Effect of four crystalloid cardioplegias on immature rabbit hearts during global ischaemia

OBJECTIVE: Controversy surrounds the reported beneficial effects of crystalloid cardioplegic solutions in the immature myocardium. In the present study, we investigated the efficacy of four clinical cardioplegic solutions in the immature myocardium to determine if cardioplegic protection could be demonstrated and, if yes, the relative efficacy of the four solutions. METHODS: Isolated, working hearts (n=6 per group) from neonatal rabbits (age, 7-14 days) were perfused aerobically (37 C) for 15 minutes in the Langendorff mode and 30 minutes in the working mode before a 2-minute infusion of one of four cardioplegic solutions: the modified St. Thomas' Hospital no. 1 cardioplegic solution, Tyers solution, Bretschneider solution or Roe solution. Hearts were then rendered globally ischaemic for 120 minutes at 14C before reperfusion for 15 minutes in the Langendorff mode and 30 minutes in the working mode. The post-ischaemic recovery of cardiac function and leakage of myocardial enzymes (GOT, CK, CK-MB, LDH, LDH1) were compared with results in non-cardioplegic control hearts. RESULTS: Good protection was observed with modified St. Thomas' Hospital and Tyers solutions: postischaemic recovery of cardiac output was increased from 80.43+/-3.62% in the non-cardioplegic group to 85.19+/-3.12% and 70.66+/-3.48% in the St. Thomas' Hospital and Tyers groups (p<0.05), respectively. In contrast, no obvious protection was observed with either the Bretschneider or Roe solutions: cardiac output recovered to 45.08+/-3.16% and 30.06+/-2.59%, respectively. Post-ischaemic CK leakage was 19.83+/-2.14 IU/mL and 21.17+/-2.32 IU/mL in the St. Thomas' Hospital and Tyers groups (p>0.05). In the Bretschneider group, CK leakage increased to 30.00+/-3.16 IU/mL (p<0.01 vs. non-cardioplegic control hearts), and in the Roe group, CK leakage was 31.00+/-5.10 IU/mL (p<0.05 vs. cardioplegic-free hearts). Post-ischaemic ATP was 1.98+/-0.54 micromol/g*dry weight and 1.35+/-0.39 micromol/g*dry weight in the St. Thomas' Hospital and Tyers groups (p<0.01 vs. non-cardioplegic control group), respectively. In the Bretschneider group, ATP decreased to 0.91+/-0.16 micromol/g*dry weight (p<0.05 vs. non-cardioplegic control hearts), and in the Roe group to 0.88+/-0.10 micromol/g*dry weight (p<0.01 vs.cardioplegic-free hearts). CONCLUSION: In conclusion, cardioplegic protection can be achieved in the immature rabbit myocardium with both St. Thomas' Hospital and Tyers solutions, but acalcaemic solutions such as Bretschneider and Roe solutions increased damage. The reported lack of cardioplegic efficacy in the immature myocardium may, therefore, reflect the choice of cardioplegic solution rather than a greater vulnerability to injury in the neonatal heart.     

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.     

L-aspartate improves the functional recovery of explanted hearts stored in St. Thomas' Hospital cardioplegic solution at 4 degrees C

Explanted rat hearts were subjected to cardioplegic arrest by 3 minutes' perfusion with oxygenated St. Thomas' Hospital solution no. 2 and then were stored by immersion in the same solution at 4 degrees C. Prearrest and postischemic left ventricular functions were compared by means of an isolated working heart apparatus. Hearts (n = 8 per group) arrested and stored for up to 8 hours all resumed the spontaneous rhythm of contraction during reperfusion for 30 minutes at 37 degrees C. There was good recovery of aortic flow rate (105% +/- 3%) against a pressure of 100 cm H2O, of heart rate (102% +/- 2%), and of aortic pressure (86% +/- 5% of prearrest values). Hearts stored for 10 and 20 hours showed poor or no postischemic recovery of cardiac pump function (aortic flow, 16% +/- 11% and 0%, respectively). Enrichment of St. Thomas' Hospital solution with L-glutamate (20 mmol/L) also failed to improve functional recovery of hearts subjected to 10 hours of storage, but hearts treated with St. Thomas' Hospital solution containing L-aspartate (20 mmol/L) or L-aspartate plus L-glutamate (20 mmol/L each) reestablished aortic flow rates of 99% +/- 5% and 93% +/- 4%, respectively. These results indicate that the addition of L-aspartate to St. Thomas' Hospital solution improves the functional recovery and extends the safe preservation of explanted hearts stored at 4 degrees C.     

