Glutamate and high-dose glucose-insulin-potassium (GIK) in the treatment of severe cardiac failure after cardiac operations

Association of Glutamate Infusion With Risk of Acute Kidney Injury After Coronary Artery Bypass Surgery: A Pooled Analysis of 2 Randomized Clinical Trials

Importance

Acute kidney injury (AKI) after cardiac surgery is associated with increased morbidity and mortality, and measures to prevent AKI have had limited success. Glutamate has been reported to enhance natural postischemic recovery of the heart, but not among animals and humans with diabetes.

Objective

To summarize pooled results from the GLUTAMICS (Glutamate for Metabolic Intervention in Coronary Surgery) trials regarding the effect of glutamate on postoperative AKI among patients without diabetes undergoing coronary artery bypass graft (CABG) surgery.

Design, Setting, and Participants

Data on a total of 791 patients without diabetes from 2 prospective, randomized, double-blind multicenter trials performed at 5 cardiac surgery centers in Sweden between October 4, 2005, and November 12, 2009, and between November 15, 2015, and September 30, 2020, were pooled. Patients had acute coronary syndrome, left ventricular ejection fraction of 0.30 or less, or a European System for Cardiac Risk Evaluation II score of 3.0 or more and underwent CABG with or without additional valve procedure. Statistical analysis was performed from May to November 2023.

Interventions

Intravenous infusion of 0.125-M l-glutamic acid or saline at 1.65 mL/kg/h for 2 hours during reperfusion, after which the infusion rate was halved and an additional 50 mL was given.

Main Outcomes and Measures

The primary end point was AKI, defined as postoperative increase of plasma creatinine of 50% or more, corresponding to the Risk stage or higher in the Risk, Injury, Failure, Loss, and End-Stage kidney disease (RIFLE) criteria.

Results

A total of 791 patients without diabetes (391 who received glutamate [mean (SD) age, 69.3 (9.1) years; 62 women (15.9%)] and 400 controls [mean (SD) age, 69.6 (9.5) years; 73 women (18.3%)]) were randomized. Baseline data did not differ between groups. Glutamate was associated with a significantly lower risk of AKI (relative risk, 0.49 [95% CI, 0.29-0.83]). Dialysis was required for 2 patients in the glutamate group and 5 patients in the control group. In multivariable analysis, glutamate remained significantly associated with a protective effect against AKI (odds ratio, 0.47 [95% CI, 0.26-0.86]). In the glutamate and control groups, the rate of postoperative mortality at 30 days or less was 0.5% (2 of 391) vs 1.0% (4 of 400), and the rate of stroke at 24 hours or less was 0.8% (3 of 391) vs 1.8% (7 of 400).

Conclusions and Relevance

In this pooled analysis of 2 randomized clinical trials, infusion of glutamate was associated with a markedly lower risk of AKI after CABG among patients without diabetes. The findings are exploratory and need to be confirmed in prospective trials.

Trial Registration

ClinicalTrials.gov Identifiers: NCT00489827 and NCT02592824.

Glutamate Infusion Reduces Myocardial Dysfunction after Coronary Artery Bypass Grafting According to NT-proBNP: Summary of 2 Randomized Controlled Trials (GLUTAmate for Metabolic Intervention in Coronary Surgery [GLUTAMICS I-II])

BACKGROUND

Glutamate is reported to enhance the recovery of oxidative metabolism and contractile function of the heart after ischemia. The effect appears to be blunted in diabetic hearts. Elevated plasma N-terminal pro-brain natriuretic peptide (NT-proBNP) reflects myocardial dysfunction. In the GLUTAmate for Metabolic Intervention in Coronary Surgery (GLUTAMICS) II trial, the proportion of patients with diabetes had nearly doubled to 47% compared with the cohort used for sample size estimation, and a significant effect on the postoperative rise in NT-proBNP was only observed in patients without diabetes.

OBJECTIVE

We aimed to summarize the pooled NT-proBNP results from both GLUTAMICS trials and address the impact of diabetes.

METHODS

Data from 2 prospective, randomized, double-blind multicenter trials with similar inclusion criteria and endpoints were pooled. Patients underwent a coronary artery bypass grafting (CABG) ± valve procedure and had a left-ventricular ejection fraction of ≤0.30 or a European System for Cardiac Operative Risk Evaluation II (EuroSCORE II) of ≥3.0 with at least 1 cardiac risk factor. Intravenous infusion of 0.125 M L-glutamic acid or saline at 1.65 mL/kg/h was started 10-20 min before reperfusion and continued for 150 min. The primary endpoint was the difference between preoperative and day 3 postoperative NT-proBNP levels.

RESULTS

A total of 451 patients, 224 receiving glutamate and 227 controls, fulfilled the inclusion criteria. Glutamate was associated with a reduced primary endpoint (5344 ± 5104 ng/L and 6662 ± 5606 ng/L in glutamate and control groups, respectively; P = 0.01). Postoperative mortality at ≤30 d was 0.9% and 3.5% (P = 0.11), whereas stroke at ≤24 h was 0.4% and 2.6% in glutamate and control groups, respectively (P = 0.12). No adverse events related to glutamate were observed. A significant interaction regarding the primary endpoint was only detected between glutamate and insulin-treated diabetes groups (P = 0.04). Among patients without insulin-treated diabetes, the primary endpoint was 5047 ± 4705 ng/L and 7001 ± 5830 ng/L in the glutamate and control groups, respectively (P = 0.001).

CONCLUSIONS

Infusion of glutamate reduced the postoperative rise in NT-proBNP after CABG in medium- to high-risk patients. A significantly blunted effect was observed only in insulin-treated patients with diabetes.

CLINICAL TRIAL DETAILS

This trial was registered at www.

CLINICALTRIALS

gov as NCT02592824.

