| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
|
|
|
|||||||
|
|||||||||
Ann Thorac Surg 1996;61:576-584
© 1996 The Society of Thoracic Surgeons
Baker Medical Research Institute, Alfred Hospital, and Department of Surgery, Monash Medical Centre, Melbourne, Victoria, Australia
Accepted for publication September 18, 1995.
 |
Abstract |
|---|
 TopFootnotes Abstract IntroductionMaterial and MethodsResultsCommentConclusionsAcknowledgmentsReferences |
|---|
Methods. Using a modified (starch-free) variant of UW (MUW) we studied: (1) recovery of function with UW compared with aspartate-containing St. Thomas' solution; (2) effect of elevation of K+ in St. Thomas' solution to the level in UW; and (3) effect of reduction of K+ in UW and addition of Ca2+ or aspartate. Isolated rat hearts underwent 7 hours of arrest at 1°C using MUW with or without 20 mmol/L aspartate or using aspartate-containing St. Thomas' solution.
Results. Functional recovery with MUW (51.8% ± 2.5%) was superior to that with aspartate-containing St. Thomas' solution (37.1% ± 4.3%; p < 0.01). Addition of aspartate to MUW had no effect. During 6 hours of arrest, lowering the K+ in MUW from 125 mmol/L to 20 mmol/L reduced functional recovery from 59.9% ± 4.2% to 42.3% ± 4.3% (p < 0.01). The addition of 1 mmol/L Ca2+ had no effect. Elevation of K+ in St. Thomas' solution produced more rapid arrest but no improvement in recovery.
Conclusions. The protective effect of starch-free UW is greater (+13%) than that of aspartate-enriched St. Thomas' solution. Reduction of K+ in UW to lessen possible deleterious effects would decrease its protective effect by about 30% to a level comparable with that of St. Thomas' solution.
|
Introduction |
|---|
|
TopFootnotesAbstractIntroductionMaterial and MethodsResultsCommentConclusionsAcknowledgmentsReferences |
|---|
The composition of UW solution differs greatly from that of standard cardioplegic solutions used during cardiac operations and from the solutions commonly used for storage of the donor heart for transplantation such as Stanford solution or St. Thomas' Hospital solution [13]. Two features of UW solution could be undesirable for the heart: the high concentration of potassium, which is potentially damaging to the coronary endothelium [14], and the absence of calcium, which could cause myocardial damage on reperfusion because of the ``calcium paradox.'' Also, hydroxyethyl starch (HES) is an expensive component of UW solution and one not readily available to hospital pharmacies that might wish to prepare UW solution. Previous studies in our laboratories have shown that the HES component of UW solution can be omitted without compromising preservation of the kidney [15] or the liver [16]. This led us to develop the simplified Monash UW solution (MUW), in which HES is replaced by additional raffinose (Table 1
), and to use MUW in the present study.
|
|
Material and Methods |
|---|
|
TopFootnotesAbstractIntroductionMaterial and MethodsResultsCommentConclusionsAcknowledgmentsReferences |
|---|
Male Munich Wistar rats weighing 300 to 400 g were anesthetized with 4% halothane in oxygen. After administration of heparin sodium (200 U intravenously), the heart was rapidly excised and immersed in Krebs-Henseleit buffer at 4°C. The aorta was then cannulated and retrograde perfusion commenced on the isolated working rat heart apparatus in the nonworking (Langendorff) mode at a pressure of 100 cm H2O with nonrecirculating Krebs-Henseleit buffer oxygenated with 95% oxygen and 5% carbon dioxide [19]. During this period, the left atrium was cannulated to allow perfusion of the heart in the working mode at a left atrial pressure of 15 cm H2O and an aortic pressure of 100 cm H2O. The buffer consisted of the following in millimoles per liter: NaCl, 118; KCl, 4.7; MgSO4, 1.2; KH2PO4, 1.2; NaHCO3, 25; CaCl2, 2.5; Na2EDTA, 0.5; and glucose, 11; pH 7.4.
