Ineffectiveness of glucose, potassium, and insulin infusion during pacing stress in chronic ischemic heart disease

Effects of GIK (glucose-insulin-potassium) on stress-induced myocardial ischaemia

Despite the evidence in experimental animal models that insulin, or GIK (glucose-insulin-potassium), improves left ventricular function and perfusion during both acute and chronic ischaemia, clinical studies have generated conflicting results. We tested the hypothesis that pretreatment with GIK attenuates the vascular and functional effects of stress-induced myocardial ischaemia in humans. Twenty-two patients with evidence of inducible myocardial ischaemia were enrolled; 11 patients with normal ventricular function underwent two dipyridamole echocardiography tests, and 11 with regional contractility defects from previous myocardial infarction were submitted to two ECG exercise tests combined with 201Tl myocardial perfusion scintigraphy; the tests were preceded by 60 min of either normal saline or an isoglycaemic GIK infusion. On a stress echocardiogram, a 30% reduction in the severity of ischaemia was observed. On ECG ergometry, GIK infusion slightly increased the time to ischaemia (+0.6 min, P=0.07); however, the higher workload (+8%, P=0.07) was achieved at a similar rate-pressure plateau. On scintigraphy, an increase in ischaemic segments (+48%, P<0.001) was imaged mainly at the expense of viable (but non-ischaemic) and non-viable segments, which were reduced by 60%. GIK affected stress-induced left ventricular underperfusion only marginally (GIK: 39.7+/-2.5 compared with saline: 35.4+/-2.2 units, P<0.05), but significantly improved its acute reversibility (-42+/-4 compared with -25+/-4%, P<0.001). We conclude that GIK pretreatment attenuates the effect of ischaemia on myocardial contractility, slightly improves exercise tolerance and causes a more rapid and diffuse recovery of post-ischaemic reperfusion.

Effects of exogenous metabolic substrate modulation on exercise-induced myocardial ischemia

BACKGROUND

The aim of the study is to compare the impact of intravenous glucose versus lipid versus saline on exercise-induced myocardial ischemia in patients with stable angina.

METHODS

Twelve men with coronary artery disease and positive exercise tests performed a symptom-limited, modified Bruce electrocardiogram (ECG) exercise test at 3 sessions, 3 weeks apart. They randomly received, in double-blind design, at each session equal intravenous volumes of 10% glucose/insulin or Intralipid plus heparin or saline. We assessed the effects on (1) ischemic threshold (heart rate x systolic pressure at 1-mm ST-segment depression [STD]) and (2) maximum ST-depression (Max STD) corresponding to the highest heart rate x systolic pressure common to the 3 tests.

RESULTS

During glucose infusion, glycemia increased from 5.7 +/- 0.4 to 9.4 +/- 3.0 mmol/L but did not change during lipid or saline infusion. During lipid infusion, free fatty acids increased from 0.32 +/- 0.19 to 1.44 +/- 0.46 mmol/L but decreased during glucose infusion from 0.39 +/- 0.21 to 0.04 +/- 0.03 mmol/L and did not change during saline. Exercise times were 10.0 +/- 3.4, 9.8 +/- 3.4, and 10.3 +/- 3.5 minutes, during glucose, lipid, and saline infusions, respectively. Ischemic thresholds (x 10(-3)) were 16.5 +/- 2.8, 16.8 +/- 2.7, and 16.6 +/- 2.6, respectively. MaxSTD was 2.5 +/- 1.4, 2.5 +/- 1.0, and 2.5 +/- 1.0 mm, respectively.

CONCLUSION

Neither glucose-insulin nor lipid infusion modified exercise ischemic parameters compared with saline control, suggesting that marked and acute changes in exogenous energy substrate are unlikely to affect exercise-induced myocardial ischemia.

