Critical timing of nitric oxide supplementation in cardioplegic arrest and reperfusion.

BACKGROUND: It has been shown that increased nitric oxide (NO) generation is associated with improved myocardial preservation during ischemia/reperfusion. This study sought to determine the optimal timing for NO supplementation in the setting of cardioplegic arrest, regional ischemia, and reperfusion. METHODS AND RESULTS: Isolated working rat hearts were arrested with normothermic oxygenated potassium cardioplegia for 5 minutes, followed by 60 minutes of normothermic continuous cardioplegic administration with left anterior descending coronary artery (LAD) occlusion. The hearts were divided into four groups. Hearts in group 1 were ischemic/reperfused controls without L-arginine treatment. Hearts in group 2 were perfused with 3 mmol/L L-arginine for 5 minutes before cardioplegic arrest. Hearts in group 3 were perfused with 3 mmol/L L-arginine in the cardioplegia solution. Hearts in group 4 were perfused with 3 mmol/L L-arginine for 5 minutes only during initial reperfusion. Myocardial contractile function after 30 minutes of reperfusion was significantly better in group 2 compared with the other groups and was significantly lower in group 4 than group 1. Coronary flow, although decreased from base line in all groups at 30 minutes of reperfusion, was highest in group 2. The tissue accumulation of cGMP in groups 2 and 3 increased significantly after L-arginine infusion compared with the control group (group 1). In contrast, the LAD regional cGMP after reperfusion in group 4 was comparable to group 1 and significantly lower than groups 2 and 3, whereas the circumflex region cGMP in group 4 was significantly increased over group 1, comparable to groups 2 and 3. LDH release in groups 2 and 3 was significantly lower compared with groups 1 and 4. CONCLUSIONS: As assessed by myocardial function and LDH release, L-arginine is most beneficial when given before cardioplegic arrest, effective during cardioplegic arrest, and detrimental during reperfusion. This suggests that L-arginine given during reperfusion is deleterious to optimal recovery of myocardial function in this ischemic model and that the effect of NO generation in the ischemic/reperfused myocardium may be dependent on the condition of the endothelium.

L-arginine reduces endothelial inflammation and myocardial stunning during ischemia/reperfusion.

BACKGROUND: This study evaluated whether the nitric oxide precursor L-arginine could reduce ischemia/reperfusion injury by preventing leukocyte-endothelial interactions. METHODS: Normothermic regional ischemia was induced in the open-chest working pig heart for 30 minutes followed by 90 minutes of reperfusion. A preischemic 10-minute intravenous infusion of 4 mg.kg-1.min-1 of L-arginine (n = 12) was compared with 12 control pigs. Nitric oxide release was measured from the coronary sinus using an amperometric probe. Left ventricular function, malonaldehyde, creatine kinase, myocardial oxygen extraction, and the soluble adhesion molecules (intracellular adhesion molecule-1, endothelial leukocyte adhesion molecule-1, and vascular cell adhesion molecule-1) were measured. RESULTS: Nitric oxide release was significantly reduced from baseline throughout ischemia/reperfusion only in the control group. Systolic and diastolic function, and myocardial oxygen extraction were also significantly decreased during early reperfusion in the control compared with the L-arginine group. Peak creatine kinase release was not significantly different between groups. The incidence of ventricular fibrillation, malonaldehyde release, and soluble intracellular adhesion molecule-1, endothelial leukocyte adhesion molecule-1, and vascular cell adhesion molecule-1 were each significantly decreased during reperfusion in the L-arginine group. CONCLUSIONS: L-Arginine reduced lipid peroxidation, plasma levels of soluble adhesion molecules, myocardial stunning, and arrhythmias. These results support an excessive endothelial injury/inflammatory response after regional ischemia/reperfusion that can be ameliorated through augmented nitric oxide.

Constitutive nitric oxide release is impaired after ischemia and reperfusion.

