Adenosine cardioplegia. Adenosine versus potassium cardioplegia: effects on cardiac arrest and postischemic recovery in the isolated rat heart

Adenosine is a potential cardioplegic agent by virtue of its specific inhibitory properties on nodal tissue. We tested the hypothesis that adenosine could be more effective than potassium in inducing rapid cardiac arrest and enhancing postischemic hemodynamic recovery. Isolated rat hearts were perfused with Krebs-Henseleit buffer or cardioplegic solutions to determine the time to cardiac arrest and the high-energy phosphate levels at the end of cardioplegia. Cardioplegic solutions contained adenosine 10 mmol/L, potassium 20 mmol/L, or adenosine 10 mmol/L + potassium 20 mmol/L and were infused at a rate of 2 ml/min for 3 minutes at 10 degrees C. Both time taken and total number of beats to cardiac arrest during 3 minutes of cardioplegia were reduced by adenosine 10 mmol/L and adenosine 10 mmol/L + potassium 20 mmol/L when compared with potassium 20 mmol/L alone (p less than 0.001). Tissue phosphocreatine was conserved by adenosine 10 mmol/L when compared with potassium 20 mmol/L, being 7.1 +/- 0.2 (mumol/gm wet weight (n = 7) and 6.0 +/- 0.3 mumol/gm wet weight (n = 5), respectively (p less than 0.05). Postischemic hemodynamic recovery was tested in isolated working rat hearts. After initial cardiac arrest, the cardioplegic solution was removed with Krebs-Henseleit buffer at a rate of 2 ml/min for 3 minutes at 10 degrees C, and thereafter total ischemia was maintained for 30 or 90 minutes at 10 degrees C before reperfusion. Adenosine 10 mmol/L enhanced recovery of aortic output when compared with potassium 20 mmol/L or adenosine 10 mmol/L + potassium 20 mmol/L, the percentage recovery after 30 minutes of ischemia being 103.0% +/- 4.4% (n = 6), 89.0% +/- 5.8% (n = 6), and 86.6% +/- 4.3% (n = 6), respectively (p less than 0.05 for comparison between adenosine 10 mmol/L and potassium 20 mmol/L). Thus adenosine cardioplegia caused rapid cardiac arrest and improved postischemic recovery when compared with potassium cardioplegia and with a combination of these two agents.     

Enhancement of low coronary reflow improves postischemic myocardial function.

The effect of reperfusion coronary vasodilatation on postischemic myocardial mechanical function has been investigated in the isolated working rat heart. After a working period to assess control function, all the hearts were subjected to a single infusion (10 ml) of St. Thomas' Hospital cardioplegic solution No. 1 at 4 degrees C and were kept immersed in the same solution for 4 hours at 4 degrees C. Then hearts (six in each group) were initially reperfused at 37 degrees C for 10 minutes, either with ordinary reperfusate (Krebs-Henseleit bicarbonate buffer) or with reperfusate containing additional coronary dilator. After this period, all hearts were subjected to a further 5 minutes of ordinary reperfusate before being put back into the working mode to assess functional recovery. Mean reperfusion coronary flows and the steady coronary flow measured after 10 minutes of reperfusion in ml/min +/- SEM were--Krebs (control): 17.4 +/- 0.39 and 13.4 +/- 0.40; adenosine (3.75 mumol/L): 19.9 +/- 0.6 and 16.7 +/- 0.8; papaverine (0.05 mmol/L): 21.8 +/- 2.3 and 17.3 +/- 1.8; dipyridamole (2 mmol/L): 20.7 +/- 1.7 and 17.9 +/- 1.0; nitroglycerin (15 mg/L): 20.5 +/- 0.45 and 19.9 +/- 1.4; diltiazem (0.05 mmol/L): 19.6 +/- 2.98 and 17.7 +/- 1.8; calcitonin gene-related peptide (0.03 mmol/L): 20.8 +/- 0.69 and 18.0 +/- 1.3; 5-hydroxytryptamine (0.01 mmol/L): 19.2 +/- 0.53 and 16.9 +/- 0.80. Mean postischemic recovery of cardiac output, peak aortic pressure, and differentiation of pressure were expressed as percent of preischemic control +/- SEM were--Krebs: 54.1 +/- 2.8, 69.1 +/- 2.8, and 53.9 +/- 3.0; adenosine: 78.0 +/- 5.6, 89.5 +/- 2.9, and 69.1 +/- 1.9; papaverine: 81.8 +/- 3.9, 91.8 +/- 3.1, and 71.0 +/- 4.1; dipyrdamole: 67.3 +/- 3.3, 84.3 +/- 2.3, and 75.0 +/- 2.7; nitroglycerin: 83.1 +/- 4.8, 79.7 +/- 2.7, and 69.0 +/- 0.5; diltiazem: 76.5 +/- 3.7, 85.9 +/- 2.9, and 73.3 +/- 1.7; calcitonin gene-related peptide: 79.5 +/- 3.6, 90.0 +/- 4.9, and 75.4 +/- 3.9; 5-hydroxytryptamine: 71.6 +/- 3.2, 85.5 +/- 3.5, and 67.9 +/- 4.8. There was a positive correlation between mean reperfusion coronary flow, steady coronary flow, and postischemic recovery of cardiac output, peak aortic pressure, and differentiation of pressure. Mean reperfusion coronary flow, steady coronary flow, and postischemic recovery of cardiac output, peak aortic pressure, and differentiation of pressure were significantly greater in groups reperfused with vasodilators (p < 0.05) compared with control values.(ABSTRACT TRUNCATED AT 400 WORDS)     

