Magnesium sulfate reduces myocardial infarct size when administered before but not after coronary reperfusion in a canine model

The bioresorbable magnesium scaffold (Magmaris)-State of the art: From basic concept to clinical application

Since its introduction to clinical practice, coronary artery stent implantation has become a crucial part of the therapy of coronary artery disease (CAD). Despite the undeniable evolution of percutaneous coronary revascularization procedures, drug-eluting stent (DES) technology shows some limitations. To overcome these limitations bioresorbable vascular scaffolds (BRS) were designed as a vessel-supporting technology allowing for anatomical and functional restoration of the vessel after the scaffold intended resorption. Various materials have been proposed as the basis of the scaffold backbone. In this narrative review, we present second-generation magnesium-alloy bioresorbable scaffold devices (Magmaris; Biotronik). Additionally, we discuss available preclinical and clinical data regarding this new magnesium BRS.

The Role of Hypomagnesemia in Cardiac Arrhythmias: A Clinical Perspective

The importance of magnesium (Mg²⁺), a micronutrient implicated in maintaining and establishing a normal heart rhythm, is still controversial. It is known that magnesium is the cofactor of 600 and the activator of another 200 enzymatic reactions in the human organism. Hypomagnesemia can be linked to many factors, causing disturbances in energy metabolism, ion channel exchanges, action potential alteration and myocardial cell instability, all mostly leading to ventricular arrhythmia. This review article focuses on identifying evidence-based implications of Mg²⁺ in cardiac arrhythmias. The main identified benefits of magnesemia correction are linked to controlling ventricular response in atrial fibrillation, decreasing the recurrence of ventricular ectopies and stopping episodes of the particular form of ventricular arrhythmia called torsade de pointes. Magnesium has also been described to have beneficial effects on the incidence of polymorphic ventricular tachycardia and supraventricular tachycardia. The implication of hypomagnesemia in the genesis of atrial fibrillation is well established; however, even if magnesium supplementation for rhythm control, cardioversion facility or cardioversion success/recurrence of AF after cardiac surgery and rate control during AF showed some benefit, it remains controversial. Although small randomised clinical trials showed a reduction in mortality when magnesium was administered to patients with acute myocardial infarction, the large randomised clinical trials failed to show any benefit of the administration of intravenous magnesium over placebo.

Biosafety and efficacy evaluation of a biodegradable magnesium-based drug-eluting stent in porcine coronary artery

Although the drug-eluting stent (DES) has become the standard for percutaneous coronary intervention (PCI)-based revascularization, concerns remain regarding the use of DES, mainly due to its permanent rigid constraint to vessels. A drug-eluting bioresorbable stent (BRS) was thus developed as an alternative to DES, which can be absorbed entirely after its therapeutic period. Magnesium (Mg)-based BRSs have attracted a great deal of attention due to their suitable mechanical properties, innovative chemical features, and well-proven biocompatibility. However, the primary disadvantage of Mg-based BRSs is the rapid degradation rate, resulting in the early loss of structural support long before the recovery of vascular function. Recently, a new type of patented Mg-Nd-Zn-Zr alloy (JDBM) was developed at Shanghai Jiao Tong University to reduce the degradation rate compared to commercial Mg alloys. In the present investigation, a poly(D,L-lactic acid)-coated and rapamycin eluting (PDLLA/RAPA) JDBM BRS was prepared, and its biosafety and efficacy for coronary artery stenosis were evaluated via in vitro and in vivo experiments. The degree of smooth muscle cell adhesion to the PDLLA/RAPA coated alloy and the rapamycin pharmacokinetics of JDBM BRS were first assessed in vitro. JDBM BRS and commercial DES FIREHAWK were then implanted in the coronary arteries of a porcine model. Neointimal hyperplasia was evaluated at 30, 90, and 180 days, and re-endothelialization was evaluated at 30 days. Furthermore, Micro-CT and optical coherence tomography (OCT) analyses were performed 180 days after stent implantation to evaluate the technical feasibility, biocompatibility, and degradation characteristics of JDBM BRS in vivo. The results show the ability of a PDLLA/RAPA coated JDBM to inhibit smooth muscle cell adhesion and moderate the drug release rate of JDBM BRS in vitro. In vivo, low local and systemic risks of JDBM BRS were demonstrated in the porcine model, with preserved mechanical integrity after 6 months of implantation. We also showed that this novel BRS was associated with a similar efficacy profile compared with standard DES and high anti-restenosis performance. These findings may confer long term advantages for using this BRS over a traditional DES.

Designing Better Cardiovascular Stent Materials - A Learning Curve

Cardiovascular stents are life-saving devices and one of the top 10 medical breakthroughs of the 21st century. Decades of research and clinical trials have taught us about the effects of material (metal or polymer), design (geometry, strut thickness, and the number of connectors), and drug-elution on vasculature mechanics, hemocompatibility, biocompatibility, and patient health. Recently developed novel bioresorbable stents are intended to overcome common issues of chronic inflammation, in-stent restenosis, and stent thrombosis associated with permanent stents, but there is still much to learn. Increased knowledge and advanced methods in material processing have led to new stent formulations aimed at improving the performance of their predecessors but often comes with potential tradeoffs. This review aims to discuss the advantages and disadvantages of stent material interactions with the host within five areas of contrasting characteristics, such as 1) metal or polymer, 2) bioresorbable or permanent, 3) drug elution or no drug elution, 4) bare or surface-modified, and 5) self-expanding or balloon-expanding perspectives, as they relate to pre-clinical and clinical outcomes and concludes with directions for future studies.

Association of Dietary Magnesium Intake with Fatal Coronary Heart Disease and Sudden Cardiac Death

Background: Postmenopausal women represent the highest population-based burden of cardiovascular disease, including sudden cardiac death (SCD). Our understanding of the etiology and risk factors contributing to fatal coronary heart disease (CHD) and SCD, particularly among women, is limited. This study examines the association between dietary magnesium intake and fatal CHD and SCD. Materials and Methods: We examined 153,569 postmenopausal women who participated in the Women's Health Initiative recruited between 1993 and 1998. Magnesium intake at baseline was assessed using a validated food frequency questionnaire, adjusting for energy via the residual method. Fatal CHD and SCD were identified over an average follow-up of 10.5 years. Results: For every standard deviation increase in magnesium intake, there was statistically significant risk reduction, after adjustment for confounders, of 7% for fatal CHD (hazard ratio [HR] 0.93, 95% confidence interval [CI] 0.89-0.97), and 18% risk reduction for SCD (HR 0.82, 95% CI 0.58-1.15) the latter of which did not reach statistical significance. In age-adjusted quartile analysis, women with the lowest magnesium intake (189 mg/day) had the greatest risk for fatal CHD (HR 1.54, 95% CI 1.40-1.69) and SCD (HR 1.70, 95% CI 0.94-3.07). This association was attenuated in the fully adjusted model, with HRs of 1.19 (95% CI 1.06-1.34) for CHD and 1.24 (95% CI 0.58-2.65) for SCD for the lowest quartile of magnesium intake. Conclusions: This study provides evidence of a potential inverse association between dietary magnesium and fatal CHD and a trend of magnesium with SCD in postmenopausal women. Future studies should confirm this association and consider clinical trials to test whether magnesium supplementation could reduce fatal CHD in high-risk individuals.

