Clinical experience with glucose-insulin-potassium therapy in acute myocardial infarction

Stress-Induced Hyperglycaemia in Non-Diabetic Patients with Acute Coronary Syndrome: From Molecular Mechanisms to New Therapeutic Perspectives

Stress-induced hyperglycaemia (SIH) at hospital admission for acute coronary syndrome is associated with poor outcome, especially in patients without known diabetes. Nevertheless, insulin treatment in these subjects was not correlated with the reduction of mortality. This is likely due to the fact that SIH in the context of an acute coronary syndrome, compared to that in known diabetes, represents an epiphenomenon of other pathological conditions, such as adrenergic and renin-angiotensin system over-activity, hyperglucagonaemia, increase of circulating free fatty acids and pancreatic beta-cell dysfunction, which are not completely reversed by insulin therapy and so worsen the prognosis. Thus, SIH may be considered not only as a biomarker of organ damage, but also as an indicator of a more complex therapeutic strategy in these subjects. The aim of this review is to analyse the molecular mechanisms by which SIH may favour a worse prognosis in non-diabetic patients with acute coronary syndrome and identify new therapeutic strategies, in addition to insulin therapy, for a more appropriate treatment and improved outcomes.

Cardiovascular Safety of Antidiabetic Drugs in the Hospital Setting

PURPOSE OF REVIEW

Patients with diabetes and/or stress hyperglycemia requires good glycemic control in the hospital setting, often requiring the use of glucose-lowering therapy. Standard-of-care dictates that non-insulin therapy be discontinued, with insulin therapy initiated using a basal-bolus approach. However, insulin is associated with a high risk for hypoglycemia and medical errors. Alternatives to insulin are needed in the inpatient setting, but the cardiovascular (CV) safety of non-insulin therapy is a concern.

RECENT FINDINGS

Most studies of antidiabetic drugs have been performed in the outpatient setting, and except for insulin therapy, trials in the inpatient setting have been insufficient to establish CV safety. Randomized controlled trials support the safety of insulin with more moderate glycemic control in the hospital, when hypoglycemia is minimized. Two recent multicenter randomized controlled clinical trials support the safety of sitagliptin, a dipeptidylpeptidase-4 inhibitor (DPP4i), in hospitalized patients, although the sample sizes were likely too small to detect CV events. Small trials suggest a possible CV benefit of glucagon-like peptide-1 receptor agonist therapy. A paucity of evidence and presence of side effects and cautions with insulin secretagogues, sodium glucose-co-transporter-2 inhibitors, and metformin preclude their routine use in the hospital setting. Available evidence is inadequate to evaluate the CV safety of most antidiabetic drug classes in the hospital setting. However, preliminary data from randomized clinical trials suggest the potential safety of the DPP4i sitagliptin.

Out-of-hospital administration of intravenous glucose-insulin-potassium in patients with suspected acute coronary syndromes: the IMMEDIATE randomized controlled trial

CONTEXT

Laboratory studies suggest that in the setting of cardiac ischemia, immediate intravenous glucose-insulin-potassium (GIK) reduces ischemia-related arrhythmias and myocardial injury. Clinical trials have not consistently shown these benefits, possibly due to delayed administration.

OBJECTIVE

To test out-of hospital emergency medical service (EMS) administration of GIK in the first hours of suspected acute coronary syndromes (ACS).

DESIGN, SETTING, AND PARTICIPANTS

Randomized, placebo-controlled, double-blind effectiveness trial in 13 US cities (36 EMS agencies), from December 2006 through July 31, 2011, in which paramedics, aided by electrocardiograph (ECG)-based decision support, randomized 911 (871 enrolled) patients (mean age, 63.6 years; 71.0% men) with high probability of ACS.

INTERVENTION

Intravenous GIK solution (n = 411) or identical-appearing 5% glucose placebo (n = 460) administered by paramedics in the out-of-hospital setting and continued for 12 hours.

MAIN OUTCOME MEASURES

The prespecified primary end point was progression of ACS to myocardial infarction (MI) within 24 hours, as assessed by biomarkers and ECG evidence. Prespecified secondary end points included survival at 30 days and a composite of prehospital or in-hospital cardiac arrest or in-hospital mortality, analyzed by intent-to-treat and by presentation with ST-segment elevation.

RESULTS

There was no significant difference in the rate of progression to MI among patients who received GIK (n = 200; 48.7%) vs those who received placebo (n = 242; 52.6%) (odds ratio [OR], 0.88; 95% CI, 0.66-1.13; P = .28). Thirty-day mortality was 4.4% with GIK vs 6.1% with placebo (hazard ratio [HR], 0.72; 95% CI, 0.40-1.29; P = .27). The composite of cardiac arrest or in-hospital mortality occurred in 4.4% with GIK vs 8.7% with placebo (OR, 0.48; 95% CI, 0.27-0.85; P = .01). Among patients with ST-segment elevation (163 with GIK and 194 with placebo), progression to MI was 85.3% with GIK vs 88.7% with placebo (OR, 0.74; 95% CI, 0.40-1.38; P = .34); 30-day mortality was 4.9% with GIK vs 7.7% with placebo (HR, 0.63; 95% CI, 0.27-1.49; P = .29). The composite outcome of cardiac arrest or in-hospital mortality was 6.1% with GIK vs 14.4% with placebo (OR, 0.39; 95% CI, 0.18-0.82; P = .01). Serious adverse events occurred in 6.8% (n = 28) with GIK vs 8.9% (n = 41) with placebo (P = .26).

CONCLUSIONS

Among patients with suspected ACS, out-of-hospital administration of intravenous GIK, compared with glucose placebo, did not reduce progression to MI. Compared with placebo, GIK administration was not associated with improvement in 30-day survival but was associated with lower rates of the composite outcome of cardiac arrest or in-hospital mortality.

TRIAL REGISTRATION

clinicaltrials.gov Identifier: NCT00091507.