Glucose-Insulin-Potassium Techniques in Cardiac Surgery: Historical Overview and Future Perspectives

Since the days of the first cardiac surgical operations in the previous century, myocardial preservation has been an essential component of the successful outcome of these procedures. Although many different techniques to achieve myocardial preservation and modulation have been described in the past 50 years, this review focuses on the use of glucose, insulin, and potassium (GIK) and its effect on ischemic and postischemic myocardium.

[Prospects of cardioprotection by volatile anesthetics]

Myocardial ischaemia is followed by some reversibile or ireversibile changes. The aim of cardioplegia is to protect numerous intracellular processes: to spare the intracellular energy stores, to reduce the free oxygen radicals synthesis, to protect the function of the endothelium and myocardial oxygen balance as well as ionic balance. The crystalloid or blood cardioplegia, with anterograde or retrograde infusion, is a basic procedure of the intraoperative cardiac protection. Glucose-insulin-potassium solution was primarily used in a myocardial infarction. After the first promising results, some surgical teams started to use the high glucose-insulin-potassium solution, as a metabolic modulation approach, during a coronary surgery as addition to cardioplegia. During ischaemia, a number of intracellular mechanisms deteriorate with bioenergy misbalance and decrease of cellular functional reserve. In particular, the regulation of contractility in response to loading, alteration in autocrine or paracrine regulation in metabolically stressed hearts and acquired, "learned" tolerance of muscle to deteriorate perfusion (preconditioning) are examples of a variety of the cardiac adaptation. The further improvement in the metabolic modulation during a coronary surgery was made with fluorine ion halogenated volatile aneasthetics used for anaesthesia. The results of some experimental and first clinical studies induced a new approach to the modulation of the intracellular metabolic mechanisms and announced a new concept of anaesthetic preconditioning in coronary surgery. Large, randomized studies are needed to evaluate anaesthetic preconditioning and dependence of its efficiency on type and dose of volatile anaesthetics as well as the role of gene regulation in cardioprotection.

The S-100B substudy of the GLUTAMICS trial: glutamate infusion not associated with sustained elevation of plasma S-100B after coronary surgery

BACKGROUND & AIMS

Concerns have been raised about potential neurological injury related to exogenous glutamate. In cardiac surgery glutamate has been administered as a putative cardioprotective agent by cardioplegia or intravenous infusion. In the GLUTAMICS trial, in addition to surveillance of clinical neurological injuries, a prespecified subgroup was analyzed with regard to postoperative S-100B levels to detect potential subclinical neurological injury related to glutamate infusion.

METHODS

Sixty-nine patients operated on for unstable coronary syndrome were randomized to intravenous infusion of glutamate (n=35) or saline (n=34) perioperatively. Plasma levels of S-100B were obtained on the third postoperative day.

RESULTS

S-100B in the glutamate group and the control group were 0.079+/-0.034microg/L and 0.090+/-0.042microg/L respectively (p=0.245). There were no patients with stroke or mortality. Three patients in the control group and two in the glutamate group had postoperative confusion. These patients had significantly elevated S-100B compared with those without confusion (0.132+/-0.047vs 0.081+/-0.036microg/L; p=0.003). Overall, 21 patients had S-100B above reference level (> or =0.10microg/L) and these patients had significantly more calcifications in the ascending aorta on epiaortic scanning.

CONCLUSIONS

Intravenous glutamate infusion during surgery for unstable coronary artery disease did not initiate a sustained elevation of plasma S-100B. Thus, no evidence for subclinical neurological injury related to glutamate infusion was found. In contrast, postoperative elevation of plasma S-100B was linked to calcification of the ascending aorta and postoperative confusion.

Potential cardiovascular applications of glutamate, aspartate, and other amino acids

Cardioplegic solutions rich in the hydrophilic, basic amino acids, glutamate and aspartate, have enhanced myocardial preservation and left ventricular function. This has been demonstrated in assorted animal preparations involving ischemia with and without reperfusion. Published clinical data, though limited, strongly support the contention that these amino acids have myocardial protective properties. Several biochemical mechanisms exist by which certain amino acids may attenuate ischemic or reperfusion injury. Glutamate and aspartate may become preferred myocardial fuels in the setting of ischemia. They may also reduce myocardial ammonia production and reduce cytoplasmic lactate levels, thereby deinhibiting glycolysis. Some amino acids may become substrate for the citric acid cycle. Glutamate and aspartate also move reducing equivalents from cytoplasm to mitochondria where they are necessary for oxidative phosphorylation and energy generation. A rationale exists for the use of an amino acid-rich cardioplegia-like solution in myocardial infarction. These solutions are safe and inexpensive.

Is the failing heart out of fuel or a worn engine running rich? A study of mitochondria in old spontaneously hypertensive rats

Hypertension now affects about 600 million people worldwide and is a leading cause of death in the Western world. The spontaneously hypertensive rat (SHR), provides a useful model to investigate hypertensive heart failure (HF). The SHR model replicates the clinical progression of hypertension in humans, wherein early development of hypertension is followed by a long stable period of compensated cardiac hypertrophy that slowly progresses to HF. Although the hypertensive failing heart generally shows increased substrate preference towards glucose and impaired mitochondrial function, the cause-and-effect relationship between these characteristics is incompletely understood. To explore these pathogenic processes, we compared cardiac mitochondrial proteomes of 20-month-old SHR and Wistar-Kyoto controls by iTRAQ-labelling combined with multidimensional LC/MS/MS. Of 137 high-scoring proteins identified, 79 differed between groups. Changes were apparent in several metabolic pathways, chaperone and antioxidant systems, and multiple subunits of the oxidative phosphorylation complexes were increased (complexes I, III and IV) or decreased (complexes II and V) in SHR heart mitochondria. Respiration assays on skinned fibres and isolated mitochondria showed markedly lower respiratory capacity on succinate. Enzyme activity assays often also showed mismatches between increased protein expression and activities suggesting elevated protein expression may be compensatory in the face of pathological stress.