Adenosine and lidocaine: a new concept in nondepolarizing surgical myocardial arrest, protection, and preservation

OBJECTIVE: Depolarizing potassium cardioplegia has been increasingly linked to left ventricular dysfunction, arrhythmia, and microvascular damage. We tested a new polarizing normokalemic cardioplegic solution employing adenosine and lidocaine as the arresting, protecting, and preserving cardioprotective combination. Adenosine hyperpolarizes the myocyte by A1 receptor activation, and lidocaine blocks the sodium fast channels. METHODS: Isolated perfused rat hearts were switched from the working mode to the Langendorff (nonworking) mode and arrested for 30 minutes, 2 hours, or 4 hours with 200 micromol/L adenosine and 500 micromol/L lidocaine in Krebs-Henseleit buffer (10 mmol/L glucose, pH 7.7, at 37 degrees C) or modified St Thomas' Hospital solution no. 2, both delivered at 70 mm Hg and 37 degrees C (arrest temperature 22 degrees C to 35 degrees C). RESULTS: Adenosine and lidocaine hearts achieved faster mechanical arrest in (25 +/- 2 seconds, n = 23) compared with St Thomas' Hospital solution hearts (70 +/- 5 seconds, n = 24; P=.001). After 30 minutes of arrest, both groups developed comparable aortic flow at approximately 5 minutes of reperfusion. After 2 and 4 hours of arrest (cardioplegic solution delivered every 20 minutes for 2 minutes at 37 degrees C), only 50% (4 of 8) and 14% (1 of 7) of St Thomas' Hospital solution hearts recovered aortic flow, respectively. All adenosine and lidocaine hearts arrested for 2 hours (n = 7) and 4 hours (n = 9) recovered 70% to 80% of their prearrest aortic flows. Similarly, heart rate, systolic pressures, and rate-pressure products recovered to 85% to 100% and coronary flows recovered to 70% to 80% of prearrest values. Coronary vascular resistance during delivery of cardioplegic solution was significantly lower (P <.05) after 2 and 4 hours in hearts arrested with adenosine and lidocaine cardioplegic solution compared with hearts arrested with St Thomas' Hospital solution. CONCLUSIONS: We conclude that adenosine and lidocaine polarizing cardioplegic solution confers superior cardiac protection during arrest and recovery compared with hyperkalemic depolarizing St Thomas' Hospital cardioplegic solution.     

Protection of the immature myocardium during global ischemia. A comparison of four clinical cardioplegic solutions in the rabbit heart

Controversy surrounds the reported beneficial effects of crystalloid cardioplegic solutions in the immature myocardium. In the present study we have investigated the efficacy of four clinical cardioplegic solutions in the immature myocardium to determine (1) whether cardioplegic protection could be demonstrated and, if so, (2) the relative efficacy of the four solutions. Isolated, working hearts (n = 6 per group) from neonatal rabbits (aged 5 to 8 days) were perfused aerobically (37 degrees C) for 20 minutes before a 2-minute infusion of one of four cardioplegic solutions: The St. Thomas' Hospital No. 2, Tyers, Bretschneider, and Roe solutions. Hearts were then rendered globally ischemic for 50 minutes at 37 degrees C before reperfusion for 15 minutes in the Langendorff mode and 20 minutes in the working mode. The postischemic recovery of cardiac function and leakage of creatine kinase were compared with results in noncardioplegic control hearts. Good protection was observed with the St. Thomas' Hospital and Tyers solutions: The postischemic recovery of cardiac output was increased from 21.2% +/- 12.7% in the cardioplegia-free group to 79.4% +/- 6.2% and 72.9% +/- 4.4%, respectively, in the St. Thomas' Hospital and Tyers groups (p less than 0.01). In contrast, no protection was observed with either the Bretschneider or Rose solutions: Cardiac output recovered to 31.7% +/- 10.3% and 5.1% +/- 3.2%, respectively, in these groups. Postischemic creatine kinase leakage was 72.4 +/- 12.3 and 92.1 +/- 18.6 IU/15 min/gm dry weight in the St. Thomas' Hospital and Tyers groups compared with 125.6 +/- 28.6 IU/15 min/gm dry weight in control hearts (p = no significant difference). In the Bretschneider group, creatine kinase leakage increased to 836.9 +/- 176.8 IU/15 min/gm dry weight (p less than 0.01 versus noncardioplegic control hearts), and with the Roe solution the value was 269.0 +/- 93.0 IU/15 min/gm dry weight (p = no significant difference). In conclusion, cardioplegic protection can be achieved in the immature rabbit myocardium with both St. Thomas' Hospital and Tyers solutions, but acalcemic solutions such as Bretschneider and Roe solutions (which may be effective in the adult heart) increased damage in this preparation. The reported lack of cardioplegic efficacy in the immature myocardium may therefore reflect the choice of cardioplegic solution rather than a greater vulnerability to injury in the neonatal heart.     

