Effects of glucose-insulin-potassium on myocardial substrate availability and utilization in stable coronary artery disease. Studies on myocardial carbohydrate, lipid and oxygen arterial-coronary sinus differences in patients with coronary artery disease

Systemic glucose-insulin-potassium reduces skeletal muscle injury, kidney injury, and pain in a murine ischaemia-reperfusion model

Glucose-insulin-potassium (GIK) is protective following cardiac myocyte ischaemia-reperfusion (IR) injury, however the role of GIK in protecting skeletal muscle from IR injury has not been evaluated. Given the similar mechanisms by which cardiac and skeletal muscle sustain an IR injury, we hypothesized that GIK would similarly protect skeletal muscle viability. A total of 20 C57BL/6 male mice (10 control, 10 GIK) sustained a hindlimb IR injury using a 2.5-hour rubber band tourniquet. Immediately prior to tourniquet placement, a subcutaneous osmotic pump was placed which infused control mice with saline (0.9% sodium chloride) and treated mice with GIK (40% glucose, 50 U/l insulin, 80 mEq/L KCl, pH 4.5) at a rate of 16 µl/hr for 26.5 hours. At 24 hours following tourniquet removal, bilateral (tourniqueted and non-tourniqueted) gastrocnemius muscles were triphenyltetrazolium chloride (TTC)-stained to quantify percentage muscle viability. Bilateral peroneal muscles were used for gene expression analysis, serum creatinine and creatine kinase activity were measured, and a validated murine ethogram was used to quantify pain before euthanasia. GIK treatment resulted in a significant protection of skeletal muscle with increased viability (GIK 22.07% (SD 15.48%)) compared to saline control (control 3.14% (SD 3.29%)) (p = 0.005). Additionally, GIK led to a statistically significant reduction in gene expression markers of cell death (CASP3, p < 0.001) and inflammation (NOS2, p < 0.001; IGF1, p = 0.007; IL-1β, p = 0.002; TNFα, p = 0.012), and a significant reduction in serum creatine kinase (p = 0.004) and creatinine (p < 0.001). GIK led to a significant reduction in IR-related pain (p = 0.030). Systemic GIK infusion during and after limb ischaemia protects murine skeletal muscle from cell death, kidneys from reperfusion metabolites, and reduces pain by reducing post-ischaemic inflammation.

One-year outcomes of out-of-hospital administration of intravenous glucose, insulin, and potassium (GIK) in patients with suspected acute coronary syndromes (from the IMMEDIATE [Immediate Myocardial Metabolic Enhancement During Initial Assessment and Treatment in Emergency Care] Trial)

The Immediate Myocardial Metabolic Enhancement During Initial Assessment and Treatment in Emergency care Trial of very early intravenous glucose-insulin-potassium (GIK) for acute coronary syndromes (ACS) in out-of-hospital emergency medical service (EMS) settings showed 80% reduction in infarct size at 30 days, suggesting potential longer-term benefits. Here we report 1-year outcomes. Prespecified 1-year end points of this randomized, placebo-controlled, double-blind, effectiveness trial included all-cause mortality and composites including cardiac arrest, mortality, or hospitalization for heart failure (HF). Of 871 participants randomized to GIK versus placebo, death occurred within 1 year in 11.6% versus 13.5%, respectively (unadjusted hazard ratio [HR] 0.83, 95% confidence interval [CI] 0.57 to 1.23, p = 0.36). The composite of cardiac arrest or 1-year mortality was 12.8% versus 17.0% (HR 0.71, 95% CI 0.50 to 1.02, p = 0.06). The composite of hospitalization for HF or mortality within 1 year was 17.2% versus 17.2% (HR 0.98, 95% CI 0.70 to 1.37, p = 0.92). The composite of mortality, cardiac arrest, or HF hospitalization within 1 year was 18.1% versus 20.4% (HR 0.85, 95% CI 0.62 to 1.16, p = 0.30). In patients presenting with suspected ST elevation myocardial infarction, HRs for 1-year mortality and the 3 composites were, respectively, 0.65 (95% CI 0.33 to 1.27, p = 0.21), 0.52 (95% CI 0.30 to 0.92, p = 0.03), 0.63 (95% CI 0.35 to 1.16, p = 0.14), and 0.51 (95% CI 0.30 to 0.87, p = 0.01). In patients with suspected acute coronary syndromes, serious end points generally were lower with GIK than placebo, but the differences were not statistically significant. However, in those with ST elevation myocardial infarction, the composites of cardiac arrest or 1-year mortality, and of cardiac arrest, mortality, or HF hospitalization within 1 year, were significantly reduced.

The effect of insulin on the heart : Part 1: Effects on metabolism and function

Positive inotropic effects of insulin were described early after the isolation of insulin from the pancreas but data on the effect of insulin on the heart are conflicting. Systemic insulin administration results in a reduction in circulating free fatty acids and an improvement in myocardial glucose uptake, which causes an efficiency improvement in the myocardial cell. There is strong evidence that insulin administration results in functional improvement in dysfunctional myocardium. (Neth Heart J 2010;18:197-201.).

Glucagon-like peptide-1 and myocardial protection: more than glycemic control

Pharmacologic intervention for the failing heart has traditionally targeted neurohormonal activation and ventricular remodeling associated with cardiac dysfunction. Despite the multitude of agents available for the treatment of heart failure, it remains a highly prevalent clinical syndrome with substantial morbidity and mortality, necessitating alternative strategies of targeted management. One such area of interest is the ability to modulate myocardial glucose uptake and its impact on cardioprotection. Glucose-insulin-potassium (GIK) infusions have been studied for decades, with conflicting results regarding benefit in acute myocardial infarction. Based on the same concepts, glucagon-like peptide-1-[7-36] amide (GLP-1) has recently been demonstrated to be a more effective alternative in left ventricular (LV) systolic dysfunction. This paper provides a review on the current evidence supporting the use of GLP-1 in both animal models and humans with ischemic and nonischemic cardiomyopathy.

