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.     

The effectiveness of University of Wisconsin solution on prolonged myocardial protection as assessed by phosphorus 31-nuclear magnetic resonance spectroscopy and functional recovery.

The effectiveness of the University of Wisconsin solution on extended myocardial preservation was examined in this study using phosphorus 31-nuclear magnetic resonance spectroscopy. Isolated perfused rat hearts were arrested and stored in four preservation solutions: group 1, modified Krebs-Henseleit solution; group 2, modified St. Thomas' Hospital solution; group 3, oxygenated modified St. Thomas' Hospital solution containing 11 mmol/L glucose; and group 4, University of Wisconsin solution. The changes in myocardial high energy phosphate profiles and the intracellular pH values were measured during 12 hours of cold (4 degrees C) global ischemia and 90 minutes of normothermic reperfusion. Following ischemia, the hearts were assessed for hemodynamic recovery and myocardial water content. During ischemia, adenosine triphosphate depletion was observed in all groups; however, after 5 hours of ischemia, the adenosine triphosphate levels were significantly higher in group 3 compared with the other groups (adenosine triphosphate levels at 6 hours in mumol/gm dry weight: group 3, 7.6; group 4, 3.2; group 2, < 1; p < 0.025). The tissue water content at the end of ischemia was lower with the University of Wisconsin solution compared with the modified St. Thomas' Hospital solution or the oxygenated modified St. Thomas' Hospital solution (in ml/gm dry weight: group 4, 3.0; group 2, 4.4; group 3, 3.9; p < 0.05). The adenosine triphosphate repletion during reperfusion was greater with the University of Wisconsin solution compared with the modified St. Thomas' Hospital solution or the oxygenated modified St. Thomas' Hospital solution (12 mumol/gm dry weight in group 4; 8.1 in group 2; 9.0 in group 3; p < 0.05). Similar findings were obtained for the recovery of left ventricular pressure (in percent of preischemic control: group 4, 70%; group 2, 42%; group 3, 52%; p < 0.01) and coronary flow (group 4, 61%; group 2, 49%; group 3, 49%; p < 0.05). These data suggest that preservation with the University of Wisconsin solution affords improved hemodynamic recovery, enhanced adenosine triphosphate repletion, and reduced tissue edema upon reperfusion; however, oxygenated St. Thomas' Hospital solution with glucose is associated with the preservation of higher myocardial adenosine triphosphate levels during prolonged cold global ischemia. In conclusion, these data indicate that the University of Wisconsin solution might improve graft tolerance of ischemia in clinical heart transplantation.     

Age-related changes in the ability of hypothermia and cardioplegia to protect ischemic rabbit myocardium

Hypothermia combined with pharmacologic cardioplegia protects the globally ischemic adult heart, but this benefit may not extend to children; poor postischemic recovery of function and increased mortality may result when this method of myocardial protection is used in children. The relative susceptibilities to ischemia-induced injury modified by hypothermia alone and by hypothermia plus cardioplegia were assessed in isolated perfused immature (7- to 10-day-old) and mature (6- to 24-month-old) rabbit hearts. Hearts were perfused aerobically with Krebs-Henseleit buffer in the working mode for 30 minutes, and aortic flow was recorded. This was followed by 3 minutes of hypothermic (14 degrees C) coronary perfusion with either Krebs or St. Thomas' Hospital cardioplegic solution No. 2, followed by hypothermic (14 degrees C) global ischemia (mature hearts 2 and 4 hours; immature hearts 2, 4, and 6 hours). Hearts were reperfused for 15 minutes in the Langendorff mode and 30 minutes in the working mode, and recovery of postischemic function was measured. Hypothermia alone provided excellent protection of the ischemic immature rabbit heart, with recovery of aortic flow after 2 and 4 hours of ischemia at 97% +/- 3% and 93% +/- 4% (mean +/- standard deviation) of the preischemic value. Mature hearts protected with hypothermia alone recovered only minimally, with 22% +/- 16% recovery of preischemic aortic flow after 2 hours; none were able to generate flow at 4 hours. St. Thomas' Hospital solution No. 2 improved postischemic recovery of aortic flow after 2 hours of ischemia in mature hearts from 22% +/- 16% to 65% +/- 6% (p less than 0.05), but actually decreased postischemic aortic flow in immature hearts from 97% +/- 3% to 86% +/- 10% (p less than 0.05). To investigate any dose-dependency of this effect, we subjected hearts from both age groups to reperfusion with either Krebs solution or St. Thomas' Hospital solution No. 2 for 3 minutes every 30 minutes throughout a 2-hour period of ischemia. Reexposure to Krebs solution during ischemia did not affect postischemic function in either age group. Reexposure of immature hearts to St. Thomas' Hospital solution No. 2 caused a decremental loss of postischemic function in contrast to incremental protection with multidose cardioplegia in the mature heart. We conclude that immature rabbit hearts are significantly more tolerant of ischemic injury than mature rabbit hearts and that, unexpectedly, St. Thomas' Hospital solution No. 2 damages immature rabbit hearts.     