Long-term preservation of explanted hearts perfused with L-aspartate-enriched cardioplegic solution. Improved function, metabolism, and ultrastructure.

The effects of supplementing oxygenated St. Thomas' Hospital cardioplegic solution No. 2 with L-aspartate and/or D-glucose for the long-term preservation of excised rat hearts were determined with isolated working heart preparations. Left ventricular function was assessed at 37 degrees C with a crystalloid perfusate, before cardioplegic arrest and after 20 hours of low-flow perfusion (1.5 ml/min) with continuing arrest at 4 degrees C, and after this period, again at 37 degrees C with a crystalloid perfusate. Four groups (n = 8/group) of hearts were studied with four cardioplegic solutions: St. Thomas' Hospital solution alone, St. Thomas' Hospital solution with aspartate 20 mmol/L, St. Thomas' Hospital solution with glucose 20 mmol/L, and St. Thomas' Hospital solution plus both aspartate and glucose (20 mmol/L each). The addition of glucose to St. Thomas' Hospital solution made no significant difference in the recovery of aortic flow rates (17.7% +/- 8.6% and 21.6% +/- 7.8% of prearrest values), but when aspartate or aspartate and glucose were present, hearts showed significant improvements (89.8% +/- 5.2% and 85.0% +/- 6.2%, respectively). These improvements were associated with a reduction in the decline of myocardial high-energy phosphates during reperfusion, a reduction in cellular uptake of Na+ and Ca++, and a reduction in ultrastructural damage. These results indicate that low-flow perfusion with St. Thomas' Hospital solution plus aspartate can considerably extend the duration of safe storage of explanted hearts.     

St. Thomas' Hospital cardioplegic solution. Beneficial effect of glucose and multidose reinfusions of cardioplegic solution

The intention of this study was to determine whether glucose is beneficial in a cardioplegic solution when the end products of metabolism produced during the ischemic period are intermittently removed. The experimental model used was the isolated working rat heart, with a 3-hour hypothermic 10 degrees C cardioplegic arrest period. Cardioplegic solutions tested were the St. Thomas' Hospital No. 2 and a modified Krebs-Henseleit cardioplegic solution. Glucose (11 mmol/L) was beneficial when multidose cardioplegia was administered every 30 minutes. Including glucose in Krebs-Henseleit cardioplegic solution improved postischemic recovery of aortic output from 57.0% +/- 1.8% to 65.8% +/- 2.2%; p less than 0.025. The addition of glucose to St. Thomas' Hospital No. 2 cardioplegic solution improved aortic output from 74.6% +/- 1.9% to 87.4% +/- 1.9%; p less than 0.005. Furthermore, a dose-response curve showed that a glucose concentration of 20 mmol/L gave no better recovery than 0 mmol/L, and glucose in St. Thomas Hospital No. 2 cardioplegic solution was beneficial only in the range of 7 to 11 mmol/L. In addition, we showed that multidose cardioplegia was beneficial independent of glucose. Multidose St. Thomas' Hospital No. 2 cardioplegia, as opposed to single-dose cardioplegia, improved aortic output recovery from 57.4% +/- 5.2% to 74.6% +/- 1.9%; p less than 0.025, and with St. Thomas' Hospital No. 2 cardioplegic solution plus glucose (11 mmol/L) aortic output recovery improved from 65.9% +/- 2.9% to 87.4% +/- 1.9%; p less than 0.005. Hence, at least in this screening model, the St. Thomas' Hospital cardioplegic solution should contain glucose in the range of 7 mmol/L to 11 mmol/L, provided multidose cardioplegia is given. We cautiously suggest extrapolation to the human heart, on the basis of supporting clinical arguments that appear general enough to apply to both rat and human metabolisms.     