Magmaris™ resorbable magnesium scaffold: state-of-art review

Bioresorbable scaffolds (BRS) have been advocated as the ‘fourth revolution’ in interventional cardiology because they could provide temporary scaffolding and then ‘disappear’ (resorb) potentially significantly improving coronary artery disease treatment. BRS technology has gradually matured, and there are many devices available worldwide, which are currently undergoing preclinical or clinical testing. Due to the concerns related to polylactide scaffolds, magnesium alloy is now one of the most promising resorbable technologies despite available evidences on its performances in vivo are limited to small observational studies. In this state-of-art review we present Magmaris™ (Biotronik AG, Buelach, Switzerland) magnesium-based BRS from bench to bedside, reviewing to date available clinical trial data and current recommendations for its optimal use in clinical practice.

Cellular and molecular approaches to enhance myocardial recovery after myocardial infarction

Reperfusion therapy has resulted in significant improvement in post-myocardial infarction morbidity and mortality in over the last 4 decades. Nonetheless, it is well recognized that simply restoring patency of the epicardial artery may not stop or reverse damage at microvascular level, and myocardial salvage is often suboptimal. Numerous efforts have been undertaken to elucidate the mechanisms underlying extensive myonecrosis to facilitate the discovery of therapies to provide additional and incremental benefits over current therapeutic pathways. To date, conclusively effective strategies to promote myocardial recovery have not yet been established. Novel approaches are investigating the foundational cellular and molecular bases of myocardial ischemia and irreversible injury. Herein, we review the emerging concepts and proposed therapies that may improve myocardial protection and reduce infarct size. We examine the preclinical and clinical evidence for reduced infarct size with these strategies, including anti-inflammatory agents, intracellular ion channel modulators, agents affecting the reperfusion injury salvage kinase (RISK) and nitric oxide signaling pathways, modulators of mitochondrial function, anti-apoptotic agents, and stem cell and gene therapy. We review the potential reasons of failures to date and the potential for new strategies to further promote myocardial recovery and improve prognosis.

Colorimetric determination of glutathione by using a nanohybrid composed of manganese dioxide and carbon dots

A kind of single-layer carbon based dots (CDs) with abundant carboxyl functional groups was hybridized with manganese dioxide (MnO₂). The resulting nanohybrid is stable and can be well dispersed in water. MnO₂ is capable of oxidizing the substrate 3,3'5,5'-tetramethylbenzidine (TMB) to form a blue product whose absorption (peaking at 655 nm) fades in the presence of glutathione (GSH). A sensitive and selective colorimetric GSH assay was worked out that has a linear response in the 10 to 0.1 µM GSH concentration range, with a 0.095 μM detection limit. The method was applied to the determination of GSH in spiked fetal calf serum where it gave excellent recoveries. Graphical abstract Schematic of the preparation of a nanohybrid composed of manganese dioxide and carbon based dots (MnO₂/CDs). They can be used for the colorimetric detection of glutathione (GSH) based on the color change of 3,3'5,5'-tetramethylbenzidine (TMB).

Magnesium sulfate protects the heart against carbon monoxide-induced cardiotoxicity in rats

Carbon monoxide (CO), a toxic gas produced via incomplete fossil fuel combustion, has several poisonous effects in the heart including induction of necrosis, apoptosis, and electrocardiogram (ECG) changes. Magnesium sulfate (MS) is a drug with cardioprotective effects especially when used after ischemia/reperfusion. In the current study, we aimed to evaluate MS cardioprotective effects following CO poisoning. Animals were exposed to CO 3000 ppm for 1 h and immediately after the exposure period and on the next 4 days (a total of 5 consecutive doses given on a daily basis), MS (75, 150 and 300 mg/kg) was injected intraperitoneally (i.p.) and ECG was recorded focusing on ST-segment, T-wave, and Q-pathologic wave changes. On day 5, animals were sacrificed and their heart was excised for determination of BAX, BCL2 and Akt expression level using western blot analysis and necrosis investigations. The results showed that MS significantly decreased necrosis and BAX/BCL2 ratio (P < 0.001) while pro-survival protein Akt was significantly increased (P < 0.001). Moreover, CO-induced ST-segment depression, T-wave inversion, and atrioventricular block (AV-block) were decreased following treatment with MS. In conclusion, our results showed that MS could decrease cardiac deleterious effects of CO poisoning including necrosis and apoptosis while increased the expression of Akt, as a cell survival protein.

Cardioprotective and Anti-arrhythmic Effects of Magnesium Pretreatment Against Ischaemia/Reperfusion Injury in Isoprenaline-Induced Hypertrophic Rat Heart

The effects of magnesium (Mg²⁺) on ischaemic complications of pathological cardiac hypertrophy are unclear. In this study, we investigated effects of Mg²⁺ pretreatment on ischaemia/reperfusion (I/R) injury in isoprenaline (ISO)-induced hypertrophic hearts. Wistar rats were treated for 7 days with different combinations of ISO (1.25 mg/kg) subcutaneously, MgSO₄ (270 mg/kg) intraperitoneally, or vehicle (saline). On the eighth day, hearts were either subjected to regional I/R during Langendorff perfusion or histologically stained with haematoxylin and eosin and Masson's trichrome. Haemodynamic and electrocardiographic parameters were recorded using the PowerLab data-acquisition system. Infarcts were identified by triphenyltetrazolium chloride staining. Plasma Mg²⁺ was measured using photometric assays. Mg²⁺ pretreatment significantly decreased I/R-induced infarct size (p = 0.001) and the overall arrhythmia score (p < 0.001) of I/R-induced ventricular ectopics, ventricular tachycardia, and ventricular fibrillation in hypertrophic hearts, but not non-hypertrophied hearts. Mg²⁺ also improved post-I/R left ventricular developed pressure in hypertrophic hearts. However, Mg²⁺ did not reverse the ISO-induced myocyte thickening and interstitial fibrosis or increases in heart weight. Plasma Mg²⁺ was not different among treatment groups. These results suggest that Mg²⁺ pretreatment may protect against I/R-induced injury and malignant arrhythmias in hypertrophic hearts, possibly via mechanisms unrelated to long-lasting changes in plasma Mg²⁺ or prevention of structural changes such as fibrosis.