The role of protein O-linked beta-N-acetylglucosamine in mediating cardiac stress responses

The modification of serine and threonine residues of nuclear and cytoplasmic proteins by O-linked beta-N-acetylglucosamine (O-GlcNAc) has emerged as a highly dynamic post-translational modification that plays a critical role in regulating numerous biological processes. Much of our understanding of the mechanisms underlying the role of O-GlcNAc on cellular function has been in the context of its adverse effects in mediating a range of chronic disease processes, including diabetes, cancer and neurodegenerative diseases. However, at the cellular level it has been shown that O-GlcNAc levels are increased in response to stress; augmentation of this response improved cell survival while attenuation decreased cell viability. Thus, it has become apparent that strategies that augment O-GlcNAc levels are pro-survival, whereas those that reduce O-GlcNAc levels decrease cell survival. There is a long history demonstrating the effectiveness of acute glucose-insulin-potassium (GIK) treatment and to a lesser extent glutamine in protecting against a range of stresses, including myocardial ischemia. A common feature of these approaches for metabolic cardioprotection is that they both have the potential to stimulate O-GlcNAc synthesis. Consequently, here we examine the links between metabolic cardioprotection with the ischemic cardioprotection associated with acute increases in O-GlcNAc levels. Some of the protective mechanisms associated with activation of O-GlcNAcylation appear to be transcriptionally mediated; however, there is also strong evidence to suggest that transcriptionally independent mechanisms also play a critical role. In this context we discuss the potential link between O-GlcNAcylation and cardiomyocyte calcium homeostasis including the role of non-voltage gated, capacitative calcium entry as a potential mechanism contributing to this protection.

Impact of anaerobic glycolysis and oxidative substrate selection on contractile function and mechanical efficiency during moderate severity ischemia

The role of anaerobic glycolysis and oxidative substrate selection on contractile function and mechanical efficiency during moderate severity myocardial ischemia is unclear. We hypothesize that 1) preventing anaerobic glycolysis worsens contractile function and mechanical efficiency and 2) increasing glycolysis and glucose oxidation while inhibiting free fatty acid oxidation improves contractile function during ischemia. Experiments were performed in anesthetized pigs, with regional ischemia induced by a 60% decrease in left anterior descending coronary artery blood flow for 40 min. Three groups were studied: 1) no treatment, 2) inhibition of glycolysis with iodoacetate (IAA), or 3) hyperinsulinemia and hyperglycemia (HI + HG). Glucose and free fatty acid oxidation were measured using radioisotopes and anaerobic glycolysis from net lactate efflux and myocardial lactate content. Regional contractile power was assessed from left ventricular pressure and segment length in the anterior wall. We found that preventing anaerobic glycolysis with IAA during ischemia in the absence of alterations in free fatty acid and glucose oxidation did not adversely affect contractile function or mechanical efficiency during myocardial ischemia, suggesting that anaerobic glycolysis is not essential for maintaining residual contractile function. Increasing glycolysis and glucose oxidation with HI + HG inhibited free fatty acid oxidation and improved contractile function and mechanical efficiency. In conclusion, these results show a dissociation between myocardial function and anaerobic glycolysis during moderate severity ischemia in vivo, suggesting that metabolic therapies should not be aimed at inhibiting anaerobic glycolysis per se, but rather activating insulin signaling and/or enhancing carbohydrate oxidation and/or decreasing fatty acid oxidation.

Perioperative hyperinsulinaemic normoglycaemic clamp causes hypolipidaemia after coronary artery surgery

BACKGROUND

Glucose-insulin-potassium (GIK) administration is advocated on the premise of preventing hyperglycaemia and hyperlipidaemia during reperfusion after cardiac interventions. Current research has focused on hyperglycaemia, largely ignoring lipids, or other substrates. The present study examines lipids and other substrates during and after on-pump coronary artery bypass grafting and how they are affected by a hyperinsulinaemic normoglycaemic clamp.

METHODS

Forty-four patients were randomized to a control group (n=21) or to a GIK group (n=23) receiving a hyperinsulinaemic normoglycaemic clamp during 26 h. Plasma levels of free fatty acid (FFA), total and lipoprotein (VLDL, HDL, and LDL)-triglycerides (TG), ketone bodies, and lactate were determined.

RESULTS

In the control group, mean FFA peaked at 0.76 (sem 0.05) mmol litre(-1) at early reperfusion and decreased to 0.3-0.5 mmol litre(-1) during the remaining part of the study. GIK decreased FFA levels to 0.38 (0.05) mmol litre(-1) at early reperfusion, and to low concentrations of 0.10 (0.01) mmol litre(-1) during the hyperinsulinaemic clamp. GIK reduced the area under the curve (AUC) for FFA by 75% and for TG by 53%. The reduction in total TG was reflected by a reduction in the VLDL (-54% AUC) and HDL (-42% AUC) fraction, but not in the LDL fraction. GIK prevented the increase in ketone bodies after reperfusion (-44 to -47% AUC), but was without effect on lactate levels.

CONCLUSIONS

Mild hyperlipidaemia was only observed during early reperfusion (before heparin reversal) and the hyperinsulinaemic normoglycaemic clamp actually resulted in hypolipidaemia during the largest part of reperfusion after cardiac surgery.

Effect of intravenous insulin therapy on clinical outcomes in critically ill patients

BACKGROUND

Hyperglycemia commonly occurs in critically ill patients, even in the absence of diabetes mellitus, and is associated with increased morbidity and mortality rates in such patients.

METHODS

Medline search using the terms intravenous insulin, intensive care, myocardial infarction, cardiac surgery and stroke.

RESULTS AND CONCLUSIONS

Intravenous insulin therapy with or without adjunctive subcutaneous insulin therapy has been shown to improve morbidity and reduce mortality rates in surgical intensive care populations compared with subcutaneous insulin alone or oral hypoglycemic therapy. The evidence for such is less compelling in medical intensive care populations. Intravenous insulin therapy alone or in combination with glucose and potassium infusion appears to improve clinical outcomes in cardiac surgery patients, but there is conflicting evidence concerning its effect on morbidity and mortality rates after myocardial infarction. Insufficient evidence exists to determine the effect of intravenous insulin therapy on outcomes in other populations including stroke patients, those undergoing major noncardiac surgery, and burn patients. Intravenous insulin nomograms and nurse-driven protocols may improve blood glucose control, resulting in improved clinical outcomes.

Insulin infusion therapy for myocardial infarction

In the last 10 years, there has been considerable interest in the administration of insulin as part of the management of myocardial infarction. This review examines the clinical trials of insulin infusion for myocardial infarction in the era of reperfusion therapy, and discusses the implications of the recently completed HI-5 (Hyperglycaemia: Intensive Insulin Infusion In Infarction) study. The clinical trials of insulin therapy for myocardial infarction can be divided into those with a primary aim of delivering insulin (insulin focus), and those with a primary aim of achieving tight glycaemic control (glycaemia focus). The evidence suggests that protocols with an insulin focus do not improve the outcome of myocardial infarction. However, the trials with a glycaemia focus are inconclusive and it remains possible that glycaemic control is beneficial.