Endothelial cell toxicity of solid-organ preservation solutions

Endothelial cell damage caused by myocardial cardioplegic solutions (Bretschneider HTK and St. Thomas' Hospital No. 2) or renal and hepatic cold storage solutions (modified Collins and University of Wisconsin solution) was assessed in monolayer cultures of adult human venous endothelial cells at 4 degrees to 10 degrees C with phase-contrast microscopy. St. Thomas' Hospital solution caused the cells to contract, resulting in disruption of monolayer integrity and opening of intercellular gaps, and resulted in a 24-hour postexposure survival of 51.0% +/- 2.4%. Bretschneider HTK solution altered cellular morphology less and produced the best postexposure survival (80.2% +/- 2.6%; p less than 0.001). Although morphology was altered the least with University of Wisconsin solution, postexposure survival with this solution, which was similar to that with modified Collins solution, was superior to that with St. Thomas' (p less than 0.01) but inferior to that with Bretschneider HTK (p less than 0.05). The superior protection provided by Bretschneider HTK was due to its additives histidine, tryptophan, and KH-2-oxygluterate (p less than 0.005), and to its low chloride content (p less than 0.005). Furthermore, modifying St. Thomas' solution by decreasing its chloride content improved cell survival to 71.2% +/- 2.3% (p less than 0.001). Normothermic (37 degrees C) exposure to Bretschneider HTK, modified Collins, and University of Wisconsin solution was cytotoxic, whereas normothermic exposure to St. Thomas' cardioplegia was not. In conclusion, the preservation solution that is the least harmful to endothelial cells at hypothermia is Bretschneider HTK cardioplegic solution.     

Comparison of three cardioplegic solutions during hypothermic ischemic arrest in neonatal blood-perfused rabbit hearts

Inadequate myocardial preservation continues to be an important cause of postoperative morbidity and mortality after pediatric cardiac operations. To investigate methods of improving preservation in neonatal myocardium, we compared three cardioplegic solutions with topical hypothermia during 120 minutes of ischemic arrest in isolated, blood-perfused, neonatal rabbit hearts. Topical hypothermia (15 degrees C) without cardioplegia resulted in 71% +/- 5% recovery of preischemic contractile function. A high potassium (30 mEq/L) cardioplegic solution resulted in a 76% +/- 6% recovery of function, not significantly different from that obtained with hypothermia alone. In contrast, the St. Thomas' Hospital and H?pital Lariboisiere cardioplegic solutions resulted in recoveries of 89% +/- 6% and 88% +/- 7%, respectively, both of which were significantly greater (p less than 0.001) than recoveries obtained with the high potassium solution or hypothermia alone. Thus the cardioplegic solutions used at St. Thomas' Hospital and H?pital Lariboisiere provided excellent protection during 2 hours of hypothermic ischemic arrest in neonatal rabbit hearts and resulted in functional recovery superior to that achieved with hypothermia alone or with the high potassium cardioplegic solution.     

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.     

Transient hypocalcemic reperfusion does not improve postischemic recovery in the rat heart after preservation with St. Thomas' Hospital cardioplegic solution.

