0.98), or Glasgow coma score (median 15 in both).

INTERPRETATION

Empirical magnesium supplementation did not improve the rate of successful resuscitation, survival to 24 h, or survival to hospital discharge overall or in any subpopulation of patients with in-hospital cardiac arrest.

Arrhythmias and sudden death in heart failure

Survival of patients with heart failure has improved over the past decade due to advances in medical therapy. Sudden death continues to cause 20 to 50% of deaths. Ventricular arrhythmias are common in patients with heart failure. Ventricular hypertrophy, scars from prior myocardial infarction, sympathetic activation, and electrolyte abnormalities contribute. Some sudden deaths are due to bradyarrhythmias and electromechanical dissociation rather than ventricular arrhythmias. The risks and benefits of antiarrhythmic therapies continue to be defined. Class I antiarrhythmic drugs should be avoided due to proarrhythmic and negative inotropic effects that may increase mortality. For patients resuscitated from sustained ventricular tachycardia (VT) or ventricular fibrillation (VF) amiodarone or an implantable cardioverter defibrillator (ICD) should be considered. ICDs markedly reduce sudden death in VT/VF survivors, but in advanced heart failure, this may not markedly extend survival. Catheter or surgical ablation can be considered for selected patients with bundle branch reentry VT or difficult to control monomorphic VT. For patients who have not had sustained VT/VF antiarrhythmic therapy should generally be avoided, but may benefit some high risk patients. Amiodarone may be beneficial in patients with advanced heart failure and rapid resting heart rates. ICDs may improve survival in selected survivors of myocardial infarction who have inducible VT.

Tissue magnesium levels and the arrhythmic substrate in humans

INTRODUCTION

Magnesium deficiency has been implicated in the pathogenesis of sudden death, but the investigation of arrhythmic mechanisms has been hindered by difficulties in measuring cellular tissue magnesium stores.

METHODS AND RESULTS

To see if magnesium deficiency is associated with a propensity toward triggered arrhythmias, we measured tissue magnesium levels and QT interval dispersion (as an index of repolarization dispersion) in 40 patients with arrhythmic complaints. Magnesium was measured in sublingual epithelium using X-ray dispersive analysis. QT interval dispersion was assessed on 12-lead surface ECGs in all patients, and programmed stimulation was performed in 28. The sublingual epithelial magnesium level ([Mg]1), but the not the serum level, correlated inversely with QT interval dispersion in 40 patients (r = 0.58, P < 0.005); in 12 patients undergoing repeat testing on therapy, the change in magnesium also correlated inversely with the change in QT dispersion (r = 0.61, P < 0.05). Patients with left ventricular ejection fractions > 40% had significantly higher tissue magnesium and lower QT dispersion (34.5 +/- 0.5 mEq/L, 81 +/- 8 msec) than those with left ventricular ejection fractions < 40% (32.7 +/- 0.5 mEq/L, P < 0.01, and 114 +/- 9 msec, P < 0.05). There was no difference in either [Mg]1 or QT dispersion in the 16 patients with inducible monomorphic ventricular tachycardia versus the 12 noninducible patients.

CONCLUSION

Reduced tissue magnesium stores may represent a significant risk factor for arrhythmias associated with abnormal repolarization, particularly in patients with poor left ventricular systolic function, but may not represent a risk for excitable gap arrhythmias associated with a fixed anatomic substrate (e.g., monomorphic ventricular tachycardia).

[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.

The influence of cardiopulmonary bypass on ionized magnesium in neonates, infants, and children undergoing repair of congenital heart lesions

The purpose of this study was to measure the ionized magnesium (iMg) concentrations in children undergoing the correction of congenital heart defects. iMg levels were measured in 115 consecutive patients at five sample periods: prebypass, onset of bypass, during rewarming, immediately postbypass, and 1 h postbypass using an ion-selective electrode of the NOVA-CRT 8 (Nova Biomedical, Watham, MA). The incidence of dysrythmias was noted. Patients were divided into two groups: those who received Plegisol as the cardioplegic solution and those who did not. This study demonstrates that iMg decreases with the onset of cardiopulmonary bypass (CPB) in patients who weigh < 10 kg. In the Plegisol group, all subgroups of patients demonstrated statistically higher iMg during the rewarming phase of CPB, immediately post-CPB, and 1 h post-CPB, when compared with control values. The probability of dysrhythmias in the Plegisol group was almost twice that of the non-Plegisol group. However, this did not reach statistical significance (P = 0.22). The results of our study demonstrate that the use of CPB on pediatric patients produces alterations in the iMg. The changes differ depending on both patient weight and the use of a magnesium-containing cardioplegic solution, exemplified here by Plegisol. The role of these changes in iMg on dysrhythmias could not be further evaluated.

Effects of pretreatment with magnesium on muscle relaxation and cardiovascular responses in tracheal intubation using the priming principle for vecuronium

In addition to its direct effects on blood vessels, the myocardium, and neuromuscular junctions, magnesium can act as an adrenergic antagonist and can inhibit the release of catecholamines both from adrenergic nerve terminals and from the adrenal medulla. This study was undertaken to evaluate these effects of magnesium on muscle relaxation and cardiovascular response during tracheal intubation. Forty ASA I or II patients undergoing elective surgery were allocated to a magnesium or a control group. Three minutes after priming with vecuronium 0.015 mg·kg^-1, the magnesium group received vecuronium 0.085 mg·kg^-1 and magnesium sulfate 40 mg·kg^-1, while the control group received an equivalent volume of vecuronium and saline. The percent change from baseline in mean arterial pressure after tracheal intubation was significantly smaller (P<0.01) in the magnesium group than in the control group, but the percent change in heart rate was similar. There were no significant changes in plasma catecholamine concentrations after tracheal intubation in either group. The onset time of vecuronium was significantly shorter in the magnesium group than in the control group. The duration of action of vecuronium was significantly longer in the magnesium group than in the control group. Serum magnesium concentrations at 90 min after its administration were significantly higher than baseline. We concluded that vecuronium priming with magnesium pretreatment inhibits the hypertension associated with tracheal intubation and shortens the onset time of vecuronium, but prolongs it duration of action.