Optimal myocardial preservation with an acalcemic crystalloid cardioplegic solution

The effect of the calcium and oxygen contents of a hyperkalemic glucose-containing cardioplegic solution on myocardial preservation was examined in the isolated working rat heart. The cardioplegic solution was delivered at 4 degrees C every 15 minutes during 2 hours of arrest, maintaining a myocardial temperature of 8 degrees +/- 2 degrees C. Hearts were reperfused in the Langendorff mode for 15 minutes and then resumed the working mode for a further 30 minutes. Groups of hearts were given the oxygenated cardioplegic solution containing an ionized calcium concentration of 0, 0.25, 0.75, or 1.25 mmol/L or the same solution nitrogenated to reduce the oxygen content and containing 0 or 0.75 mmol ionized calcium per liter. The myocardial adenosine triphosphate concentrations at the end of arrest in these six groups of hearts were 15.6 +/- 1.2, 9.5 +/- 0.5, 8.2 +/- 1.1, 4.9 +/- 1.8, 10.1 +/- 2.0, and 1.6 +/- 0.4 nmol/mg dry weight, respectively. At 5 minutes of working reperfusion, the percentages of prearrest aortic flow were 80 +/- 2, 62 +/- 4, 33 +/- 6, 37 +/- 5, 48 +/- 7 and 46 +/- 8, respectively. The differences among the groups in adenosine triphosphate concentrations and in functional recovery diminished during reperfusion. In hearts given the hypoxic calcium-containing solution, there was a marked increase in coronary vascular resistance during the administration of successive doses of cardioplegic solution, which was rapidly reversible upon reperfusion. These data indicate that hearts given the acalcemic oxygenated solution had better adenosine triphosphate preservation during arrest and better functional recovery than hearts in any other group. Addition of calcium to the oxygenated cardioplegic solution decreased adenosine triphosphate preservation and functional recovery. Oxygenation of the acalcemic solution increased adenosine triphosphate preservation and functional recovery. The lowest adenosine triphosphate levels at end arrest were observed in hearts given the hypoxic calcium-containing solution. In the setting of hypothermia and multidose administration, the addition of calcium to a cardioplegic solution resulted in increased energy depletion during arrest and depressed recovery.     

The effect of amino acids on the ischemic heart. Improvement of oxygenated crystalloid cardioplegic solution by an enriched branched chain amino acid formulation

This study was designed to test the effect of glucose and a formulation enriched with branched chain amino acids as additives to oxygenated crystalloid cardioplegic solution in the ischemic heart. Energy-depleted isolated working rat hearts were subjected to 68 minutes of normothermic global ischemia during which oxygenated cardioplegic solution was used to protect them. The hearts were then reperfused in the nonworking mode for 10 minutes and for a further 30 minutes in the working mode. The hearts were randomly divided into three groups, in which various oxygenated cardioplegic solutions were perfused. Group 1 (control) was subjected to modified St. Thomas' Hospital cardioplegic solution and groups 2 and 3 to the same solution with the addition of glucose (11.1 mmol/L) and glucose (11.1 mmol/L) and branched chain amino acids, respectively. Recovery of aortic flow, coronary flow, cardiac output, aortic pressure, adenosine triphosphate, creatine phosphate, and oxygen consumption was significantly better in group 2 than in group 1. In addition, recovery of aortic flow, coronary flow, cardiac output, aortic pressure, stroke volume, minute work, adenosine triphosphate, and creatine phosphate was found to be significantly enhanced in group 3. Release of adenine catabolites and lactic dehydrogenase from these hearts during postischemic reperfusion was significantly decreased. Thus, during global ischemia in the energy-depleted heart, the presence of glucose and branched chain amino acids in oxygenated crystalloid cardioplegic solution enhanced myocardial protection.     

Studies of myocardial protection in the immature heart. V. Safety of prolonged aortic clamping with hypocalcemic glutamate/aspartate blood cardioplegia