Study design for the Immediate Myocardial Metabolic Enhancement During Initial Assessment and Treatment in Emergency Care (IMMEDIATE) Trial: A double-blind randomized controlled trial of intravenous glucose, insulin, and potassium for acute coronary syndromes in emergency medical services

BACKGROUND

Experimental studies suggest that metabolic myocardial support by intravenous (IV) glucose, insulin, and potassium (GIK) reduces ischemia-induced arrhythmias, cardiac arrest, mortality, progression from unstable angina pectoris to acute myocardial infarction (AMI), and myocardial infarction size. However, trials of hospital administration of IV GIK to patients with ST-elevation myocardial infarction (STEMI) have generally not shown favorable effects possibly because of the GIK intervention taking place many hours after ischemic symptom onset. A trial of GIK used in the very first hours of ischemia has been needed, consistent with the timing of benefit seen in experimental studies.

OBJECTIVE

The IMMEDIATE Trial tested whether, if given very early, GIK could have the impact seen in experimental studies. Accordingly, distinct from prior trials, IMMEDIATE tested the impact of GIK (1) in patients with acute coronary syndromes (ACS), rather than only AMI or STEMI, and (2) administered in prehospital emergency medical service settings, rather than later, in hospitals, after emergency department evaluation.

DESIGN

The IMMEDIATE Trial was an emergency medical service-based randomized placebo-controlled clinical effectiveness trial conducted in 13 cities across the United States that enrolled 911 participants. Eligible were patients 30 years or older for whom a paramedic performed a 12-lead electrocardiogram to evaluate chest pain or other symptoms suggestive of ACS for whom electrocardiograph-based acute cardiac ischemia time-insensitive predictive instrument indicated a ≥75% probability of ACS, and/or the thrombolytic predictive instrument indicated the presence of a STEMI, or if local criteria for STEMI notification of receiving hospitals were met. Prehospital IV GIK or placebo was started immediately. Prespecified were the primary end point of progression of ACS to infarction and, as major secondary end points, the composite of cardiac arrest or in-hospital mortality, 30-day mortality, and the composite of cardiac arrest, 30-day mortality, or hospitalization for heart failure. Analyses were planned on an intent-to-treat basis, on a modified intent-to-treat group who were confirmed in emergency departments to have ACS, and for participants presenting with STEMI.

CONCLUSION

The IMMEDIATE Trial tested whether GIK, when administered as early as possible in the course of ACS by paramedics using acute cardiac ischemia time-insensitive predictive instrument and thrombolytic predictive instrument decision support, would reduce progression to AMI, mortality, cardiac arrest, and heart failure. It also tested whether it would provide clinical and pathophysiologic information on GIK's biological mechanisms.

High-dose glucose-insulin-potassium has hemodynamic benefits and can improve cardiac remodeling in acute myocardial infarction treated with primary percutaneous coronary intervention: From a randomized controlled study

Objective:

To evaluate the effects of high-dose glucose–insulin–potassium (GIK) solution on hemodynamics and cardiac remodeling in patients with acute myocardial infarction (AMI) treated with primary percutaneous coronary intervention (PCI).

Patients and Methods:

We observed the changes in the hemodynamic parameters in 26 patients with AMI. All patients received primary PCI before entering the study. All patients in the study were randomized into the GIK group (n = 14) or the control group (n = 12). Patients in the GIK group received high-dose GIK solution (25% glucose, 80 mmol/L KCl and 50 IU/L insulin; 1.5 ml/kg/h) over 24 h. Patients in the control group received standard therapy. We monitored the hemodynamic parameters at baseline and after 6 h, 12 h, 18 h and 24 h, respectively. Then, we followed-up the cardiac function with echocardiography after 7 days, 1 month and 6 months.

Results:

The basic clinical data was similar between the groups. Primary PCI was performed successfully in 25 patients. The two groups were indistinguishable in all factors measured. GIK solution did not have a deleterious effect on the hemodynamic parameters. The pulmonary capillary wedge pressure increased during the first 12-h period and then decreased smoothly (F = 3.75, P = 0.02). The trends were similar between the two groups. The system vascular resistance index (SVRI) and pulmonary vascular resistance index (PVRI) decreased during the first 12 h in the GIK group but increased in the control group. The GIK solution significantly influenced SVRI (F = 4.71, P = 0.02). GIK solution improved the cardiac function measured by stroke volume (F = 4.11, P = 0.03) and cardiac index (F = 4.40, P = 0.02). In the 6-month follow-up, GIK improved cardiac remodeling (left ventricular diastolic diameter: 49.2 ± 2.89 vs. 53.9 ± 2.48, P < 0.001; left ventricular systolic diameter: 32.9 ± 2.24 vs. 35.9 ± 2.78, P < 0.01).

Conclusion:

High-dose GIK solution had no adverse effects on the hemodynamics in AMI patients treated with primary PCI. It can improve cardiac function by lowering SVRI. In the 6-month follow-up, it improved cardiac remodeling.

Insulin therapy in acute coronary syndromes: an appraisal of completed and ongoing randomised trials with important clinical end points

Insulin therapy was first proposed as an adjunctive therapy in patients with acute coronary syndromes (ACS) in the 1960s. Since then, numerous randomised clinical trials have been conducted to determine the efficacy and to define the role of insulin therapy in ACS. This review will discuss: 1) completed trials of insulin therapy in ACS, including both glucose-insulin-potassium (GIK) approaches and non-GIK approaches; 2) trials of insulin therapy in critically ill non-ACS patients and the lessons from these trials that can be applied to trials of insulin in ACS patients; and 3) a summary of ongoing and planned trials of insulin in ACS patients.