Effect of hyperglycemia and fatty acid oxidation inhibition during aerobic conditions and demand-induced ischemia

Metabolic interventions improve performance during demand-induced ischemia by reducing myocardial lactate production and improving regional systolic function. We tested the hypotheses that 1) stimulation of glycolysis would increase lactate production and improve ventricular wall motion, and 2) the addition of fatty acid oxidation inhibition would reduce lactate production and further improve contractile function. Measurements were made in anesthetized open-chest swine hearts. Three groups, hyperglycemia (HG), HG + oxfenicine (HG + Oxf), and control (CTRL), were treated under aerobic conditions and during demand-induced ischemia. During demand-induced ischemia, HG resulted in greater lactate production and tissue lactate content but had no significant effect on glucose oxidation. HG + Oxf significantly lowered lactate production and increased glucose oxidation compared with both the CTRL and HG groups. Myocardial energy efficiency was greater in the HG and HG + Oxf groups under aerobic conditions but did not change during demand-induced ischemia. Thus enhanced glycolysis resulted in increased energy efficiency under aerobic conditions but significantly enhanced lactate production with no further improvement in function during demand-induced ischemia. Partial inhibition of free fatty acid oxidation in the presence of accelerated glycolysis increased energy efficiency under aerobic conditions and significantly reduced lactate production and enhanced glucose oxidation during demand-induced ischemia.

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.

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.

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.

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.

Improved myocardial contractility with glucose-insulin-potassium infusion during pacing in coronary artery disease

The metabolic and mechanical effects of a solution of glucose-insulin-potassium (G-I-K) were investigated in 18 patients who underwent diagnostic cardiac catheterization for coronary artery disease. All patients were paced at a rate of approximately 140 beats/min before and after infusion of G-I-K. Basal and paced left ventricular (LV) end-diastolic pressure, dP/dt, arterial substrate levels and osmolarity were measured in all 18 patients. In 13 patients cardiac index was also measured. In 5 patients arterial-coronary sinus measurements of oxygen, carbon dioxide, glucose, free fatty acids, lactate, alanine, glutamate, glutamine, ammonia and urea were made, in addition to coronary sinus blood flow. G-I-K increased the blood sugar level to approximately 200 mg/dl and raised the serum osmolarity 9 mosmol. Pacing alone raised the cardiac index 4% and pacing with G-I-K increased the cardiac index 6% (p less than 0.05). Pacing before G-I-K augmented dP/dt (21%) and pacing with G-I-K increased it (30%) (p less than 0.01). The metabolic changes noted included a shift in the respiratory quotient from 0.77 to 0.96 with G-I-K infusion (p less than 0.05). During G-I-K infusion the myocardial oxygen consumption at rest increased from 17.1 to 21.8 ml/min (23%, p less than 0.05). Myocardial oxygen consumption during pacing was similar before and after G-I-K infusion. Before G-I-K infusion nitrogen balance was slightly positive; after G-I-K infusion it was negative with regard to the nitrogen-containing compounds measured.(ABSTRACT TRUNCATED AT 250 WORDS)

Different effects of interventions suppressing free fatty acid metabolism on myocardial ischemia

We studied the effects of different metabolic interventions, which stimulate oxidative myocardial carbohydrate metabolism, on ischemic stress during repeated coronary occlusions of three minutes in open-chest dog hearts. Increase of glucose concentration in plasma and decrease of peripheral lipolysis by glucose-insulin-potassium (n = 6) had no substantial beneficial effects on myocardial damage indicated by hemodynamic, electrocardiographic, and metabolic parameters. Infusion of lactate and pyruvate (10 mM, n = 6) was detrimental. Only activation of pyruvate dehydrogenase by dichloroacetate (n = 6) without influence on plasma osmolality reduced epicardial ST-segment elevations (-42%) and myocardial release of potassium (-36%), phosphate (-58%), and lactate (-39%). Elevations of plasma osmolalities by 10 and 20 mOsm with the metabolically inert mannitol increased ECG changes, functional loss and release of potassium, phosphate, and lactate during ischemia in our model. It is suggested, that the oxygen-saving potency of metabolic interventions can exert univocal beneficial effects in experimental and in clinical conditions only when systemic hyperosmolality and hypervolemia are avoided.