This study tests the hypothesis that multidose, hypocalcemic aspartate/glutamate-enriched blood cardioplegia provides safe and effective protection during prolonged aortic clamping of immature hearts. Of 17 puppies (6 to 8 weeks of age, 3 to 5 kg) placed on vented cardiopulmonary bypass, five were subjected to 60 minutes of 37 degrees C global ischemia without cardioplegic protection and seven underwent 120 minutes of aortic clamping with 4 degrees C multidose aspartate/glutamate-enriched blood cardioplegia ([Ca++] = 0.2 mmol/L), preceded and followed by 37 degrees C blood cardioplegic induction and reperfusion. Five puppies underwent blood cardioplegic perfusion for 10 minutes without intervening ischemia to assess the effect of the cardioplegic solution and the delivery techniques. Left ventricular performance was assessed 30 minutes after bypass was discontinued (Starling function curves). Hearts were studied for high-energy phosphates and tissue amino acids. One hour of normothermic ischemia resulted in profound functional depression, with peak stroke work index only 43% of control (0.7 +/- 0.1 versus 1.7 +/- 0.2 gm x m/kg, p less than 0.05). There was 70% depletion of adenosine triphosphate (7.6 +/- 1 versus control 20.3 +/- 1 mumol/gm dry weight, p less than 0.05) and 75% glutamate loss (6.6 +/- 1 versus control 26.4 +/- 3 mumol/gm, p less than 0.05). In contrast, after 2 hours of aortic clamping with multidose blood cardioplegia preceded and followed by 37 degrees C blood cardioplegia, there was complete recovery of left ventricular function (peak stroke work index 1.6 +/- 0.2 gm x m/kg) and maintenance of adenosine triphosphates, glutamate, and aspartate levels at or above control levels adenosine triphosphate 18 +/- 2 mumol/gm, aspartate 21 +/- 1 versus control 2 mumol/gm, and glutamate 25.4 +/- 2 mumol/gm). Puppy hearts receiving blood cardioplegic perfusion without ischemia had complete recovery of control stroke work index. We conclude that methods of myocardial protection used in adults, with amino acid-enriched, reduced-calcium blood cardioplegia, can be applied safely to the neonatal heart and allow for complete functional and metabolic recovery after prolonged aortic clamping.     

Effect of sodium aspartate on the recovery of the rat heart from long-term hypothermic storage.

We have investigated the reported ability of aspartate to enhance greatly the cardioprotective properties of the St. Thomas' Hospital cardioplegic solution after prolonged hypothermic storage. Rat hearts (n = 8 per group) were excised and subjected to immediate arrest with St. Thomas' Hospital cardioplegic solution (2 minutes at 4 degrees C) with or without addition of monosodium aspartate (20 mmol/L). The hearts were then immersed in the same solution for 8 hours (4 degrees C) before heterotopic transplantation into the abdomen of homozygous rats and reperfusion in vivo for 24 hours. The hearts were then excised and perfused in the Langendorff mode (20 minutes). Addition of aspartate to St. Thomas' Hospital cardioplegic solution gave a small but significant improvement in left ventricular developed pressure, which recovered to 82 +/- 3 mm Hg compared with 70 +/- 2 mm Hg in control hearts (p less than 0.05). However, coronary flow and high-energy phosphate content were similar in both groups. In subsequent experiments hearts (n = 8 per group) were excised, arrested (2 minutes at 4 degrees C) with St. Thomas' Hospital cardioplegic solution containing a 0, 5, 10, 20, 30, 40, or 50 mmol/L concentration of aspartate, stored for 8 hours at 4 degrees C, and then reperfused for 35 minutes. A bell-shaped dose-response curve was obtained, with maximum recovery in the 20 mmol/L aspartate group (cardiac output, 48 +/- 5 ml/min versus 32 +/- 5 ml/min in the aspartate-free control group; p less than 0.05). However, additional experiments showed that a comparable improvement could be achieved simply by increasing the sodium concentration of St. Thomas' Hospital cardioplegic solution by 20 mmol/L. Similarly, if sodium aspartate (20 mmol/L) was added and the sodium content of the St. Thomas' Hospital cardioplegic solution reduced by 20 mmol/L, no significant protection was observed when recovery was compared with that of unmodified St. Thomas' Hospital cardioplegic solution alone. In still further studies, hearts (n = 8 per group) were perfused in the working mode at either high (greater than 80 ml/min) or low (less than 50 ml/min) left atrial filling rates. Under these conditions, if functional recovery was expressed as a percentage of preischemic function, artifactually high recoveries could be obtained in the low-filling-rate group. In conclusion, assessment of the protective properties of organic additives to cardioplegic solutions requires careful consideration of (1) the consequences of coincident changes in ionic composition and (2) the characteristics of the model used for assessment.     

Safety of prolonged aortic clamping with blood cardioplegia. III. Aspartate enrichment of glutamate-blood cardioplegia in energy-depleted hearts after ischemic and reperfusion injury

This study tests the hypothesis that aspartate enrichment of glutamate-blood cardioplegia improves metabolic and functional recovery after ischemic and reperfusion damage. Ischemic and reperfusion damage were produced in 15 dogs by 45 minutes of aortic clamping at 37 degrees C and 5 minutes of blood reperfusion, before 2 more hours of aortic clamping (simulated operation). Six received multidose blood cardioplegia at 4 degrees C. In nine others, the cardioplegic solution was infused at 37 degrees C for the first 5 minutes, followed by multidose infusions at 4 degrees C. Four received 26 mmol glutamate-enriched cardioplegic solution. In five, the glutamate (13 mmol) cardioplegic solution was enriched with aspartate (13 mmol). Oxygen uptake and ventricular function (stroke work index, left atrial pressure) were measured. These data suggest aspartate enrichment produced the highest oxygen uptake (32 +/- 4 versus 17 +/- 2 ml/100 gm for glutamate and 7 +/- 1 ml/100 gm for 4 degrees C blood cardioplegia). Complete functional recovery occurred in aspartate/glutamate-treated hearts (stroke work index 90% +/- 4%, left atrial pressure 12 +/- 2 mm Hg), whereas recovery was incomplete with both glutamate alone (stroke work index 66% +/- 14%, left atrial pressure 20 +/- 3 mm Hg) and 4 degrees C blood cardioplegia at low cardiac outputs. Eight of 10 hearts not receiving aspartate failed at high cardiac outputs. Aspartate enrichment of glutamate-blood cardioplegia improves recovery after severe ischemic/reperfusion damage by improving oxidative metabolism during cardioplegic infusion and during postischemic work.     