Effect of modified glucose-insulin-potassium on free fatty acids, matrix metalloproteinase, and myoglobin in ST-elevation myocardial infarction

Insulin has a free fatty acid (FFA)-suppressive effect, vascular endothelial growth factor (VEGF)- and matrix metalloproteinase (MMP)-lowering effect, and a potential myocardial-protective effect. Whether low-dose insulin exerts these effects in patients with acute myocardial infarction (MI) was investigated. Thirty-two patients administered thrombolytics and heparin were randomly assigned to a modified glucose-insulin-potassium (GIK) regimen (insulin 2.5 U/hour, dextrose and potassium titrated to prevent hyperglycemia) or normal saline solution and potassium (controls) for 48 hours. Plasma FFA, serum VEGF, pro-MMP-1, and myoglobin were measured at baseline and sequentially for 48 hours. FFA concentrations were increased at baseline; increased further in the first 4 hours in controls (p<or=0.008), but not in the GIK group, and were higher at 4 hours in controls compared with the GIK group (p=0.0009). VEGF decreased to 7% of baseline at 2 hours and remained suppressed in both groups (p=0.0008). Pro-MMP-1 decreased in both groups (p<0.005), but this decrease was seen earlier at 2 hours in the GIK group compared with 4 hours in controls. There was no significant increase in myoglobin at 2 hours in the GIK group, whereas there was a significant increase in controls. Mean blood glucose was 131 mg/dl in controls and 124 mg/dl in the GIK group (p=NS). In conclusion, this modified GIK regimen attenuated the increase in FFA, but did not suppress it to less than the threshold for myocardial FFA uptake. It suppressed pro-MMP-1 rapidly and decreased myoglobin, whereas heparin suppressed VEGF in patients with acute MI. This provided additional rationale for conducting a trial to assess the clinical benefits of this modified GIK regimen in patients with acute MI.

The impact of glucose-insulin-potassium infusion in acute myocardial infarction on infarct size and left ventricular ejection fraction [ISRCTN56720616]

BACKGROUND

Favorable clinical outcomes have been observed with glucose-insulin-potassium infusion (GIK) in acute myocardial infarction (MI). The mechanisms of this beneficial effect have not been delineated clearly. GIK has metabolic, anti-inflammatory and profibrinolytic effects and it may preserve the ischemic myocardium. We sought to assess the effect of GIK infusion on infarct size and left ventricular function, as part of a randomized controlled trial.

METHODS

Patients (n = 940) treated for acute MI by primary percutaneous coronary intervention (PCI) were randomized to GIK infusion or no infusion. Endpoints were the creatinine kinase MB-fraction (CK-MB) and left ventricular ejection fraction (LVEF). CK-MB levels were determined 0, 2, 4, 6, 24, 48, 72 and 96 hours after admission and the LVEF was measured before discharge.

RESULTS

There were no differences between the two groups in the time course or magnitude of CK-MB release: the peak CK-MB level was 249 +/- 228 U/L in the GIK group and 240 +/- 200 U/L in the control group (NS). The mean LVEF was 43.7 +/- 11.0 % in the GIK group and 42.4 +/- 11.7% in the control group (P = 0.12). A LVEF < or = 30% was observed in 18% in the controls and in 12% of the GIK group (P = 0.01).

CONCLUSION

Treatment with GIK has no effect on myocardial function as determined by LVEF and by the pattern or magnitude of enzyme release. However, left ventricular function was preserved in GIK treated patients.

ST-segment elevation resolution and outcome in patients treated with primary angioplasty and glucose-insulin-potassium infusion

BACKGROUND

To evaluate the impact of adjunctive high-dose glucose-insulin-potassium (GIK) on ST-segment elevation resolution in patients with ST-segment elevation myocardial infarction (MI).

METHODS

As part of a randomized controlled trial of GIK versus no GIK in patients treated with primary percutaneous coronary intervention (PCI) for ST-elevation MI in a tertiary referral center, we analyzed ST-segment elevation resolution. Paired electrocardiographic recordings (baseline and 3 hours after primary PCI) were available in 612 (65%) of 940 patients.

RESULTS

We analyzed paired electrocardiograms of 310 patients randomized to GIK and 302 control patients. Baseline characteristics of the groups were comparable. Combined complete (>70%) and partial (30%-70%) resolution was more commonly observed in the GIK group (87%) when compared with the control group (78%), odds ratio 1.92 (95% CI 1.23-3.02, P = .004); 1-year mortality was lower in patients with combined complete and partial resolution compared with patients without resolution (3.8% vs 10.3%, P = .011). There was no difference in 1-year mortality between GIK and control patients (5.5% vs 4.3%, P = .58).

CONCLUSIONS

In patients with ST-elevation MI treated with primary PCI, addition of GIK is associated with improved ST-segment elevation resolution. ST-segment elevation resolution is related to improved 1-year survival. No benefit of GIK on 1-year outcome was observed. Future trials should investigate whether GIK-induced improvement of ST-segment elevation resolution results in more favorable clinical outcome.

Glucose-insulin-potassium and reperfusion in acute myocardial infarction: rationale and design of the Glucose-Insulin-Potassium Study-2 (GIPS-2)

BACKGROUND

The combination of reperfusion therapy and high-dose glucose-insulin-potassium (GIK) infusion seems beneficial in acute myocardial infarction (MI). Current evidence, however, is not considered conclusive.

STUDY DESIGN

The Glucose-Insulin-Potassium Study-2 (GIPS-2) will investigate whether GIK, in adjunction to reperfusion therapy, is beneficial in MI patients without signs of heart failure at admission. A total of at least 1044 patients with an acute MI treated with either thrombolysis or primary percutaneous coronary intervention will be randomized to an infusion of high-dose GIK or no infusion. The primary end point of the study is 30-day mortality. Secondary end points are mortality at 1 year, recurrence of MI, repeat intervention, and infarct size.

IMPLICATIONS

If high-dose GIK significantly reduces mortality at 30 days in all patients, the adjunction of this treatment to reperfusion therapy may become part of standard regimen for patients with acute MI without heart failure.

Akute Herzinsuffizienz und kardiogener Schock

Irrespective of improved medical and interventional therapeutic options, mortality among patients with acute heart failure and cardiogenic shock has remained disappointingly high. Early diagnosis and rapid initiation of basic treatment measures to improve hemodynamics and metabolism are of vital importance until causal therapy, e. g. revascularization, is initiated. Due to the principal difficulty to set up larger clinical trials, in patients with cardiogenic shock empirical rather than firm evidence supports the various treatment and management strategies currently in use. Continuous hemodynamic monitoring to tailor fluid therapy, new drugs, and prognostic markers have been developed for the treatment and monitoring of cardiogenic shock, all of which await testing in larger-scale studies. Ongoing challenges remain the right ventricular pump failure or hemodynamically compromising arrhythmia which may be either cause or consequence of cardiogenic shock.