The power output of the working rat heart was calculated from the formula: Wp = Pdev x CO x 0.0022, where Wp is the power in millijoules, Pdev is the developed pressure in millimeters of mercury (peak systolic aortic pressure - left atrial pressure), CO is the cardiac output in milliliters per minute (aortic flow + coronary flow), and the numerical factor is for conversion to the International System of Units.
Experimental Time Sequence
To stimulate the events of a cardiac transplantation procedure, the following experimental time sequence was employed:
Coronary flow was measured at the end of each working and nonworking period, and cardiac function was measured at the end of each working period.
Solutions Tested
The composition of solutions used in this study is shown in Table 1
. The formulation of UW solution is included for comparison.
Experimental Design
Four experimental comparisons were designed in logical progression. Comparison 1 contrasted recovery using MUW with that using aspartate-enriched St. Thomas' solution as employed in our clinical transplant program and also determined (1) whether, as others [20] had suggested, it was preferable to arrest the heart with a conventional extracellular type of cardioplegic solution (St. Thomas' solution) before storing it in an intracellular type of solution (MUW) and (2) whether the efficacy of MUW could be improved by the addition of aspartate (MUWA). Comparison 2 examined whether a beneficial effect could be gained in St. Thomas' solution simply by raising the potassium concentration to the same high level as in UW solution. Comparison 3 tested whether the high level of potassium in MUW solution was necessary and also examined the effect of the addition of calcium. The order of performance of experiments within comparisons was randomized (Latin square design).
COMPARISON 1: MUW AND MUW PLUS ASPARTATE VERSUS ST. THOMAS' SOLUTION PLUS ASPARTATE.
A 7-hour period of arrest was used to accentuate differences between solutions of proven potency. Four treatment protocols were studied:
COMPARISON 2: INCREASE IN POTASSIUM IN ST. THOMAS' SOLUTION.
The hearts were arrested and stored for 6 hours. Two solutions were tested:
COMPARISON 3: REDUCTION OF POTASSIUM AND ADDITION OF CALCIUM TO MUW SOLUTION.
The hearts were arrested and stored for 6 hours. Four solutions were tested:
The low K+ MUW solutions were made isotonic using NaCl.
Tissue Sampling and Biochemical Analysis
Samples of the left ventricle from the hearts in comparison 1 were frozen in liquid nitrogen at the end of the postreperfusion working period. Extraction of metabolites was performed by homogenizaton in ice-cooled perchloric acid followed by centrifugation and neutralization of the supernatant with potassium hydroxide. The concentrations of adenosine triphosphate, adenosine diphosphate, adenosine monophosphate, phosphocreatine, and lactate in these extracts were assessed by enzymatic methods [21]. Other samples of the left ventricle were weighed and then dried to constant weight for determination of water content.
Statistical Methods
The results are expressed as the mean ± the standard error of the mean. Differences between the groups in comparisons 1 and 3 were evaluated by one-way analysis of variance followed by the orthogonal comparison method for multiple comparisons [22]. In comparison 2, the unpaired t test was used except where the conditions for equal variance or normality were not satisfied, when the Mann-Whitney U test was used. A p value of less than 0.05 was considered significant.
|
Results |
|---|
|
TopFootnotesAbstractIntroductionMaterial and MethodsResultsCommentConclusionsAcknowledgmentsReferences |
|---|
; Fig 1). Also for hearts arrested with STA, subsequent storage in MUWA made no difference to the recovery of function (p = 0.75). Therefore, to compare the effect of induction of arrest with MUW with induction of arrest with STA, it was possible to combine MUW–MUW with MUWA–MUWA and also STA–STA with STA–MUWA. This showed that recovery after MUW arrest and storage (with or without aspartate) was superior to STA arrest with or without MUW storage (51.8% ± 2.46% versus 37.1% ± 4.3%; p < 0.01). In absolute terms, the postarrest power in the MUW groups averaged 5.3 mJ•s-1•g-1, which was 13% greater than that in the STA groups (4.6 mJ•s-1•g-1).
|
|
). The time taken for spontaneous defibrillation was less in all three groups of hearts for which MUW was used as the storage solution (99.4 ± 15.8 seconds in STA-MUWA, 53.8 ± 8.3 seconds in MUW-MUW; 52.3 ± 6.0 seconds in MUWA-MUWA) than the group stored in St. Thomas' solution (STA-STA) (360 ± 44 seconds; p < 0.001 in all cases).