Lowering the calcium concentration in St. Thomas' Hospital cardioplegic solution improves protection during hypothermic ischemia

The concentration of calcium (1.2 mmol/L) in clinical St. Thomas' Hospital cardioplegic solution was chosen several years ago after dose-response studies in the normothermic isolated heart. However, recent studies with creatine phosphate in St. Thomas' Hospital solution demonstrated that additional myocardial protection during hypothermia resulted principally from its calcium-lowering effect in the solution. The isolated working rat heart model was therefore used to establish the optimal calcium concentration in St. Thomas' Hospital solution during lengthy hypothermic ischemia (20 degrees C, 300 minutes). The calcium content of standard St. Thomas' Hospital solution was varied from 0.0 to 1.5 mmol/L in eight treatment groups (n = 6 for each group). During ischemia, hearts were exposed to multidose cardioplegia (3 minutes every 30 minutes). Postischemic recovery of function was expressed as a percentage of preischemic control values. Release of creatine kinase and the time to return of sinus rhythm during the reperfusion period were also measured. These dose-response studies during hypothermic ischemia revealed a broad range of acceptable calcium concentrations (0.3 to 0.9 mmol/L), which appear optimal in St. Thomas' Hospital solution at 0.6 mmol/L. This concentration improved the postischemic recovery of aortic flow from 22.0% +/- 5.9% with control St. Thomas' Hospital solution (calcium concentration 1.2 mmol/L) to 86.0% +/- 4.0% (p less than 0.001). Other indices of functional recovery showed similar dramatic results. Creatine kinase release was reduced 84% (p less than 0.01) in the optimal calcium group. Postischemic reperfusion arrhythmias were diminished with the loser calcium concentration, with a significant decrease in the time between initial reperfusion until the return of sinus rhythm. In contrast, acalcemic St. Thomas' Hospital solution precipitated the calcium paradox with massive enzyme release and no functional recovery. Unlike prior published calcium dose-response studies at normothermia, these results demonstrate that the optimal calcium concentration during clinically relevant hypothermic ischemia is considerably lower than that of normal serum ionized calcium (1.2 mmol/L) and appears ideal at 0.6 mmol/L to realize even greater cardioprotective and antiarrhythmic effects with St. Thomas' Hospital solution.     

Benefits of glucose and oxygen in multidose cold cardioplegia.

We tested the effects of glucose and oxygen in cardioplegic solutions on myocardial protection in the isolated perfused working rat heart. Recovery from 2 hours' hypothermic (8 degrees C) cardioplegic arrest was examined in 93 hearts. Cardioplegic solution, which was delivered every 15 minutes, was supplemented with glucose 28 mmol/L as a substrate or sucrose 28 mmol/L as a nonmetabolizable osmotic control; it was equilibrated with either 98% oxygen or 98% nitrogen, both with 2% carbon dioxide. Four combinations of hyperkalemic cardioplegic solution were studied: nitrogen-sucrose, nitrogen-glucose, oxygen-sucrose, and oxygen-glucose. During hypothermic arrest, oxygenation of cardioplegic solution greatly reduced myocardial lactate production and prevented ischemic contracture as indicated by coronary vascular resistance. Glucose increased lactate production modestly but significantly only when the cardioplegic solution was nitrogenated. Although end-arrest myocardial adenosine triphosphate and creatine phosphate were greatly increased by oxygenation of cardioplegic solution (p less than 0.005), we could not detect improved preservation of these high-energy phosphates by glucose. Averaged over reperfusion, percent recovery of cardiac output for the nitrogen-sucrose, nitrogen-glucose, oxygen-sucrose, and oxygen-glucose solutions was 32.3% +/- 6.1%, 45.9% +/- 4.6%, 44.5% +/- 4.6%, and 62.2% +/- 4.5%, respectively. Oxygenation of the glucose solution or addition of glucose to the oxygenated solution significantly improved recovery of cardiac output. The benefits of glucose and oxygen were additive, so that the oxygen-glucose cardioplegic solution provided the best functional recovery. We conclude that the addition of glucose to the fully oxygenated multidose cold cardioplegic solution improves functional recovery without increasing lactate production during arrest.     