Effect of glucose-insulin-potassium infusion on plasma free fatty acid concentrations in patients undergoing primary percutaneous coronary intervention for ST-elevation myocardial infarction

To determine the effect of glucose-insulin-potassium infusion on circulating levels of free fatty acids in the setting of contemporary management of ST-elevation myocardial infarction, we randomly assigned 20 patients who were undergoing primary angioplasty to glucose-insulin-potassium infusion or to standard care. Treatment with glucose-insulin-potassium was associated with significantly lower levels of free fatty acid after 24 hours compared with standard care.

Intensive Insulin Therapy for Critically III Patients

OBJECTIVE:

To evaluate the clinical outcomes of glycemic control of intensive insulin therapy and recommend its place in the management of critically ill patients.

DATA SOURCES:

Searches of MEDLINE (1966—March 2004) and Cochrane Library, as well as an extensive manual review of abstracts were performed using the key search terms hyperglycemia, insulin, intensive care unit, critically ill, outcomes, and guidelines and algorithms.

STUDY SELECTION AND DATA EXTRACTION:

All articles identified from the data sources were evaluated and deemed relevant if they included and assessed clinical outcomes.

DATA SYNTHESIS:

Mortality among patients with prolonged critical illness exceeds 20%, and most deaths are attributable to sepsis and multisystem organ failure. Hyperglycemia is common in critically ill patients, even in those with no history of diabetes mellitus. Maintaining normoglycemia with insulin in critically ill patients has been shown to improve neurologic, cardiovascular, and infectious outcomes. Most importantly, morbidity and mortality are reduced with aggressive insulin therapy. This information can be implemented into protocols to maintain strict control of glucose.

CONCLUSIONS:

Use of insulin protocols in critically ill patients improves blood glucose control and reduces morbidity and mortality in critically ill populations. Glucose levels in critically ill patients should be controlled through implementation of insulin protocols with the goal to achieve normoglycemia, regardless of a history of diabetes. Frequent monitoring is imperative to avoid hypoglycemia.

Reduction of cardiovascular morbidity and mortality in type 2 diabetes. A rational approach to hypoglycemic therapy

Type 2 diabetes mellitus is the single most important risk factor for the development of coronary artery disease. Unfortunately, the traditional therapeutic strategies for the treatment of hyperglycemia have proven to be ineffective in preventing cardiovascular complications. In recent years the number of available hypoglycemic agents has increased and considerable progress has been made regarding the comprehension of the pathophysiology of diabetes and its vascular complications. In the present article we firstly present benefits and risks of intensive vs standard hypoglycemic intervention, and the pros and cons of therapy targeted to postprandial hyperglycemia. Secondly, we discuss the cardiovascular effects of sulfonylurea agents and insulin, focusing on the role of intensive insulin treatment in the context of acute coronary syndromes. Thirdly, we review the epidemiological, clinical and experimental evidence linking insulin resistance and cardiovascular disease. Finally, we present the rationale and the role of metformin and thiazolidinedionetherapy in the prevention of cardiovascular complications. We conclude that the optimal use of the full spectrum of hypoglycemic agents has the potential to play a key role in the prevention of diabetes-related macrovascular complications.

Anti-ischemic effects and long-term survival during ranolazine monotherapy in patients with chronic severe angina

OBJECTIVES

The primary objective of the Monotherapy Assessment of Ranolazine In Stable Angina (MARISA) trial was to determine the dose-response relationship of ranolazine, a potentially new anti-anginal compound, on symptom-limited exercise duration.

BACKGROUND

Fatty acids rise precipitously in response to stress, including acute myocardial ischemia. Ranolazine is believed to partially inhibit fatty acid oxidation, shift metabolism toward carbohydrate oxidation, and increase the efficiency of oxygen use.

METHODS

Patients (n = 191) with angina-limited exercise discontinued anti-anginal medications and were randomized into a double-blind four-period crossover study of sustained-release ranolazine 500, 1,000, or 1,500 mg, or placebo, each administered twice daily for one week. Exercise testing was performed at the end of each treatment during both trough and peak ranolazine plasma concentrations.

RESULTS

Exercise duration at trough increased with ranolazine 500, 1,000, and 1,500 mg twice daily by 94, 103, and 116 s, respectively, all greater (p < 0.005) than the 70-s increase on placebo. Dose-related increases in exercise duration at peak and in times to 1 mm ST-segment depression at trough and peak and to angina at trough and peak were also demonstrated (all p < 0.005). Ranolazine had negligible effects on heart rate and blood pressure. One year survival rate combining data from the MARISA trial and its open-label follow-on study was 96.3 +/- 1.7%.

CONCLUSIONS

In chronic angina patients, ranolazine monotherapy was well tolerated and increased exercise performance throughout its dosing interval at all doses studied without clinically meaningful hemodynamic effects. One-year survival was not lower than expected in this high-risk patient population. This metabolic approach to treating myocardial ischemia may offer a new therapeutic option for chronic angina patients.

