Ann Thorac Surg 2001;71:219-225
© 2001 The Society of Thoracic Surgeons
Original article: cardiovascular
Effects of metabolic stimulation on cardiac allograft recovery
Vivek Rao, MD, PhDb,c,
Christopher M. Feindel, MDb,c,
Gideon Cohen, MDb,
Michael A. Borger, MDb,
Heather J. Ross, MDa,c,
Richard D. Weisel, MDb
a Division of Cardiology, The Toronto Hospital, University of Toronto, Toronto, Ontario, Canada
b Division of Cardiovascular Surgery, The Toronto Hospital, University of Toronto, Toronto, Ontario, Canada
c Division of the Heart Transplant Program, The Toronto Hospital, University of Toronto, Toronto, Ontario, Canada
Accepted for publication June 10, 2000.
Address reprint requests to Dr Feindel, EN 14-222, The Toronto Hospital, 200 Elizabeth St, Toronto, ON, M5G 2C4, Canada
e-mail: cfeindel{at}torhosp.toronto.on.ca
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Abstract
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Background. We previously demonstrated that continuous perfusion of cardiac allografts during hypothermic storage with donor blood harvested at the time of organ retrieval improves myocardial recovery after transplantation. However, myocardial metabolism and function remain depressed compared to base line values. This study evaluated the use of a continuous infusion of donor blood enhanced with insulin to augment aerobic myocardial metabolism during and after hypothermic storage.
Methods. Yorkshire pigs (45 to 50 kg) were used to perform 14 orthotopic cardiac transplants using either continuous perfusion with donor blood (blood group, n = 7) or perfusion with donor blood enhanced with 10 IU/L insulin (insulin group, n = 7). After heparinization, hypothermic (4°C) cardioplegic arrest, and donor heart extraction, donor blood (2844 ± 210 mL) was harvested in both groups and perfused at room temperature (20°C) at a pressure of 60 mm Hg for 3 hours. Blood cardioplegia was delivered after each anastomosis in both groups and arterial and coronary sinus blood samples were obtained to examine myocardial metabolism. A Millar micromanometer was used to measure left ventricular developed pressure and the rate–pressure product at varying preloads.
Results. There were no differences in either myocardial lactate or acid release between the two groups. Hearts in the insulin group displayed higher myocardial oxygen extraction than those in the blood group. The recovery of developed pressure was higher in the insulin group compared to the blood group (91% ± 19% vs 73% ± 2%, p = 0.04).
Conclusions. In this model, continuous perfusion of cardiac allografts with donor blood and insulin preserves myocardial metabolism during hypothermic storage and improves metabolic and functional recovery after orthotopic cardiac transplantation.
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Introduction
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The number of patients waiting for a cardiac transplant is increasing with time. A recent report by Hauptman and colleagues [1] demonstrated that the average waiting time for stable (out of hospital) patients has increased from 88 ± 13 days to 146 ± 15 days over a 10-year period. Unfortunately, the limited supply of donor organs remains a major problem in most clinical cardiac transplant programs. Hauptman’s [1] report recognized an attempt to expand the donor pool by an increased use of older donors, greater weight differences between donor and recipient, and a shift towards longer ischemic times (180 ± 4 mins vs 152 ± 4 mins, p < 0.0001). Unfortunately, the primary cause of early morbidity and mortality following cardiac transplantation continues to be primary graft dysfunction. In a recent registry report from the International Society for Heart and Lung Transplantation [2], primary graft dysfunction was responsible for almost 50% of the early mortality after isolated heart transplantation.
Improved methods of allograft preservation are required in order to safely use marginal donor organs and to enable retrieval from distant sites that require prolonged ischemic times. Several investigators have reported their results with preservation systems designed to provide either blood or crystalloid perfusion to hearts during storage [3–12]. Unfortunately, these systems have not been adopted for widespread clinical use. These circuits often require sealed glass or Plexiglas containers, oxygen cylinders, and elaborate perfusion tubing.
We previously demonstrated that collection of shed blood from the donor at the time of organ retrieval for subsequent perfusion during storage improved myocardial recovery in a porcine model of orthotopic transplantation [13]. This perfusate represented a mixture of venous and arterial blood in addition to crystalloid cardioplegia. Continuous perfusion of donor blood enabled the end products of myocardial metabolism, namely lactate and hydrogen ions, to be washed out, and resulted in persistent anaerobic metabolism during storage and implantation. We had assumed that this mixture would provide sufficient oxygen delivery to permit aerobic myocardial metabolism during storage when the oxygen demands of the arrested heart are low [14]. Unfortunately, perfusion of donor blood alone did not allow for the recovery of aerobic metabolism during reperfusion, and the recovery of left ventricular-developed pressure remained below 80% of base line values.