Myocardial metabolic alterations after contrast angiography

Contrast media used during angiography are known to produce transient alterations in cardiovascular physiology. However, little information is available concerning what alterations, if any, occur in myocardial metabolism after contrast angiography. Sixteen patients with symptoms of ischemic heart disease undergoing elective left ventriculography were studied. Coronary sinus and arterial blood samples were obtained for free fatty acids, glucose and lactate before and after performing left ventriculography with Renografin-76. Coronary blood flow was determined by the thermodilution technique. Five minutes after ventriculography, the arterial level of free fatty acids had decreased by 18.0 +/- 4.9 percent (mean +/- standard deviation) from the baseline (before angiography) samples (probability [p] less than 0.001). Associated with this decrease in arterial free fatty acids was an increase in the myocardial uptake of this substrate. At 5 minutes after left ventriculography, the free fatty acid uptake had increased 48.5 +/- 33.0 percent compared with the baseline value (p less than 0.001). After the injection of contrast medium, there was no significant change in the arterial levels of glucose or lactate. However, significant decreases in the myocardial uptake of glucose and lactate were demonstrated (-72.5 +/- 44.5 percent [p less than 0.001] and -43.2 +/- 22.9 percent [p less than 0.001], respectively) at 5 minutes. The changes in arterial free fatty acids and in the myocardial uptake of the various substrates persisted throughout the sampling period of 20 minutes after ventriculography. These results demonstrate that contrast medium significantly alters myocardial metabolism. These metabolic alterations persist longer than the hemodynamic changes induced by contrast angiography.

Hemodynamic, electrocardiographic, and metabolic effects of fructose diphosphate on acute myocardial ischemia

The hemodynamic, electrocardiographic, and metabolic responses of dogs with acute myocardial ischemia to intravenous administration of fructose-1,6-diphosphate (FDP) were assessed. Analysis of the results (compared to dextrose control) revealed evidence of major improvement of LVEDP and cardiac output, significant decrease of the ST segment, and large increases of ATP and CP in the ischemic district and to a lesser degree in the normally perfused myocardium. These results indicate that FDP intervenes in the Embden-Meyerhof pathway not only as a high energy substrate but also as a metabolic regulator influencing the activity of phosphofructokinase and that of pyruvate kinase. FDP also stimulates glycolysis in dog erythrocytes and increases their ATP and 2-3 DPG content by a factor of 2. The most significant finding in these studies is that this biochemical intervention appears to restore the depressed activity of glycolysis in ischemic myocardium.

Reduction of hospital mortality rate of acute myocardial infarction with glucose-insulin-potassium infusion

Free fatty acids (FFA), the predominant myocardial energy substrate, are present in increased quantities immediately following acute myocardial infarction (AMI) and may cause deleterious alterations in cardiac rhythm, oxygen consumption, and mechanical performance. In an attempt to suppress FFA and simultaneously increase the availability of carbohydrate as a myocardial substrate, 70 patients with unequivocal AMI were administered a right atrial infusion of glucose-insulin-potassium (GIK) (300 gm. of glucose, 50 U. of regular insulin, and 80 mEq. of KC1 per liter of H2O) at a constant rate of 0.5 to 2.0 ml. per kilogram per hour for 48 hours. A dramatic fall in FFA (944 +/- 57 to 289 +/- 16 muEq per liter, p less than 0.0005) occurred during GIK infusion, and FFA rebounded to 420 +/- 39 muEq per liter (p less than 0.005) when GIK was discontinued. The hospital mortality rate in the 70 GIK recipients was compared to that of 64 untreated patients (controls) from the same coronary-care unit during the previous year. GIK and control groups had similar severity of infarction as assessed by prognostic scales of Killip, Peel, and Norris, respectively. The hospital mortality rate was reduced in the GIK recipients compared to the control group (11/70 vs. 19/64, p less than 0.05). In patients without history of prior myocardial infarction, the mortality rate was reduced four-fold in GIK recipients compared to controls (6 vs. 24 per cent, p less than 0.05). Complications of GIK infusion were infrequent and included chiefly hyperglycemia and hyperkalemia, both of which dictated meticulous monitoring of serum chemistries. The data suggest that suppression of plasma FFA with GIK infusion may be associated with a significant reduction in the hospital mortality rate of acute myocardial infarction.