Long-Term Consequences of Postoperative Heart Failure After Surgery for Aortic Stenosis Compared With Coronary Surgery

BACKGROUND

Although postoperative heart failure is a major determinant of operative mortality in cardiac surgery it has received little attention in the literature, and long-term consequences remain to be addressed. Therefore, the impact of postoperative heart failure on long-term survival in relation to other risk factors was studied.

METHODS

All patients undergoing aortic valve replacement (AVR) for aortic stenosis from 1995 through 2000 in the southeast region of Sweden (n = 398) were compared with a cohort, matched for age and sex, undergoing coronary artery bypass grafting (CABG [n = 398]). Risk factors for 5-year mortality were analyzed.

RESULTS

Forty-five AVR and 47 CABG patients required treatment for postoperative heart failure. Thirty-day, 1-year, and 5-year mortality in patients with and without postoperative heart failure after AVR were 6.7% versus 1.4% (p = 0.05), 8.9% versus 4.0% (p = 0.13), and 42.2% versus 14.2% (p < 0.0001) respectively. Corresponding results in the CABG group were 21.3% versus 1.1% (p < 0.0001), 25.5% versus 3.1% (p < 0.0001), and 36.2% versus 11.1% (p = 0.0015). Postoperative heart failure, preoperative renal dysfunction, procedure-associated stroke, body mass index less than 19 kg/m2, older age, preoperative atrial fibrillation, and preoperative anemia turned out as independent risk factors for 5-year mortality after AVR. In the CABG group, postoperative heart failure, diabetes mellitus, older age, and procedure-associated stroke emerged as independent risk factor for 5-year mortality.

CONCLUSIONS

Postoperative heart failure was associated with high early mortality after CABG whereas the grave consequences of postoperative heart failure after AVR for aortic stenosis became evident only with time.

Anti-inflammatory effect of high-dose insulin treatment after urgent coronary revascularization surgery

BACKGROUND

The administration of insulin has been shown to exert cardioprotective and immunomodulatory properties. Ischemia and inflammation are typical features of acute coronary syndrome, thus it was hypothesized that high-dose glucose-insulin-potassium (GIK) treatment could suppress the systemic inflammatory reaction and attenuate myocardial ischemia-reperfusion injury in patients with unstable angina pectoris after urgent coronary artery bypass surgery.

METHODS

Forty patients with unstable angina pectoris scheduled for urgent coronary artery bypass surgery and cardiopulmonary bypass were randomly assigned to receive either high-dose insulin treatment (short-acting insulin 1 IU/kg/h with 30% glucose 1.5 ml/kg/h administered separately) or control treatment (saline). Blood glucose levels were targeted to 6.0-8.0 mmol/l in both groups by adjusting the rate of glucose infusion in the GIK group and by additional insulin in the control group as needed.

RESULTS

High-dose insulin treatment was associated with significantly lower average C-reactive protein (23.8 vs. 40.1 mg/l, P= 0.008) and free fatty acid levels (0.22 vs. 0.41 mmol/l, P= < 0.001) post-operatively. Average blood glucose levels were comparable during the intensive care unit (ICU) stay (7.1 vs. 6.9 mmol/l, P= 0.5) and 95% of the control patients received supplemental insulin. The pro-inflammatory cytokine response [interleukin-6 (IL-6), interleukin-8 (IL-8) and tumor necrosis factor-alpha (TNF-alpha)] did not differ between the groups and beneficial effects on myocardial injury were not detected.

CONCLUSIONS

High-dose insulin treatment has potential anti-inflammatory properties independent of its ability to lower blood glucose levels. Even profound suppression of free fatty acid levels, the attenuation of myocardial ischemia-reperfusion injury was not detected.

Risk Factors for Postoperative Heart Failure in Patients Operated on for Aortic Stenosis

BACKGROUND

Risk factors for postoperative heart failure (PHF) have not been specifically studied in valve surgery although it has been acknowledged that patient variables may have a more profound influence on postoperative outcome than valve-related factors.

METHODS

All patients undergoing isolated aortic valve replacement for aortic stenosis from January 1995 to December 2000 in the southeast region of Sweden were studied (n = 398). Forty-five patients with aortic valve replacement required treatment for PHF. Univariate and multivariate logistic regression analysis was carried out to identify risk factors for PHF.

RESULTS

Thirty-day mortality was 6.7% versus 1.4% for patients with and without PHF, respectively (p = 0.05). With regard to clinical presentation of aortic stenosis, angina was associated with reduced risk, whereas history of congestive heart failure increased the risk for PHF. Five preoperative (hypertension, history of congestive heart failure, severe systolic left ventricular dysfunction, pulmonary hypertension, preoperative hemodynamic instability) and two intraoperative (aortic cross-clamp time, intraoperative myocardial infarction) variables were identified as independent risk factors for PHF. Patient-prosthesis mismatch did not influence the risk of PHF significantly.

CONCLUSIONS

Postoperative heart failure was associated with a marked increase in postoperative mortality and morbidity. Risk factors for PHF were variables indicating preexisting myocardial dysfunction, increased right or left ventricular afterload, and intraoperative myocardial injury. Our results highlight issues concerning cross-clamp time and myocardial protection, particularly for patients with preoperatively compromised myocardial function. Asymptomatic patients with significant aortic stenosis should be considered for surgery before substantial echocardiographic evidence of left ventricular dysfunction or increased pulmonary artery pressure develops.

Glucose, insulin and potassium applied as perioperative hyperinsulinaemic normoglycaemic clamp: effects on inflammatory response during coronary artery surgery

BACKGROUND

The clinical benefits of glucose-insulin-potassium (GIK) and tight glycaemic control in patients undergoing coronary artery bypass grafting (CABG) may be partly explained by an anti-inflammatory effect. We applied GIK as a hyperinsulinaemic normoglycaemic clamp for >25 h and quantified its effect on systemic inflammation in patients undergoing CABG.