Oxygenation of cardioplegic solutions. Potential for the calcium paradox

Oxygenation of crystalloid cardioplegic solutions is beneficial, yet bicarbonate-containing solutions equilibrated with 100% oxygen become highly alkaline as carbon dioxide is released. In the isolated perfused rat heart fitted with an intraventricular balloon, we recently observed a sustained contraction related to infusion of cardioplegic solution. In the same model, to record these contractions, we studied myocardial preservation by multidose bicarbonate-containing cardioplegic solutions in which first the calcium content and then the pH was varied. An acalcemic cardioplegic solution (Group 1) and the same solution with calcium provided by adding calcium chloride (Group 2) or blood (Group 3) were equilibrated with 100% oxygen. Ionized calcium concentrations were 0, 0.10 +/- 0.06, and 0.11 +/- 0.07 mmol/L and pH values were 8.74 +/- 0.07, 8.54 +/- 0.08, and 8.40 +/- 0.07, all highly alkaline. Hearts were arrested for 2 hours at 8 degrees +/- 2.5 degrees C and reperfused for 1 hour at 37 degrees C. At end-arrest, myocardial adenosine triphosphate was depleted in all three groups, significantly in Groups 2 and 3. In Group 1 the calcium paradox developed upon reperfusion, with contracture (left ventricular end-diastolic pressure = 60 +/- 7 mm Hg), creatine kinase release up to 620 +/- 134 U/L, a profound further decrease in adenosine triphosphate to 1.9 +/- 1.7 nmol/mg dry weight, and either greatly impaired or no functional recovery (17% +/- 10% of prearrest developed pressure). Three hearts in this group released creatine kinase during arrest and did not resume beating during reperfusion. In Groups 2 and 3, the calcium paradox did not occur; functional recovery was 61% +/- 4% and 71% +/- 9% at 5 minutes of reperfusion. In two additional groups (4 and 5), the pH of the acalcemic cardioplegic solution was decreased by equilibration with 2% and 5% carbon dioxide in oxygen to 7.53 +/- 0.03 and 7.11 +/- 0.02. Contractions during arrest were smaller than in Groups 1, 2, and 3; adenosine triphosphate was maintained during arrest; functional recovery was 101% +/- 3% and 96% +/- 4% at 5 minutes of reperfusion. We conclude that acalcemic solutions with carbon dioxide are superior to highly alkaline calcium-containing solutions. If oxygenation of cardioplegic solutions, of proved value, causes severe alkalinity, then calcium paradox may result even with hypothermia. This hazard is prevented by adding calcium or blood to the solution or carbon dioxide to the oxygen used for equilibration.     

Adenosine as adjunct to potassium cardioplegia: effect on function, energy metabolism, and electrophysiology

Adenosine is known to induce rapid cardioplegic arrest and to improve postischemic recovery in the isolated rat heart. Long exposures to high doses of adenosine impair postischemic recovery, however. In this paper we tested the combination of low-dose adenosine (1 mmol/L) with potassium (26 mmol/L), with the aim of achieving rapid arrest (as with high-dose adenosine) but eliminating the need for postarrest washout of adenosine. Cardioplegic solutions studied were (1) Krebs-Henseleit potassium (26 mmol/L) (K); (2) K plus adenosine (1 mmol/L) (KA); (3) K plus an adenosine deaminase inhibitor [erythro-9-(2-hydroxy-3-nonyl)adenine] (0.1 mmol/L) (KE); and as control (4) Krebs-Henseleit potassium (6 mmol/L) (C). We induced cardiac arrest in Langendorff-perfused rat hearts by infusing the cardioplegic solution for 3 minutes at 3 ml/min. Total ischemia lasted 20 minutes at 37 degrees C, followed by reperfusion for 30 minutes. High potassium decreased the arrest time from 260 +/- 16 seconds (group C, mean values +/- standard error of the mean) to 22 +/- 4 seconds (group K). A further decrease to 10 +/- 2 seconds was observed with KA (p = 0.016 versus K). KE, which increased endogenous adenosine, gave intermediate effects. All hearts recovered during reperfusion; the product of developed tension and heart rate (grams per minute) was superior in KA hearts (6250 +/- 740 versus K hearts 4380 +/- 390; p = 0.050). KE gave an intermediate result (5290 +/- 900), while C showed the worst recovery (3180 +/- 830). Our electrophysiologic studies with sinus node and atrial tissue suggest that adenosine induced hyperpolarization and an increase in potassium permeability, thereby arresting the sinus node before depolarization of the membrane by potassium (26 mmol/L). We conclude that low-dose adenosine as an adjunct to potassium shortens the arrest time in this model and improves postischemic recovery.     

Magnesium ion is beneficial in hypothermic crystalloid cardioplegia

The role of magnesium ion and its relation to the calcium concentration of cardioplegic solutions was reexamined in this study. Isolated rat hearts were used with an oxygenated modified Krebs-Henseleit bicarbonate buffer as perfusion medium. The hearts were arrested for 20 minutes at 37 degrees C or 90 minutes at 24 degrees C. Treatment groups received one dose of nine possible cardioplegic solutions containing magnesium (0, 1.2, or 15 mmol/L) and calcium (0.05, 1.5, or 4.5 mmol/L). Ninety-six percent of the 75 magnesium-treated hearts recovered, regardless of the calcium concentration, in contrast to a 52% recovery rate in the 69 hearts that did not receive magnesium. The addition of 15 mmol/L Mg2+ to a cardioplegic solution containing no magnesium but 0.05 mmol/L Ca2+ significantly increased (p less than 0.01) the percent recovery of the following parameters of cardiac function: systolic pressure, 74% to 93% (37 degrees C), 64% to 98% (24 degrees C); cardiac output, 76% to 101% (37 degrees C), 71% to 102% (24 degrees C); stroke work, 64% to 104% (37 degrees C), 52% to 99% (24 degrees C); and adenosine triphosphate level, 75% to 83% (37 degrees C), 58% to 90% (24 degrees C). There were significant reductions (p less than 0.03) in percent recovery (37 degrees C and 24 degrees C) of cardiac output, stroke work, and adenosine triphosphate level in the groups that contained 0 or 15 mmol/L Mg2+ as the calcium concentration was increased from 0.05 to 4.5 mmol/L.(ABSTRACT TRUNCATED AT 250 WORDS)     