The role of intensive glycemic control in the management of patients who have acute myocardial infarction

Hyperglycemia is associated with excess mortality in AMI and should be treated aggressively in the intensive care setting. The exact goal of therapy is unclear because different blood glucose targets were used in earlier studies (eg, 215 mg/dL in DIGAMI versus 110 mg/dL in the Belgian study of critically-ill patients). In the setting of AMI, it is prudent to avoid excessive hypoglycemia and, thus, more modest goals for blood glucose may be considered until more definitive data are present. Aggressive therapy with continuous infusion of insulin seems to improve a host of metabolic and physiologic effects that are associated with acute hyperglycemia and improves mortality in the acute setting. Aggressive glycemic control should be coupled with appropriate use of reperfusion therapies, glycoprotein IIb/IIa inhibitors, aspirin, 1-blockers, ACE inhibitors, and antithrombotic agents. The role of intensive chronic glucose control in reducing CV events is less clear but earlier studies were not well-powered; did not achieve aggressive, durable glycemic control; and did not use insulin-sensitizing agents routinely. Given the results of the DIGAMI trial, the goal of therapy postdischarge should include strict glycemic control while future studies help to delineate the role of insulin-sensitizing agents versus insulin-providing agents in reducing recurrent macrovascular events. Careful attention also should be paid to aggressive lifestyle modifications and treatment of hypertension, hyperlipidemia, and left ventricular dysfunction, as well as appropriate use of anti-platelet and antithrombotic agents.

High-dose glucose-insulin-potassium treatment reduces myocardial apoptosis in patients with acute myocardial infarction

BACKGROUND

Several clinical trials have suggested that a metabolic cocktail of glucose-insulin-potassium (GIK) decreases mortality rates in patients with acute myocardial infarction (AMI). It has also been reported that Fas-mediated apoptosis plays an important role in ischaemic/reperfusion injury in the rat model. This study was designed to evaluate the interaction of ischaemic/reperfusion and reperfusion therapy coadministered with high-dose GIK treatment on soluble Fas/APO-1 (sFas) and Fas ligand (sFasL) plasma concentration in patients with AMI.

MATERIALS AND METHODS

Seventy-four patients presenting with AMI who underwent reperfusion therapy were randomized into a GIK group (n = 35) receiving high-dose GIK for 24 h or a vehicle group (n = 39). Thirty-four control subjects were also enrolled in the present study. Strepavidin-biotin ELISA was used to determine the soluble sFas and sFasL plasma concentration at baseline, 24 h (h), 3 day (d), 7 d and 14 d.

RESULTS

Soluble Fas and sFas-L serum concentrations ([sFas] and [sFas-L]) of patients with AMI were significantly elevated at baseline as compared with normal controls (NCs; P < 0.01 vs. NC). The sFas in the GIK and vehicle groups markedly decreased 24 h after the GIK infusion (10.7-->5.9 ng mL(-1) and 9.7-->6.5 ng mL(-1); P < 0.01 vs. baseline) and then increased during the 3-7-d period (5.9-->12.1 ng mL(-1) and 6.5-->11.1 ng mL(-1); P < 0.01 vs. 24 h). The GIK group demonstrated reduced sFas (12.1-->5.9 ng mL(-1)) at 14 d (P < 0.01 vs. 7 d), with no concomitant changes in the vehicle group. The sFas-L in the GIK and vehicle groups was not significant different during the 14-d period.

CONCLUSIONS

These results indicate that the sFas and sFasL in patients with AMI increased significantly compared with NC. Owing to the cardioprotective effects reported here and by others, a high-dose GIK infusion co-administered with the timely re-establishment of nutritive perfusion should be strongly considered as a treatment of choice for AMI. Additionally, sFas may be a valuable marker of the physiological response to ischaemic/reperfusion injury and reperfusion associated with high-dose GIK treatment.

Insulina: efeitos cardiovasculares e aplicações terapêuticas

Vários estudos têm sugerido benefício do uso de insulina após o infarto do miocárdio e em pacientes criticamente doentes, diabéticos e não diabéticos. No entanto, não se estabeleceu rotineiramente o uso das infusões de insulina e glicose, pela ausência de estudos randomizados de grande porte, entendimento precário dos mecanismos pelos quais estas infusões seriam efetivas, complexidade para administrá-las e principalmente pela mudança cultural que é exigida dos profissionais de saúde para aplicá-las na sua prática. A insulina tem efeitos benéficos no coração, tais como a otimização do uso de substratos pelos cardiomiócitos, o aumento do fluxo coronariano, efeito anti-inflamatório e também ações diretas anti-apoptóticas nas células miocárdicas. Dentro deste contexto, são revisados os resultados clínicos das infusões de insulina e glicose após infarto e cirurgia cardíaca, possíveis mecanismos fisiopatológicos responsáveis por estes benefícios e, finalmente, uma proposta de um protocolo padrão para o uso em unidades de terapia intensiva e de pós-operatório de cirurgia cardíaca.

Insulin therapy in critically ill patients

PURPOSE OF REVIEW

The recent publication of the results of an aggressive approach to the treatment of hyperglycaemia in critically ill patients, and a rekindling of interest in the use of an infusion of glucose insulin and potassium as adjunctive therapy in a diverse group of patients with cardiovascular disease, warrants a review of the multiple effects of insulin and a review of laboratory and clinical studies.

RECENT FINDINGS

The use of an aggressive protocol to maintain normoglycaemia in critically ill patients has been demonstrated to be a beneficial technique in the critical care setting. Implementation of the protocol outside of a research setting appears to be feasible. Recent studies on the use of insulin in addition to glucose and potassium in patients with diverse cardiovascular diseases have also demonstrated positive results.

SUMMARY

This review will summarize some of the putative beneficial effects of insulin as a pharmacological agent, and review recent clinical data. Although the relative benefits of normoglycaemia in the critical care setting and the beneficial effects of insulin are difficult to differentiate, a substantial overlap exists. The extent to which these converging therapies (aggressive normoglycaemia and insulin pharmacotherapy) will be applicable to diverse clinical settings has yet to be determined.