Using insulin as a drug rather than as a replacement hormone during acute illness: a new paradigm

The direct correlation between glucose levels and cardiovascular disease in individuals with type 2 diabetes can now be applied to individuals that share an abnormal metabolic milieu similar to that found in central obesity, the metabolic syndrome, and type 2 diabetes. Premature macrovascular complications with a very high morbidity and mortality rate can be found in these nondiabetic populations. The typical phenotype has visceral or central obesity, excess of free fatty acids, insulin resistance, increased insulin secretion, and hypertension. A more complex metabolic-cardiovascular syndrome develops that includes dyslipidemia, abnormal production of cytokines, chronic inflammatory state, and abnormal coagulation. The interplay of all these cardiovascular risk factors is responsible for the accelerated atherosclerotic process. The different terminologies used for populations sharing this common ground for premature cardiovascular disease now generally accepted as the metabolic syndrome, are also discussed. Aggressive insulin treatment during acute illness in individuals with the abnormal metabolic milieu is beneficial. Insulin treatment is changing from using insulin as a hormone to treat only severe hyperglycemia, to a new paradigm using insulin in high doses as a drug. Aggressive insulin regimens should be used to treat only minimal elevations of blood glucose or to prevent hyperglycemia. The newly observed properties of insulin are reviewed which include suppression of inflammatory cytokines and adhesion molecules, improved hemostasis, and other cardiac beneficial effects. The concomitant administration of intravenous glucose and insulin permits the administration of higher insulin doses that can result in improved outcome due to its nonglycemic-related benefits. The use of aggressive insulin therapy requires both better and more cost-effective algorithms to successfully treat this high-risk population during acute illness.

Glucose-insulin-potassium infusion inpatients treated with primary angioplasty for acute myocardial infarction: the glucose-insulin-potassium study: a randomized trial

OBJECTIVES

In this study we considered the question of whether adjunction of glucose-insulin-potassium (GIK) infusion to primary coronary transluminal angioplasty (PTCA) is effective in patients with an acute myocardial infarction (MI).

BACKGROUND

A combined treatment of early and sustained reperfusion of the infarct-related coronary artery and the metabolic modulation with GIK infusion has been proposed to protect the ischemic myocardium.

METHODS

From April 1998 to September 2001, 940 patients with an acute MI and eligible for PTCA were randomly assigned, by open-label, to either a continuous GIK infusion for 8 to 12 h or no infusion.

RESULTS

The 30-day mortality was 23 of 476 patients (4.8%) receiving GIK compared with 27 of 464 patients (5.8%) in the control group (relative risk [RR] 0.82, 95% confidence interval [CI] 0.46 to 1.46). In 856 patients (91.1%) without signs of heart failure (HF) (Killip class 1), 30-day mortality was 5 of 426 patients (1.2%) in the GIK group versus 18 of 430 patients (4.2%) in the control group (RR 0.28, 95% CI 0.1 to 0.75). In 84 patients (8.9%) with signs of HF (Killip class > or =2), 30-day mortality was 18 of 50 patients (36%) in the GIK group versus 9 of 34 patients (26.5%) in the control group (RR 1.44, 95% CI 0.65 to 3.22).

CONCLUSIONS

Glucose-insulin-potassium infusion as adjunctive therapy to PTCA in acute MI did not result in a significant mortality reduction in all patients. In the subgroup of 856 patients without signs of HF, a significant reduction was seen. The effect of GIK infusion in patients with signs of HF (Killip class > or =2) at admission is uncertain.

Coronary revascularization: a procedure in transition from on-pump to off-pump? The role of glucose-insulin-potassium revisited in a randomized, placebo-controlled study

OBJECTIVE

To investigate an optimized glucose-insulin-potassium (GIK) solution regimen as an alternate myocardial protective strategy in off-pump coronary artery bypass graft (OP-CAB) surgery and as a supplement to conventional coronary artery bypass graft (CABG) surgery using cardiopulmonary bypass (CPB).

DESIGN

Prospective, randomized, placebo-controlled.

SETTING

Single institution, cardiothoracic specialty hospital.

PARTICIPANTS

Forty-four patients scheduled for elective multivessel coronary artery surgery using either conventional CPB (n = 22) or OP-CAB techniques (n = 22).

INTERVENTIONS

Preischemic, ischemic, and postischemic administration of GIK solution was carried out, optimally dosed to ensure nonesterified fatty acid (NEFA) suppression, and supplemented with magnesium, a glycolytic enzymatic cofactor.

MEASUREMENTS AND MAIN RESULTS

GIK solution therapy reduced plasma NEFA levels (p < 0.001) in OP-CAB surgery and CPB groups but failed to affect the incidence of non-Q wave perioperative myocardial infarction, incidence of postoperative atrial fibrillation, incidence of postoperative infection, reduction in creatinine clearance, or duration of postoperative intensive care unit or hospital length of stay. After adjusting for GIK solution therapy, OP-CAB surgery resulted in significantly less ischemic injury (troponin I >15 microg/L, 19.0% v 91.3%; p = 0.0001) and reduced postoperative infections (14.3% v 43.5%; p = 0.049).

CONCLUSION

GIK solution therapy achieved NEFA suppression and an insignificant trend toward reduced biochemical parameters of ischemic injury in OP-CAB surgery and CPB groups, but no major clinical benefit (perioperative myocardial infarction, intensive care unit length of stay, or hospital length of stay) was shown after elective CABG surgery in low-risk patients. Compared with CPB, OP-CAB surgery significantly reduced ischemic injury and postoperative infections.

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.

Glucose-insulin-potassium preserves systolic and diastolic function in ischemia and reperfusion in pigs

Clinical and experimental studies have suggested benefit of treatment with intravenous glucose-insulin-potassium (GIK) in acute myocardial infarction. However, patients hospitalized with acute coronary syndromes often experience recurrent myocardial ischemia without infarction that may cause progressive left ventricular (LV) dysfunction. This study tested the hypothesis that anticipatory treatment with GIK attenuates both systolic and diastolic LV dysfunction resulting from ischemia and reperfusion without infarction in vivo. Open-chest, anesthetized pigs underwent 90 min of moderate regional ischemia (mean subendocardial blood flow 0.3 ml x g(-1) x min(-1)) and 90 min reperfusion. Eight pigs were treated with GIK (300 g/l glucose, 50 U/l insulin, and 80 meq/l KCl; infused at 2 ml x kg(-1) x h(-1)) beginning 30 min before ischemia and continuing through reperfusion. Eight untreated pigs comprised the control group. Regional LV wall area was measured with orthogonal pairs of sonomicrometry crystals. GIK significantly increased myocardial glucose uptake and lactate release during ischemia. After reperfusion, indexes of regional systolic function (external work and fractional systolic wall area reduction), regional diastolic function (maximum rate of diastolic wall area expansion), and global LV function (LV positive and negative maximum rate of change in pressure with respect to time) recovered to a significantly greater extent in GIK-treated pigs than in control pigs (all P < 0.05). The findings suggest that the clinical utility of GIK may extend beyond treatment of acute myocardial infarction to anticipatory metabolic protection of myocardium in patients at risk for recurrent episodes of ischemia.