Magmaris: a new generation metallic sirolimus-eluting fully bioresorbable scaffold: present status and future perspectives

Drug-eluting stents (DES) have reached a high safety and efficacy profile, becoming the best option for percutaneous coronary interventions (PCI) based revascularization. However, despite their optimal performance, a few concerns remain regarding their use, mainly due to permanent caging of the vessels and its consequences, first of all late stent thrombosis (ST). Bioresorbable scaffolds (BRS) aim to overcome these issues. The results achieved in randomized controlled trials (RCT) by the first generation of poly-L-lactic acid (PLLA) based scaffolds were promising at 1 year, but the first long term reports (albeit flawed by non-optimal implantation technique) have been disappointing, showing, for instance, an increased risk of ST and target vessel myocardial infarction (TV-MI). In such a scenario the advent of a newer generation magnesium (Mg) based BRS is welcome, mainly because of its innovative mechanical and chemical features coupled with well proven biocompatibility. Despite being in its infancy, this technology seems to promise a great potential. In our article, we review the Magmaris (Biotronik AG, Bülach, Switzerland) Mg BRS development from animal models to human use, underscore its best qualities and weaknesses, and provide hints of its possible future perspectives.

Enhanced in Vitro and in Vivo Performance of Mg-Zn-Y-Nd Alloy Achieved with APTES Pretreatment for Drug-Eluting Vascular Stent Application

Bioabsorbable magnesium alloys are becoming prominent as temporary functional implants, as they avoid the risks generated by permanent metallic implants such as persistent inflammation and late restenosis. Nevertheless, the overfast corrosion of Mg alloys under physiological conditions hinders their wider application as medical implant materials. Here we investigate a simple one-step process to introduce a cross-linked 3-amino-propyltrimethoxysilane (APTES) silane physical barrier layer on the surface of Mg-Zn-Y-Nd alloys prior to electrostatic spraying with rapamycin-eluting poly(lactic-co-glycolic acid) (PLGA) layer. Surface microstructure was characterized by scanning electron microscope and Fourier transform infrared spectroscopy. Nanoscratch test verified the superior adhesion strength of PLGA coating in the group pretreated with APTES. Electrochemical tests combined with long-term immersion results suggested that the preferable in vitro anticorrosion behavior could be achieved by dense APTES barrier. Cell morphology and proliferation data demonstrated that APTES pretreated group resulted in remarkably preferable compatibility for both human umbilical vein endothelial cells and vascular smooth muscle cells. On the basis of excellent in vitro mechenical property, the animal study on the APTES pretreated Mg-Zn-Y-Nd stent implanted into porcine coronary arteries confirmed benign tissue compatibility as well as re-endothelialization without thrombogenesis or in-stent restenosis at six-month followup.

Lack of cardioprotection by single-dose magnesium prophylaxis on isoprenaline-induced myocardial infarction in adult Wistar rats

Aim

Magnesium (Mg²⁺) is effective in treating cardiovascular disorders such as arrhythmias and pre-eclampsia, but its role during myocardial infarction (MI) remains uncertain. In this study, we investigated the effects of Mg²⁺ pre-treatment on isoprenaline (ISO)-induced MI in vivo.

Methods

Rats divided into four groups were each pre-treated with either MgSO₄ (270 mg/kg intraperitoneally) or an equivalent volume of physiological saline, prior to the ISO (67 mg/kg subcutaneously) or saline treatments. One day post-treatment, the electrocardiogram and left ventricular blood pressures were recorded. Infarcts were determined using 2,3,5-triphenyltetrazolium chloride staining, and serum markers of lipid peroxidation were measured with spectrophotometric assays.

Results

Mg²⁺ pre-treatment neither altered the ISO-induced infarct size compared with ISO treatment alone (^p > 0.05), nor reversed the low-voltage electrocardiogram or the prominent Q waves induced by ISO, despite a trend to decreased Q waves. Similarly, Mg²⁺ did not prevent the ISO-induced decrease in peak left ventricular blood pressure or the decrease in minimal rate of pressure change. Mg²⁺ did not reverse the ISO-induced gain in heart weight or loss of body weight. Neither ISO nor Mg²⁺ altered the concentrations of lipid peroxidation markers 24 hours post MI induction.

Conclusion

Although Mg²⁺ had no detrimental effects on electrical or haemodynamic activity in ISO-induced MI, the lack of infarct prevention may detract from its utility in MI therapy.

Magnesium reduces matrix metalloproteinase-9, but not glial fibrillary acidic protein, in cardiac surgery patients

Magnesium (Mg) is one of the most important ions in the brain. Its supplementation decreases intracellular disorders and improves final outcomes following traumatic brain injury. Aim: The aim of the study was to analyze the effects of magnesium supplementation on arteriovenous differences in plasma magnesium concentration in brain circulation (a–vMg), plasma matrix metalloproteinase-9 (MMP-9) and glial fibrillary acidic protein (GFAP) concentrations in cardiac surgery patients. Methods: A total of 92 adult patients were enrolled. Patients were allocated into three groups: A, receiving 6.66 mg of MgSO4 per min intravenously; B, receiving 10 mg of MgSO4; and C, receiving 13.33 mg of MgSO4. Results: In all groups, GFAP and MMP-9 increased after extracorporeal circulation and immediately after surgery. Sequentially higher concentrations of MMP-9 and a–vMg were noted in groups A, B and C. Plasma GFAP concentrations were similar in all groups. Conclusion: Magnesium supplementation reduces plasma MMP-9 and a-vMg in brain circulation but does not affect plasma GFAP.

The effects of magnesium pretreatment on reperfusion injury during living donor liver transplantation

Background

Ischemia reperfusion (IR) injury is a complex phenomenon that leads to organ dysfunction and causes primary liver failure following liver transplantation. We investigated whether an intravenous administration of magnesium before reperfusion can prevent or reduce IR injury.

Methods

Fifty-nine living donor liver transplant recipients were randomly assigned to an MG group (n = 31) or an NS group (n = 28). Each group was also divided in two groups based on the preoperative magnesium levels (normal: ≥ 0.70 mmol/L, low: < 0.70 mmol/L). The MG groups received 25 mg/kg of MgSO₄ mixed in 100 ml normal saline intravenously before reperfusion and the NS groups received an equal volume of normal saline. The levels of lactate, pH, arterial oxygen tension, and base excess were measured to assess reperfusion injury at five specific times, which were 10 min after the beginning of anhepatic phase, and 10, 30, 60 and 120 min after reperfusion. To evaluate postoperative organ function, the serum aspartate aminotransferase (AST), alanine aminotransferase (ALT), total bilirubin and creatinine levels were measured at preoperative day 1, postoperative day 1 and 5.

Results

The blood lactate levels were significantly lower at 10, 30, 60 and 120 min after reperfusion in the MG groups compared to the NS groups. In addition, significantly higher blood lactate levels were observed in the NS group with preoperative hypomagnesemia than in MG groups.

Conclusions

Magnesium administration before reperfusion of liver transplantation significantly reduces blood lactate levels. These findings suggest that magnesium treatment may have protective effects on IR injury during living donor liver transplantation.

Myocardial cooling for reperfusion injury protection achieved by organ specific hypothermic autologous perfusion

OBJECTIVE

Whole body hypothermia has been suggested to reduce myocardial injury in patients with ST-segment elevation myocardial infarction. Because of the large human thermal mass, induction of generalized hypothermia is slow and the technique has encountered considerable side effects. The aim was to develop and validate a method for regional cooling during myocardial reperfusion using hypothermic autologous blood.