We used the isolated perfused working rat heart to investigate the effects of transient hypocalcemic reperfusion after cardioplegic arrest with the St. Thomas' Hospital cardioplegic solution and 25 minutes of global normothermic (37 degrees C) ischemia. Hearts were reperfused (Langendorff mode) transiently (20 minutes) with solutions containing various concentrations of calcium; this was followed by 30 minutes of reperfusion with standard (1.4 mmol/L, the physiologic concentration) calcium buffer (10 minutes in the Langendorff mode and 20 minutes in the working mode). Recovery of cardiac output in control hearts (calcium concentration 1.4 mmol/L throughout) was 51.7% +/- 4.6%; in hearts transiently reperfused with hypocalcemic buffer (0.25, 0.5, 0.75, or 1.0 mmol/L) the recoveries of cardiac output were 49.3% +/- 6.4%, 52.2% +/- 7.2%, 58.7% +/- 3.2%, and 47.2 +/- 4.7%, respectively (all not significant), whereas recovery was only 14.7% +/- 2.8% (p less than 0.05) in hearts transiently reperfused with calcium 0.1 mmol/L. Creatine kinase leakage was significantly (p less than 0.05) greater in the group reperfused with calcium 0.1 mmol/L, but it did not vary significantly between the other groups. Tissue high-energy phosphate content was similar and in the normal range in all groups except for the group reperfused with calcium 0.1 mmol/L. In further experiments, the duration of hypocalcemic (0.5 mmol/L) reperfusion was varied (0, 5, 10, 15, 20, or 30 minutes). No significant differences in recovery of cardiac output were observed (58.2% +/- 5.0%, 52.3% +/- 5.7%, 52.0% +/- 8.2%, 61.2% +/- 5.0%, 62.2% +/- 4.3%, and 66.2% +/- 3.2%, respectively). In additional studies, the standard calcium concentration (1.4 mmol/L) used before and after ischemia was replaced by hypercalcemic solution (2.5 mmol/L). Despite this, transient (10 minutes) hypocalcemic (0.5 mmol/L) reperfusion did not improve recovery. Finally, studies were undertaken with a longer duration of ischemia (40 minutes), and although recovery of cardiac output in the hypocalcemic group (0.5 mmol/L for 10 minutes) tended to be higher than in the control group (29.7% +/- 4.8% versus 18.5% +/- 4.9%, respectively), statistical significance was not achieved. We conclude that in these studies transient hypocalcemic reperfusion did not afford any additional protection over and above that afforded by cardioplegia alone.     

Myocardial protection with oxygenated esmolol cardioplegia during prolonged normothermic ischemia in the rat

OBJECTIVE: We previously showed that arrest with multidose infusions of high-dose (1 mmol/L) esmolol (an ultra-short-acting beta-blocker) in oxygenated Krebs-Henseleit buffer (esmolol cardioplegia) provided complete myocardial protection after 40 minutes of normothermic (37 degrees C) global ischemia in isolated rat hearts. In this study we investigated the importance of oxygenation for protection with esmolol cardioplegia, compared it with that of St Thomas' Hospital cardioplegia, and determined the protective efficacy of multidose esmolol cardioplegia for extended ischemic durations. METHODS: Isolated rat hearts (n = 6/group) were perfused in the Langendorff mode at constant pressure (75 mm Hg) with oxygenated Krebs-Henseleit bicarbonate buffer at 37 degrees C. The first part of the first study had four groups: (i) multidose (every 15 minutes) oxygenated (95% oxygen/5% carbon dioxide) Krebs-Henseleit buffer during 60 minutes of global ischemia, (ii) multidose deoxygenated (95% nitrogen/5% carbon dioxide) Krebs-Henseleit buffer during 60 minutes of global ischemia, (iii) multidose oxygenated esmolol cardioplegia during 60 minutes of global ischemia, and (iv) multidose deoxygenated esmolol cardioplegia during 60 minutes of global ischemia. The second part of the first study had three groups: (v) multidose St Thomas' Hospital solution during 60 minutes of global ischemia, (vi) multidose oxygenated St Thomas' Hospital solution during 60 minutes of global ischemia, and (vii) multidose oxygenated esmolol cardioplegia during 60 minutes of global ischemia. In the second study, hearts were randomly assigned to 60, 75, 90, or 120 minutes of global ischemia and at each ischemic duration were subjected to multidose oxygenated constant flow or constant pressure infusion of (i) Krebs-Henseleit buffer (constant flow), (ii) Krebs-Henseleit buffer (constant pressure), (iii) esmolol cardioplegia (constant flow), or (iv) esmolol cardioplegia (constant pressure). All hearts were reperfused for 60 minutes, and recovery of function was measured. RESULTS: Multidose infusion of oxygenated esmolol cardioplegia completely protected the hearts (97% +/- 5%) after 60 minutes of 37 degrees C global ischemia. Deoxygenated esmolol cardioplegia was significantly less protective (45% +/- 8%). Oxygenation of St Thomas' Hospital solution did not alter its protective efficacy in this study (70% +/- 4% vs 69% +/- 7%). Infusion of esmolol cardioplegia at constant pressure provided complete protection for 60, 75, and 90 minutes (104% +/- 5%, 95% +/- 5%, and 95% +/- 3%, respectively), whereas protection with constant-flow esmolol cardioplegic infusion was significantly decreased at ischemic durations longer than 60 minutes. This decrease in efficacy of constant-flow esmolol cardioplegia was associated with increasing coronary perfusion pressure leading to myocardial injury. CONCLUSIONS: Oxygenation of esmolol cardioplegia (Krebs-Henseleit buffer plus 1.0 mmol/L esmolol) was essential for optimal myocardial protection. Multidose infusion of oxygenated esmolol cardioplegia provided good myocardial protection during extended periods of normothermic ischemia. Esmolol cardioplegia may provide an efficacious alternative to hyperkalemia.     