Myocardial ischemia and reperfusion may result in endothelial dysfunction and reduced release of nitric oxide. With the use of an amperometric sensor, the first direct measurements of constitutive nitric oxide release from a beating heart were measured from the coronary effluent of isolated working rat hearts subjected to ischemia and reperfusion. Rats, six to eight per group, were randomly studied as follows: control (no pretreatment) and pretreatment with the nitric oxide donor L-arginine (3 mmol/L), its enantiomer D-arginine (3 mmol/L), nitric oxide inhibitor N omega-nitro-L-arginine methyl ester (100 mumol/L), and combined N omega-nitro-L-arginine methyl ester/L-arginine. Isolated hearts were pretreated for 10 minutes before 30 minutes of global ischemia and 30 minutes of reperfusion. A nonischemic control group (n = 4) was continuously perfused with oxygenated unsupplemented buffer. After ischemia/reperfusion, hearts supplemented with L-arginine recovered significantly (p < 0.05) increased developed pressure, first derivative of the aortic pressure (dP/dtmax), and aortic flow compared with all other hearts that underwent ischemia/reperfusion. In addition, nitric oxide release was significantly (p < 0.05) increased during reperfusion in the L-arginine group. During reperfusion, the recovery of aortic flow correlated with nitric oxide release (r = 0.81, p < 0.0001). We conclude that after ischemia/reperfusion, endothelial dysfunction results in decreased nitric oxide release, which can be ameliorated with L-arginine pretreatment. The direct cytoprotective properties of nitric oxide may contribute to improved functional recovery in hearts pretreated with L-arginine. Augmentation of the L-arginine/nitric oxide pathway may provide a new approach for improved recovery after cardiovascular operations.

Reduction of infarct size by systemic amino acid supplementation during reperfusion.

The amino acids aspartate and glutamate, in combination, were evaluated as a means of reducing infarct size and improving cardiac function during reperfusion in an intact pig having an acute anteroseptal infarct. Three groups of 6 pigs each were randomly studied in a blinded manner: control (no amino acids), aspartate/glutamate 3 mmol/L, and aspartate/glutamate 13 mmol/L. The left anterior descending coronary artery was occluded distal to its first diagonal branch for 60 minutes followed by reperfusion for 6 hours. Aspartate and glutamate were administered systemically immediately before reperfusion. The following parameters were measured: infarct size and percent area at risk, global metabolic function, global and regional myocardial function, and tissue parameters of metabolic function. The results clearly showed a significant decrease in infarct size from 60% of the area at risk in control pigs to 37% in both 3 mmol/L and 13 mmol/L amino acid groups. Cardiac output, coronary blood flow, and global oxygen consumption were not significantly affected by the use of amino acids relative to the control group. Global left ventricular mechanical function was also not adversely affected by the infarct and was not altered by amino acid administration. Regional function, however, was significantly decreased by occlusion of the left anterior descending coronary artery in all groups to near 20% and only significantly recovered to 64% in the 13 mmol/L amino acid group. Adenosine triphosphate and acetyl coenzyme A measurements documented significant increases in the 13 mmol/L amino acid group relative to the control group. The conclusions of this study strongly support aspartate/glutamate supplementation for stunned, reperfused myocardium. It is apparent that the effect of amino acid supplementation on glycolysis is directly translated into improved regional function and reduced infarct size.

Enhanced myocardial preservation by nicotinic acid, an antilipolytic compound: mechanism of action.

The cardioprotective effects of an antilipolytic compound, nicotinic acid, on arrested-reperfused myocardium were investigated in the isolated in situ pig heart preparation. Hearts were preperfused for 15 min in the presence of (5-3H)-glucose and (U-14C)-palmitic acid. Half of the hearts were then perfused with 0.08 mM nicotinic acid for an additional 15-min period, while the remaining control hearts received unmodified perfusion. Arrest was then induced in all animals for 2 h using hypothermic K+ cardioplegia, followed by 60 min of normothermic reperfusion. In control hearts, there were significantly greater levels of long-chain acyl Co-A and acyl carnitine and lower levels of membrane phospholipids than in the nicotinic acid group. While nicotinic acid inhibited beta-oxidation during pre-ischemia and reperfusion, it also prevented the degradation of membrane phospholipids. The net result was a reduction of free fatty acid accumulation during arrest and reperfusion in the nicotinic acid group. Glycolysis, as reflected in 3H2O production, was significantly increased by nicotinic acid administration. In the control heart as compared to the nicotinic acid group, the incorporation of 14C-label from palmitate into triglyceride and cholesterol during arrest was enhanced, while incorporation into phospholipids was depressed. The cardioprotective effects of nicotinic acid were demonstrated by decreased release of creatine kinase and improved coronary blood flow, and cardiac contractility in the reperfused myocardium supplemented with nicotinic acid compared to the control group. These results suggest that nicotinic acid significantly protects the arrested-reperfused myocardium by a) preventing elevation of myocardial fatty acid levels, b) stimulating glycolysis by limiting fatty acid oxidation, c) inhibiting degradation of membrane phospholipids, and d) preventing accumulation of fatty acid metabolites with harmful detergent properties.