Because the high potassium content of MUW could have a vasoconstrictive effect, we measured the flow rate during the cardioplegia infusion and also compared the change in coronary flow before and after arrest in hearts arrested and stored in MUW solution (MUW-MUW, MUWA-MUWA) with corresponding values observed in hearts arrested and stored in St. Thomas' solution (STA-STA). We found that during the cardioplegia infusion, the flow rate did not differ between the two groups (p = 0.6). Also, there were no between-group differences in coronary flow before arrest either in the nonworking (p = 0.16) or the working state (p = 0.70) (Table 3). After ischemia, coronary flow rate recovered significantly better in the MUW groups than in the STA group in both the nonworking and working phases. Thus there was no evidence of coronary vasoconstriction in the MUW groups.
|
). The total adenine nucleotide levels in the MUW-MUW and in the MUWA-MUWA groups were similar to the prearrest value in this model. There were no significant between-group differences in other metabolite levels. There was no significant difference in water content between the four groups: STA-STA, 87.9% ± 0.5%; STA-MUWA, 87.7% ± 0.3%; MUW-MUW, 89.4% ± 0.8%; and MUWA-MUWA, 89.6% ± 0.7% (p = 0.16).
|
Comparison 3: Reduction of Potassium and Addition of Calcium to MUW Solution
After 6 hours of cardioplegic arrest and ice storage, recovery of prearrest function in the standard MUW group was 59.9% ± 7.5% (Table 5; Fig 2). The addition of Ca2+ was associated with a similar level of recovery (p = 0.99). Recovery of function after arrest and storage in Low K+ MUW was 41.0% ± 4.5%, and the addition of Ca2+ did not significantly affect recovery (p = 0.78).
|
|
The time to induction of arrest (from commencement of cardioplegia infusion to cessation of mechanical activity) was slightly shorter in the standard MUW hearts than in the Low K+ MUW hearts (7.2 ± 0.2 seconds versus 8.9 ± 0.5 seconds; p < 0.01) (see Fig 2). Also, the time taken for spontaneous defibrillation (from onset of reperfusion to resumption of a coordinated beat) was significantly shorter in the standard MUW hearts than in the Low K+ MUW hearts (1.8 ± 0.2 seconds versus 5.6 ± 0.7 seconds; p < 0.005).
|
Comment |
|---|
|
TopFootnotesAbstractIntroductionMaterial and MethodsResultsCommentConclusionsAcknowledgmentsReferences |
|---|
Varying the Composition of UW Solution
In our laboratory, we have previously shown that the colloid component of UW, HES, can be omitted from UW solution without loss of efficacy for experimental transplantation of the kidney [15], liver [16], and pancreas [23]. Also Ko and colleagues [24] found in isolated canine hearts that omission of HES had no effect on recovery of systolic function, although there was a deterioration in diastolic function. On the basis of this work, we developed a simplified form of UW solution, or MUW, in which HES was omitted and raffinose concentration was doubled to maintain osmolality. In a rat heterotopic transplant model, we [25] have previously shown that the heart can recover a coordinated beat after preservation for up to 20 hours in MUW.
In comparison 3, we showed that the protective effect of MUW is reduced by about 30% when the concentration of potassium is reduced from 125 mmol/L to 20 mmol/L (approximately the concentration found in most standard cardioplegic solutions). However, in comparison 2, we demonstrated that simply raising the potassium concentration in St. Thomas' solution to 104 mmol/L produced no improvement in protection. Clearly, high potassium is beneficial in UW solution but not in St. Thomas' solution.