Low-potassium University of Wisconsin solution for cardioplegia: improved protection of the isolated ischemic neonatal rabbit heart

Recovery of cardiac function and high-energy phosphates following ischemia and reperfusion were determined for hearts perfused with low potassium University of Wisconsin solution, high potassium University of Wisconsin solution, St Thomas' solution, or subjected to hypothermia alone. Isolated hearts were arrested for either 3 h at 15 degrees C or 6 h at 20 degrees C (n = 7 for each group) with one of the four solutions and then reperfused. Aortic flow after ischemic arrest at 20 degrees C was 40.3 +/- 13.3%, 79.3 +/- 10.0%, 64.3 +/- 11.9% and 43.9 +/- 15.9% of control values for high potassium University of Wisconsin solution, low potassium University of Wisconsin solution, St Thomas' solution and hypothermia alone, respectively. Similar results were observed in hearts subjected to ischemic arrest at 15 degrees C. Myocardial adenosine triphosphate and creatine phosphate after reperfusion tended to be higher in the low potassium University of Wisconsin solution group. It is concluded that low potassium University of Wisconsin solution may provide reliable cardioplegia during surgery that requires prolonged cardiac arrest in neonates and infants.     

Cardioplegia-induced damage to ischemic immature myocardium is independent of oxygen availability

The known benefits of hypothermic pharmacological cardioplegia in protecting the ischemic adult heart may not extend to children. Protection of the ischemic immature rabbit heart with hypothermic Krebs-Henseleit bicarbonate buffer is better than with hypothermic St. Thomas' II cardioplegic solution. We investigated whether the availability of oxygen in the preischemic perfusate is responsible for the increased tolerance to ischemia of immature (7- to 10-day-old) hearts perfused with Krebs buffer in comparison with St. Thomas' II solution immediately before ischemia. After obtaining preischemic control data in the "working" mode, we perfused hearts (n = 8 per group) for 3 minutes with hypothermic (14 degrees C) Krebs buffer or hypothermic St. Thomas' II solution saturated with 0%, 25%, or 95% oxygen. This was followed by 2 hours of global ischemia at 14 degrees C. Hearts were reperfused for 15 minutes in the Langendorff mode and 35 minutes in the working mode, and recovery of function was measured. For preischemic oxygen concentrations of 0%, 25%, and 95%, recovery of aortic flow in hearts protected by hypothermia alone during ischemia was 74% +/- 9%, 82% +/- 4%, and 99% +/- 2% of preischemic values, respectively. In hearts protected by hypothermia plus cardioplegia, the values were 69% +/- 6%, 72% +/- 3%, and 86% +/- 5%, respectively. Thus, at equal oxygen concentrations, recovery of postischemic function was better in hearts protected by hypothermia alone compared with hypothermia plus cardioplegia. We conclude that factors other than oxygen availability are responsible for the damaging effect of St. Thomas' II solution on the ischemic immature rabbit heart.     

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.     

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.     

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.     

Is protection of ischemic neonatal myocardium by cardioplegia species dependent?

Hypothermia combined with pharmacologic cardioplegia protects the globally ischemic adult heart, but this benefit may not extend to children, resulting in poor postischemic recovery of function and increased mortality. The relative susceptibilities to ischemia modified by hypothermia alone and by hypothermia plus cardioplegia were assessed in isolated perfused neonatal (3- to 4-day-old) rabbit and pig hearts. Hearts were perfused aerobically with Krebs buffer solution in the working mode for 30 minutes and aortic flow was recorded. This was followed by 3 minutes of hypothermic (14 degrees C) coronary perfusion with either Krebs or St. Thomas' Hospital cardioplegic solution No. 2 followed by hypothermic (14 degrees C) global ischemia (rabbits 2, 4, and 6 hours; pigs 2 and 4 hours). Hearts were reperfused for 15 minutes in the Langendorff mode and 30 minutes in the working mode, and recovery of postischemic aortic flow was measured. Hypothermia alone provided excellent protection of the ischemic neonatal rabbit heart, with recovery of aortic flow after 2 and 4 hours of ischemia at 91% +/- 4% and 87% +/- 5% (mean +/- standard deviation) of its preischemic value. Recovery after 6 hours of ischemia was depressed to 58% +/- 9% of its preischemic value. Ischemic neonatal pig hearts protected with hypothermia alone recovered 94% +/- 3% of preischemic aortic flow after 2 hours; none was able to generate flow after 4 hours. St. Thomas' Hospital solution No. 2 decreased postischemic aortic flow after 4 hours of ischemia in rabbit hearts from 87% +/- 5% to 70% +/- 7% (p less than 0.05, hypothermia alone versus hypothermia plus cardioplegia) but improved postischemic recovery of aortic flow in pig hearts after 4 hours of ischemia from 0 to 73% +/- 13% (p less than 0.0001, hypothermia alone versus hypothermia plus cardioplegia). This effect was dose related in both species. We conclude that the neonatal pig heart is more susceptible to ischemia modified by hypothermia alone than the neonatal rabbit and that St. Thomas' Hospital solution No. 2 improves postischemic recovery of function in the neonatal pig but decreases it in the neonatal rabbit. This species-dependent protection of the neonatal heart may be related to differences in the extent of myocardial maturity at the time of study.     

