Benefits of glucose and oxygen in multidose cold cardioplegia

Benefits of Glucose-Insulin-Potassium before Mitral Valve Replacement

Of 30 consecutive patients undergoing mitral valve replacement, 15 were randomly assigned to receive pretreatment with glucose-insulin-potassium, while the other 15 received the same volume of normal saline. The characteristics of both groups were similar and all patients were in New York Heart Association functional class III or IV. Papillary muscle samples were obtained at the time of surgery and analyzed for glycogen both biochemically and histochemically. The clinical course was monitored closely during the first 24 hours after surgery. The treated patients had significantly higher glycogen levels (mean, 43 ± 13.54 μmol·g−1) in their heart muscle samples compared to the controls (mean, 22 ± 10.39 μmol·g−1). The treated patients required less pharmacological inotropic support and they had fewer ventricular arrhythmias and more favorable cardiac output and systemic vascular resistance. However, there was no difference in postoperative pulmonary capillary wedge pressure or mortality between the 2 groups. It was concluded that pretreatment with glucose-insulin-potassium had a significant myocardial protective effect in patients in advanced functional class undergoing mitral valve replacement.

Insulin stimulates pyruvate dehydrogenase and protects human ventricular cardiomyocytes from simulated ischemia

Impaired myocardial metabolism after cardioplegic arrest results in persistent anaerobic lactate production. Insulin may protect the heart from ischemia and reperfusion by enhancing myocardial metabolic recovery. However, the stimulation of glycolysis during ischemia may be detrimental because of an accumulation of metabolic end-products. We examined the effect of insulin on quiescent human ventricular cardiomyocytes subjected to simulated cardioplegic ischemia and reperfusion.

METHODS

Primary cardiomyocyte cultures were established from patients undergoing corrective repair of tetralogy of Fallot. Cells were exposed to varying concentrations of glucose and insulin during 30 minutes of stabilization in 10 mL of phosphate-buffered saline solution. Ischemia was simulated by exposing the cells to a low volume (1.5 mL) of deoxygenated phosphate-buffered saline solution for 90 minutes followed by 30 minutes of simulated reperfusion in 10 mL of normoxic phosphate-buffered saline solution. Cell viability was assessed by trypan blue exclusion. The activity of mitochondrial pyruvate dehydrogenase was measured in 3 states: stabilization, ischemia, and reperfusion. In addition intracellular lactate, adenine nucleotides, extracellular lactate, pyruvate, and acid release were measured.

RESULTS

Higher ambient glucose concentrations resulted in greater cellular injury although insulin-treated cells displayed less injury after ischemia and reperfusion. Insulin increased the pyruvate dehydrogenase activity by 31% in cardiomyocytes and reduced extracellular lactate production by 40%. Intracellular adenosine triphosphate was improved by 75% in cells exposed to high glucose concentrations in the presence of insulin.

CONCLUSIONS

Insulin protected human ventricular cardiomyocytes from ischemia and reperfusion. This protection may be due to a stimulation of pyruvate dehydrogenase activity which resulted in improved aerobic metabolism.

Temperature threshold and modulation of energy metabolism in the cardioplegic arrested rabbit heart

Hypothermia protects ischemic tissues by reducing ATP utilization and accumulation of harmful metabolites. However, it also reduces ATP production, which might cause deterioration in the energy supply/demand ratio. Modulation of energy supply/demand according to temperature has not been previously studied in detail. In this study, isolated, perfused rabbit hearts (n = 60) were used to determine the effects of various temperatures on myocardial energy metabolism and function during cardioplegic arrest. Ischemia was induced by crystalloid cardioplegic solution at 4, 18, 30, and 34 degrees C for 120 min, respectively. At each temperature, the hearts were divided into a glucose-treated group which contained 22 mM glucose in cardioplegic solution as the only substrate and a control group which contained 22 mM mannitol to keep same osmolarity. Following 15 min reperfusion, recovery of left ventricular developed pressure (DP), +/- dP/dtmax, and the product of heart rate and DP were significantly higher in 30, 18, and 4 degrees C groups than those in 34 degrees C control group. The functional recovery was also significantly higher in the 34 degrees C glucose-treated group than that in the 34 degrees C control group, but there was no difference between those groups at 30 degrees C and the temperature below 30 degrees C. Myocardial ATP concentration was significantly lower in 34 degrees C control group than those in other groups. There is a close relationship between myocardial ATP concentration and functional recovery (R2 = 0.90). The accumulations of lactate and CO2 were significantly higher at 34 degrees C in glucose-treated group than those in the control group. However, there was no significant difference between these two groups at 30 degrees C and the temperature below 30 degrees C. These results indicate that under these study conditions: (1) a marked decrease in energy supply/demand occurs above 30 degrees C, implying that a temperature threshold exists; and (2) this can be ameliorated by provision of glucose as substrate in cardioplegia solution.