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.

Antiarrhythmic effects of magnesium sulphate. Report of three cases

A wide variety of antiarrhythmic agents is used in treatment of both supraventricular and ventricular arrhythmias. Magnesium sulphate has previously been used mainly in the treatment of torsade de pointe arrhythmias but several reports show that this agent may be used in the treatment of arrhythmias of different aetiology. We describe 3 patients who exhibited arrhythmias affecting haemodynamic performance. Case #1 had a subarachnoid haemorrhage and developed a supraventricular tachycardia. In case #2, ventricular tachycardia appeared during the postoperative course after abdominal surgery. Case #3 experienced critical heart failure due to dilated cardiomyopathy and had an irregular heart rhythm with multiple ectopic beats. In all three cases the administration of intravenous magnesium sulphate was successful in treating the arrhythmias. Magnesium sulphate is an antiarrhythmic agent that is effective mainly in treatment of ventricular arrhythmias. The drug can also be employed as second-line treatment of supraventricular arrhythmias.

Progressive magnesium deficiency increases mortality from endotoxin challenge: protective effects of acute magnesium replacement therapy

OBJECTIVES

To study the effects of endotoxin on magnesium homeostasis; to determine if progressive magnesium deficiency alters outcome from endotoxin challenge; and to evaluate the efficacy of magnesium therapy in reducing endotoxin-induced mortality.

DESIGN

Prospective, placebo-controlled, randomized, multiexperiment studies.

SETTING

Research laboratory of a university hospital.

SUBJECTS

Male Sprague Dawley rats (n = 299).

INTERVENTIONS

Experiment 1 was designed to test if endotoxin alters magnesium homeostasis. Circulating total and ionized magnesium (estimated by ultrafilterable values) concentrations were determined in blood samples collected from animals after the randomized administration of placebo or 0.3, 3.0, or 30 mg/kg of endotoxin. A baseline blood sample was collected and then a second blood sample was obtained at 5, 15, 30, 60, 120, or 180 mins after endotoxin or placebo administration. In experiment 2, animals were randomized to receive magnesium-sufficient diets or magnesium-deficient diets for 6 wks. After 6 wks, the effects of the randomized administration of 3.0 mg/kg endotoxin or placebo were evaluated on mortality and analyte values (pH and blood gases, sodium, potassium, chloride, glucose, ionized calcium, hematocrit, total and ultrafilterable magnesium concentrations) in the three study groups (magnesium-sufficient, 3-wk magnesium-deficient, or 6-wk magnesium-deficient). In experiment 3, magnesium-deficient animals were randomized to receive 50 mmol/kg magnesium chloride or placebo, before or after the administration of 3.0 mg/kg of endotoxin. Baseline and 24-hr analyte determinations were performed and outcome was analyzed.

MEASUREMENTS AND MAIN RESULTS

Experiment 1: Significant increases (p < .05) in circulating total magnesium concentrations were found in animals that received 30 mg/kg of endotoxin, at 120 mins (0.79 +/- 0.10 vs. 0.60 +/- 0.05 mmol/L), and 180 mins (0.74 +/- 0.04 vs. 0.56 +/- 0.04 mmol/L) compared with baseline values. Similarly, significant increases (p < .05) in ionized magnesium concentrations were observed 120 and 180 mins after 3.0 and 30 mg/kg of endotoxin compared with baseline values. Experiment 2: Magnesium deficiency was strongly (p < .02) associated with increased mortality from endotoxin challenge. Endotoxin administration (3.0 mg/kg) was lethal in 10 (43%) of 23 magnesium-sufficient animals, 15 (65%) of 23 3-wk magnesium-deficient animals, and 20 (83%) of 24 6-wk magnesium-deficient animals. Experiment 3: In magnesium-deficient animals, rats treated with magnesium replacement therapy had significantly increased survival from endotoxin administration (15 [52%] of 29 vs. five [17%] of 29, p < .01) compared with placebo-treated animals.

CONCLUSIONS

a) Endotoxin challenge causes significant increases in circulating total and ionized magnesium concentrations. b) Progressive magnesium deficiency is strongly associated with increased lethality, and magnesium replacement therapy provides significant protection from endotoxin challenge. c) These experimental results support the concept that cellular injury is probably associated with increases in circulating magnesium concentrations. Furthermore, these experimental findings suggest that magnesium deficiency predisposes to worse outcome from endotoxin challenge, and that replacement therapy in the setting of magnesium deficiency may be warranted, especially in critically ill subjects.

Review of nonparametric methods for the analysis of crossover studies

This paper reviews nonparametric methods for the analysis of crossover studies. Primary attention is given to crossover studies to compare two treatments for a response variable that has a metric measurement level. For this situation, one can often test hypotheses or obtain confidence intervals for parameters of interest by applying well known univariate nonparametric rank methods (e.g., the Wilcoxon rank sum test, or the Wilcoxon signed rank test) to appropriately specified functions of the data. Related extensions are also available, to some degree, for crossover studies to compare more than two treatments or those for which the measurement level of the response variable is ordinal or has a censored time-to-event nature. Methods for several specific situations along these lines are discussed in terms of principles with potentially broader applicability. Several examples are provided to illustrate the performance of some of the methods.