Protection of the neonatal myocardium during hypothermic ischemia. Effect of cardioplegia on left ventricular function in the rabbit

The protective effect of cardioplegia upon neonatal myocardium during ischemia has not been clearly established. This study evaluated the effects of cardioplegia on left ventricular function in isolated working neonatal rabbit hearts (aged 1 week) subjected to 120 minutes of global ischemia at 28 degrees C. Four groups were studied: Group 1, hypothermia alone; Group 2, intermittent washout with an oxygenated noncardioplegic solution; Group 3, multidose cardioplegia; Group 4, single-dose cardioplegia. After ischemia, cardiac output was reduced to 72% +/- 5% (mean +/- standard error of the mean) of control (p less than 0.02) in Group 1 and to 56% +/- 4% in Group 2 (p less than 0.001). In contrast, there was no significant reduction from baseline cardiac output in those animals receiving cardioplegic solution (Group 3, 93% +/- 6%, and Group 4, 97% +/- 4%). Group 2 hearts demonstrated significantly worse recovery of cardiac output and stroke volume than all other groups. After ischemia, the first derivative of left ventricular pressure fell to 73% +/- 13% of control in Group 1 (p less than 0.1) and to 89% +/- 5% in Group 2 (p less than 0.05). However, the first derivative of left ventricular pressure was restored to control values in Group 3 (118% +/- 11%) and Group 4 (114% +/- 9%). When compared to baseline, creatine kinase was higher 30 minutes after reperfusion in Group 1 (40 +/- 8 versus 143 +/- 32 IU/L/gm, p less than 0.05) and in Group 2 (39 +/- 7 versus 163 +/- 33 IU/L/gm, p less than 0.05). Creatine kinase remained unchanged from baseline in Groups 3 and 4. This study demonstrates excellent preservation of left ventricular function in the neonatal rabbit heart protected with cardioplegic solution. In contrast, neither hypothermia alone nor intermittent washout with an oxygenated noncardioplegic solution was effective in preventing myocardial dysfunction. As in adults, the administration of cardioplegic solution preserves ventricular function during ischemia in neonatal hearts.     

Cold cardioplegic arrest enhances heat shock protein 70 in the heat-shocked rat heart

BACKGROUND: Myocardial content of the 70-kd heat shock protein has been found to correlate with improved cardiac recovery after ischemia, but the mechanisms and conditions that regulate its level, particularly under clinical conditions, are unclear. The aim of this study was to assess the effect of hypothermic cardioplegic arrest and reperfusion on the expression of 70-kd heat shock protein in a protocol mimicking conditions of preservation for cardiac transplantation. METHODS: Heat-shocked and control hearts were subjected to 4 hours of cardioplegic arrest and global ischemia at 4 degrees C and then to 20 minutes of reperfusion. Hearts were freeze clamped at different time points-after 15 minutes of Langendorff perfusion, at the end of ischemia, and after 20 minutes of reperfusion, and analyzed for heat shock protein 70 content by Western blotting. Another set of hearts was subjected to 10 minutes of normothermic ischemia and 20 minutes of reperfusion followed by freeze clamping and analysis of heat shock protein 70 content as in cardioplegic arrest protocol. Cardiac function was measured by means of a left ventricular balloon at the end of reperfusion. RESULTS: Preischemic concentration of 70-kd heat shock protein was increased in heat-shocked hearts compared with control hearts. The content of 70-kd heat shock protein in heat-shocked hearts was further increased from 5.0 +/- 2.4 ng/microg at the end of ischemia to 11.0 +/- 4.9 ng/microg (n = 8, mean +/- SD; P <.05) at 20 minutes of reperfusion after cold cardioplegic arrest. No further rise in 70-kd heat shock protein of the heat-shocked hearts was observed after normothermic ischemia. Maximal developed pressure was 120.8 +/- 13.4 mm Hg in control hearts compared with 164.7 +/- 22.5 mm Hg in heat-shocked hearts (n = 5, mean +/- SD; P =.037) after cardioplegic arrest. By contrast, after normothermic ischemia, maximum developed pressure was 111.2 +/- 10.9 mm Hg in control hearts compared with 139.2 +/- 11.0 mm Hg in heat-shocked hearts (n = 4, mean +/- SD; P =.031). CONCLUSION: Hypothermic cardioplegic arrest but not short normothermic ischemia triggered a further increase in the level of 70-kd heat shock protein in heat-shocked rat hearts, which may enhance endogenous cardiac protection.     

Isolated, perfused neonatal rat heart preparation for studies of calcium and functional stability

We describe an isolated, perfused preparation for neonatal rat hearts to assess the relationship between extracellular calcium and (1) cardiac function and (2) contractile stability over 2 hours of perfusion. Neonatal (3 to 5 days old) rat hearts (n = 6 per group) were perfused for 30 minutes (Langendorff) with oxygenated buffer (37 degrees C) containing 1.4 mmol/L calcium (control period) and 90 minutes with buffer containing 0.5, 0.8, 1.0, 1.2, 1.4, 1.8, or 2.5 mmol/L calcium. Upon changing from 1.4 mumol/L to either a higher or low calcium concentration there were no significant changes in left ventricular developed pressure, heart rate, or coronary flow. However, left ventricular developed pressure progressively deteriorated in a time-dependent and calcium-dependent manner. Thus, after 90 minutes, developed pressure fell to 18% +/- 2%, 27% +/- 3%, 41% +/- 5%, 47% +/- 8%, 55% +/- 10%, 64% +/- 5% and 76% +/- 4% of its initial value with 0.5, 0.8, 1.0, 1.2, 1.4, 1.8, and 2.5 mmol/L calcium. In conclusion, in studies with the neonatal rat heart, extracellular calcium concentrations in the range of 1.8 to 2.5 mmol/L are recommended.     