Increased glycolytic substrate protection improves ischemic cardiac dysfunction and reduces injury

Early clinical trials of glucose-insulin-potassium for acute myocardial infarction were inconclusive. However, several recent placebo-controlled, prospective, randomized clinical trials of glucose-insulin-potassium for acute myocardial infarction or metabolic support during and after cardiac surgery have demonstrated its efficacy. These clinical results are supported by experimental studies that have shown a strong protective effect of increased glycolytic substrate on ischemic myocardium in concert with an improved bioenergetic status.

Diabetic control in the patient with acute myocardial infarction

Diabetes mellitus affects 2% of the population and up to 5% of people over 65 years of age (Thomas, 1993). Diabetic patients have more coronary artery disease and a higher mortality from acute myocardial infarction (AMI) than the rest of the population (Patmore and Jennings, 1996). They have similar-size infarcts to those without diabetes, but the total mortality post-MI is higher (Karlson et al, 1993). This article examines the literature on AMI in diabetic patients to ascertain the most effective management of these patients and hence improve their prognosis.

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.

Substrate metabolism as a determinant for postischemic functional recovery of the heart

The mammalian myocardium meets its high energy needs through the oxidation of a variety of substrates, chiefly fatty acids. This review examines the hypothesis that efficient energy transfer in the heart occurs through a series of moiety-conserved cycles, which makes the heart an obligatory "omnivore." Ischemia results in a transformation of efficient metabolic cycles to less-efficient linear pathways. Substrate metabolism during reperfusion requires the replenishment of depleted cycles and is a major determinant for the return of contractile function. Although there is growing recognition of the concept that regulation of substrate flux through metabolic pathways is shared by several of the pathway enzymes it is apparent that glucose oxidation and glycogen resynthesis promote the return of normal contractile function in the postischemic heart. This concept is supported by clinical observations on the beneficial effects of a solution containing glucose, insulin, and potassium (GIK) for treatment of refractory left ventricular contractile failure after hypothermic ischemic arrest during cardiac surgery.

Substrate signaling by insulin: a ketone bodies ratio mimics insulin action in heart

The administration of saturating doses of insulin to the glucose perfused, working rat heart acutely increased activity of the glucose transporter 4, GLUT 4, in the plasma membrane (equilibrating extracellular glucose and intracellular [glucose]), activated glycogen synthase (stimulating the rate of glycogen synthesis), and increased mitochondrial acetyl CoA production by the pyruvate dehydrogenase multienzyme complex. Unexpectedly, insulin increased cardiac hydraulic work but decreased net glycolytic flux and O2 consumption, improving net cardiac efficiency by 28%. These improvements in physiologic performance and metabolic efficiency resulted from reduction of the mitochondrial free [NAD+]/[NADH] and oxidation of mitochondrial [coenzyme Q]/[coenzyme QH2], increasing the energy of the proton gradient between cytosolic and mitochondrial phases and leading to a doubling of the cytosolic free [sigmaATP]/[sigmaADP][sigmaPi]. The acute metabolic effects of insulin were qualitatively duplicated by addition of a ratio of 4 mM D-beta-hydroxybutyrate and 1 mM acetoacetate, and the increase in the efficiency was the same as with addition of insulin. Addition of both insulin and ketones to the glucose perfusate increased the efficiency of cardiac hydraulic work by 35%. The ability of a physiologic ratio of ketone bodies to correct most of the metabolic defects of acute insulin deficiency suggests therapeutic roles for these natural substrates during periods of impaired cardiac performance and in insulin-resistant states.

Randomized trial of insulin-glucose infusion followed by subcutaneous insulin treatment in diabetic patients with acute myocardial infarction (DIGAMI study): effects on mortality at 1 year

OBJECTIVES

We tested how insulin-glucose infusion followed by multidose insulin treatment in diabetic patients with acute myocardial infarction affected mortality during the subsequent 12 months of follow-up.

BACKGROUND

Despite significant improvements in acute coronary care, diabetic patients with acute myocardial infarction still have a high mortality rate.

METHODS

A total of 620 patients were studied: 306 randomized to treatment with insulin-glucose infusion followed by multidose subcutaneous insulin for > or = 3 months and 314 to conventional therapy.

RESULTS

The two groups were well matched for baseline characteristics. Blood glucose decreased from 15.4 +/- 4.1 to 9.6 +/- 3.3 mmol/liter (mean +/- SD) in the infusion group during the 1st 24 h, and from 15.7 +/- 4.2 to 11.7 +/- 4.1 among control patients (p < 0.0001). After 1 year 57 subjects (18.6%) in the infusion group and 82 (26.1%) in the control group had died (relative mortality reduction 29%, p = 0.027). The mortality reduction was particularly evident in patients who had a low cardiovascular risk profile and no previous insulin treatment (3-month mortality rate 6.5% in the infusion group vs. 13.5% in the control group [relative reduction 52%, p = 0.046]; 1-year mortality rate 8.6% in the infusion group vs. 18.0% in the control group [relative reduction 52%, p = 0.020]).

CONCLUSIONS

Insulin-glucose infusion followed by a multidose insulin regimen improved long-term prognosis in diabetic patients with acute myocardial infarction.

Ischemia induces translocation of the insulin-responsive glucose transporter GLUT4 to the plasma membrane of cardiac myocytes

BACKGROUND

Acute myocardial ischemia is accompanied by an increase in glucose uptake and metabolism, which appears to be important in protecting myocardial cells from irreversible ischemic injury. Because insulin augments myocardial glucose uptake by inducing the translocation of glucose transporters from an intracellular compartment to the plasma membrane, we hypothesized that acute ischemia would trigger a similar translocation.