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.     

Cultured neonatal rat cardiomyocytes and 99mTc-sestamibi to assess the direct effects of cardioplegia.

The efficacy of cardioplegia in neonatal myocardial protection is still a matter of debate. 99mTc-sestamibi cellular accumulation reflects sarcolemmal and mitochondrial electrical gradients. It was used to monitor the direct effects of two cardioplegic solutions, modified St Thomas' Hospital and Bretschneider, on normoxic and metabolically-inhibited cultured cells. Cellular accumulation of 99mTc-sestamibi, expressed by the ratio between intra and extra cellular concentrations, was assessed in three different sets of neonatal rat cardiomyocytes. Cells were either treated with different concentrations of modified St Thomas' solution (50, 75, 100%), they were treated or recovering from a treatment with modified St Thomas and Bretschneider solutions at 50% concentrations, or were recovering from treatment with modified St Thomas' and Bretschneider solution at 50% concentrations mixed with metabolic inhibitors. Cardioplegia depressed the tracer accumulation in a concentration-dependent manner. This effect was independent of the type of cardioplegia (120-min uptake, as a percentage of control values, modified St Thomas' 68+/-12 and Bretschneider 59+/-7) and was rapidly reversible. Cardioplegia was unable to prevent the depression of tracer accumulation induced by metabolic inhibitors and even induced a deleterious effect (120-min uptake, as a percentage of control values, metabolic inhibitors 69+/-12, metabolic inhibitors + modified St Thomas 38+/-14, metabolic inhibitors + Bretschneider 43+/-6) during recovery after 30 min of metabolic inhibition. It was concluded that cardioplegia has an apparent detrimental effect on neonatal cardiomyocytes accumulation of 99mTc-sestamibi during recovery from an ischaemic-like insult.     

Creatine phosphate: an additive myocardial protective and antiarrhythmic agent in cardioplegia

The potential for enhancing myocardial protection by adding high-energy phosphates to cardioplegic solutions was investigated in a rat heart model of cardiopulmonary bypass and ischemic arrest. Creatine phosphate (CP) was evaluated as an additive to the St. Thomas' Hospital cardioplegic solution. Dose-response studies (CP 0 to 50 mmol/L) revealed 10.0 mmol/L as the optimal concentration which improved recovery of aortic flow and cardiac output after a 40 minute period of normothermic (37 degrees C) ischemic arrest from 21.2% +/- 5.4% and 32.8% +/- 4.6% in the CP-free control group to 82.5% +/- 3.7% and 82.6% +/- 4.2% (p less than 0.001), respectively. Creatine kinase (CK) leakage was reduced by 68.7% (p less than 0.001) in the CP group. With hypothermic (20 degrees C) ischemia (240 minutes) and multidose (every 30 minutes) cardioplegia, recoveries of aortic flow and cardiac output were improved from 33.1% +/- 8.4% and 42.2% +/- 7.7% in the CP-free control group to 77.9% +/- 4.2% and 79.6% +/- 4.3% (p less than 0.001), respectively, in the drug group. In addition to improving function and decreasing CK release, CP reduced reperfusion arrhythmias, significantly decreasing the time between cross-clamp removal and return of regular rhythm and also completely obviating the need for electrical defibrillation. 51Chromium-ethylenediaminetetraacetic acid (51Cr-EDTA), an extracellular space marker, was used to study the disappearance of CP from the cardioplegic solution during its stasis in the heart. Upon reperfusion, two thirds of the infused dose appeared unchanged in the coronary effluent; the remainder was either degraded or accumulated by the myocardium. Despite its alleged inability to enter the myocardial cell, exogenous CP exerts potent protective and antiarrhythmic effects when added to the St. Thomas' Hospital cardioplegic solution. Although the mechanism of action remains to be elucidated, it may involve binding or uptake of the drug.     