METHODS

Data obtained in 21 non-diabetic patients with normal left ventricular function scheduled for elective coronary artery surgery, who were randomly allocated to a control or GIK group, were analysed. In GIK patients, regular insulin was infused at a fixed rate of 0.1 IU kg(-1) h(-1). The infusion rate of glucose (30%) was adjusted to maintain blood glucose levels within a target range of 4.0-5.5 mmol litre(-1). Plasma concentrations of interleukins 6, 8 and 10, C-reactive protein (CRP) and serum amyloid A (SAA) were measured on the day of surgery and on the first and second postoperative days (POD1 and POD2).

RESULTS

In the GIK group hypoglycaemia (glucose <2.2 mmol litre(-1)) did not occur, whereas hyperglycemia (glucose >6.1 mmol litre(-1)) developed in 15% of all measurements. In control patients, hyperglycaemia developed in >80% of all measurements in the presence of low endogenous insulin levels. CRP and SAA levels increased in both groups, with maximum levels measured on POD2. GIK treatment significantly reduced CRP and SAA levels. Interleukin levels increased significantly in both groups following cardiopulmonary bypass, but no differences were found between the groups.

CONCLUSION

Hyperinsulinaemic normoglycaemic clamp is an effective method of maintaining tight glycaemic control in patients undergoing CABG and it attenuates the systemic inflammatory response in these patients. This effect may partly contribute to the reported beneficial effect of glycaemic control in patients undergoing CABG.

Metabolic and Hemodynamic Effects of High-Dose Insulin Treatment in Aortic Valve and Coronary Surgery

BACKGROUND

Glucose and insulin have been used as an adjuvant therapy in cardiac surgery because of their potentially beneficial effects on myocardial metabolism and contractile function. This study evaluated the effects of high-dose insulin on systemic metabolism and hemodynamics after combined heart surgery.

METHODS

Forty elective patients scheduled for combined aortic valve replacement and coronary artery bypass surgery were randomly assigned to receive either high-dose insulin treatment (short-acting insulin 1 IU.kg(-1).h(-1) with 30% glucose 1.5 mL.kg(-1).h(-1) administered separately) or control treatment (saline). The blood glucose levels were maintained within a targeted range by adjusting the rate of glucose infusion in the treatment group and by short-acting insulin bolus doses in the control group.

RESULTS

The lactate clearance was faster (p = 0.046), and the lactate levels (p = 0.016), blood glucose levels (p < 0.001), and free fatty acid levels (p < 0.001) were lower in the insulin group postoperatively. Besides, there was lesser need for dobutamine support (p = 0.013) and a trend toward better cardiac indices. Insulin treatment increased the respiratory quotient (p < 0.001), but there were no differences between the groups with regard to systemic oxygen consumption or energy expenditure measured by indirect calorimetry. The average glucose uptake in the insulin group was 7.1 g/kg in 24 hours (28 kcal.kg(-1).day(-1)).

CONCLUSIONS

The high-dose insulin treatment was associated with lower blood glucose levels, better preserved myocardial contractile function, and less need for inotropic support, and hence led to lower lactate levels postoperatively. The protocol is safe, but requires strict control of blood glucose level.

Glucose-Insulin-Potassium in Cardiac Surgery: A Meta-Analysis

BACKGROUND

Glucose-insulin-potassium therapy (GIK) has been suggested to reduce mortality and improve postoperative recovery after cardiac surgery. We performed a meta-analysis of all randomized studies using GIK in cardiac surgery.

METHODS

A systematic Medline search for all GIK studies in cardiac surgery was carried out. Randomized studies investigating the recovery of contractile function as a primary endpoint were included in the meta-analysis.

RESULTS

Thirty-five GIK trials were identified. Twenty-four studies were excluded because of lack of randomization, supplementary administration of other substances, or due to other primary endpoints. Eleven studies were included with a total of 468 patients who underwent either coronary artery bypass grafting or heart valve replacement. Six studies noted a significant improvement in postoperative recovery. One study demonstrated no effect. In four studies, no comparable statistical analysis was available. GIK patients required similar or lesser doses of catecholamines. From the available data we estimated a weighted mean of relative improvement in postoperative recovery of cardiac index for GIK patients versus controls of 11.4%. Five of 11 studies reported the incidence of postoperative atrial fibrillation (AF). AF occurred in 23% (20/86) in GIK versus 42% (36/86) in control patients (p = 0.009).

CONCLUSIONS

The findings indicate that GIK may considerably improve postoperative recovery of contractile function and reduce the incidence of atrial arrhythmias after cardiac surgery. However, several factors limit the power of this analysis and large, randomized multicenter trials are needed to fully assess the efficacy of GIK after cardiac surgery.

The rationale and management of hyperglycemia for in-patients with cardiovascular disease: time for change

There is increasing evidence that aggressive glycemic control for patients admitted into the hospital improves clinical outcomes, especially for patients with cardiovascular disease. There appear to be a variety of mechanisms for this. Although hyperglycemia has been shown to result in poor wound healing and more infectious complications, especially after cardiac surgical procedures, what has become clear is that the treatment of hyperglycemia with i.v. glucose, insulin, and potassium (GIK) results in better clinical outcomes even in patients without diabetes. The mechanisms for this are not year clear, but could be related to the insulin administration, perhaps due to suppression of various cytokines or free fatty acids. The practical use of insulin in these patients requires basic understanding of the use of both i.v. and s.c. insulin. Although there are several appropriate options for both of these routes of administration, it is critical that all caregivers involved in this population's care are knowledgeable about insulin strategies.