Effects of excess glucose and insulin on glycolytic metabolism during experimental myocardial ischemia

The selective metabolic effects of glucose and insulin were tested in an intact working swine heart preparation. Supplements of glucose (26.6 millimolar [mM] and insulin (0.025 units/ml) were provided to 18 hearts, 9 control hearts (coronary flow 151 ml/min) and 9 hearts rendered globally ischemic (coronary flow reduced from 167 to 85 ml/min). These hearts were compared with 14 additional hearts (6 control and 8 ischemic) given no supplements (glucose 8.6 mM, no excess insulin). In hearts without supplements, ischemic significantly decreased mechanical performance, myocardial oxygen consumption, fatty acid oxidation and tissue high energy phosphate stores. Glucose consumption was reduced from 133 micromoles (mumol)/hr per g (before ischemia) to 58 mumol/hr per g (P less than 0.05), presumably from inhibition at glyceraldehyde-3-phosphate dehydrogenase. Data for control hearts with excess glucose and insulin were similar to data in control hearts without supplements except that glucose consumption and glycolytic flux were increased. Ischemia in treated hearts, as compared with untreated ischemic hearts, effected similar significant decreases in myocardial oxygen consumption, fatty acid oxidation and high energy phosphate stores and resulted in greater reductions in mechanical performance and in 10 minutes' less average survival time. Glucose consumption was reduced from 483 (before ischemia) to 242 mumol/hr per g (P less than 0.005) and inhibition at glyceraldehyde-3-phosphate dehydrogenase was again noted. Thus, excess carbohydrate and insulin hormone, when infused directly into the ischemic myocardium, did not provide an efficacious increase in either glycolytic flux or energy production. These findings suggest that an alternative explanation for the reported efficacy of glucose-insulin-potassium infusions must be sought.

The QRS complex during myocardial ischemia. An experimental analysis in the porcine heart

Although ST segment deflections have been widely utilized as a means of assessing the degree of underlying ischemic injury, the relationship of QRS complex alterations to the ischemic process is poorly understood. In this study we made a beat-to-beat analysis of the QRS complex in terms of ventricular activation time (CT) and R wave voltage (V) in the acutely ischemic porcine myocardium and analyzed the relationship of these responses to changes in the area of ischemic involvement, altered myocardial energy demands, and plasma [K+]0 levels. With the onset of ischemia the QRS complex underwent a specific and reproducible biphasic sequence with an initial decrease in CT and V indicating a transient increase in the conduction velocity of the ischemic tissue. Subsequently both CT and V returned briefly to control and then increased dramatically, now indicating a marked decrease in conduction velocity. The time when CT first began to increase (Tc) was shortened by enlarging the area of ischemia or after an inotropic intervention and was lengthened by decreasing the area of ischemia or with administration of propranolol. Moreover Tc was found to be inversely proportional to plasma [K+]0 in the range 3.4-8.8 mM, above which the initial decrease in CT and V was no longer present. We conclude that this biphasic sequence of QRS alterations in early myocardial ischemia is attributable to a progressive leakage of potassium out of the ischemic cells which in turn alters both the time-course and transmural pathway of the activation process through the ischemic tissue. These changes are related to both inotropic state and the area of ischemic involvement.

Effects of intravenous glucose during pacing-induced angina pectoris in patients with coronary artery disease

The effects of hypertonic glucose infusion on the anginal threshold determined by atrial pacing was studied in 14 patients with significant coronary artery disease. After glucose, angina occurred at a significantly lower heart rate and double product (systolic arterial pressure x heart rate), suggesting a decreased tolerance to ischemic stress. No stoichiometric relationship was noted between glucose uptake and lactate production, and there was no evidence that hypertonic glucose infusion resulted in enhanced anaerobic glycolysis in the ischemic myocardium. Acute elevation of plasma glucose levels may not be beneficial to patients with coronary artery disease.