DESIGN

In a myocardial ischemia-reperfusion pig model (n = 10), arterial blood was cooled in a closed circuit, and returned to the myocardium during reperfusion either through a perfusion catheter or through the guiding catheter. Myocardial temperatures were recorded using temperature electrodes.

RESULTS

Stabile regional myocardial cooling was induced without complications within 4 min. Both flow rate and blood temperature had significant impact on temperature in the reperfused myocardium but did not influence systemic temperature.

CONCLUSION

A method for organ specific hypothermic autologous arterial blood reperfusion has been developed and validated. The method is a simple and much faster alternative to systemic cooling and may have the potential to reduce myocardial injury in patients with acute myocardial infarction.

Adjunctive therapy after reperfusion therapy in acute myocardial infarction

The current era has witnessed dramatic improvement in the treatment of acute myocardial infarction, due in large part to the more widespread use of thrombolytic therapy aimed at quickly restoring perfusion in the infarct-related artery. This review addresses the role of adjunctive pharmacologic therapy in the thrombolytic era, recognizing that much of the available clinical trial data supporting the role of adjunctive pharmacologic treatment strategies was conducted in patient populations not widely exposed to reperfusion therapy. This review, therefore, explores the data supporting the incremental benefit of therapy with beta blockers, nitrates, angiotensin-converting enzyme inhibitors, or magnesium in addition to thrombolytic therapy. Heparin and aspirin will not be discussed.

Preventive role of magnesium on skeletal muscle ischemia-reperfusion injury-an experimental study

The present study aims to explore whether Mg infusion has a preventive effect on ischemia-reperfusion injury in rats. A total of 20 Sprague-Dawley-type adult male rats were used. In group 1 (control), 0.9% isotonic solution was administered. In group 2 (experiment), magnesium sulfate (0.5 mg per 100 g) was administered. Ischemia was induced for 15 min for the two groups. Magnesium (Mg), interleukin 8 (IL-8), and malondialdehyde levels were analyzed in blood, while edema, neutrophil infiltration, eosinophilia, loss of striation, and nucleolization were evaluated in histopathological examination. Mg levels in the experiment group were higher than those in the control group after ischemia-reperfusion (p < 0.05). In the control group, postischemia and postreperfusion IL-8 values were higher than preoperative values (p < 0.05). As for eosinophilia and loss of striation values, these were higher in the experiment group after ischemia-reperfusion than the values in the control group (p < 0.05). Histopathologically, Mg infusion cannot prevent the tissue injury triggered in ischemia-reperfusion periods. Eosinophilia can be one of the major and earliest markers of ischemia-reperfusion injury.

Intravenous magnesium for acute myocardial infarction

BACKGROUND

Mortality and morbidity from acute myocardial infarction (AMI) remain high. Intravenous magnesium started early after the onset of AMI is thought to be a promising adjuvant treatment. Conflicting results from earlier trials and meta-analyses warrant a systematic review of available evidence.

OBJECTIVES

To examine the effect of intravenous magnesium versus placebo on early mortality and morbidity.

SEARCH STRATEGY

We searched CENTRAL (The Cochrane Library Issue 3, 2006), MEDLINE (January 1966 to June 2006) and EMBASE (January 1980 to June 2006), and the Chinese Biomedical Disk (CBM disk) (January 1978 to June 2006). Some core Chinese medical journals relevant to the cardiovascular field were hand searched from their starting date to the first-half year of 2006.

SELECTION CRITERIA

All randomized controlled trials that compared intravenous magnesium with placebo in the presence or absence of fibrinolytic therapy in addition to routine treatment were eligible if they reported mortality and morbidity within 35 days of AMI onset.

DATA COLLECTION AND ANALYSIS

Two reviewers independently assessed the trial quality and extracted data using a standard form. Odds ratio (OR) were used to pool the effect if appropriate. Where heterogeneity of effects was found, clinical and methodological sources of this were explored.

MAIN RESULTS

For early mortality where there was evidence of heterogeneity, a fixed-effect meta-analysis showed no difference between magnesium and placebo groups (OR 0.99, 95%CI 0.94 to 1.04), while a random-effects meta-analysis showed a significant reduction comparing magnesium with placebo (OR 0.66, 95% CI 0.53 to 0.82). Stratification by timing of treatment (< 6 hrs, 6+ hrs) reduced heterogeneity, and in both fixed-effect and random-effects models no significant effect of magnesium was found. In stratified analyses, early mortality was reduced for patients not treated with thrombolysis (OR=0.73, 95% CI 0.56 to 0.94 by random-effects model) and for those treated with less than 75 mmol of magnesium (OR=0.59, 95% CI 0.49 to 0.70) in the magnesium compared with placebo groups.Meta-analysis for the secondary outcomes where there was no evidence of heterogeneity showed reductions in the odds of ventricular fibrillation (OR=0.88, 95% CI 0.81 to 0.96), but increases in the odds of profound hypotension (OR=1.13, 95% CI 1.09 to 1.19) and bradycardia (OR=1.49, 95% CI 1.26 to 1.77) comparing magnesium with placebo. No difference was observed for heart block (OR=1.05, 95% CI 0.97-1.14). For those outcomes where there was evidence of heterogeneity, meta-analysis with both fixed-effect and random-effects models showed that magnesium could decrease ventricular tachycardia (OR=0.45, 95% CI 0.31 to 0.66 by fixed-effect model; OR=0.40, 95% CI 0.19 to 0.84 by random-effects model) and severe arrhythmia needing treatment or Lown 2-5 (OR=0.72, 95% CI 0.60 to 0.85 by fixed-effect model; OR=0.51, 95% CI 0.33 to 0.79 by random-effects model) compared with placebo. There was no difference on the effect of cardiogenic shock between the two groups.

AUTHORS' CONCLUSIONS

Owing to the likelihood of publication bias and marked heterogeneity of treatment effects, it is essential that the findings are interpreted cautiously. From the evidence reviewed here, we consider that: (1) it is unlikely that magnesium is beneficial in reducing mortality both in patients treated early and in patients treated late, and in patients already receiving thrombolytic therapy; (2) it is unlikely that magnesium will reduce mortality when used at high dose (>=75 mmol); (3) magnesium treatment may reduce the incidence of ventricular fibrillation, ventricular tachycardia, severe arrhythmia needing treatment or Lown 2-5, but it may increase the incidence of profound hypotension, bradycardia and flushing; and (4) the areas of uncertainty regarding the effect of magnesium on mortality remain the effect of low dose treatment (< 75 mmol) and in patients not treated with thrombolysis.

MgSO4 prevents left ventricular dysfunction in an animal model of preeclampsia

OBJECTIVE

We hypothesized that cardiac function would be reduced in a pregnant rat model of preeclampsia induced by L-NAME, a NOS inhibitor, and be reversed with magnesium sulfate prophylaxis.