High-dose glucose-insulin-potassium after cardiac surgery: a retrospective analysis of clinical safety issues

BACKGROUND

Metabolic treatment with insulin or glucose-insulin-potassium (GIK) has received attention in association with myocardial infarction, cardiac surgery and critical care. As a result of insulin resistance during neuroendocrine stress, doses of insulin up to 1 IU kg-1 b.w.*h are required to achieve maximal metabolic effects after cardiac surgery. The clinical experience with regard to safety issues of such a high-dose GIK regime in critically ill patients after cardiac surgery is reported.

METHODS

Retrospective, observational study involving all patients treated with high-dose GIK after cardiac surgery during one year in a cardiovascular center at a University Hospital.

RESULTS

Eighty-nine patients out of 854 adult patients undergoing cardiac surgery were treated with high-dose GIK. Mean age was 69 +/- 1 years, Higgins score 5.3 +/- 0.3. Preoperatively 31.4% had left ventricular function EF< or =0.35 and 32.5% had sustained a myocardial infarct during surgery. Mortality was 5.6% and the average ICU stay was 3.7 +/- 0.5 days. The main indication for GIK was intraoperative heart failure (69.7%). The average glucose infusion rate during the first 6 h was 4.22 +/- 0.15 and 4.91 +/- 0.14 mg kg-1 b.w.*min, respectively, in diabetic and non-diabetic patients (P = 0.023). Blood glucose and s-potassium control was acceptable.

CONCLUSIONS

The high-dose GIK regime allowed substantial amounts of glucose to be infused both in diabetic and critically ill patients with maintenance of acceptable blood glucose control. Provided careful monitoring, this regime can be safely used in clinical practice and deserves further evaluation for treatment of critically ill patients following cardiac surgery.

Improving Energy Metabolism in the Postischemic Heart-The Story of GIK

Heart muscle is a metabolic omnivore. The normal heart derives its energy for contraction from the oxidation of longchain fatty acids. The stressed heart switches to carbohydrate substrates for greater efficiency of energy production. Here we review the evidence for glucose-insulin-potassium as an effective strategy to treat postischemic contractile dysfunction of the heart. There is a strong rationale for both glucose and insulin to restore efficient energy transfer in the metabolically depleted postischemic heart. In spite ofits long history and abundant opportunities for translational research, the field is still in its infancy. Further progress is tied to two broad areas of research: randomized, multicenter clinical trialsand systematic studies addressing cellular signaling mechanisms, including nutrient sensing of myocardial gene expression.

Early postoperative outcome and medium-term survival in 540 diabetic and 2239 nondiabetic patients undergoing coronary artery bypass grafting

BACKGROUND

An increasing proportion of patients undergoing coronary artery bypass grafting (CABG) are diabetics. Patient characteristics, early postoperative outcome, and midterm survival in diabetic patients after CABG were investigated.

METHODS

A total of 2779 consecutive patients undergoing isolated CABG during 1995 to 1999 were studied, 19.4% of whom had diabetes mellitus. Demographic and peri-procedural data were registered prospectively in a computerized institutional database.

RESULTS

The diabetic group was younger and included a higher proportion of women, and patients with hypertension, triple-vessel disease, and unstable angina. They required a higher number of bypasses, and longer cross-clamp and cardiopulmonary bypass times. Intensive care unit and hospital stays were prolonged and the need for inotropic agents, hemotransfusions, and dialysis was higher in the diabetic group. Renal failure, stroke (4.3% versus 1.7%), mediastinitis, and wound infections were more frequently encountered. Thirty-day mortality was 2.6% versus 1.6% (p = 0.15). Cumulative 5-year survival was 84.4% versus 91.3% (p < 0.001).

CONCLUSIONS

Short-term mortality was acceptable in diabetic patients after CABG but they had increased postoperative morbidity in comparison with nondiabetic patients, particularly with regard to renal function, cerebral complications, and infections. Midterm survival was impaired in diabetic patients mainly because of a less favorable outcome in patients treated with insulin.

Glucose, insulin and potassium for heart protection during cardiac surgery

BACKGROUND

Coronary artery bypass grafting with hypothermic cardiac arrest and cardiopulmonary bypass (CPB) is associated with myocardial injury. Our study investigated whether an infusion of glucose, insulin and potassium (GIK) during elective coronary artery bypass surgery decreases myocardial cell death.

METHODS

We measured cardiac troponin I (cTnI), a myofibrillar structural protein, which is a sensitive and specific indicator of myocytic injury. With ethics committee approval, 42 patients were enrolled into a randomized, prospective, double-blinded study. In the GIK group, 500 ml of 50% dextrose solution containing 100 IU insulin and potassium 80 mmol was infused at the rate of 0.75 ml kg(-1) h(-1). Patients in the non-GIK group received 5% dextrose solution at the same rate. Arterial blood samples were taken before induction of anaesthesia, after removal of the aortic clamp and 6 and 12 h after CPB.

RESULTS

In both groups there was an increase in cTnI concentration (P<0.05), which was greatest about 6 h after CPB. At no time did the cTnI concentration differ between the two groups.

CONCLUSION

The results suggest that GIK does not decrease the irreversible myocardial damage associated with routine coronary artery bypass surgery.

Cardiac dysfunction and inefficiency after substrate-enriched warm blood cardioplegia

OBJECTIVE

The study assessed the outcome after prolonged warm continuous antegrade blood cardioplegia (WCBC) with substrate enrichment, in terms of mechanical performance and mechanoenergetic efficiency.

METHODS

WCBC was given for 3 h to three groups of pigs on cardiopulmonary bypass; WCBC alone (n=7), WCBC+glucose and insulin (+GIK, n=7) and WCBC+L-glutamine (+GLN, n=7). Cardiac systolic and diastolic function, pressure-volume area (PVA) and myocardial oxygen consumption (MVO(2)) were assessed before, and twice after WCBC using pressure-conductance catheter, coronary flow-probes and O(2)-content difference.