The inclusion of 1 mmol/L calcium in MUW in the present study provided no benefit compared with the calcium-free formulation of standard UW solution. In a similar study, Stringham and co-workers [26] found that the addition of calcium to UW solution accelerated the onset of ischemic contracture during cold storage. In contrast, in St. Thomas' solution, calcium is essential and its concentration, critical. Robinson and Harwood [27] described a bell-shaped dose–response curve for functional recovery versus ionized calcium concentration in St. Thomas' solution, with zero recovery from calcium-free solution (resulting from the calcium paradox) and the optimal concentration at 0.6 mmol/L.
We found that the addition of 20 mmol/L sodium aspartate had no effect on the efficacy of MUW despite its beneficial properties when added to St. Thomas' solution [9, 17]. Aspartate most likely acts to improve the energy status of the heart during storage. This may be accomplished either by enhancing anaerobic conversion of pyruvate to alanine with resulting regeneration of nicotinamide adenine dinucleotide (oxidized form) thus allowing glycolysis to continue or by conversion of aspartate to oxaloacetate, which may prevent the depletion of tricarboxylic acid cycle intermediates, which occurs during ischemia, and thus ``prime the pump'' for reperfusion [17]. However, during storage in UW solution, the intracellular type of ionic environment reduces transsarcolemmal ionic gradients and thus may reduce the work required of ion pumps that rely on anaerobic energy production. Hence the anaerobic action of aspartate may be less beneficial in UW solution–preserved hearts.
Mechanism of Action of UW Solution
The mechanism of action of such a complex solution as MUW is likely to be complex. Consideration of the arrest times and the times to spontaneous defibrillation associated with the high and low potassium solutions we tested gives insights into their possible mechanisms of action. Increasing the potassium concentration in St. Thomas' solution shortened the arrest time by 17%. A similar increase in potassium between low-potassium MUW and standard MUW solution shortened the arrest time by a comparable amount (18%) (see Fig 2). However, comparing the arrest time for MUW with that for high-potassium St. Thomas' solution showed that although the potassium concentrations were similar, there was still a marked difference in the arrest times: the 7.2 ± 0.2 seconds in MUW hearts was only one third of that for high-potassium St. Thomas' solution, 23.8 ± 1.8 seconds. Clearly there must be another active component in UW solution, not contained in St. Thomas' solution, that has a more powerful arresting action than potassium.
The hypothesis that adenosine is the probable agent was supported by an additional test we carried out using adenosine-free MUW. For 6 hearts arrested with adenosine-free MUW, the arrest time was significantly longer than that for adenosine-containing MUW (18.3 ± 1.1 seconds versus 12.7 ± 0.5 seconds; p < 0.05). However, we found no difference between the two groups in the myocardial levels of adenosine triphosphate measured immediately after arrest: MUW, 20.0 ± 1.1 µmol/g of dry weight versus adenosine-free MUW, 20.2 ± 0.90 µmol/g of dry weight (p = 0.77). The results of Schubert and co-workers [28] closely parallel these findings. They found that compared with potassium, adenosine had a more rapid arresting (cardioplegic) action and improved postischemic recovery of function without any change in postarrest adenosine triphosphate levels. Although we did not study the recovery of function using MUW with and without adenosine, studies by Lasley and Mentzer [29] suggest that omission of adenosine from UW solution reduces recovery of function by about 30%. Adenosine is an important cardioprotective component of UW solution but does not act simply by causing rapid arrest.
Comparison 1 showed that the effect of MUW in improving recovery of function and preserving high-energy phosphates was not present in hearts arrested with a 1-minute infusion of St. Thomas' solution and then flushed with and stored in MUWA for 7 hours (see Table 2). This led us to conclude that adenosine acts in MUW mainly in the cardioplegic phase rather than during storage and therefore probably does not act as a precursor for ongoing adenine nucleotide synthesis. This conclusion was supported by the observation of Schubert and colleagues [28] that the protective effect of adenosine cardioplegia was not abolished even if the adenosine-containing cardioplegic solution was washed out of the heart immediately after a 3-minute arrest period. An important, recently discovered cardioprotective mechanism of adenosine that may be operative here is its ability to precondition the myocardium against subsequent ischemic damage. The effect is similar to ischemic preconditioning and is mediated by the adenosine A2 receptor [30].