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.     

Effect of oxygenation and consequent pH changes on the efficacy of St. Thomas' Hospital cardioplegic solution

The hypothesis tested is that shifts in pH, induced when a cardioplegic solution is oxygenated, can be detrimental. We added either 100% nitrogen, 95% nitrogen and 5% carbon dioxide, 100% oxygen, or 95% oxygen and 5% carbon dioxide to the cardioplegic solution (St. Thomas' Hospital No. 2 plus glucose 11 mmol/L), and determined postischemic recovery of isolated rat hearts after 3 hours of 10 degrees C cardioplegic protected ischemia. Hearts were arrested and reinfused every 30 minutes throughout the ischemic period with cardioplegic solution. When 5% carbon dioxide was added to nitrogen, the pH of the cardioplegic solution decreased from 9.1 (100% nitrogen) to 7.0 (95% nitrogen: 5% carbon dioxide), a change associated with improved postischemic functional recovery. Aortic output improved from 52.3% +/- 2.7% to 63.9% +/- 2.8%, p less than 0.05, and cardiac output from 60.8% +/- 3.6% to 75.4% +/- 3.3%, p less than 0.01. This improvement was associated with diminished efflux of lactate during ischemia but increased postischemic release of lactate dehydrogenase. When nitrogen was replaced with oxygen, the addition of 5% carbon dioxide resulted in a similar decrease of pH, which again was associated with improved postischemic functional recovery. Aortic output improved from 66.3% +/- 2.8% (100% oxygen) to 88.9% +/- 3.7% (95% oxygen: 5% carbon dioxide), p less than 0.005, and cardiac output from 75.3% +/- 4.1% to 88.9% +/- 2.4%, p less than 0.01. The efflux of lactate during ischemia and the postischemic release of lactate dehydrogenase were similar in both groups. Furthermore, provision of additional oxygen with perfluorocarbons in an electrolyte solution identical to the St. Thomas' Hospital plus glucose solution and oxygenated with 95% oxygen: 5% carbon dioxide conferred no extra protection. In conclusion, the St. Thomas' Hospital No. 2 plus glucose cardioplegic solution should be oxygenated but with 95% oxygen: 5% carbon dioxide and not 100% oxygen because of the additive effect of a relatively "acidotic" pH.     

Endothelial dysfunction caused by University of Wisconsin preservation solution in the rat heart. The importance of temperature.

The superiority of the University of Wisconsin solution over routinely used crystalloid cardioplegic solutions for myocardial preservation has been demonstrated in animal studies. We have investigated the effect of the University of Wisconsin solution at different temperatures on endothelial function by examining its influence on 5-hydroxytryptamine- and nitroglycerin-induced increase in coronary flow in the isolated rat heart. Thirty-eight rat hearts were perfused on a modified Langendorff preparation. In the control experiments, there was no significant difference in the percentage increase in coronary flow induced by 5-hydroxytryptamine and nitroglycerin after 30 minutes of perfusion with Krebs-Henseleit buffer (n = 6). Continuous infusion of the University of Wisconsin solution for 30 minutes at 4 degrees C or at 10 degrees C did not alter the 5-hydroxytryptamine or nitroglycerin response. However, infusion at 15 degrees C reduced the 5-hydroxytryptamine-induced vasodilation, while at 20 degrees C the 5-hydroxytryptamine response was converted to vasoconstriction without a significant change in nitroglycerin effect (15 degrees C, 5-hydroxytryptamine, before: 30.2% +/- 1.5%, after: 6.0% +/- 1.0%, nitroglycerin, before: 28.8% +/- 1.3%, after: 31.2% +/- 1.8%; 20 degrees C, 5-hydroxytryptamine, before: 32.2% +/- 2.5%, after: -23.8% +/- 3.6%, nitroglycerin, before: 30.3% +/- 1.9%, after: 33.5% +/- 1.7%). Coronary vascular resistance in the control experiments rose from 55.0 +/- 2.5 cm H2O/ml/gm/min to 58.4 +/- 2.3 cm H2O/ml/gm/min (p = not significant). The increase after University of Wisconsin solution infusion at 4 degrees C and at 10 degrees C was similarly not significant. Coronary vascular resistance increased significantly following infusion of University of Wisconsin solution at 15 degrees C (p < 0.001) or at 20 degrees C (p < 0.01). We conclude that University of Wisconsin solution produces temperature-dependent endothelial dysfunction in the isolated rat heart.     