METHODS AND RESULTS

We used a subcellular fractionation method to separate intracellular membrane and plasma membranes from control, ischemic, and hypoxic Langendorff-isolated perfused rat hearts and determined the expression of the major myocardial glucose transporter, GLUT4, in these separated membrane fractions. We found that translocation of GLUT4 molecules occurred in ischemic, hypoxic, and insulin-treated hearts and in hearts that underwent ischemia plus insulin treatment. The percentages of GLUT4 molecules present on the plasma membrane in the different conditions were as follows: control, 18.0 +/- 2.8%; ischemia, 41.3 +/- 9.4%; hypoxia, 31.1 +/- 2.9%; insulin, 61.1 +/- 2.6%; and ischemia plus insulin, 66.8 +/- 5.7%. Among the statistically significant differences in these values were the difference between control and ischemia and the difference between ischemia alone and insulin plus ischemia.

CONCLUSIONS

Ischemia causes substantial translocation of GLUT4 molecules to the plasma membrane of cardiac myocytes. A combination of insulin plus ischemia stimulates an even greater degree of GLUT4 translocation. GLUT4 translocation is likely to mediate at least part of the increased glucose uptake of ischemic myocardium and may be a mechanism for the cardioprotective effect of insulin during acute myocardial ischemia.

Effects of glucose and fatty acids on myocardial ischaemia and arrhythmias

Evidence for the utilisation of substrates by the ischaemic myocardium and its dependence for viability on a critical supply of glucose was established many years ago. It was recognised that an excess of free fatty acids (FFA) could increase the severity of ischaemic damage and possibly be arrhythmogenic. But metabolic intervention to improve survival during acute myocardial infarction was not regarded as a priority, perhaps because of uncertainty about its value and the advent of trials of beta-blocker and antiarrhythmic drugs. There has never been an adequate trial of the benefit to the ischaemic or infarcting myocardium of increasing local glucose concentrations or reducing the availability of FFA. We have taken into account new knowledge of the effects of fatty acids on cation channels and brought up to date the arguments for metabolic intervention with glucose-insulin solutions or antilipolytic drugs sustained ischaemia.

ISIS 5 possibilities

There are five major therapeutic groups for possible evaluation in the ISIS 5 trial. They include intravenous beta-blocking agents, glucose-insulin-potassium (GIK) therapy, newer anticoagulant and antithrombotic agents (hirudin and Hirulog), newer thrombolytic drugs such as recombinant plasminogen activator (r-PA) and surfactant and emulsifying agents such as Rheothrx. Many pilot studies are underway. Selection of agents will depend on the scientific interest of collaborating hospitals as well as the agent's safety and efficacy.

Enhanced utilization of exogenous glucose improves cardiac function in hypoxic rabbit ventricle without increasing total glycolytic flux

The effects of elevated glucose on cardiac function during hypoxia were investigated in isolated arterially perfused rabbit interventricular septa. Rest tension, developed tension, intracellular potential, 42K+ efflux, lactate production, exogenous glucose utilization, and tissue high-energy phosphate levels were measured during a 50-min period of hypoxia with 4, 5, or 50 mM glucose present (isosmotically balanced with sucrose) and during reoxygenation for 60 min with perfusate containing 5 mM glucose/45 mM sucrose. At physiologic (4 or 5 mM) and supraphysiologic glucose (50 mM), lactate production and high-energy phosphate levels during hypoxia were equally well maintained, yet cardiac dysfunction was markedly attenuated by 50 mM glucose. Despite identical rates of total glycolytic flux, exogenous glucose utilization was enhanced by 50 mM glucose so that tissue glycogen levels remained normal during hypoxia, whereas glycogen became depleted with 4 or 5 mM glucose present during hypoxia. Most of the beneficial effects of 50 mM glucose occurred during the first 25 min of hypoxia. Prior glycogen depletion had no deleterious effects during hypoxia with 50 mM glucose present, but exacerbated cardiac dysfunction during hypoxia with 5 mM glucose present. These findings indicate that enhanced utilization of exogenous glucose improved cardiac function during hypoxia without increasing total glycolytic flux or tissue high-energy phosphate levels, suggesting a novel cardioprotective mechanism.

Effects of acute hyperglycemia on myocardial glycolytic activity in humans

The effects of hyperglycemia on myocardial glucose metabolism were investigated in seven healthy male subjects (age 24 +/- 4 yr). [6-14C]Glucose and [U-13C]lactate were infused as tracers. Circulating glucose was elevated to two hyperglycemic levels using a clamp technique for 1 h at each level. The mean arterial glucose concentration was 4.95 +/- 0.29 (control), 8.33 +/- 0.31 and 10.84 +/- 0.60 mumols/ml, respectively. Glucose extraction increased significantly from control (0.15 +/- 0.13 mumols/ml) during each level of the glucose clamp (0.28 +/- 0.12, P less than 0.02, and 0.54 +/- 0.14 mumols/ml, P less than 0.005, respectively). Myocardial production of 14CO2 showed that during control 9 +/- 10% of exogenous glucose was oxidized immediately upon extraction. Despite a significant increase in the amount of exogenous glucose oxidized with level II hyperglycemia, it represented only 32 +/- 10% of the glucose extracted. [13C]Lactate analysis showed that the myocardium was releasing lactate; during control 40 +/- 30% of this lactate was derived from exogenous glucose and during hyperglycemia this value increased to 97 +/- 37% (P less than 0.005). Thus, these data show that during short-term hyperglycemia, myocardial glucose extraction is enhanced. However, despite increases in exogenous glucose oxidation and the contribution of exogenous glucose to lactate release, the majority of the extracted glucose (i.e., 57%) is probably stored as glycogen.