Effects of hypothermia on energy metabolism in rat and Richardson's ground squirrel hearts

Glycolysis, glucose oxidation, palmitate oxidation, and cardiac function were measured in isolated working hearts from ground squirrels and rats subjected to a hypothermia-rewarming protocol. Hearts were perfused initially for 30 min at 37 degrees C, followed by 2 h of hypothermic perfusion at 15 degrees C, after which hearts were rewarmed to 37 degrees C and further perfused for 30 min. Functional recovery in ground squirrel hearts was greater than in rat hearts after rewarming. Hypothermia-rewarming had a similar general effect on the various metabolic pathways in both species. Despite these similarities, total energy substrate metabolic rates were greater in rat than ground squirrel hearts during hypothermia despite a lower level of work being performed by the rat hearts, indicating that rat hearts are less efficient than ground squirrel hearts during hypothermia. After rewarming, energy substrate metabolism recovered completely in both species, although cardiac work remained depressed in rat hearts. The difference in functional recovery between rat and ground squirrel hearts after rewarming cannot be explained by general differences in energy substrate metabolism during hypothermia or after rewarming.

Glucose level and myocardial recovery after warm arrest

BACKGROUND

During induced cold ischemia for cardiac operations, increasing glucose concentration is not thought to enhance myocardial protection and may detrimentally affect recovery. However, during "warm aerobic" arrest, increased glucose availability as substrate could enhance postischemic metabolic and functional recovery, as during and after ischemia, myocytes shift preference for substrate from fatty acids to glucose. Unfortunately, hyperglycemia may also increase patient susceptibility to neurologic injury.

METHODS

This experiment was designed to study the optimal dose of glucose and its effect on function during warm arrest. Isolated, retrograde-perfused rabbit hearts received multidose cardioplegia containing increasing concentrations of glucose, from 0 to 88 mmol/L, and underwent 120 minutes of "warm" 34 degrees C global ischemia. Osmolarities were adjusted equivalently.

RESULTS

After 34 degrees C ischemia, hearts treated with 5 to 88 mmol/L glucose showed significantly better functional recovery than those treated with 0 to 1 mmol/L glucose. However, the addition of 22 mmol/L glucose demonstrated optimal recovery with no further incremental enhancement with more glucose. Additional hearts receiving 0 or 22 mmol/L glucose had high-energy phosphates, lactate, CO2, and pH measured. The 22 mmol/L glucose hearts demonstrated active metabolism and significantly better recovery of high-energy phosphate levels than controls.

CONCLUSIONS

Increasing glucose level modestly during warm arrest enhanced recovery, but profound hyperglycemia did not incrementally improve this effect, mandating a cautious use of glucose.

Cardiac storage with UW solution and glucose

Previous investigations from our institution using an isolated human cardiomyocyte model concluded that glucose supplementation of University of Wisconsin solution (UWS) was beneficial with respect to adenine nucleotide and protein recovery. We wished to confirm these results using an isolated heart model. Rodent hearts were frozen in liquid nitrogen (control) or flushed and stored in UWS for 8 hours at 0 degrees C or UWS supplemented with 10, 20, or 30 mmol/L glucose. Experimental hearts were assessed at end-storage or after 45 minutes of reperfusion on a Langendorff apparatus. Adenine nucleotides were assessed by high performance liquid chromatography. In parallel experiments, ventricular function was assessed before and after storage in Langendorff-perfused hearts instrumented with a left ventricular balloon. Glucose supplementation was associated with greater poststorage (20 and 30 mmol/L glucose) and postreperfusion (10, 20, and 30 mmol/L glucose) adenosine triphosphate levels than unmodified UWS. Developed pressure (expressed as a percentage of control values) was increased with 10 mmol/L glucose (75.2% +/- 7.9%, mean +/- standard deviation) compared with unmodified UWS (64.6% +/- 6.6%; p < 0.05). Coronary flow was greater with 10 (72.6% +/- 10.7%) or 20 mmol/L (71.2% +/- 12.5%) versus 0 mmol/L glucose (58.6% +/- 12.1%, p < 0.05). The data support previous in vitro findings and suggest that the addition of 10 mmol/L glucose to UWS is associated with enhanced recovery after prolonged hypothermic storage.