Enhanced myocardial protection with high-energy phosphates in St. Thomas' Hospital cardioplegic solution. Synergism of adenosine triphosphate and creatine phosphate

The potential for improving myocardial protection with the high-energy phosphates adenosine triphosphate and creatine phosphate was evaluated by adding them to the St. Thomas' Hospital cardioplegic solution in the isolated, working rat heart model of cardiopulmonary bypass and ischemic arrest. Dose-response studies with an adenosine triphosphate range of 0.05 to 10.0 mmol/L showed 0.1 mmol/L to be the optimal concentration for recovery of aortic flow and cardiac output after 40 minutes of normothermic (37 degrees C) ischemic arrest (from 24.1% +/- 4.4% and 35.9% +/- 4.1% in the unmodified cardioplegia group to 62.6% +/- 4.7% and 71.0% +/- 3.0%, respectively, p less than 0.001). Adenosine triphosphate at its optimal concentration (0.1 mmol/L) also reduced creatine kinase leakage by 39% (p less than 0.001). Postischemic arrhythmias were also significantly reduced, which obviated the need for electrical defibrillation and reduced the time to return of regular rhythm from 7.9 +/- 2.0 minutes in the control group to 3.5 +/- 0.4 minutes in the adenosine triphosphate group. Under more clinically relevant conditions of hypothermic ischemia (20 degrees C, 270 minutes) with multidose (every 30 minutes) cardioplegia, adenosine triphosphate addition improved postischemic recovery of aortic flow and cardiac output from control values of 26.8% +/- 8.4% and 35.4% +/- 6.3% to 58.0% +/- 4.7% and 64.4% +/- 3.7% (p less than 0.01), respectively, and creatine kinase leakage was significantly reduced. Parallel hypothermic ischemia studies (270 minutes, 20 degrees C) using the previously demonstrated optimal creatinine phosphate concentration (10.0 mmol/L) gave nearly identical improvements in recovery and enzyme leakage. The combination of the optimal concentrations of adenosine triphosphate and creatine phosphate resulted in even greater myocardial protection; aortic flow and cardiac output improved from their control values of 26.8% +/- 8.4% and 35.4% +/- 6.3% to 79.7% +/- 1.1 and 80.7% +/- 1.0% (p less than 0.001), respectively. In conclusion, both extracellular adenosine triphosphate and creatine phosphate alone markedly improve the cardioprotective properties of the St. Thomas' Hospital cardioplegic solution during prolonged hypothermic ischemic arrest, but together they act additively to provide even greater protection.     

L-arginine during long-term ischemia: effects on cardiac function, energetic metabolism and endothelial damage.

BACKGROUND: We have evaluated the addition of L-arginine, a precursor of nitric oxide, to a cardioplegic solution (named CRMBM) designed for long-term heart preservation. METHODS: Isolated isovolumic-perfused rat hearts (n = 22) were arrested with the CRMBM solution either with (Arg) or without L-arginine (2 mmol/L) (Arg group, n = 12, vs control group n = 10), submitted to 8 hours of cold storage (4 degrees C) in the solution, and then reperfused for 60 minutes at 37 degrees C. In 11 hearts, we evaluated the quality of cardiac preservation with P-31 magnetic resonance spectroscopy and the measure of function and cellular integrity. Endothelium-dependent and independent vasodilatations were measured in 11 other hearts, using 5-hydroxytryptamine and papaverine to assess endothelial and smooth muscle function. RESULTS: Adding L-arginine to the cardioplegic solution improved functional recovery during reflow, as shown by the rate pressure product (31% +/- 3% for control vs 47% +/- 3% for Arg, p = 0.003) together with higher coronary flow and diminished contracture. Purine release in coronary effluents during reperfusion was lower in the Arg group. During ischemia and reflow kinetics of intracellular pH and high-energy phosphates were similar in both groups. Coronary endothelium-dependent vasodilatation was similarly impaired in both groups, but smooth muscle was less altered with L-arginine. CONCLUSIONS: As an additive to the CRMBM cardioplegic solution, L-arginine provides a protective effect for long-term heart preservation. Our data do not show coronary endothelial protection as the prominent mechanism.     