Improved cardiac function with glucose-insulin-potassium after aortocoronary bypass grafting

To assess the effectiveness of metabolic support for the heart in patients with refractory heart failure after hypothermic ischemic arrest for aortocoronary bypass grafting we assigned 22 patients to receive either intravenous glucose (50%), insulin (80 IU/L), and potassium (100 mEq/L) at a rate of 1 mL/kg/h for up to 48 hours (GIK) or glucose (5%) and NaCl (0.225%) at the same rate (control). All patients started out with a mean cardiac index of less than 3.0 L/min/m2, were on intraaortic balloon pump assistance, and required inotropic drugs. At 12 and 24 hours cardiac index had increased significantly in the GIK group when compared with the control group (3.6 and 3.4 versus 2.5 and 2.7 L/min/m2, respectively). Time on the intraaortic balloon pump (39 versus 61 hours) and requirements for inotropic drug support were significantly less in GIK group than in the control group. All 11 GIK patients could be weaned from intraaortic balloon pump assistance. At 30 days after operation survival was 10/11 in the GIK group, compared with 7/11 in the control group. We conclude that GIK is both safe and effective in the treatment of refractory left ventricular failure after aortocoronary bypass grafting. The exact mechanism for the beneficial effect of GIK on myocardial contractility remains to be elucidated.

Rates of glycolysis and glycogenolysis during ischemia in glucose-insulin-potassium-treated perfused hearts: A 13C, 31P nuclear magnetic resonance study

The effects of 11.7 mM glucose, insulin, and potassium (GIK) on metabolism during ischemia were investigated in the perfused guinea pig heart using magnetic resonance spectroscopy. Intracellular metabolites, primarily glycogen and glutamate, were labeled with 13C by addition of [1-13C]glucose to the perfusate during a normoxic, preischemic period. 13C and 31P NMR spectroscopy was used to observe the metabolism of 13C-labeled metabolites simultaneously with high-energy phosphorus metabolites and pH. The extent of acidosis and the rate and amount of labeled lactate accumulation during ischemia were the same in control (3 mM glucose + insulin) and GIK-treated hearts. In contrast, the rate of labeled glycogen mobilization during ischemia in GIK-treated hearts was one third the rate observed in control hearts. These observations suggest that GIK decreased the rate of glycogenolysis during ischemia without affecting the rate of glycolysis. We propose that glucose contributed as a glycolytic substrate to a greater extent during ischemia in GIK-treated hearts than in hearts perfused with 3 mM glucose and insulin. The glycogen-sparing effect of GIK demonstrated in these studies could delay the onset of ischemic damage in a clinical setting by prolonging the availability of glycolytic substrate necessary for production of high-energy phosphate.

Severe hypophosphataemia induced by glucose-insulin-potassium therapy. A case report and proposal for altered protocol

A case is described where severe hypophosphataemia was induced by a widely used protocol for glucose-insulin-potassium (GIK) infusion. Hypophosphataemia was found to be a universal sequel to the use of this infusion. A new regimen for administering this agent was designed, and shown to lack the potentially serious side effect of phosphate depletion.

Metabolic fate of extracted glucose in normal human myocardium

Glucose is an important substrate for myocardial metabolism. This study was designed to determine the effect of circulating metabolic substrates on myocardial glucose extraction and to determine the metabolic fate of glucose in normal human myocardium. Coronary sinus and arterial catheters were placed in 23 healthy male volunteers. [6-14C]Glucose was infused as a tracer in 10 subjects. [6-14C]Glucose and [U-13C]lactate were simultaneously infused in the other 13 subjects. Simultaneous blood samples were obtained for chemical analyses of glucose, lactate, and free fatty acids and for the the isotopic analyses of glucose and lactate. Glucose oxidation was assessed by measuring myocardial 14CO2 production. The amount of glucose extracted and oxidized by the myocardium was inversely correlated with the arterial level of free fatty acids (r = -0.71; P less than 0.0001). 20% (range, 0-63%) of the glucose extraction underwent immediate oxidation. Chemical lactate analysis showed a net extraction of 26.0 +/- 16.4%. However, isotopic analysis demonstrated that lactate was being released by the myocardium. In the 13 subjects receiving the dual-carbon-labeled isotopes, the lactate released was 0.09 +/- 0.04 mumol/ml and 49.5 +/- 29.5% of this lactate was from exogenous glucose. This study demonstrates that the circulating level of free fatty acids plays a major role in determining the amount of glucose extracted and oxidized by the normal human myocardium. Only 20.1 +/- 19.4% of the glucose extracted underwent oxidation, and 13.0 +/- 9.0% of the glucose extracted was metabolized to lactate and released by the myocardium. Thus, 60-70% of the glucose extracted by the normal myocardium is probably stored as glycogen in the fasting, resting state.

Myocardial infarction in the diabetic patient

It has long been thought that the symptomatology and prognosis of coronary events in patients with diabetes may differ from those in nondiabetic persons. A review of recent data demonstrates a higher mortality during the acute phase of myocardial infarction for diabetic patients than for their nondiabetic counterparts, possibly related to a higher incidence of congestive heart failure and cardiogenic shock. The clinical course of diabetic patients with infarction and the role of insulin in myocardial adaptation to ischemia are both reviewed. Diabetic patients surviving the acute phase of myocardial infarction have a lower survival in follow-up than nondiabetic survivors, although some improvement in survival has been noted following beta-adrenergic-blocker therapy.

Glucose and insulin infusion directly after cardiac surgery: effects on systemic glucose uptake, catecholamine excretion, O2 consumption, and CO2 production

Systemic glucose uptake was studied in 31 patients during 4 hr starting 1 hr after open heart surgery, using the hyperinsulinemic "clamp" technique at different plasma insulin levels and at a glucose concentration of 6 or 10 mmol/liter. Possible metabolic side effects related to the glucose uptake were studied by measurements of urinary catecholamine excretion, O2 consumption, CO2 production, and arterial PCO2. A peak systemic glucose uptake of 7.0 +/- 0.4 mg/kg body weight/min was found at a plasma insulin concentration of 3192 +/- 150 mU/liter and a blood glucose concentration of 10.2 +/- 0.1 mmol/liter. No significant difference was found in urinary catecholamine excretion compared to control patients. O2 consumption was unaltered while a 15% increase in CO2 production was observed.