STUDY DESIGN

Female Sprague-Dawley rats were bred in-house. On gestational day 17, rats were anesthetized and osmotic minipumps were implanted to continuously deliver saline, L-NAME, or L-NAME and MgSO4. On gestational day 21, hearts were isolated and perfused in the working mode using Krebs Henseleit buffer.

RESULTS

Pregnant rats treated with L-NAME displayed significant hypertension compared to the saline-treated controls (P < 0.05). Moreover, cardiac output and cardiac work were significantly reduced in the L-NAME-treated rats compared to controls (P < 0.05). In the L-NAME-treated rats given MgSO4, cardiac function remained normal.

CONCLUSION

Cardiac function is depressed in an animal model of preeclampsia induced by L-NAME infusion. MgSO4 prevented the reduction in cardiac function and is clearly beneficial in preserving normal heart function in preeclampsia.

Fibrin(ogen) and its fragments in the pathophysiology and treatment of myocardial infarction

The occlusion of a coronary artery leads to ischemia of the myocardium, while permanent occlusion results in cell death and myocardial dysfunction. Early restoration of blood flow is the only means to reduce or prevent myocardial necrosis, but-paradoxically-reperfusion itself contributes to injury of the heart. In animal models, this phenomenon is well described, and there are many different unrelated approaches to reduce reperfusion injury. In humans, however, pharmacological interventions have so far failed to reduce myocardial reperfusion injury. We summarize the pathogenesis of reperfusion injury, detailing the role of fibrin(ogen) and its derivatives. Moreover, we introduce a new concept for fibrin derivatives as potential targets for reperfusion therapy.

Anti-infarct effect of magnesium is not mediated by adenosine A1 receptors in rat globally ischaemic isolated hearts

1. The aim of present study was to investigate the effects of magnesium (Mg) on cardiac function and infarct size and to compare it effects with those of adenosine. The mechanism of Mg-mediated cardioprotection was explored by combined use of Mg and a selective adenosine A(1) receptor antagonist. 2. Rat isolated hearts were used for Langendorff perfusion. Hearts were either non-preconditioned or preconditioned with Mg (6 mmol/L) or adenosine (1 mmol/L) before 30 min sustained ischaemia followed by 120 min reperfusion. Within each of these protocols, hearts were divided into two groups; one group was exposed to the A(1) receptor antagonist 8-cyclopentyl-1,3-dipropylxanthine (DPCPX; 200 nmol/L). Infarct size was measured by the triphenyltetrazolium chloride method. Left ventricular function was assessed by left ventricular developed pressure (LVDP), the product of heart rate x LVDP and coronary flow (CF). 3. The administration of Mg had an anti-infarct effect independent of its effect on postischaemic functional recovery in rats. Both Mg and adenosine equipotently reduced infarct size, but this effect of Mg was not blocked by the simultaneous administration of DPCPX. Cardiac function was improved by both adenosine and Mg and blockade of adenosine A(1) receptors attenuated these effects for both agents. 4. In conclusion, the results of the present study indicate that stimulation of adenosine A(1) receptors is not responsible for the anti-infarct effect of Mg in ischaemic myocardium in rats, but that the Mg-mediated protection of postischaemic functional recovery in rats is mediated by these receptors.

Drug-eluting bioabsorbable magnesium stent

Current stent technology is based on the use of permanent implants that remain life long in the vessel wall, far beyond the time required for the prosthesis to accomplish its main goals of sealing dissection and preventing wall recoil. With the possibility to implant long vessel segments using antiproliferative drugs to prevent restenosis, the practice of transforming the coronary vessels into stiff tubes with a full metal jacket covering all side branches and being unable to adjust to the long-term wall changes, including wall remodeling with lumen ectasia becomes a serious concern. In this article, we describe the first biodegradable stent based on a magnesium alloy that allows controlled corrosion with release to the vessel wall and the blood stream of a natural body component such as magnesium with beneficial antithrombotic, antiarrhythmic, and antiproliferative properties. We also discuss the animal experiments and the initial clinical applications in 20 patients with implants below the knee, with final results soon to be released, and the plans for the first coronary study. The results of these last two studies will indicate whether the absence of a permanent implant and the antiproliferative properties shown in animals are sufficient to prevent the restenotic process in humans or whether the prosthesis must be modified by adding the biodegradable coating with conventional antiproliferative drugs.

Cardioprotective effects of magnesium sulfate in patients undergoing primary coronary angioplasty for acute myocardial infarction

BACKGROUND

Experimental evidence indicates that magnesium sulfate may have potential cardioprotective properties as an adjunct to coronary reperfusion. The present study was designed to examine the hypothesis that magnesium might have beneficial effects on left ventricular (LV) function and coronary microvascular function in patients with acute myocardial infarction (AMI).

METHODS AND RESULTS

The study population of 180 consecutive patients with a first AMI (anterior or inferior) underwent successful primary coronary intervention. Patients were randomized to treatment with either intravenous magnesium (magnesium group, n=89) or normal saline (control group, n=91). Pre-discharge left ventriculograms were used to assess LV ejection fraction (LVEF), regional wall motion (RWM) within the infarct-zone and LV end-diastolic volume index. The Doppler guidewire was used to assess coronary flow velocity reserve (CFVR) as an index of coronary microvascular function. Magnesium group subjects showed significantly better LV systolic function (LVEF 63+/-9% vs 55+/-13%, p<0.001; RWM: -1.01+/-1.29 SD/chord vs -1.65+/-1.11 SD/chord, p=0.004), significantly smaller LV end-diastolic volume index (63+/-17 ml/m(2) vs 76+/-20 ml/m(2), p<0.001), and significantly higher CFVR (2.95+/-0.76 vs 2.50+/-0.99, p=0.023) than controls.

CONCLUSION

Magnesium sulfate as an adjunct to primary coronary intervention shows favorable functional outcomes in patients with AMI.

Comparison Between Nicorandil and Magnesium as an Adjunct Cardioprotective Agent to Percutaneous Coronary Intervention in Acute Anterior Myocardial Infarction

BACKGROUND

It has been reported that both nicorandil and magnesium have a cardioprotective effect in experimental ischemia - reperfusion models. In the present study, the cardioprotective effects of nicorandil and magnesium as an adjunct to reperfusion therapy in patients with acute myocardial infarction (AMI) were compared.

METHODS AND RESULTS

Forty consecutive patients with AMI caused by occlusion of anterior descending coronary artery were randomized into 3 groups: (1) Group N: nicorandil was given as 4 mg iv and 4 mg ic before reperfusion, followed by continuous infusion at 4 mg/h for 24 h; (2) Group M: magnesium was administered at 10 mmol iv before reperfusion, followed by continuous infusion at 0.4 mmol/h for 24 h; and (3) Group C: neither nicorandil nor magnesium was given. Left ventriculography was performed immediately after reperfusion and 3 months later. There was no significant change in regional wall motion (RWM) in either Group C or M, whereas that of group N improved significantly. The change in RWM in Group N was significantly greater than in Group C (Group N: 0.92+/-0.92, Group M: 0.44+/-0.80, Group C: -0.01+/-0.65, p<0.05).