Blood cardioplegic protection in profoundly damaged hearts: role of Na+-H+ exchange inhibition during pretreatment or during controlled reperfusion supplementation

BACKGROUND: Inhibition of the Na+/H+ exchanger before ischemia protects against ischemia-reperfusion injury, but use as pretreatment before blood cardioplegic protection or as a supplement to controlled blood cardioplegic reperfusion was not previously tested in jeopardized hearts. METHODS: Control studies tested the safety of glutamate-aspartate-enriched blood cardioplegic solution in 4 Yorkshire-Duroc pigs undergoing 30 minutes of aortic clamping without prior unprotected ischemia. Twenty-four pigs underwent 30 minutes of unprotected normothermic global ischemia to create a jeopardized heart. Six of these hearts received normal blood reperfusion, and the other 18 jeopardized hearts underwent 30 more minutes of aortic clamping with cardioplegic protection. In 12 of these, the Na+/H+ exchanger inhibitor cariporide was used as intravenous pretreatment (n = 6) or added to the cardioplegic reperfusate (n = 6). RESULTS: Complete functional, biochemical, and endothelial recovery occurred after 30 minutes of blood cardioplegic arrest without preceding unprotected ischemia. Thirty minutes of normothermic ischemia and normal blood reperfusion produced 33% mortality and severe left ventricular dysfunction in survivors (preload recruitable stroke work, 23% +/- 6% of baseline levels), with raised creatine kinase MB, conjugated dienes, endothelin-1, myeloperoxidase activity, and extensive myocardial edema. Blood cardioplegia was functionally protective, despite adding 30 more minutes of ischemia; there was no mortality, and left ventricular function improved (preload recruitable stroke work, 58% +/- 21%, p < 0.05 versus normal blood reperfusion), but adverse biochemical and endothelial variables did not change. In contrast, Na+/H+ exchanger inhibition as either pretreatment or added during cardioplegic reperfusion improved myocardial recovery (preload recruitable stroke work, 88% +/- 9% and 80% +/- 7%, respectively, p < 0.05 versus without cariporide) and comparably restored injury variables. CONCLUSIONS: Na+/H+ exchanger blockage as either pretreatment or during blood cardioplegic reperfusion comparably delays functional, biochemical, and endothelial injury in jeopardized hearts.     

TPEN, a transition metal chelator, improves myocardial protection during prolonged ischemia.

In view of the hypothesis that free radicals induced damage during ischemia and reperfusion is mediated by transition metals, we investigated the effect of the potent metal chelator TPEN (N,N,N'N'-tetrakis(-)[2-pyridylmethyl]-ethylenediamine) on cardiac function after prolonged myocardial ischemia. Isolated working rat hearts were subjected to 12 hours of cold ischemic arrest followed by reperfusion for 1 hour. The study was carried out on five groups (nine hearts in each): (1) St. Thomas' Hospital cardioplegic solution; (2) St. Thomas' Hospital cardioplegic solution with 7.5 mumol/L TPEN; (3) protection conditions as in group 2, but with TPEN administration during preischemic and reperfusion periods; (4) University of Wisconsin solution; and (5) the same conditions as in group 4 with TPEN administration during the preischemic and reperfusion periods. Significant enhancement of hemodynamic recovery was observed in the presence of TPEN throughout the experiment. The recovery of cardiac output was 24% +/- 4% in group 3, as compared to 12% +/- 4% in group 1 (p < 0.01). The postischemic left ventricular pressure recovery was 57% +/- 4% in group 3, as compared to 18% +/- 7% in group 1 (p < 0.005). The hearts in group 5 recovered, reaching 29% +/- 2% of the preischemic cardiac output and at 65% +/- 2% of the left ventricular pressure recovery (p < 0.05 versus group 3). Lactate dehydrogenase was released throughout the reperfusion. TPEN addition to groups 2 and 3 did not significantly reduce lactate dehydrogenase release; however, TPEN in University of Wisconsin solution and throughout the experiment significantly decreased lactate dehydrogenase release.(ABSTRACT TRUNCATED AT 250 WORDS)     

Overdose reperfusion of blood cardioplegic solution. A preventable cause of postischemic myocardial depression

Reperfusion of warm blood cardioplegic solution is useful in minimizing reperfusion damage after ischemia. This study tests the hypothesis that overzealous administration of blood cardioplegic solution at reperfusion counteracts these benefits and can lead to a prevalence of depressed ventricular performance and mortality similar to that seen after normal blood reperfusion. Thirty-one dogs underwent 45 minutes of 37 degrees C global ischemia on vented bypass. Six received normal blood reperfusion and 25 were reperfused with a warm aspartate/glutamate-enriched blood cardioplegic solution; of these, eight received high-dose (3600 +/- 600 ml) and 17 received limited-dose (1180 +/- 120 ml) blood cardioplegic reperfusion over 10 to 20 minutes. High-dose blood cardioplegic perfusion (5100 +/- 200 ml) without prior ischemia was tested in an additional five dogs. High-dose blood cardioplegia without preceding ischemia did not alter ventricular function (peak stroke work index 96% of control). After ischemia, normal blood reperfusion (no cardioplegia) resulted in marked left ventricular dysfunction (peak stroke work index 36% of control, p less than 0.05 versus control) and a 33% mortality rate (2/6 died). High-dose cardioplegic reperfusion yielded marginal recovery of stroke work index (40% of control, p less than 0.05 versus control) and a 25% mortality rate (2/8 died). In contrast, limited-dose reperfusion of blood cardioplegic solution allowed 100% survival (17/17) and restored stroke work index to 90% of control (1.3 versus 1.45 gm.m/kg). We conclude that reperfusion damage can be avoided by initial reoxygenation with limited doses of substrate-enriched blood cardioplegic solution. Conversely, high-dose reperfusion of blood cardioplegic solution offsets this benefit, reduces recovery substantially, and may be lethal.