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.     

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.     

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.     

Improved myocardial protection by oxygenation of St. Thomas' Hospital cardioplegic solutions. Studies in the rat

The effect of oxygenation (100% oxygen) of the St. Thomas' Hospital cardioplegic solutions No. 1 (MacCarthy) and No.2 (Plegisol, Abbott Laboratories, North Chicago, Ill.) was examined in the isolated working rat heart subjected to long periods (3 hours for studies with solution No. 1 and 4 hours for studies with solution No. 2) of hypothermic (20 degrees C) ischemic arrest with multidose (every 30 minutes) cardioplegic infusion. At the aortic infusion point the oxygen tension of the oxygenated solutions (measured at 20 degrees C) was in the range of 320 to 560 mm Hg whereas that of the nonoxygenated solutions was less than 150 mm Hg. Twenty hearts (10 oxygenated and 10 nonoxygenated) were studied for each solution. The studies with solution No. 1 demonstrated that oxygenation led to a significant (p less than 0.05) reduction in the incidence of persistent ventricular fibrillation during postischemic reperfusion. Oxygenation of the cardioplegic solution also improved postischemic functional recovery so that the recovery of aortic flow was improved from 18.7% +/- 8.9% (of its preischemic control level) in the nonoxygenated group to 54.6% +/- 6.6% in the oxygenated group (p less than 0.025). Creatine kinase leakage was also significantly reduced from 27.5 +/- 4.8 to 9.9 +/- 0.6 IU/15 min/gm dry weight (p less than 0.005). Studies with solution No. 2 indicated that protection was better than with solution No. 1, even in the absence of oxygenation. A better degree of functional recovery was obtained after 4 hours of arrest with solution No. 2 than that obtained after only 3 hours of arrest with solution No. 1, and persistent ventricular ventricular fibrillation was never observed with solution No. 2. However, despite the superior performance with solution No. 2, further improvements could be obtained by oxygenation, with that time from the onset of reperfusion to the return of regular sinus rhythm being reduced from 55 +/- 8 to 35 +/- 2 seconds (p less than 0.01), postischemic recovery of aortic flow increasing from 59.8% +/- 7.4% to 85.7% +/- 2.5% (p less than 0.005), and creatine kinase leakage being reduced from 38.1 +/- 7.3 to 16.2 +/- 1.5 IU/15 min/gm dry weight (p less than 0.005). It is concluded that oxygenation of the St. Thomas' Hospital cardioplegic solutions improves their ability to protect the heart against long periods of ischemia and that this is manifested by improved postischemic electrical stability, functional recovery, and reduced creatine kinase leakage.     

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.     

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.     

Mechanisms of myocardial protection by adenosine-supplemented cardioplegic solution: myofilament and metabolic responses

OBJECTIVE: Adenosine supplementation of cardioplegic solutions in cardiac operations improves postarrest myocardial recovery after cardioplegic arrest and reperfusion; however, the mechanism of the action of adenosine remains unknown. We tested the hypotheses that adenosine-supplemented cardioplegic solution improves myofibrillar protein cooperative interaction and increases myocardial anaerobic glycolysis. METHODS: The hearts of male Sprague-Dawley rats were randomized to undergo 120 minutes of cardioplegic arrest with 1 of 3 cardioplegic solutions: (1) St Thomas' Hospital No. 2 cardioplegic solution (St Thomas group), (2) St Thomas' Hospital No. 2 cardioplegic solution plus adenosine (100 micromol/L) (adenosine group), and (3) St Thomas' Hospital No. 2 cardioplegic solution plus adenosine (100 micromol/L) plus the nonspecific adenosine receptor antagonist 8-p -sulfophenyltheophylline (50 micromol/L) (sulfophenyltheophylline group). A fourth group of hearts underwent no cardioplegic arrest. RESULTS: Systolic and diastolic functional recovery was improved in the adenosine group compared with that in the other two groups, independent of coronary flow. Adenosine supplementation of cardioplegic solution prevented the decrease in myofibrillar protein cooperative interaction seen after cardioplegic arrest and reperfusion (St Thomas and sulfophenyltheophylline groups). Adenosine-supplemented cardioplegic solution also caused significantly increased anaerobic glycolysis during cardioplegic arrest. These responses were blocked in the sulfophenyltheophylline group. CONCLUSIONS: The changes in myocardial glycolytic activity and myofilament cooperativity coincided with functional recovery in the three cardioplegia groups and may represent mechanisms underlying protection with adenosine-supplemented cardioplegic solution.     

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.     

Superior qualities of University of Wisconsin solution for ex vivo preservation of the pig heart.