CONCLUSIONS

The early administration of nicorandil as an adjunct to reperfusion is useful for cardioprotection in AMI, but magnesium is not.

Mg-gluconate provides superior protection against postischemic dysfunction and oxidative injury compared to Mg-sulfate

Cardioprotection by Mg Sulfate (MgSO4) during ischemia/reperfusion (I/R) is attributed largely to the Mg2+ cation. However, Mg-gluconate (MgGl2) may provide added benefit, possibly through its anion's antioxidant properties. Protective effects of both Mg-salts and their anions during 30 min global I and 50 min R were assessed in Langendorff-perfused (Krebs-Henseleit buffer) rat hearts. Recovery of function was compared between untreated hearts and those receiving supplement (2.4 mM MgGl2, MgSO4, or Na2SO4, or 4.8 mM NaGI) for 5 min prior to I and during the initial 30 min R. The final 20 min R was conducted without supplement. End diastolic pressure (EDP, mmHg) of the 50 min reperfused MgGl2 group (2.6) was lower than MgSO4 (16.2) and untreated (35.6) groups, and the NaGI group (25.2) was considerably lower than Na2SO4 (38.8). Recovery of developed pressure (% preischemic DP) at the onset of R for MgGl2 (74.9) was greater than MgSO4 (37.9) and untreated (33.2). After 50 min, MgGl2 (77.9) and MgSO4 (66.9) provided protection compared to untreated (51.8). In separate studies, ESR spin trapping with alpha-phenyl-N-tert-butylnitrone (3 mM PBN) showed that I/R alkoxyl radical production was reduced with MgGl2 (0.0 vs. 2.4 vs. 3.6 mM: 184 vs. 97 vs. 54.8 nM/g tissue x min) to a greater extent than seen with MgSO4 (3.6 mM: 108). Additional studies suggest that Gl(1-), unlike SO4(2-), may scavenge hydroxyl radicals, accounting for the added protection. MgGl2 treated hearts exhibited less postischemic dysfunction and oxidative injury compared to MgSO4, suggesting the contribution of Gl(1-) to cardioprotection.

Myocardial Protection During Minimally Invasive Cardiac Surgery

Minimally invasive cardiac surgery or beating heart surgery requires very precise observation, explanation, diagnosis, and proper treatment of all changes in the cardiovascular system that occur during the procedure. A major concern in beating heart surgery is the risk of inducing myocardial ischemia without the circulatory support of cardiopulmonary bypass. Protection of myocardium in different stages of the perioperative period is crucial. The following issues should be taken into consideration: preoperative preparation of the myocardium, providing anesthesia techniques that may help to protect the myocardium, and the use of surgical techniques for myocardial protection. Hemodynamic alterations during dislocations of the heart require understanding of these changes and the effects they have on the myocardium. Proper monitoring during the whole procedure, correlation of all findings with the treatment and therapeutic maneuvers, and excellent cooperation between anesthesiologist and surgeon are essential for myocardial protection. New pharmacologic methods, some experimental, should be considered in near future for myocardial protection during beating heart surgery.

Magnesium-enriched coronary sinus retroperfusion during acute coronary artery occlusion

BACKGROUND

The protective effect of coronary sinus retroperfusion in cases of ischaemic myocardium is clearly known. It restores the blood flow to the ischaemic tissue, reduces the infarct size, and improves the left ventricular pump function.

METHODS

In this study, we investigated the effects of coronary sinus retroperfusion with the addition of magnesium sulphate on myocardial haemodynamics. A total of sixteen animals were entered into the study and divided equally into four groups: group I, control group, left anterior descending (LAD) coronary artery occlusion only; group II, LAD artery occlusion and Mg SO infusion; group III, LAD occlusion and retrograde coronary sinus perfusion; and group IV, LAD occlusion, retrograde coronary sinus perfusion and Mg SO infusion.(4) (4)

RESULTS

Haemodynamic measurements were obtained throughout the study, at baseline, during the first and third hour of occlusion, and in the second, fourth and sixth hour of reperfusion. Although, the cardiac index was decreased in all groups, in the second hour of reperfusion it was significantly higher in groups III and IV compared to the control group. In the second hour of reperfusion cardiac index values were 56 +/- 5 and 63 +/- 6 ml/kg per min in groups III and IV respectively (P < 0.05) and as time passed this incremental change in groups III and IV became more apparent. In the fourth hour of reperfusion, group II showed significantly higher values than the control group. Group IV had higher values compared to group III at the fourth and sixth hours post-reperfusion. In general there were significant differences between groups II, III and IV at four and six hours post-reperfusion. The first derivative of pressure measured over time-the dP/dt value-was higher in groups III and IV compared to the control group in the first hour of occlusion (being 1650 +/- 55 and 1700 +/- 35 in groups III and IV respectively, and 1420 +/- 45 in the control group) and these differences continued throughout the occlusion and the reperfusion periods (P < 0.05). Group IV had the highest left ventricular stroke work index (LVSWI) values compared to the other groups in various pulmonary capillary wedge pressure (PCWP) measurements (P < 0.05). It was 0.78 g.m/kg at the 20 mmHg PCWP.

CONCLUSIONS

Magnesium, if administered in an antegrade direction had only a limited effect, whereas magnesium-enriched retrograde coronary sinus perfusions appeared to significantly protect the ischaemic myocardium against the hazardous effects of ischaemic reperfusion injury.

Protective effect of magnesium on the endothelial function mediated by endothelium-derived hyperpolarizing factor in coronary arteries during cardioplegic arrest in a porcine model

OBJECTIVES

Hyperkalemia in cardioplegia impairs the function mediated by endothelium-derived hyperpolarizing factor. This study examined the effect and mechanism of magnesium ion on the relaxation mediated by endothelium-derived hyperpolarizing factor.

METHODS

In the isometric force study, porcine coronary microarteries in a myograph (diameter 200-450 microm) were incubated in Krebs solution (subgroups Ia, IIa, and IIIa), potassium ion (20 mmol/L, subgroups Ib, IIb, and IIIb), magnesium ion (16 mmol/L, subgroups Ic, IIc, and IIIc), or potassium ion plus magnesium ion (subgroups Id, IId, and IIId) for 1 hour at 37 degrees C in group I or II, followed by washout for 45 minutes in group III (n = 8). Relaxation to bradykinin (groups I and III) or sodium nitroprusside (group II) in U(46619)-stimulated contraction was established. In the electrophysiologic study, the membrane potentials of single smooth muscle cells of arteries were measured by microelectrode after superfusion with the previously described solutions (subgroups IVa-IVc).