Blood conservation for myocardial revascularization. Is it cost effective?

A total of 284 patients undergoing myocardial revascularization were prospectively studied to determine if the use of intraoperative autotransfusion or intraoperative autotransfusion plus postoperative reinfusion of shed mediastinal blood decreased transfusion requirements and the use of one or both techniques was cost effective. The Haemonetics Cell Saver System was used for intraoperative autotransfusion and the Sorenson Receptaseal autotransfusion system for postoperative reinfusion of shed mediastinal blood. During Phase 1, the Cell Saver System was used for 57 patients and 93 patients served as a control group. During Phase 2, the Cell Saver System plus the autotransfusion system were used in 43 patients and 91 patients were in the control group. Separate parallel analyses to compare the blood conservation groups to control groups were conducted for each phase of the study. The patient groups were comparable with regard to age, sex, preoperative red cell mass, preoperative hematocrit value, number of bypasses, and use of internal mammary grafts. Blood conservation techniques resulted in significant reductions in the use of bank blood. During Phase 1, Cell Saver System patients received an average of 2.8 units of packed cells versus 4.7 units for control patients. Transfusion was avoided entirely in 14% of Cell Saver System patients compared to 3% of control patients. During Phase 2, patients subjected to both the Cell Saver System and the autotransfusion system received an average of 1 unit of packed red cells versus 3 units for control patients. Transfusion was required in only 42% of patients subjected to both the Cell Saver System and the autotransfusion system compared to 85% of control patients. Multiple logistic regression analysis confirmed that the use of the Cell Saver System in Phase 1 and the Cell Saver System and autotransfusion system in Phase 2 were each independently predictive of decreased transfusion requirements. The total "blood-related costs" (including cost for all bank blood products plus Receptaseal and Cell Saver System equipment) was slightly lower for the blood conservation patients in both Phase 1 ($555.00 versus $615.00, no significant difference) and Phase 2 ($373.00 versus $426.00, no significant difference). Intraoperative use of the Cell Saver System is associated with substantial savings of bank blood, and the addition of postoperative reinfusion of shed mediastinal blood results in further bank blood savings. The use of blood conservation techniques is cost effective; that is, the costs incurred for the blood conservation equipment are more than offset by the resultant dollar savings for blood products.

A comparison of blood and Fluosol-DA for cardiopulmonary bypass.

Fluosol-DA was compared to blood as a pump prime for total cardiopulmonary bypass in the pig animal model. Nineteen pigs weighing between 14 and 22 kg were studied, nine with blood and ten with Fluosol. Metabolic and hemodynamic measurements were determined before, during and after 60 minute bypass to establish the adequacy of Fluosol to sustain perfusion as compared to blood. The measurements and subsequent calculations included blood gases, arterial and mixed venous oxygen content, oxygen extraction and consumption, cardiac output, systemic and pulmonary vascular resistance and arterial, venous, pulmonary artery and left atrial pressures. The result showed a significant decrease in hematocrit during bypass in the Fluosol group as compared to blood perfusion (20 vs. 30%). While the arterial oxygen content fell from control levels with Fluosol during bypass, in the blood prime group, oxygen content remained at pre-control levels. Whole body oxygen consumption decreased during bypass, in both groups equally, but this decrease did not lead to acidosis and was stable during recovery. Oxygen and carbon dioxide transport were adequately maintained during bypass in both Fluosol and blood groups. Systemic pressures remained stable during bypass and were lower, but stable, during recovery. Pulmonary vascular resistance was elevated in both groups during recovery which probably explains a concomitantly decreased cardiac output. There was a 40% mortality in both experimental groups secondary to postpump pulmonary hypertension. It is concluded that Fluosol is a satisfactory oxygen carrying agent to be used instead of blood during cardiopulmonary bypass, and in the pig model both blood and Fluosol were associated with a high incidence of pulmonary hypertension.