RESULTS

In the WCBC, +GIK and +GLN groups respectively, the following parameters decreased after WCBC compared to baseline: left ventricular developed pressure by 26, 19 and 25% (P<0.001); dP/dt(max) by 36, 37 and 34% (P<0.001); preload recruitable stroke work by 35, 41 and 28% (P<0.001); mechanoenergetic efficiency (PVA/MVO(2)) by 44, 41 and 22% (P<0.001). End-diastolic stiffness increased early after WCBC in the WCBC and +GLN groups, while it was unchanged in the +GIK group (P=0.032).

CONCLUSION

Despite continuous aerobic conditions and additional substrates, post-WCBC cardiac contractile function and mechanoenergetic efficiency was severely depressed. The results demonstrate the hazards of sustained normothermic hyperkalemic perfusion.

Beneficial haemodynamic effects of insulin in chronic heart failure

OBJECTIVE

To characterise the central and regional haemodynamic effects of insulin in patients with chronic heart failure.

DESIGN

Single blind, placebo controlled study.

SETTING

University teaching hospital.

PATIENTS

Ten patients with stable chronic heart failure.

INTERVENTIONS

Hyperinsulinaemic euglycaemic clamp and non-invasive haemodynamic measurements.

MAIN OUTCOME MEASURES

Change in resting heart rate, blood pressure, cardiac output, and regional splanchnic and skeletal muscle blood flow.

RESULTS

Insulin infusion led to a dose dependent increase in skeletal muscle blood flow of 0.36 (0.13) and 0.73 (0.14) ml/dl/min during low and high dose insulin infusions (p < 0.05 and p < 0.005 v placebo, respectively). Low and high dose insulin infusions led to a fall in heart rate of 4.6 (1.4) and 5.1 (1.3) beats/min (p < 0.05 and p < 0.005 v placebo, respectively) and a modest increase in cardiac output. There was no significant change in superior mesenteric artery blood flow.

CONCLUSION

In patients with chronic heart failure insulin is a selective skeletal muscle vasodilator that leads to increased muscle perfusion primarily through redistribution of regional blood flow rather than by increased cardiac output. These results provide a rational haemodynamic explanation for the apparent beneficial effects of insulin infusion in the setting of heart failure.

Beneficial haemodynamic effects of insulin in chronic heart failure

OBJECTIVE

To characterise the central and regional haemodynamic effects of insulin in patients with chronic heart failure.

DESIGN

Single blind, placebo controlled study.

SETTING

University teaching hospital.

PATIENTS

Ten patients with stable chronic heart failure.

INTERVENTIONS

Hyperinsulinaemic euglycaemic clamp and non-invasive haemodynamic measurements.

MAIN OUTCOME MEASURES

Change in resting heart rate, blood pressure, cardiac output, and regional splanchnic and skeletal muscle blood flow.

RESULTS

Insulin infusion led to a dose dependent increase in skeletal muscle blood flow of 0.36 (0.13) and 0.73 (0.14) ml/dl/min during low and high dose insulin infusions (p < 0.05 and p < 0.005 v placebo, respectively). Low and high dose insulin infusions led to a fall in heart rate of 4.6 (1.4) and 5.1 (1.3) beats/min (p < 0.05 and p < 0.005 v placebo, respectively) and a modest increase in cardiac output. There was no significant change in superior mesenteric artery blood flow.

CONCLUSION

In patients with chronic heart failure insulin is a selective skeletal muscle vasodilator that leads to increased muscle perfusion primarily through redistribution of regional blood flow rather than by increased cardiac output. These results provide a rational haemodynamic explanation for the apparent beneficial effects of insulin infusion in the setting of heart failure.

Neurological injury after surgery for ischemic heart disease: risk factors, outcome and role of metabolic interventions

OBJECTIVES

Neurological complication remains a feared and increasing problem in association with cardiac surgery. The aim of this study was to analyze risk factors for neurological complications in a cohort of patients in whom inotropes for weaning from cardiopulmonary bypass was gradually replaced by metabolic treatment.

METHODS

The records of 775 consecutive patients undergoing coronary artery bypass grafting (CABG) or combined CABG+valve procedures were examined. Forward stepwise multiple logistic regression analysis was used for statistical evaluation of independent risk factors.

RESULTS

The incidence of neurological injury was 1.8% in patients undergoing isolated CABG and 5.4% after combined CABG+valve procedures. After cross-validation multivariate analysis identified history of cerebrovascular disease, advanced age and aortic cross-clamp time as independent risk factors for postoperative cerebral complications. Chronic obstructive pulmonary disease and number of bypasses also emerged as risk factors in the primary analysis.

CONCLUSIONS

In general, markers for advanced atherosclerosis, with history of cerebrovascular disease as the most important, emerged as predictors for neurological injury. Although it did not enter the final risk model, the results also suggest that postoperative heart failure deserves further surveillance as a potential risk factor for neurological complications. However, no evidence for untoward neurological effects associated with glutamate or glucose-insulin-potassium treatment was found.

The effect of insulin cardioplegia on atrial fibrillation after high-risk coronary bypass surgery: a double-blinded, randomized, controlled trial

Atrial fibrillation after coronary bypass (CABG) surgery is an important cause of morbidity and increased resource utilization. Insulin-enhanced cardioplegia may reduce postoperative arrhythmias by improving aerobic myocardial metabolism and mitigating the deleterious effects of ischemia. We performed a double-blinded, randomized, controlled clinical trial to determine if insulin-enhanced cardioplegia decreases the risk of post-CABG atrial fibrillation in a high-risk patient population. We randomized 501 patients undergoing urgent CABG to receive insulin-enhanced (Humulin R 10 IU/L, Insulin group, n = 243) or standard (Control group, n = 258) blood cardioplegia during cardiopulmonary bypass. Patients were monitored by using continuous electrocardiography for a minimum of 3 days postoperatively. All standard cardiac medications, including beta-adrenergic blockers, were continued postoperatively. Insulin-enhanced cardioplegia did not result in a significant reduction in postoperative atrial fibrillation. Furthermore, we failed to detect a difference in the incidence of conduction defects, ventricular tachycardia, or pacemaker requirements between insulin and placebo patients. Atrial fibrillation was the most common arrhythmia, occurring in 31% of all patients. Independent predictors of atrial fibrillation were elderly age, preoperative atrial fibrillation, and renal insufficiency. Right bundle branch block was the most common conduction abnormality. Predictors of right bundle branch block were elderly age, female sex, and circumflex coronary artery disease. The incidence of postoperative ventricular tachycardia, left bundle branch block, and permanent pacemaker requirement was small. We conclude that insulin-enhanced cardioplegia does not reduce the incidence of postoperative atrial fibrillation in high-risk CABG patients.