A distinctive feature of the MUW–preserved hearts was the more rapid resumption of a coordinated beat (spontaneous defibrillation). In comparison 3, earlier spontaneous defibrillation was seen in the hearts preserved in MUW than in Low K+ MUW (see Fig 2). During storage of the arrested heart at low temperatures, the sodium-potassium ATPase is markedly inhibited [31], and intracellular potassium and sodium tend to equilibrate with the extracellular space. If the concentration of these ions in the extracellular space is normal, the myocyte experiences a steady loss of potassium and uptake of sodium and water during arrest. During reperfusion when the cell temperature returns to normal, time is required for the sodium-potassium ATPase to restore across the cell membrane the ionic gradients necessary for normal electromechanical activity. If the heart is flushed with UW solution (intracellular type) prior to ischemia, the extracellular space is equilibrated with potassium and sodium at intracellular levels, the diffusion gradients are eliminated, and the ionic changes during arrest are minimized. Thus it would be expected that normal electromechanical activity would be restored sooner, resulting in earlier spontaneous defibrillation.
This also explains the observation in comparison 1 that in the two groups of hearts arrested with St. Thomas' solution, spontaneous defibrillation occurred sooner in hearts subsequently stored in MUW solution than in those stored in St. Thomas' solution (see Fig 1). However, this effect did not result in any difference in recovery of function between these two groups and therefore probably has no great relevance to the cardioprotective action of UW solution. Also, in comparison 3, we observed that the Low K+ MUW hearts took longer to defibrillate (see Fig 2). We conclude that the effect of UW solution in stabilizing the cardiac rhythm after reperfusion is due to its high potassium concentration.
Possible Deleterious Effects of High Potassium on the Heart
A long-standing concern about the use of high potassium solutions in myocardial preservation is damage to the coronary endothelium and the myocardium [14]. Damage to the coronary endothelium is particularly undesirable in cardiac transplantation as accelerated coronary atherosclerosis is the main cause of late graft failure [32]. Drinkwater and co-workers [33] reported that in cardiac allografts preserved in UW solution, the incidence of late graft atherosclerosis was twice as high as in grafts preserved in Stanford solution. This was explained in terms of an adverse effect on the coronary endothelium of the high potassium concentration in UW solution, and their group has switched to a low potassium UW solution in their clinical program (Drinkwater D, Laks H: personal communication, 1995). However, the results of our study suggest that if the potassium concentration of UW solution were to be lowered, then the myocardial protective effect of the solution would be reduced by about 30%, possibly removing its advantage over St. Thomas' solution.
Coronary Vasoconstriction
Mankad and associates [34] found in the isolated perfused rat heart that coronary vascular resistance increased significantly after a 30-minute perfusion of the coronary circulation with UW solution at 15° or 20°C but not at 4°C. Kohno and co-workers [20] described coronary vasoconstriction even at 4°C with Collins solution, which has a potassium concentration similar to that of UW solution, and concluded that for this reason Collins solution should not be used as a cardioplegia infusion. In the present study we found no evidence of coronary vasoconstriction with the use of MUW, but this may have been prevented by hypothermia because the hearts were kept at 1° to 2°C throughout the period of contact with UW solution. After reperfusion and rewarming, the UW solution was immediately washed out of the heart.
Clinical Implications
This study suggests that starch-free UW solution has a protective action that is slightly more powerful than that of aspartate-enriched St. Thomas' solution, which our group [18] has shown to be very effective (5% early mortality rate in 150 heart transplantations). The present study was performed in crystalloid-perfused rat hearts, and therefore caution should be used in extrapolating the results directly to the clinical arena. However, the findings of a modest improvement in functional recovery with UW solution are in accord with similar experimental studies in blood-perfused hearts in dogs [5], pigs [6], and baboons [7].