The effects of glucose-insulin-potassium solution and BN 52021 in intestinal ischemia-reperfusion injury

The objective of this study was to investigate effects of glucose-insulin-potassium (GIK) solution and BN 52021, a platelet-activating factor antagonist, on intestinal ischemia-reperfusion injury. Fifty male Sprague-Dawley rats (200-225 g) were divided into 5 groups each containing 10 rats; group SO, sham operation group; group I, mesenteric ischemia group (for 30 minutes); group R, ischemia plus reperfusion (for 60 minutes); group BR, ischemia-reperfusion plus BN 52021; group GR, ischemia-reperfusion plus GIK solution. Samples for malondialdehyde (MDA) and ileum (for mucosal injury score) were obtained. The mucosal injury scores of group R were significantly higher than those of group I (4 +/-0.20 and 3 +/-0.16, respectively, p<0.0001). The scores of groups BR and GR were significantly lower than those of group R (p<0.0001 and p<0.0001, respectively). When it was compared with the injuries in BR and GR groups, similar results were obtained in both groups (p=0.190). Mean MDA levels of group R were significantly higher than those of group I, BR and GR (131.33 +/-3.99 nmol/g, 93.74 +/-3.22 nmol/g, 104.81 +/-2.56 and 100.34 +/-5.30, respectively, p<0.0001). MDA levels of group BR and GR were significantly lower than those of group I (p<0.0001 and p=0.003, respectively). These observations suggest that treatment with GIK solution and BN 52021 before reperfusion and during reperfusion period may be useful in decreasing intestinal reperfusion injury.

Glycometabolic status and acute myocardial infarction: has the time come for glucose-insulin-(potassium) therapy?

Glucose-insulin-potassium infusion as a metabolic therapy was first advocated for the management of acute myocardial infarction (AMI) in 1960s. Over the subsequent decades, enthusiasm for its use has been patchy, especially with the availability of other effective treatments such as reperfusion therapy for AMI. Several clinical studies in the mid-1990s revived the interest in the glycometabolic aspects of patients with AMI. The somewhat conflicting results of these recent studies have generated debate over the significance of the glycometabolic state following acute coronary occlusion and the role of insulin-based infusion therapy. Although most of the available evidence is in favour of an insulin-based therapy, there are still many aspects of this therapy that require clarification. More evidence will be required from further clinical trials before it is adopted in routine clinical practice.

Insulin therapy as an adjunct to reperfusion after acute coronary ischemia: a proposed direct myocardial cell survival effect independent of metabolic modulation

Reperfusion therapy has become a practical and effective strategy in the salvage of ischemic myocardium. The direct enhancement of cardiac cellular tolerance against ischemic and reperfusion injury should further improve patient outcome in acute coronary syndromes (ACS). This approach has been explored for many decades, and although we await mortality-weighted randomized clinical trials, the infusion of glucose-insulin-potassium (GIK) has shown promise in protecting post-infarct myocardium. The current dogma is that this cardioprotective effect of GIK acts via the modulation of cardiac and circulating metabolites to provide the heart with an optimal metabolic milieu to resist ischemia and reperfusion injury. This concept of metabolic modulation has gained favor in coronary heart disease, and its efficacy currently is being investigated in stable angina using the new class of partial fatty acid oxidation inhibitors, including trimetazidine and ranolazine. We contend that the mitogen insulin, itself, promotes tolerance against ischemic cell death via the activation of innate cell-survival pathways in the heart. To advance this viewpoint, we will present clinical data that support a dose-dependent effect of insulin's beneficial action in the management of acute myocardial infarction. Furthermore, we present experimental data that identify cell-survival programs that are directly activated by the administration of insulin. Finally, as intravenous insulin therapy is both labor intensive and associated with metabolic perturbations, we propose that the development of pharmaco-therapeutic agents that target downstream cell-survival insulin-activated signaling molecules may be an alternate approach to promote cardioprotection during ACS.

Effects of polarizing solution on glucose uptake of rat oxygenated or hypoxic ventricular myocytes

1. Although adult cardiac metabolism depends on fatty acids rather than on carbohydrates, hypoxic hearts consume glucose and infusion with a glucose-insulin-potassium solution (GIK) helps in the recovery of the pressure register, the heart rate and electrocardiogram of rat hypoxic whole hearts. 2. Rat myocytes obtained by enzymatic disaggregation captured significant amounts of glucose in Tyrode's solution (9.8 +/- 2.05% during oxygenation and 16.26 +/- 2.76% during hypoxia) after 60 min incubation. Cells incubated with GIK showed a significantly increased glucose uptake (to 30.04 +/- 1.99% during oxygenation and to 37.06 +/- 1.97% during hypoxia). 3. Glucose was the component of the Tyrode's solution that most enhanced its own entry, increasing glucose entry to 45.42 +/- 2.64% with oxygen and 41.42 +/- 2.69% under hypoxia. 4. Antibodies against glucose transporters 1 and 4 (GLUT-1 and -4, respectively) decreased glucose transport during GIK treatment under hypoxia. 5. We conclude that GIK has beneficial effects mediated by GLUT-1 and -4 during hypoxia, inducing recovery of the damaged tissue.

Glucose-insulin-potassium infusion for myocardial protection during off-pump coronary artery surgery

BACKGROUND

The purpose of this randomized, double-blind, placebo-controlled pilot study was to determine the effectiveness of an intravenous glucose-insulin-potassium (GIK) infusion in preventing myocardial damage and maintaining cardiac performance in patients undergoing "off-pump" myocardial revascularization.

METHODS

Forty-six adult patients undergoing elective off-pump coronary artery bypass received either normal saline or a GIK infusion immediately after the induction of anesthesia through the first 12 hours of intensive care unit convalescence. Measurements of blood glucose, circulating creatine kinase MB and troponin I concentrations, as well as cardiac index (CI) and mixed venous oxygen saturation (SvO2), were obtained immediately before starting the infusion (baseline) and at 6, 12, and 24 hours post-initial coronary artery occlusion.

RESULTS

Five patients (8%) requiring cardiopulmonary bypass were excluded from data analysis. Twenty patients received saline. Twenty-one received GIK. Blood glucose was significantly higher in the GIK group. The concentration of circulating creatine kinase MB and troponin I significantly increased over time after off-pump coronary artery bypass, with no significant intergroup differences. Cardiac index and SvO2 did not differ significantly between groups.

CONCLUSIONS

A GIK infusion protocol commonly used as an adjunct to reperfusion therapy for acute myocardial infarction causes insulin-resistant hyperglycemia in elective off-pump coronary artery bypass patients with no demonstrable benefit. The finding of significant release of cardio-specific enzymes in individual patients implies an ongoing need to develop more effective strategies for myocardial protection during off-pump coronary artery bypass.