IMPLICATIONS

We conducted a double-blinded, randomized, placebo-controlled trial of insulin-enhanced cardioplegia in 501 patients undergoing urgent coronary bypass surgery. Insulin did not decrease the incidence of postoperative atrial fibrillation when compared with placebo. We also failed to demonstrate a difference in the incidence of other postoperative arrhythmias between the two groups of patients.

Predicting the risk of death from heart failure after coronary artery bypass graft surgery

Heart failure is the most common cause of death among coronary artery bypass graft (CABG) patients. In addition, most variation in observed mortality rates for CABG surgery is explained by fatal heart failure. The purpose of this study was to develop a clinical risk assessment tool so that clinicians can rapidly and easily assess the risk of fatal heart failure while caring for individual patients. Using prospective data for 8,641 CABG patients, we used logistic regression analysis to predict the risk of fatal heart failure. In multivariate analysis, female sex, prior CABG surgery, ejection fraction <40%, urgent or emergency surgery, advanced age (70-79 yr and >80 yr), peripheral vascular disease, diabetes, dialysis-dependent renal failure and three-vessel coronary disease were significant predictors of fatal postoperative heart failure. A clinical risk assessment tool was developed from this logistic regression model, which had good discriminating characteristics (receiver operating characteristic clinical source = 0.75, 95% confidence interval: 0.71, 0.78).

IMPLICATIONS

In contrast to previous cardiac surgical scoring systems that predicted total mortality, we developed a clinical risk assessment tool that evaluates risk of fatal heart failure. This distinction is relevant for quality improvement initiatives, because most of the variation in CABG mortality rates is explained by postoperative heart failure.

Management of perioperative ventricular dysfunction

With the recognition of the clinical importance of the right ventricle; the development of new techniques for the perioperative evaluation of RV function, particularly transesophageal echocardiography; and new treatment modalities (pharmacologic and mechanical), clinicians will be able to more accurately diagnose and precisely manage patients who have sustained RV injury.

Cardioplegia solutions--unproven herbal approach versus tested scientific study

Cardioplegic solutions are used throughout the world, but must undergo careful testing before their clinical application. This study points out the importance of recognizing the hemodynamic changes produced by tested solutions so that appropriate decisions can be made in selecting crystalloid or blood solutions. Examples are provided, in which arbitrary changes made by the well-intentioned surgeon can produce damage through unanticipated alterations that are introduced without prior testing, and then used clinically. Recognition of the advantages and disadvantages of each solution is the underpinning of selection for clinical use so that unanticipated misadventures do not occur. Furthermore, the importance of making solutions in pharmacies with good manufacturing practices can avoid causing problems that would otherwise be prevented. Fundamentally, cardioplegic solutions are direct cardiac medications that must be tested as other drugs are so that unforeseen problems are avoided.

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.

Routine SvO2 measurement after CABG surgery with a surgically introduced pulmonary artery catheter

OBJECTIVE

It has been argued that the poor correlation between cardiac output and mixed venous oxygen saturation (SvO2) reduces the value of SvO2. Routine use of Swan Ganz catheters is also controversial in cardiac surgery. Here our clinical experience with a simplified method for routine hemodynamic monitoring and the short-term prognostic value of SvO2 after CABG surgery is presented.

METHOD

Peroperatively an epidural catheter is routinely introduced through the outflow tract of the right ventricle into the pulmonary artery for monitoring of pressure and blood sampling. Clinical data were retrospectively retrieved from the records and related to SvO2 routinely obtained on admission to the ICU after 488 CABG procedures.

RESULTS

Average SvO2 on arrival to ICU was 67+/-7%. The SvO2 value of 55% represented a cut off point below which a high incidence of complications were found. Outcome after 456 procedures with SvO2 > or = 55% compared with 32 procedures with SvO2 < 55%: mortality 0 vs. 9.4% (P = 0.0003), perioperative myocardial infarction 6.2 vs. 29% (P < 0.0001), ventilator treatment 8.9+/-10.1 vs. 25.7+/-54.9 h (P = 0.0074), ICU stay 1.4+/-1.2 vs. 2.1+/-1.7 days (P = 0.0010).

CONCLUSIONS

SvO2 was of prognostic value and due to its specificity it seems particularly useful for telling which patients are unlikely to develop cardiorespiratory problems. Thus, this simple method for hemodynamic monitoring could contribute to cost containment as it seems that we can safely reserve Swan Ganz catheters for high-risk patients.

Inhibition of vasoconstriction by the thromboxane A2 antagonist GR32191B in the human radial artery

AIMS

The newly revived coronary bypass graft, the radial artery (RA), is more spastic than the internal mammary artery. Thromboxane A2 is a potent vasoconstrictor for arterial grafts. This study was therefore designed to determine whether the specific thromboxane A2 (TP) receptor antagonist, GR32191B, is effective in inhibition of prostanoid or nonprostanoid receptors in the RA.