RESULTS

In group I, 20-mmol/L potassium ion greatly reduced the bradykinin-induced relaxation (35.0% +/- 4.9% vs 86.0% +/- 5.3%, P <.001), which was significantly restored by magnesium ion (51.9% +/- 4.0%, P =.017). In groups II and III, the bradykinin- or nitroprusside-induced relaxation had no significant differences. In group IV, potassium ion depolarized the smooth muscle and decreased the bradykinin-induced hyperpolarization (-72.0 +/- 1.5 vs -61.7 +/- 0.7 mV, n = 7, P <.001), which was significantly restored by magnesium ion (-68.0 +/- 2.5 mV vs -72.5 +/- 1.5 mV, n = 6, P =.029).

CONCLUSIONS

Magnesium ion, either alone or added to hyperkalemic solutions, preserves or helps to restore the endothelial function mediated by endothelium-derived hyperpolarizing factor. The mechanism is related to preservation of the membrane hyperpolarization and reversal of the potassium-induced membrane depolarization of the smooth muscle cell.

Magnesium reduces myocardial infarct size via enhancement of adenosine mechanism in rabbits

OBJECTIVES

Clinical impact of magnesium (Mg) therapy remains controversial in acute myocardial infarction. We investigated the infarct size limiting effects of Mg and its mechanism in rabbits.

METHODS

Anesthetized rabbits underwent 30 min coronary occlusion and 3 h reperfusion in ten groups: (1) Control, (2) Low Mg, (3) Mg, (4) High Mg, (5) calcium (Ca), (6) Mg+Ca, (7) 8-phenyltheophylline (8PT), an adenosine receptor blockade, (8) 8PT+Mg, (9) alpha, beta-methylene-adenosine diphosphate (AOPCP), a selective inhibitor of ecto-5'-nucleotidase, and (10) AOPCP+Mg groups. Infract size (IS) to area at risk (AR) was measured by triphenyltetrazorium chloride method.

RESULTS

The IS/AR ratio was significantly smaller in Mg, 27+/-3% (P<0.05) and High Mg, 24+/-2% (P<0.05) compared to Control, 50+/-3% and Low Mg, 42+/-4%. The IS limiting effects of Mg were abolished in 8PT+Mg, AOPCP+Mg and Mg+Ca. The IS/AR ratio correlated with neither rate-pressure products nor incidence of arrhythmia.

CONCLUSION

Magnesium administration has an infarct size limiting effect independent of its effects on myocardial oxygen consumption and incidence of arrhythmia in rabbits. The infarct size limiting effect of magnesium is attributable, at least in part, to augmentation of adenosine mechanism.

Magnesium-supplemented warm blood cardioplegia in patients undergoing coronary artery revascularization

BACKGROUND

Although there is growing evidence to suggest that the administration of magnesium (Mg2+) to patients undergoing coronary artery bypass grafting (CABG) and to patients after myocardial infarction is beneficial, the addition of Mg2+ to cardioplegic solutions remains controversial. The aim of this study was to compare the effects of intermittent warm blood cardioplegia with and without Mg2+ supplementation on the early postoperative clinical outcomes in patients undergoing both elective or urgent CABG.

METHODS

Four hundred patients undergoing CABG were prospectively randomized to receive either blood cardioplegia without Mg2+ (BC, n = 200) or supplemented with Mg2+ (BC-Mg2+, n = 200). Serial plasma Mg2+ concentrations were recorded at base line and postoperatively from days 1 to 4.

RESULTS

Patient characteristics were similar and no significant differences were found in early mortality and morbidity in the two groups. Analysis of 178 patients undergoing urgent CABG for unstable symptoms (BC = 95, BC-Mg2+ = 83) demonstrated a significantly lower requirement for internal defibrillation and temporary epicardial pacing in the BC-Mg2+ group. Furthermore, there was a nearly twofold lower incidence of new postoperative atrial fibrillation in the BC-Mg2+ group compared with the BC group (19% versus 34%, p = 0.03). Postoperative plasma Mg2+ levels were consistently lower in those patients who developed new postoperative atrial fibrillation compared with those who did not (p = 0.05).

CONCLUSIONS

The addition of Mg2+ to warm blood cardioplegia resulted in a lower incidence of intraoperative and postoperative arrhythmias in patients undergoing urgent CABG for unstable angina.

The importance of effect mechanism in the design and interpretation of clinical trials: the role of magnesium in acute myocardial infarction

The design and interpretation of randomized clinical trials and of meta-analyses of trials should be informed by a biologically plausible hypothesis of treatment effect. Without some insight on likely mechanism, trial conditions may not be optimum to allow a true treatment effect to be detected. Judgments on mechanism underpin decisions on the appropriateness of pooling studies in meta-analysis. Where statistical heterogeneity of trial results is found, the possibility of true biological effect modification can only be assessed by considering potential treatment mechanisms. These can then be tested in carefully designed laboratory models. Meta-analysis of 12 randomized controlled trials of intravenous Mg(2+) in acute myocardial infarction gives a null effect (odds ratio 1.02, 95% CI 0.96 to 1.08) with a fixed effects model, but with strong evidence of heterogeneity (P <.0001) due to a single large study in which Mg(2+) was generally given late and after fibrinolytic treatment. A random effects model gives a pooled odds ratio 0.61 (95% CI 0.43 to 0.87, P = 0.006). Laboratory models show that timing of Mg(2+) administration before or after reperfusion critically determines whether myocardial protection occurs.

Bioavailability and pharmacokinetics of magnesium after administration of magnesium salts to humans

Therapeutically, magnesium salts represent an important class of compounds and exhibit various pharmacologic actions. Examples of magnesium salts are ionic magnesium and magnesium citrate in nephrolithiasis, magnesium salicylate in rheumatoid arthritis, magnesium hydroxide as an antacid as well as a cathartic, and magnesium mandelate as urinary antiseptic. Various anions attached to the cation magnesium, such as oxide, chloride, gluconate, and lactate, affect the delivery of the amounts of elemental magnesium to the target site and thereby produce different pharmacodynamic effects. This review examines the bioavailability and pharmacokinetics of various magnesium salts and correlates pharmacodynamic action with the structure-activity relationship.

Intravenous magnesium does not influence the activity of the coagulation cascade

Experimental arterial thrombus formation is reduced during intravenous magnesium infusion. It is well documented that magnesium reduces platelet reactivity, but the antithrombotic effect could also originate from anticoagulant properties or increased fibrinolysis. We therefore evaluated the effect of intravenous magnesium on prothrombin fragment 1 + 2 (F1 + 2), thrombin-antithrombin III complex (TAT) concentrations, and fibrin degradation products (FbDP) in a randomized, cross-over study in 14 healthy volunteers. Citrated blood samples were collected at 0, 30, and 180 min. An additional in vitro study on magnesium's effect on the activity of different coagulation factors was carried out. A transient increase was seen in F1 + 2 and TAT after 30 min but without any significant difference between the placebo and magnesium period. FbDP did not change significantly between the two treatments. Increasing concentrations of magnesium dose-dependently decreased binding of activated factor X to activated factor VII (FVIIa), but the decrease was slight and probably without any significance for coagulation at the concentrations tested. No effect was observed on the activity of FVIIa or activated factor VIII. In conclusion, no significant differences were observed on markers of coagulation or fibrinolytic activity during intravenous magnesium infusion. These results indicate that the observed antithrombotic effect of magnesium is more likely to arise from the previously observed platelet inhibition.