The effect of glucose-insulin-potassium solution on ventricular late potentials and heart rate variability in acute myocardial infarction

BACKGROUND

Blunted heart rate variability (HRV) and presence of ventricular late potentials (VLPs) are known to correlate with an increased risk of ventricular tachycardia and sudden cardiac death in acute myocardial infarction (AMI). In the present study, we investigated the effect of glucose-insulin-potassium (GIK) solution on the VLPs and HRV in AMI.

METHODS

Seventy-two consecutive patients with first Q wave AMI were randomized to GIK solution and placebo. HRV analysis and ambulatory electrocardiographic recordings were taken in all patients between 24 and 48 h. Sub-maximal exercise testing and echocardiography were performed and signal-averaged electrocardiography (SAECG) was recorded before discharge.

RESULTS

Total filtered QRS duration (FQRS: 102 +/- 7 versus 108 +/- 11 ms; P < 0.05), low-amplitude signal (LAS: 25 +/- 8 versus 32 +/- 11 ms; P < 0.01) and frequency of VLPs (21 versus 45%; P < 0.05) were found to be significantly lower while root-mean-square voltage of the terminal 40 ms of QRS (RMS-40: 45 +/- 18 versus 36 +/- 20 microV; P < 0.05), and left ventricular ejection fraction (EF: 55 +/- 6 versus 48 +/- 7; P < 0.05) were significantly higher in the GIK group when compared to placebo. During the hospital period, the presence and frequency of post-myocardial infarction angina were significantly lower in the GIK group (15 versus 29%, P < 0.05), whereas an insignificant decrease in frequency of ventricular arrhythmias was observed in these patients. On HRV analysis, there was no significant difference between two groups in either time domain (SD, SDNN, RMS-SD) or frequency domain (HF, LF, LF/HF ratio) parameters.

CONCLUSION

GIK solution may be beneficial to VLPs, ischaemic events, and left ventricular systolic performance in the early period of AMI. This therapy has no significant effect on HRV in AMI patients.

Protection of ischemic hearts by high glucose is mediated, in part, by GLUT-4

Metabolic interventions that promote glucose use during ischemia have been shown to protect ischemic myocardium and improve functional recovery on reperfusion. We evaluated whether the cardioprotection afforded by high glucose during low-flow ischemia is associated with changes in the sarcolemmal content of glucose transporters, specifically GLUT-4. Isolated rat hearts were paced at 300 beats/min and perfused under normal glucose (5 mM) or high glucose (10 mM) conditions in buffer containing 0.4 mM albumin, 0.4 mM palmitate, and 70 mU/l insulin and subjected to 50 min of low-flow ischemia and 60 min of reperfusion. To determine the importance of insulin-sensitive glucose transporters in mediating cardioprotection, a separate group of hearts were perfused in the presence of cytochalasin B (10 microM), a preferential inhibitor of insulin-sensitive glucose transporters. Ischemic contracture during low-flow ischemia and creatine kinase release on reperfusion was decreased, and the percent recovery of left ventricular function with reperfusion was enhanced in hearts perfused with high glucose (P < 0.03). Hearts perfused with high glucose exhibited increased GLUT-4 protein expression in the sarcolemmal membrane compared with control hearts under baseline conditions, and these changes were additive with low-flow ischemia. In addition, high glucose did not affect the baseline distribution of sarcolemmal GLUT-1 and blunted any changes with low-flow ischemia. These salutary effects were abolished when glucose transporters are blocked with cytochalasin B. These data demonstrate that protection of ischemic myocardium by high glucose is associated with increased sarcolemmal content of the insulin-sensitive GLUT-4 and suggest a target for the protection of jeopardized myocardium.

Fructose-2,6-bisphosphate, a potent stimulator of phosphofructokinase, is increased by high exogenous glucose perfusion

BACKGROUND

We have previously demonstrated that perfusion of isolated hearts with high concentrations of glucose results in increased glycolysis during ischemia, diminished ischemic injury, and improved functional recovery with reperfusion.

OBJECTIVE

To evaluate a possible mechanism by which glucose conferred this protection. We examined the hypothesis that increased exogenous glucose concentrations results in increased concentrations of fructose-2,6-bisphosphate, a potent activator of phosphofructokinase-1, and thus increases glycolysis.

METHODS

Perfused rabbit hearts were subjected to 60 min of low-flow ischemia. Control hearts were perfused with buffer containing 0.4 mmol/l palmitate, 5 mmol/l glucose, and 70 mU/l insulin, and treated hearts were perfused with buffer containing 0.4 mmol/l palmitate, 15 mmol/l glucose and 210 mU/l insulin.

RESULTS

Ischemic contracture was attenuated by perfusion of high concentrations of glucose (high glucose) (P < 0.05 compared with control). Glucose uptake and lactate production were greater in hearts perfused with high glucose, as was the ATP concentration at the end of ischemia (P < 0.05 compared with controls). Exogenous glucose uptake and lactate production correlated well with fructose-2,6-bisphosphate content (P = 0.007).

CONCLUSIONS

Enhancement of glycolysis in hearts perfused with high glucose may be the result of stimulation of phosphofructokinase-1 by fructose-2,6-bisphosphate. Accordingly, this may serve as an important mechanism by which cardioprotection may be achieved.

Metabolic modulation of acute myocardial infarction. The ECLA (Estudios Cardiológicos Latinoamérica) Collaborative Group

BACKGROUND

Several trials have been performed in the past using glucose, insulin, and potassium infusion (GIK) for the treatment of acute myocardial infarction (AMI). Because of continuing uncertainty about the potential role of this therapeutic intervention, we conducted a randomized trial to evaluate the impact of a GIK solution during the first hours of AMI.

METHODS AND RESULTS

Four hundred seven patients with suspected AMI admitted within 24 hours of symptoms onset were enrolled. In a ratio of 2:1, 268 patients were allocated to receive GIK (high- or low-dose) and 139 to receive control. Phlebitis and serum changes in the plasma concentration of glucose or potassium were observed more often with GIK. A trend toward a nonsignificant reduction in major and minor in-hospital events was observed in patients allocated to GIK. In 252 patients (61.9%) treated with reperfusion strategies, a statistically significant reduction in mortality (relative risk [RR] 0.34; 95% CI: 0.15 to 0.78; 2P=0.008) and a consistent trend toward fewer in-hospital events in the GIK group were observed.

CONCLUSIONS

Our results confirm that a metabolic modulation strategy in the first hours of an AMI is feasible, applicable worldwide, and has mild side effects. The statistically significant mortality reduction in patients who underwent a reperfusion strategy might have important implications for the management of AMI patients. It is now essential to perform a large-scale trial to reliably determine the magnitude of benefit.