METHODS

The effect of GR32191B was studied in human RA segments, taken from coronary bypass patients, in organ chambers. Two effects of GR32191B were tested: (1) the relaxation induced by GR32191B in the RA precontracted with the TP receptor agonists U46619 and PGF2alpha or nonprostanoid vasoconstrictors (noradrenaline [NA], angiotensin II [AII], and K+ ) and (2) the inhibitory effect of GR32191B on TP receptor agonists and nonprostanoid vasoconstrictors.

RESULTS

In U46619 (10 nm, n=7) and PGF2alpha (1 microm, n=7) precontracted RA, GR32191B induced 100% relaxation (10-100 microm ) but not after precontraction with nonprostanoid stimuli (5.8% for K+, 25 mm, n=6, 24.4% for NA, 3 microm, n=8, and 53.2% for AII, 3 nm, n=5) (P<0.001). Treatment with GR32191B (30 nm ) significantly depressed the contraction with U46619 (from 160.1+/-11.0% to 116.8+/-13.1%, P<0. 05) or PGF2alpha (from 91.3+/-12.3% to 42.2+/-9.2%, P<0.01). The contraction was further abolished by 3 microm GR32191B. However, GR32191B at 3 microm did not significantly inhibit the contraction induced by either NA, AII, or K+.

CONCLUSIONS

GR32191B is a highly potent and specific TP receptor antagonist for the human RA. It may be particularly useful in inhibiting TXA2-mediated vasoconstriction and therefore in reducing the complications related to vasospasm in this graft.

Myocardial substrate uptake and oxidation during and after routine cardiac surgery

OBJECTIVE

This study was designed to clarify whether myocardial substrate uptake and oxidation change after a period of hypothermic cardioplegic arrest during coronary artery bypass grafting procedures.

METHODS

In 30 patients arterial and coronary sinus blood was sampled and coronary sinus flow measurements were performed before and after sternotomy and 10 minutes, 20 minutes, 50 minutes, and 6 hours after release of the aortic crossclamp. Measurement of free fatty acids, lactate, glucose, oxygen content, and carbon dioxide content in arterial and coronary sinus blood allowed calculations of myocardial substrate use, respiratory quotients, and myocardial oxidation rates of carbohydrates and fat.

RESULTS

Uptake of free fatty acids and lactate was significant throughout the study and did not change in association with release of the crossclamp. Free fatty acid and lactate uptake measured 6 +/- 4 micromol/min and 23 +/- 26 micromol/min, respectively, before crossclamping compared with 8 +/- 7 micromol/min and 19 +/- 21 micromol/min, respectively, after release of the clamp. Glucose uptake was significant only during the first hour after crossclamp release and increased from 7 +/- 50 to 28 +/- 34 micromol/L after crossclamp release. Myocardial oxygen consumption did not change significantly (0.5 +/- 0.2 mmol/L compared with 0.35 +/- 0.2 mmol/L) after release of the crossclamp. Myocardial oxygen extraction ratio decreased from 58% +/- 8% to 41% +/- 13% after crossclamp release. Respiratory quotient increased after crossclamp release (0.85 +/- 0. 2 compared with 1.00 +/- 0.2), which implies that carbohydrate oxidation increased at the expense of free fatty acid oxidation.

CONCLUSION

We conclude that hypothermic cardioplegic arrest during coronary artery bypass graft operations is associated with a transiently increased uptake and oxidation of carbohydrates during the immediate reperfusion phase.

Glutamate metabolism of the heart during coronary artery bypass grafting

Glutamate infusion has been shown to exert beneficial hemodynamic effects in patients with heart failure after cardiac surgery. To elucidate the underlying mechanism we studied the possibility that glutamate is a Krebs-cycle precursor in the human heart. Therefore [1-13C]glutamate was infused in order to show production of 13CO2 by the heart. In five patients a primed constant infusion of [1-13C]glutamate was started 2|h before the start of sampling from coronary sinus and arterial blood. Plasma concentrations of glutamate and glutamine were determined by high pressure liquid chromatography. Blood concentration of CO2 and enrichment of [1-13C]glutamate, [1-13C]glutamine and [1-13C]glutmaine and 13CO2 were measured by GC-IRMS. The results show that approximately 85% of [1-13C]glutamate taken up by the heart is released released as 13CO2. These results show that synthesis of Krebs-cycle intermediates is a major fate of the glutamate extracted by the human heart.

Preconditioning to improve myocardial protection

Major advances in the composition and delivery of cardioplegia have helped to reduce the morbidity and mortality associated with coronary bypass surgery. The discovery of the preconditioning response should facilitate the development of more powerful myocardial protective agents. These new agents may act to directly stimulate the preconditioning response or may act in a supplementary fashion to either augment the response or provide protection from alternate pathways. As new techniques of myocardial protection continue to be developed, the risk-to-benefit ratio of coronary bypass surgery will continue to improve. As a result of these improvements, surgeons will be able to offer surgery to an increasingly high risk patient population without increasing the morbidity or mortality currently associated with coronary bypass.

Rationale for metabolic support with amino acids and glucose-insulin-potassium (GIK) in cardiac surgery

Myocardial metabolism and the current state of metabolic intervention under conditions relevant to cardiac surgery are reviewed. The rationale for metabolic support differs considerably in various settings of cardiac surgery. Although preventive measures are theoretically attractive, their use in the preoperative setting remains to be clarified. Amino acid enrichment of blood cardioplegia seems to be justified by an abundance of animal experimental data. In the postoperative setting of cardiac surgery, metabolic abnormalities may explain reversible myocardial dysfunction. Further, the combined effects of ischemia and the systemic neuroendocrine response to surgical trauma may adversely affect recovery. Amino acids, particularly glutamate, seem vital for metabolic recovery in this setting. Treating the relative shortage of glutamate occurring during this period by the administration of exogenous glutamate and counteracting the effects of the systemic neuroendocrine stress response by high-dose glucose-insulin-potassium are measures that have been shown to improve the metabolic state of the heart and subsequently myocardial performance.