The components of the University of Wisconsin solution have the potential to enhance and extend heart preservation. We have evaluated University of Wisconsin solution by comparing it with St. Thomas' Hospital cardioplegic solution in the isolated pig heart subjected to 8 hours of ischemia at 4 degrees C (n = 6 in each). The hearts were perfused ex vivo with enriched autologous blood for the control and the postpreservation assessments. Morphologic, metabolic, and functional evaluations were performed. Left and right ventricular function as assessed by the slope values of systolic and diastolic pressure-volume relationships of isovolumically contracting isolated heart was better preserved by University of Wisconsin solution (percent reduction: left ventricular systolic, 52.4% +/- 5.5% versus 17.7% +/- 6.7% [p less than 0.001]; right ventricular systolic, 125.6% +/- 46.4% versus 65.5% +/- 31.4% [p less than 0.05]; right ventricular diastolic, 112.3% +/- 48.7% versus 40.2% +/- 31.3% [p less than 0.02] after St. Thomas' Hospital and University of Wisconsin preservation, respectively). Postischemic recovery of left ventricular rate of rise of pressure and myocardial oxygen consumption were significantly improved after University of Wisconsin preservation (percent reduction, rate of rise of pressure: St. Thomas' Hospital 39.3% +/- 8.1%; University of Wisconsin 18.1% +/- 4.6%; percent reduction, myocardial oxygen consumption St. Thomas' Hospital 55.1% +/- 6.9%, University of Wisconsin 24.8% +/- 6.7%; p less than 0.001). Microvascular functional integrity as assessed by coronary vascular resistance was well maintained throughout the postischemic period and was similar to the preischemic control value in the University of Wisconsin group. By contrast, a significant increase was found at the beginning of postpreservation reperfusion, with a progressive rise thereafter in the St. Thomas' Hospital group (p less than 0.001). Preservation of myocardial adenosine triphosphate was improved and energy charge was unchanged after 8 hours of ischemia and reperfusion in the University of Wisconsin-preserved hearts compared with the St. Thomas' Hospital-preserved hearts (p less than 0.01). Electron microscopic examination revealed substantially better preservation of the contractile apparatus after preservation with University of Wisconsin solution. Myocytes from hearts receiving University of Wisconsin solution, unlike those given St. Thomas' Hospital solution, showed relaxed myofibrils with prominent I-bands. We conclude that University of Wisconsin solution has the potential to improve the preservation of the heart and possibly prolong the ischemic period in clinical cardiac transplantation.     

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.     

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.     

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)     

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.     

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 myocardial protective effects between GIK solution and St. Thomas solution by use of canine isolated heart-lung preparations

The myocardial protection afforded by GIK solution, widely used as cardioplegic solution in this country, was compared with that provided by St. Thomas solution or oxygenated St. Thomas solution. Eighteen isolated heart-lung preparations of dogs were made and their hearts were subjected to 3 hours cold (4 degrees C) cardioplegic arrest. GIK group hearts (n = 6) received 20 ml/kg of GIK solution at the time of aortic cross-clamp perfused through the aortic root and were subsequently given 10 ml/kg of GIK solution every 30 minutes. St. Thomas group hearts (n = 6) and oxygenated St. Thomas group hearts (n = 6) were treated identically except that cardioplegic solution were St. Thomas solution or fully oxygenated one. Four hearts of GIK group showed ventricular fibrillation immediately after reperfusion that required DC countershock. Temporary A-V block was recognized in two hearts. In the other two groups, however, neither ventricular fibrillation nor A-V block was found. Heart rate, coronary flow, aortic flow and LVSW were measured before arrest and after 60 minutes of reperfusion (mean aortic pressure 70 mmHg, left atrial pressure 4 mmHg). Post reperfusion % recovery rates (post-reperfusion/before arrest) of heart rate, coronary flow, aortic flow and LVSW (mean value +/- standard deviation) were 93.4 +/- 10.32%, 104.6 +/- 24.91%, 18.8 +/- 8.54%, 32.6 +/- 6.12% respectively for GIK group, 81.4 +/- 6.50%, 125.9 +/- 15.23%, 35.4 +/- 9.91%, 56.3 +/- 12.90% for St. Thomas group and 83.1 +/- 8.40%, 121.6 +/- 16.92%, 47.0 +/- 7.89%, 69.1 +/- 9.71% for oxygenated St. Thomas group. St. Thomas and oxygenated St. Thomas groups revealed significantly (p less than 0.05, p less than 0.01 respectively) more excellent functional preservation than GIK group. Intramyocardial pH was also measured by use of glass needle pH electrode punctured into the anterior interventricular septum. Preischemic intramyocardial pH (at 37 degrees C) was 7.49 +/- 0.106 in GIK group, 7.48 +/- 0.113 in St. Thomas group and 7.43 +/- 0.114 in oxygenated St. Thomas group. During 3 hours of cardioplegic arrest, intramyocardial pH (at 4 degrees C) decreased to 6.84 +/- 0.101 in GIK group, 7.03 +/- 0.088 in St. Thomas group and 7.23 +/- 0.239 in oxygenated St. Thomas group, which was significantly higher than GIK group (p less than 0.01). Therefore oxygenated St. Thomas solution was found to maintain more favorable energy supply to ischemic myocardium. These results clearly evidenced that St. Thomas and oxygenated St. Thomas solutions would provide more effective myocardial protection during ischemic arrest than GIK solution.     