[Therapy with glucose-insulin-potassium reduces the complications in the acute phase of myocardial infarct. Arguments in favor]

Several therapeutic approaches have been proposed for the management of acute myocardial infarction (AMI). In 1961, Sodi-Pallarés presented the Glucose-Insulin-Potassium (GIK) infusion as a valid adjunctive therapy for the treatment of the acute phase. He observed a decrease in mortality which could be explained by some mechanisms such as: arrhythmia prevention, hypoxic cell nutrition, diminution of infarct size and others. Due to the lack of Coronary Care Units at that time, acute myocardial ischemia was considered a high mortality disease. Therefore, the first studies concerning the efficacy of this treatment showed a significant decrease in mortality. After the development of better care and medical attention of AMI patients, and above all after the introduction of fibrinolysis, mortality dramatically diminished. Thus, GIK was considered to give no additional benefit, and its use became restricted to a small number of centers. In this review the physiopathological bases of GIK solution use are given, as well as the results of the main experimental studies and a critical analysis of the scarce clinical studies available. It is concluded that there are enough data to support the use of GIK solution in non-thrombolized AMIs. It could probably also benefit thrombolised ones, although there is no available evidence in this context.

Metabolic effects of aldose reductase inhibition during low-flow ischemia and reperfusion

Several studies have shown that maintenance of glycolysis limits the metabolic and functional consequences of low-flow ischemia. Because diabetic animals are known to have impaired glycolytic metabolism coupled with increased flux through the aldose reductase (AR) pathway, we hypothesized that inhibition of AR would enhance glycolysis and thereby improve metabolic and functional recovery during low-flow ischemia. Hearts (n = 12) from nondiabetic control and diabetic rats were isolated and retrograde perfused using 11 mM glucose with or without the AR inhibitor zopolrestat (1 microM). Hearts were subjected to 30 min of low-flow ischemia (10% of baseline flow) and 30 min of reperfusion. 31P NMR spectroscopy was used to monitor time-dependent changes in phosphocreatine (PCr), ATP, and intracellular pH. Changes in the cytosolic redox ratio of NADH to NAD+ were obtained by measuring the ratio of tissue lactate to pyruvate. Effluent lactate concentrations and oxygen consumption were determined from the perfusate. AR inhibition improved functional recovery in both control and diabetic hearts, coupled with a lower cytosolic redox state and greater effluent lactate concentrations during ischemia. ATP levels during ischemia were significantly higher in AR-inhibited hearts, as was recovery of PCr. In diabetic hearts, AR inhibition also limited acidosis during ischemia and normalized pH recovery on reperfusion. These data demonstrate that AR inhibition maintains higher levels of high-energy phosphates and improves functional recovery upon reperfusion in hearts subjected to low-flow ischemia, consistent with an increase in glycolysis. Accordingly, this approach of inhibiting AR offers a novel method for protecting ischemic myocardium.

Glucose-insulin-potassium therapy for treatment of acute myocardial infarction: an overview of randomized placebo-controlled trials

BACKGROUND

Glucose-insulin-potassium (GIK) therapy has been advocated for the treatment of acute myocardial infarction. However, the results from the clinical trials have been inconclusive, largely because of the small number of patients recruited and discrepancies between protocols used in these studies.

METHOD AND RESULTS

A systematic MEDLINE search for all the randomized placebo-controlled studies of GIK therapy in acute myocardial infarction was made, and a meta-analysis of the mortality data was performed. Fifteen trials were identified, 5 were excluded because of poor randomization, and 1 was excluded because recruitment was limited to diabetic patients. The 9 remaining trials with a total of 1932 patients were included in the analysis. Hospital mortality was reduced from 21% (205 of 972 patients) in the placebo group to 16.1% (154 of 956) in the GIK group (P=.004; odds ratio, 0.72; 95% confidence interval [CI], 0.57 to 0.90). The proportional mortality reduction was 28% (CI, 10% to 43%). The number of lives saved per 1000 patients treated was 49 (95% CI, 14 to 83).

CONCLUSIONS

The findings indicate that GIK therapy may have an important role in reducing the in-hospital mortality after acute myocardial infarction. The value of this therapy in the era of thrombolysis and acute revascularization by primary angioplasty can be fully resolved only by conducting a large randomized mortality study.

Glucose-insulin-potassium solutions enhance recovery after urgent coronary artery bypass grafting

OBJECTIVE

This prospective, randomized, clinical study was undertaken to determine whether glucose-insulin-potassium solutions would benefit patients undergoing coronary artery bypass grafting because of unstable angina.

METHODS

The study group consisted of 30 patients with unstable angina who required coronary artery bypass grafting. In 15 patients, glucose-insulin-potassium solution (30% dextrose in water; K+, 80 mEq/L: regular insulin, 50 units) was given intravenously at 1 ml/kg per hour after induction of anesthesia and administration continued for 12 hours after aortic unclamping. Fifteen patients in a separate group received 5% dextrose in water intravenously at 50 ml/hr.

RESULTS

Patients treated with glucose-insulin-potassium solution had higher cardiac indices (2.8 +/- 0.1 vs 2.0 +/- 1 L/min per square meter; p < 0.001), lower inotrope scores (0.06 +/- 0.01 vs 0.46 +/- 0.19; p = 0.041), and less weight gain (6.4 +/- 9 vs 11.6 +/- 1.1 pounds; p < 0.001) and had shorter times of ventilator support (8.3 +/- 0.6 vs 14.2 +/- 0.2 hours; p = 0.003). They had a significantly lower incidence of atrial fibrillation (13.3% vs 53.3%; p = 0.020) and had shorter stays in the intensive care unit (14.8 +/- 1.3 vs 31.6 +/- 5.2 hours; p = 0.002) and in the hospital (6.0 +/- 0.4 vs 8.0 +/- 0.7 days; p = 0.010).

CONCLUSIONS

We conclude that glucose insulin-potassium therapy enhances myocardial performance and results in faster recovery from urgent coronary artery bypass grafting.

Effects of dobutamine versus insulin on cardiac performance, myocardial oxygen demand, and total body metabolism after coronary artery bypass grafting

OBJECTIVE

The purpose was to study whether the hemodynamic benefit of a catabolic catecholamine (dobutamine) induces a certain oxygen cost for the myocardial energy demand and whether this effect would be less pronounced if an anabolic intervention, such as the administration of insulin, was used.

DESIGN

A prospective and randomized study.

SETTING

A university hospital.

PARTICIPANTS

Investigation of two comparable groups of cardiac patients.