In the clinical arena, several trials of donor heart preservation have studied UW solution versus other preservative solutions. Stein and co-workers [10] compared UW solution and Stanford solution for mean ischemic times of less than 3 hours. With the use of UW solution, they found a small improvement in preservation of high-energy phosphate levels in the right ventricle and more stable rhythm intraoperatively but no improvement in hemodynamics. Jeevanandam and associates [11] compared UW solution with a glucose-mannitol solution for a mean ischemic time of 2.5 hours. The UW group regained electric activity more rapidly and had reduced enzyme release, but there was no difference in hemodynamic performance between the groups. Demertzis and associates [12] compared UW and St. Thomas' solutions and concluded that they were of comparable efficacy for ischemic times of less than 4 hours. A trial of UW solution versus cold cardioplegic solution in 10 patients during 4 hours of ischemia led Kawai and colleagues [35] to conclude that UW solution had no superior effect on cardiac function as assessed by load-independent mechanical factors. Thus, most published clinical studies show no hemodynamic superiority for UW solution–preserved hearts; however, if the improvement over conventional cardioplegic solutions is only around 13%, as indicated in the present study, this may not be readily detectable clinically. As mentioned previously, an important concern with the clinical use of standard (high potassium) UW solution in the heart is its possible association with accelerated coronary atherosclerosis.
|
Conclusions |
|---|
|
TopFootnotesAbstractIntroductionMaterial and MethodsResultsCommentConclusionsAcknowledgmentsReferences |
|---|
|
Acknowledgments |
|---|
|
TopFootnotesAbstractIntroductionMaterial and MethodsResultsCommentConclusionsAcknowledgmentsReferences |
|---|
We acknowledge the assistance of Marion Attwater, Marianne Galanis, and Heather Gallichio.
|
Footnotes |
|---|
|
TopFootnotesAbstractIntroductionMaterial and MethodsResultsCommentConclusionsAcknowledgmentsReferences |
|---|
|
References |
|---|
|
TopFootnotesAbstractIntroductionMaterial and MethodsResultsCommentConclusionsAcknowledgmentsReferences |
|---|
This article has been cited by other articles:
|
|
 |
|
  K. L. Sloots, J. Vinten-Johansen, and G. P. Dobson Warm nondepolarizing adenosine and lidocaine cardioplegia: Continuous versus intermittent delivery J. Thorac. Cardiovasc. Surg., May 1, 2007; 133(5): 1171 - 1178. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 N. Kajihara, S. Morita, Y. Tanoue, N. Boku, M. Eto, T. Nishida, and R. Tominaga The UW solution has greater potential for longer preservation periods than the Celsior solution: comparative study for ventricular and coronary endothelial function after 24-h heart preservation. Eur. J. Cardiothorac. Surg., May 1, 2006; 29(5): 784 - 789. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 D. Ebel, B. Preckel, A. You, J. Mullenheim, W. Schlack, and V. Thamer Cardioprotection by sevoflurane against reperfusion injury after cardioplegic arrest in the rat is independent of three types of cardioplegia Br. J. Anaesth., June 1, 2002; 88(6): 828 - 835. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
S. C. Stoica, D. K. Satchithananda, J. Dunning, and S. R. Large Two-decade analysis of cardiac storage for transplantation Eur. J. Cardiothorac. Surg., October 1, 2001; 20(4): 792 - 798. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 T. L. Demmy, T. A. Turpin, and C. C. Wagner-Mann Laboratory confirmation of clinical heart allograft preservation variability Ann. Thorac. Surg., April 1, 2001; 71(4): 1312 - 1319. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
R. Ou, J. B. Gavin, D. S. Esmore, and F. L. Rosenfeldt Increased temperature reduces the protective effect of University of Wisconsin solution in the heart Ann. Thorac. Surg., November 1, 1999; 68(5): 1628 - 1634. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
D. K. Nickless, M. Rabinov, S. M. Richards, R. A.J. Conyers, and F. L. Rosenfeldt Continuous Perfusion Improves Preservation of Donor Rat Hearts: Importance of the Implantation Phase Ann. Thorac. Surg., May 1, 1998; 65(5): 1265 - 1272. [Abstract] [Full Text] [PDF]
|
|
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
| ANN THORAC SURG | ASIAN CARDIOVASC THORAC ANN | EUR J CARDIOTHORAC SURG |
| J THORAC CARDIOVASC SURG | ICVTS | ALL CTSNet JOURNALS |