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.     

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.     

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.     

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.     

Myocardial protection: the efficacy of an ultra-short-acting beta-blocker, esmolol, as a cardioplegic agent.

OBJECTIVE: During myocardial revascularization, some surgeons (particularly in the United Kingdom) use intermittent crossclamping with fibrillation as an alternative to cardioplegia. We recently showed that intermittent crossclamping with fibrillation has an intrinsic protection equivalent to that of cardioplegia. In this study we hypothesized that arrest, rather than fibrillation, during intermittent crossclamping may be beneficial. Because esmolol, an ultra-short-acting beta-blocker, is known to attenuate myocardial ischemia-reperfusion injury, we compared the protective effect of esmolol arrest with that of intermittent crossclamping with fibrillation and conventional cardioplegia (St Thomas' Hospital solution). METHODS: Isolated rat hearts were Langendorff perfused at either constant flow (14 mL/min) or constant pressure (75 mm Hg) with oxygenated Krebs-Henseleit bicarbonate buffer (37 degrees C), and left ventricular developed pressure was assessed. In study 1 (constant flow perfusion) 8 groups (n = 6 hearts per group) were studied: (1) 40 minutes of global ischemia; (2) 2 minutes of St Thomas' Hospital infusion and 40 minutes of ischemia; (3) multidose (every 10 minutes) infusions of St Thomas' Hospital solution during 40 minutes of ischemia; (4) 2 minutes of esmolol infusion and 40 minutes of ischemia; (5) multidose (every 10 minutes) esmolol infusions during 40 minutes of ischemia; (6) continuous infusion of esmolol for 40 minutes during coronary perfusion; (7) intermittent (4 x 10 minutes) ischemia with ventricular fibrillation; and (8) intermittent (4 x 10 minutes) ischemia preceded by intermittent esmolol administration. All protocols were followed by 60 minutes of reperfusion. Further experiments (study 2) examined the esmolol administration method in hearts perfused by constant pressure. RESULTS: An optimal arresting dose of 1.0 mmol/L esmolol was established. In study 1 recovery of left ventricular developed pressure (expressed as percentage of preischemic value) was 7% +/- 4%, 28% +/- 8%, 70% +/- 5%, 8% +/- 1%, 90% +/- 4%, 65% +/- 3%, 71% +/- 5%, and 76% +/- 5% in groups 1 to 8, respectively. Intermittent esmolol arrest with global ischemia provided equivalent myocardial protection to intermittent crossclamping with fibrillation, continuous esmolol perfusion, and multidose St Thomas' Hospital solution. Surprisingly, multidose esmolol infusion was more protective than all other treatments. In further experiments (study 2) optimal recovery was obtained with multiple esmolol infusions (by constant flow or constant pressure), but continuous esmolol infusion (at constant flow) was less effective than constant pressure infusion. CONCLUSIONS: Intermittent arrest with esmolol did not enhance protection of intermittent crossclamping with fibrillation; however, multiple esmolol infusions during global ischemia provided improved protection. Administration (constant flow or constant pressure) of arresting solutions influenced outcome only during continuous infusion. Multidose esmolol arrest may be a beneficial alternative to intermittent crossclamping with fibrillation or conventional cardioplegia.     