INTERVENTIONS

The interventions were postoperative infusions of dobutamine, 7 micrograms/kg/min, and of insulin, 1.5 U/kg/h, respectively, over a period of 30 minutes.

MEASUREMENTS AND MAIN RESULTS

The effects of the interventions were measured using parameters relating to cardiac work and myocardial oxygen demand. Moreover, parameters relating to total body metabolism were also recorded. In the dobutamine group, cardiac index (CI) and left ventricular stroke work index (LVSWI) increased significantly (p < 0.05) during therapy by 30% and 40%, respectively. Cardiac effort index (CEI) and tension time index (TTI) also increased (p < 0.05) during therapy by 41% and 30%, respectively. However, in the insulin group, CI and LVSWI also increased (p < 0.01 and p < 0.05) during therapy, although to a lesser extent (16% and 14%), but CEI and TTI did not change at all during therapy. Total body CO2 production (VCO2) and O2 consumption (VO2) in the dobutamine group increased (p < 0.05) during therapy by 9% and 11%, respectively, whereas in the insulin group only CO2 production increased (p < 0.05) by 13%. O2 consumption remained unchanged in this group.

CONCLUSIONS

It is concluded that dobutamine as well as insulin administration increase cardiac performance. However, in contrast to dobutamine, insulin does not appear to increase myocardial oxygen demand. Therefore, the anabolic insulin administration may represent a more economic pattern of energy-consuming hemodynamic intervention than does the catabolic catecholamine administration.

Requirement of glycolytic substrate for metabolic recovery during moderate low flow ischemia

Low flow ischemia with stable hemodynamic function can result in partial metabolic recovery characterized by an increase in phosphocreatine (PCr). Prior data suggest that glycolytic production of adenosine triphosphate (ATP) may be critical for this recovery and that the ATP produced by oxidative phosphorylation alone may be insufficient. This study tested the hypotheses that, during moderate low flow ischemia, (a) metabolic recovery is dependent on glycolytic production of ATP, and, therefore, (b) a mitochondrial substrate such as pyruvate alone is inadequate to allow metabolic recovery. High energy phosphates, pH, and lactate release were measured during 2 h of moderate low flow ischemia. Hearts were perfused with either a glycolytic plus mitochondrial substrate (glucose, insulin and pyruvate) or a mitochondrial substrate alone (pyruvate). Flow reductions required to reduce PCr by approximately 8% resulted in stable and equal reductions of rate-pressure product in each group. PCr recovered fully during the ischemic period in control hearts with glycolytic substrate, associated with preservation of normal end-diastolic pressure, and increased lactate release during the first hour of ischemia. Reperfusion of these hearts restored hemodynamic function and increased PCr above baseline values. In contrast, the use of pyruvate alone as a substrate resulted in a progressive fall of PCr during ischemia, increased end-diastolic pressure, and no significant increase in lactate release. Reperfusion in these hearts restored hemodynamic function, but did not result in normalization of PCr. Both groups had significant reductions in ATP during ischemia. Recovery of PCr during ongoing moderate low flow ischemia is observed in the presence of mixed glycolytic and mitochondrial substrates (glucose, insulin and pyruvate) but is not observed with pyruvate as a sole mitochondrial substrate. These data support a critical role for glycolytic flux under these conditions, suggesting that ATP generated solely by oxidative phosphorylation is not sufficient to promote metabolic recovery or maintain diastolic function during moderate low flow ischemia.

Enhanced preservation of acutely ischemic myocardium using glucose-insulin-potassium solutions

"Surgical myocardial stunning" represents a model of both ischemia and infarction that unlike regular "stunning" has the potential for permanent or partially reversible cellular function. While substrate enhancement may not play an important role in myocardial stunning, it may be critical during surgical stunning when mitochondrial dysfunction is present. The primary myocardial substrate for the normal myocardium is free fatty acids; however, this may not be the optimal energy source for the ischemic heart. Exogenous glucose appears to be a superior substrate during periods of myocardial ischemia. Glucose-insulin-potassium (GIK) solutions appear to have an important role in the revascularization of acutely ischemic myocardium. In isolated hearts with regional ischemia, GIK was shown to decrease infarct size, increase ATP and creatine phosphate levels, and improve ventricular function. GIK appears to protect the ischemic myocardium by preserving cellular function and improving myocardial perfusion. Our preliminary experimental studies indicate that GIK may effectively reduce necrosis and stunning in a model of acute surgical revascularization.

Protective effect of increased glycolytic substrate against systolic and diastolic dysfunction and increased coronary resistance from prolonged global underperfusion and reperfusion in isolated rabbit hearts perfused with erythrocyte suspensions

Current therapy of myocardial infarction may include early reperfusion. We simulated myocardial perfusion conditions during evolving myocardial infarction in isolated, normothermic, isovolumic rabbit hearts perfused with buffer containing bovine red blood cells (hematocrit of 40%), and we assessed the effects of high levels of glucose and insulin as "therapy" during prolonged (150-minute) severe underperfusion and reperfusion. Protocol 1 consisted of underperfusion at a constant coronary perfusion pressure of 8 mm Hg. The control group (n = 8) received 5.5 mmol/l glucose and 15 microunits/ml insulin; the group treated with high levels of glucose and insulin (G + I) (n = 8) received 19.5 mmol/l glucose and 250 microunits/ml insulin during both underperfusion and reperfusion. Relative to the control group, the G + I group experienced 1) greater developed pressure during underperfusion and increased recovery during reperfusion, 2) preserved diastolic function during underperfusion and reperfusion, 3) lower coronary resistance and greater coronary flow during the underperfusion period, 4) increased glycolytic flux and preserved glycogen stores and high energy phosphate levels, and 5) less loss of myocyte enzymes (creatine kinase and alanine aminotransferase). In protocol 2, coronary flow was kept identical in control (n = 8) and G + I hearts (n = 8) during the underperfusion period, and left ventricular end-diastolic pressure was kept below 10 mm Hg in both groups to minimize subendocardial damage and vascular compression. In this protocol, the effect of the G + I intervention in the prevention of an increase in coronary resistance during the underperfusion period was distinguished from its myocellular metabolic effects; the high G + I substrate had protective effects on mechanical and metabolic function that were less marked than, but similar to, those in protocol 1, indicating that its mechanisms of protection during underperfusion affected both cardiac function and coronary resistance. We conclude that the G + I intervention, in clinically relevant concentrations, markedly protected severely underperfused myocardium for 150 minutes and may be a beneficial intervention in combination with reperfusion therapy in acute myocardial infarction.