Superior protective effect of low-calcium, magnesium-free potassium cardioplegic solution on ischemic myocardium. Clinical study in comparison with St. Thomas' Hospital solution

The protective effect of low-calcium, magnesium-free potassium cardioplegic solution on ischemic myocardium has been assessed in adult patients undergoing heart operations. Postreperfusion recovery of cardiac function and electrical activity was evaluated in 34 patients; 16 received low-calcium, magnesium-free potassium cardioplegic solution (group I) and 18 received St. Thomas' Hospital solution, which is enriched with calcium and magnesium (group II). There were no significant differences between the two groups in age, sex, body weight, and New York Heart Association functional class. Aortic occlusion time (107.3 +/- 46.8 minutes versus 113.6 +/- 44.3 minutes), highest myocardial temperature during elective global ischemia (11.5 degrees C +/- 3.1 degrees C versus 9.3 degrees C +/- 3.2 degrees C), and total volume of cardioplegic solution (44.2 +/- 20.5 ml/kg versus 43.4 +/- 17.6 ml/kg) were also similar in the two groups. On reperfusion, electrical defibrillation was required in four cases (25.5%) in group I and in 15 cases (83.3%) in group II (p less than 0.005), and bradyarrhythmias were significantly more prevalent in group II (6.3% versus 44.4%; p less than 0.05). Serum creatine kinase MB activity at 15 minutes of reperfusion (12.3 +/- 17.0 IU/L versus 42.6 +/- 46.1 IU/L; p less than 0.05) and the dose of dopamine or dobutamine required during the early phase of reperfusion (1.8 +/- 2.5 micrograms/kg/min versus 6.1 +/- 3.3 micrograms/kg/min; p less than 0.0002) were both significantly greater in group II. Postischemic left ventricular function, as assessed by percent recovery of the left ventricular end-systolic pressure-volume relationship in patients who underwent aortic valve replacement alone, was significantly better in group I (160.4% +/- 45.5% versus 47.8% +/- 12.9%; p less than 0.05). Serum level of calcium and magnesium ions was significantly lower in group I. Thus low-calcium, magnesium-free potassium cardioplegic solution provided excellent protection of the ischemic heart, whereas St. Thomas' Hospital solution with calcium and magnesium enabled relatively poor functional and electrical recovery of the heart during the early reperfusion period. These results might be related to differing levels of extracellular calcium and magnesium on reperfusion.     

Comparison of the protective properties of four clinical crystalloid cardioplegic solutions in the rat heart

Although few surgeons dispute the benefits of high-potassium crystalloid cardioplegia, objective comparison of the efficacy of various formulations is difficult in clinical practice. We compared four commonly used cardioplegic solutions in the isolated rat heart (N = 6 for each solution) subjected to 180 minutes of hypothermic (20 degrees C) ischemic arrest with multidose cardioplegia (3 minutes every half-hour). The clinical solutions studied were St. Thomas' Hospital solution, Tyers' solution, lactated Ringer's solution with added potassium, and a balanced saline solution with glucose and potassium. Postischemic recovery of function was expressed as a percentage of preischemic control values. Release of creatine kinase during reperfusion was measured as an additional index of protection. St. Thomas' Hospital solution provided almost complete recovery of all indexes of cardiac function following ischemia including 88.1 +/- 1.6% recovery of aortic flow, compared with poor recovery for the Tyers', lactated Ringer's, and balanced saline solutions (20.6 +/- 6.5%, 12.5 +/- 6.4%, and 9.6 +/- 4.2%, respectively) (p less than 0.001). Spontaneous defibrillation was rapid (less than 1 minute) and complete (100%) in all hearts in the St. Thomas' Hospital solution group, but much less satisfactory with the other formulations. Finally, St. Thomas' Hospital solution had a low postischemic level of creatine kinase leakage, contrasting with significantly higher enzyme release in the other solutions tested (p less than 0.001). Although differences in composition are subtle, all potassium crystalloid cardioplegic solutions are not alike in the myocardial protection they provide. Comparative studies under controlled conditions are important to define which formulation is superior for clinical application.