Superior myocardial preservation with modified UW solution after prolonged ischemia in the rat heart

Cardiac transplantation remains constrained by poor graft tolerance of prolonged cold ischemia. University of Wisconsin solution has remarkably extended ischemic preservation in pancreas, kidney, and liver transplantation. To assess its efficacy in cardiac preservation, modified University of Wisconsin solution flush and storage were tested against St. Thomas' cardioplegia flush and normal saline solution storage after six hours of ischemia at 0 degrees C in 46 isolated rat hearts. After ischemia, groups were compared before and after reperfusion. After ischemia but before reperfusion, University of Wisconsin solution hearts had significantly less tissue water (3.8%), superior tissue sodium, potassium, calcium, and magnesium profiles, and elevated adenosine and inosine levels, and tended toward better histological preservation. After reperfusion, University of Wisconsin solution more effectively preserved left ventricular compliance (75% versus 35% of baseline), developed pressure (71% versus 45% of baseline), histological integrity, and tissue potassium and calcium profiles than St. Thomas' solution. The University of Wisconsin solution provided superior preservation of systolic and diastolic ventricular function, tissue histology, tissue water, and tissue electrolytes than did St. Thomas' cardioplegia and normal saline solution storage in this experimental model, and might result in improved graft tolerance of ischemia in clinical cardiac transplantation.     

Comparison of single- and multi-dose crystalloid cardioplegia to protect the immature myocardium

The primary objective of this study was to compare the protective effects of single-dose and multi-dose St. Thomas' Hospital cardioplegic solution number 1 in the ischemic and reperfused neonatal rabbit heart. In addition, the effect of including bicarbonate (a component of St. Thomas' Hospital cardioplegic solution number 2) was also studied. Hearts (n=8 per group) were excised from rabbits (7–10 days old) and aerobically perfused in the working mode with crystalloid media for 20 min (37°C). After assessing cardiac function, the hearts were arrested by an infusion of cold cardioplegic solution (2 min at 15°C with or without the addition of bicarbonate (10 mmol). The hearts were then subjected to 6 h of hypothermic ischemia (15°C and, during this period, some hearts received multiple infusions (2 min/h at 15°C) of cardioplegic solution. All hearts were reperfused for 35 min (15 min Langendorff plus 20 min working), cardiac function was then re-assessed and expressed as a percent of the preischemic value. The coronary effluent, collected during the first 15 min of reperfusion, was assayed for creatine kinase activity. At the end of the reperfusion period, the hearts were freeze clamped and taken for metabolic analysis. With multi-dose cardioplegia (without bicarbonate) the postischemic recovery of cardiac output was 67.0±6.5% and with single-dose the value was 39.3±10.0% (NS). The same pattern of postischemic recovery (that varied between 30% and 60%) for aortic flow, stroke volume and stroke work was observed with both multi-dose and single-dose infusion. The inclusion of bicarbonate in the cardioplegic solution did not significantly alter the recovery of cardiac output with single-dose (51.7±8.9% vs 39.3±10.0%) or multi-dose infusion (60.6±7.6% vs 67.0±6.5%). Creatine kinase leakage was similar in all groups, as was the myocardial high energy phosphate content. In conclusion, in the neonatal rabbit heart, multi-dose St. Thomas' Hospital cardioplegia affords similar protection to single-dose administration and this was not modified by the addition of bicarbonate.     

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.     

A comparison of UW cold storage solution and St. Thomas' solution II: a 31P NMR and functional study of isolated porcine hearts.

Although University of Wisconsin cold storage solution provides excellent preservation for the pancreas, the kidney, and the liver after extended cold ischemic storage, its ability to preserve the heart for extended cold storage periods is not yet proved. This study was carried out to evaluate the effect of University of Wisconsin solution on heart preservation and to compare it to modified St. Thomas' solution II with respect to the capacity to preserve high-energy phosphates and contractile function in pig hearts. Hearts were arrested with either University of Wisconsin cold storage solution or St. Thomas' solution II (10 ml/kg) and kept ischemic at 12 degrees C or 4 degrees C for 8 hours. Functional recovery after the preservation period was assessed by means of ventricular function curves of the isovolumically contracting Langendorff model perfused with modified Krebs-Henseleit solution. Phosphorus 31 nuclear magnetic resonance spectroscopy was used to monitor high-energy phosphates and intracellular pH during preservation and reperfusion. At 12 degrees C, hearts arrested and preserved with University of Wisconsin solution showed a rapid decrease in phosphocreatine and adenosine triphosphate. With St. Thomas' solution, phosphocreatine and adenosine triphosphate decreased slowly. Functional recovery was poorer with University of Wisconsin solution than with St. Thomas' solution. Hearts preserved at 4 degrees C with either solution showed no significant differences in high-energy phosphate content and functional recovery. Rigorous control of the low temperature (4 degrees C) is necessary when University of Wisconsin solution is used for heart preservation.