Antianginal and cardiac metabolic effects of low-dose glucose infusion during pacing in patients with and without coronary artery disease

Anginal threshold and cardiac metabolism during infusion of glucose, 350 mg/min, were compared with control values before, during, and after pacing in nine patients with coronary artery disease (CAD) and nine patients without coronary artery disease (non-CAD). Pacing induced no ischemia in non-CAD patients; in CAD patients, intolerable angina developed in less than 5 minutes. However, glucose infusion in the latter group increased the time to onset of angina (110 +/- 24 seconds before infusion versus 140 +/- 24 seconds following infusion) and decreased the extent of ST segment depression (1.8 +/- 0.3 mm before infusion versus 0.9 +/- 0.2 mm following infusion, p less than 0.01) following pacing. In all subjects, arterial levels and cardiac uptake of glucose rose by 100% (p less than 0.001) and those of free fatty acids fell by 50% (p less than 0.01). Arterial lactate and uptake of lactate by nonischemic myocardium increased by 30% (p less than 0.05). During pacing in CAD patients, this elevated uptake was outweighed by similar increases of lactate release from ischemic areas, leaving mean negative global exchanges unaltered. In CAD patients solely, rebuilding of cardiac glycogen after pacing was suggested from augmented citrate efflux in the control period but not during glucose infusion, suggesting a glycogen-sparing effect. Arterial concentrations and net cardiac fluxes of oxygen, glutamate, and alanine remained unaltered. In conclusion, beneficial effects of glucose during ischemia are associated with increased aerobic and anaerobic glycolysis, saving of glycogen, and decreased lipolysis.

Myocardial fuel and energy balance, acute ischemia and diabetes

When glucose-insulin-potassium (GIK) is infused, glucose supplies most of the energy demands of the heart. Fatty acid becomes the major substrate during fasting, pathologically increased work loads or insulin deficiency. Myocardial purine breakdown reflects myocardial energy status and influences coronary tone. Ischemia accelerates breakdown of ATP to AMP, which is further metabolized to adenosine, which causes vasodilatation and a blunted response to catecholamines. If normal circulation is restored, ADP and AMP are rapidly converted to ATP and purine metabolism is changed from degradation to salvage and de novo synthesis of purines. Ischemia impairs mitochondrial function, causing decreased capacity to oxidize fatty acids once aerobic conditions return. Thus, reperfusion with elevated plasma free fatty acids results in acyl-CoA accumulation in the heart. In diabetic animals, phosphorylation of AMP to ATP is defective in the heart, and AMP degradation is increased. Therefore, careful regulation of the blood sugar with concomitant lowering of plasma free fatty acids in diabetics with ischemic heart disease should improve myocardial salvage by preserving and repleting myocardial ATP. Thus, along with reestablishment of coronary flow and reduction in myocardial oxygen demands, may significantly reduce the morbidity of acute ischemia in diabetics.

Myocardial metabolic and hemodynamic effects of dichloroacetate in coronary artery disease

Dichloroacetate (DCA), which activates pyruvate dehydrogenase, has the potential to enhance carbohydrate and lactate utilization in animals, but data from patients with coronary artery disease are lacking. Accordingly, 9 patients (ages 49 to 72 years) with angina and coronary artery disease undergoing catheterization were studied. Systemic and coronary hemodynamic and metabolic measurements were made before and during DCA administration (mean dose 35 mg/kg, intravenously). DCA increased left ventricular (LV) stroke volume from 77 +/- 7 to 87 +/- 7 ml and decreased systemic vascular resistance from 1,573 +/- 199 to 1,319 +/- 180 dynes.s.cm-5 (both, p less than 0.01). There were no significant changes in heart rate, mean aortic pressure, LV end-diastolic pressure, LV dP/dt max, coronary sinus flow, coronary resistance or myocardial oxygen consumption, but myocardial efficiency index (LV work/myocardial oxygen consumption) improved from 24 to 32% (p less than 0.05). Myocardial lactate consumption was maintained (21 +/- 8 vs 19 +/- 11 X 10(-3) mEq/min, p is not significant at p less than or equal to 0.05 level) at a lower arterial lactate concentration (0.72 +/- 0.09 to 0.47 +/- 0.08 mEq/liter, p less than 0.05). DCA appears to stimulate myocardial lactate utilization at a lower arterial concentration, cause peripheral vasodilation, augment stroke volume and enhance myocardial efficiency in patients with coronary artery disease.

The effects of glucose on myocardial substrate utilization in acute myocardial infarction or angina pectoris

Infusion of glucose-insulin-potassium during acute myocardial infarction has favorable clinical and hemodynamic effects, presumably as a result of decreased myocardial utilization of free fatty acids. In 14 patients with coronary artery disease, hypertonic glucose (a bolus of 10 g followed by infusion of a 30% glucose solution at a constant rate of 10 mg/kg/min) was infused and arterial and coronary sinus levels of glucose, lactate and free fatty acids were measured before and after 15 and 30 minutes of infusion. Arterial glucose and lactate levels increased significantly after glucose infusion, whereas free fatty acid levels decreased significantly. Modest but significant correlations also existed between glucose arterial levels and the arterial-coronary sinus glucose difference (r = 0.53, p less than 0.001); arterial lactate and the arterial-coronary sinus lactate difference (r = 0.35, p less than 0.01); arterial free fatty acids; and the arterial-coronary sinus free fatty acid difference (r = 0.62, p less than 0.001). These results with a hypertonic glucose infusion are similar to those reported after infusion of glucose-insulin-potassium without the potential for harmful adverse effects from infusions of insulin or potassium. Therefore, infusion of hypertonic glucose may be beneficial in patients with coronary artery disease. Further work is necessary to study its effects in different subgroups of patients with coronary artery disease.

Infarct size--can it be measured or modified in humans?

Despite more than 15 years of intensive experimental and clinical research in the general area of limiting infarct size, no treatment has been shown to be so efficacious and relatively free of side effects that its routine use can be recommended. In addition, there is no ideal means of measuring infarct size as yet. However, considerable progress has been made in understanding mechanisms responsible for irreversible cellular injury and in identifying factors and anatomic alterations responsible for or contributing to the development of transmural (Q wave) and non-transmural (non-Q wave) myocardial infarcts. Interventions are available that are capable of causing rapid coronary thrombolysis, and techniques are becoming available tht have increasing power to size myocardial infarcts and estimate both segmental and ventricular function. Experimental studies have also suggested a potential benefit from a combination of reperfusion therapy with selected pharmacologic intervention in reducing infarct size and preserving ventricular function. It seems likely that this general area will remain an intensive area of clinical research in the immediate future.