A randomized study of intravenous magnesium in acute myocardial infarction treated with direct coronary angioplasty

BACKGROUND

Notwithstanding the negative result of the International Study of Infarct Survival-4 (ISIS-4), the controversy about the role of magnesium in acute myocardial infarction is still open because, according to experimental data, magnesium could decrease myocardial damage and mortality only if infusion is started before reperfusion. This randomized placebo-controlled trial was designed to evaluate the effect of intravenous magnesium, delivered before, during, and after direct coronary angioplasty, in patients with acute myocardial infarction.

METHODS

One-hundred fifty patients were randomized to intravenous magnesium sulfate or placebo. The primary end point was an infarct zone wall motion score index at 30 days, as a measure of infarct size. The secondary end points included creatine kinase peak, ventricular fibrillation/tachycardia within the first 24 hours, death and congestive heart failure within the 30-day follow-up, and 30-day left ventricular ejection fraction. Analysis was by intention to treat.

RESULTS

There were no significant differences between the magnesium and placebo groups in the 30-day infarct zone wall motion score index (1.93 +/- 0.61 vs 1.85 +/- 0.51, P =.39), ventricular arrhythmias (24% vs 15%, P =.15), death (0 vs 1%, P =.32), heart failure (8% vs 7%, P =.75), and 30-day left ventricular ejection fraction (49% +/- 11% vs 50% +/- 9%, P = 0.55). There was a trend toward a higher creatine kinase peak in the magnesium group (3059 +/- 2359 vs 2404 +/- 1673,P =.052).

CONCLUSIONS

Intravenous magnesium delivered before, during, and after reperfusion did not decrease myocardial damage and did not improve the short-term clinical outcome in patients with acute myocardial infarction treated with direct angioplasty.

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.

Modern adjunctive pharmacotherapy of myocardial infarction

During acute myocardial infarction (MI), aspirin, beta-adrenergic antagonists and oral angiotensin converting enzyme (ACE) inhibitors should be used as an adjunct to reperfusion therapy. Medications upon discharge from the hospital should include aspirin and a beta-blocker. An ACE inhibitor should also be prescribed unless the ejection fraction is > 45%. Particular indications for an ACE inhibitor are an anterior MI, congestive heart failure, ejection fraction < 45% and mitral regurgitation. beta-blockers, when given to patients treated with ACE inhibitors, appear to produce an additional benefit compared with an ACE inhibitor alone. Based on the Scandinavian Simvastatin Survival Study (4S), Cholesterol and Recurrent Events (CARE) and Long-Term Intervention with Pravastatin in Ischemic Disease (LIPID) trials, a statin should also be given to subjects with low density lipoprotein (LDL)-cholesterol levels above 125 mg/dl, independent of total cholesterol levels. Therapy should be administered in an attempt to reduce the LDL-cholesterol level to 90-100 mg/dl (2.3-2.6 mM/l). In patients with normal or low levels on initial evaluation, screening for lipid abnormalities should be deferred for 2 months since acute phase responses and passive hepatic congestion can cause spuriously normal levels. Calcium channel blockers, nitrates, lidocaine, anti-arrhythmic drugs and i.v. magnesium should not be administered routinely after acute MI and their use should be restricted to selected settings.

Protective effect of intravenous magnesium in acute myocardial infarction following thrombolytic therapy

The role of intravenous magnesium therapy in patients with acute myocardial infarction (AMI) who received thrombolytic therapy is controversial. The results from previous clinical trials were not in consonance. We therefore conducted a prospective, randomized, double-blind, placebo controlled study in 350 patients with confirmed AMI during the period January 1994 to December 1996. The role of intravenous magnesium sulphate therapy (2 g over 5 min followed by 16 g over 24 h) was evaluated in patients with AMI who received thrombolytic therapy. Study group consisted of 169 patients who were administered magnesium sulphate. Control group comprised of 181 patients who were given isotonic saline. Among those in the magnesium group, 70% received magnesium within 6 h after the onset of symptoms. All patients received magnesium immediately after the completion of thrombolytic therapy. Patients were followed up for 30 days after AMI. The number of deaths in the study group was 6 (3.5%) compared with control arm in which 18 patients (9.9%) died (P value <0.01 95% Confidence intervals [CI] 1.2 to 11.6). Ventricular arrhythmias were also less in the magnesium arm; 27 patients (13%) compared with 83 patients (48.6%) in the control arm (P value 0.00001 95% Cl 26.7 to 44.5). In the magnesium group 15 patients (8.8%) had re-infarction compared with 23 patients (12.7%) in the placebo arm (P value not significant). Post myocardial infarction angina was observed in 47 patients (27.8%) in the magnesium arm compared with 60 patients (33.1%) in the placebo arm (P value not significant). The main side effect of intravenous magnesium was transient flushing observed in 152 (90%) patients. Intravenous magnesium sulphate in patients with AMI is a safe and useful adjunct to thrombolytic therapy in reducing the short-term mortality and ventricular arrhythmias after AMI.

Minimally invasive direct coronary artery bypass grafting: changes in anesthetic management and surgical procedure

OBJECTIVE

The authors hypothesized that changes in surgical procedures for minimally invasive direct coronary artery bypass grafting (MIDCAB) have led to changes in anesthetic management with a resultant decrease in the complexity of care.

DESIGN

Retrospective observational study.

SETTING

University teaching hospital.

PARTICIPANTS

Review of the records of 60 patients who underwent MIDCAB surgery.

MEASUREMENTS AND MAIN RESULTS

Data included preoperative demographics, perioperative anesthetic management, and postoperative cardiac and noncardiac issues and complications. Two groups were formed: in group I, a coronary stabilizer (CS) was not used, and in group II, it was. With the exception of a greater incidence of those with no preoperative comorbidities in group II (CS), there were no differences between the two groups with respect to demographics or preoperative variables. A surgical design called H-graft was used in a greater number of group II (CS) patients, whereas a direct anastomosis was performed in the majority of group I patients. Use of pharmacologically induced bradycardia/asystole has not been performed after the introduction of the CS. The use of central venous catheters (instead of pulmonary artery catheters) and single-lumen (v double-lumen) endotracheal tubes was greater in group II (CS) patients. Despite changes in intraoperative management, there was no significant change in the incidence of postoperative complications, intensive care unit stay, and hospital stay between groups I and II. New-onset atrial fibrillation was the most common postoperative complication (13 of 56 patients; 23%). Three of 24 patients (12.5%) who received intraoperative magnesium experienced atrial fibrillation compared with 10 of 32 patients (31%) who did not receive magnesium.

CONCLUSIONS

The complexity of anesthetic technique has decreased since the onset of MIDCAB surgery. The decrease in complexity may be related to changes in surgical design and technology.