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.     

Enhancement of crystalloid cardioplegic protection against global normothermic ischemia by superoxide dismutase plus catalase but not diltiazem in the isolated, working rat heart

Oxygen-derived free radicals and intracellular calcium overload have been implicated as mediators of myocardial ischemia/reperfusion injury. We hypothesized that free radical scavengers or calcium channel blockers could enhance the protection afforded the isolated, working rat heart by crystalloid cardioplegia against this type of injury at 37 degrees C. Hearts from 42 male rats in seven groups (n = 6) were studied in an isolated, working heart preparation measuring aortic flow (ml/min/gm dry wt), peak systolic pressure (mm Hg), coronary artery flow (ml/min/gm dry wt), and calculated coronary vascular resistance (dyne.sec.cm-5/gm dry wt). Creatine kinase and lactate dehydrogenase release were measured before ischemia and at various times during the postischemic reperfusion period. Time-matched control hearts (group 1) were perfused for 2 hours. After finding that 30 minutes of ischemia and 10 minutes of reperfusion (group 2) produced significant (p less than 0.01) functional impairment that was completely protected (group 3) by a preischemic bolus of St. Thomas' Hospital cardioplegic solution, we again found significant (p less than 0.01) functional impairment after 40 minutes of ischemia and 10 minutes (group 4) or 20 minutes (group 5) of reperfusion despite a preischemic bolus of St. Thomas' Hospital cardioplegic solution. Diltiazem (10 mg/L) plus St. Thomas' Hospital cardioplegic solution (group 6) did not significantly (p less than 0.01) enhance functional recovery. Addition of superoxide dismutase plus catalase (200 microns/ml) (group 7) produced marked improvement in functional recovery that did not differ significantly (p less than 0.01) from control results (group 1). The creatine kinase and lactate dehydrogenase data strongly supported the preceding functional data. Coronary flow and vascular resistance were not significantly (p less than 0.01) changed from control values in any group. We conclude that the addition of superoxide dismutase and catalase but not diltiazem to St. Thomas' Hospital cardioplegic solution can significantly enhance myocardial protection against normothermic ischemia/reperfusion injury. This implicates oxygen-derived free radicals as mediators of this type of injury.     

Oxygen-derived free radical scavengers for amelioration of reperfusion damage in heart transplantation

In this study we tried to define the possible benefits of the oxygen-derived free radical scavengers after 3 hours of cold myocardial global ischemia, as required in the setting of cardiac transplantation. Twenty-one pig hearts were harvested after preservation with a cold cardioplegic solution (St. Thomas' Hospital solution) and topical cooling. Normothermic reperfusion with blood was achieved with a special heart-lung machine preparation, which allows the heart to beat in a working or nonworking mode. Twelve hearts served as control hearts (group I), and nine (group II) were subjected to superoxide dismutase and catalase. Superoxide dismutase was applied at a dose of 40 U/ml of cardioplegic solution and 1500 U/kg body weight with the start of reperfusion. Catalase was added to the cardioplegic solution in a dose of 100 U/kg and 3500 U/kg body weight with the start of reperfusion. After 15 minutes of retrograde reperfusion, both left ventricular developed pressure and its first derivative were significantly higher in group II (137 +/- 7.6 mm Hg, 2467 +/- 162 mm Hg/sec) than in group I (105 +/- 6 mm Hg, 1676 +/- 231 mm Hg/sec, p less than 0.05 for each). In addition, a considerably higher coronary blood flow was observed in group II throughout the 180-minute period of reperfusion (p = 0.047). We therefore conclude that the combined administration of superoxide dismutase and catalase during the initial period of cardioplegic arrest and during early reperfusion of donor hearts submitted to 3 hours of cold ischemia has a beneficial effect on myocardial performance.     

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-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.