Kobayashi and Neely [15] demonstrated that a key metabolic enzyme, mitochondrial pyruvate dehydrogenase (PDH), is inhibited early during reperfusion. PDH regulates the conversion of pyruvate to acetyl-coenzyme A, which is subsequently utilized by the Krebs’ cycle for oxidative phosphorylation. Inhibition of PDH leads to persistent anaerobic lactate production despite adequate oxygen delivery. In addition to the increased efficiency of adenosine triphosphate (ATP) production by oxidative phosphorylation, it has been demonstrated that ATP produced by anaerobic glycolysis is preferably used for membrane stability while aerobically produced ATP is preferably used for contractile function [16]. Therefore, facilitating the transition from anaerobic to aerobic metabolism following ischemia should lead to an earlier recovery of ventricular function. Insulin has been shown to stimulate PDH in adipocytes [17], hepatocytes [18], and isolated cardiac myocytes [19, 20]. In a previous study we determined that preischemic insulin exposure stimulated mitochondrial PDH and improved the recovery of aerobic metabolism in isolated human ventricular cardiomyocytes subjected to simulated ischemia and reperfusion [20]. Based on this finding we hypothesized that supplementing the donor blood perfusate with insulin would improve the recovery of aerobic metabolism after hypothermic storage and lead to improved ventricular function after orthotopic transplantation.
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Material and methods
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The experimental protocol was approved by our institutional animal care committee and in accordance with the Guide for the Care and Use of Laboratory Animals published by the National Institutes of Health (NIH Publication No. 86-23, revised 1985). Twenty-eight female Yorkshire pigs (50 to 60 kg) were used to perform 14 orthotopic cardiac transplants using either continuous donor blood perfusion (blood, n = 7) or continuous perfusion with donor blood supplemented with 10 IU/L of humulin R (insulin, n = 7). The size mismatch between donor and recipient was less than 5% of body weight in all experiments.
Donor operation
The animals were anesthetized with intramuscular ketamine (30 mg/kg) and isoflurane, intubated and ventilated with 100% oxygen to maintain normocarbia. After sternotomy the heart and great vessels were exposed. Umbilical tapes were placed around the superior and inferior vena cava to permit adjustment of cardiac preload by caval snaring. Systemic anticoagulation was achieved with the intravenous injection of 10,000 units of heparin.
A Millar micromanometer was inserted through the apex of the left ventricle to permit on-line measurements of heart rate, left ventricular systolic and diastolic pressures, as well as the maximum positive derivative of the systolic pressure curve. Base line measurements of all hemodynamic factors were made at a left ventricular end-diastolic pressure of 10 mm Hg and after bicaval snaring to achieve a left ventricular end-diastolic pressure of 2 mm Hg. A third measurement was made after release of the bicaval snares. Donor hearts that failed to recover a left ventricular developed pressure of 80 mm Hg after release of the snares were discarded.
A purse string suture was placed in the ascending aorta to permit placement of a cardioplegic cannula. Arterial and coronary sinus blood samples were obtained just before aortic cross clamping and then one liter of a hypothermic (4°C), hyperkalemic crystalloid solution (composition in mmol/L: Na+ 127, K+ 20, Mg2+ 6, Cl- 7, SO4- 6, tris-hydroxymethyl aminomethane 4, Dextrose 135) was infused into the aortic root to achieve cardioplegic arrest. After cardioplegic infusion, the donor heart was extracted, placed in a bag containing 300 mL of hypothermic cardioplegia, and stored on ice. The cardioplegic cannula and aortic cross-clamp was left in place to permit perfusion during storage.
In both groups, donor blood was harvested from the chest after organ extraction. After filtration for particulate matter and the addition of 10,000 units of heparin, the blood was stored in standard transfusion bags (Travenol, Baxter Healthcare Corp, Deerfield, IL). In the insulin group, both the crystalloid cardioplegia and the donor blood perfusate were supplemented with 10 IU/L of humulin R. Blood perfusion was initiated within 10 minutes of cardioplegic arrest and was delivered at room temperature (20°C) at a vertical height of 100 cm (to correspond to a perfusion pressure of 60 mm Hg) using a standard intravenous transfusion apparatus (Fenwal, Baxter Healthcare Corp, Deerfield, IL). A schematic representation of this perfusion technique is displayed in Figure 1. Blood perfusion was maintained throughout the storage period while the donor heart was on ice. A myocardial probe was inserted into the apex of the left ventricle in each of the hearts to monitor temperature during storage. Coronary flow rate was determined as the total volume of perfusate delivered was corrected for storage time in minutes.
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Fig 1. A schematic representation of the perfusion apparatus. (Left panel) Shed mediastinal blood is filtered and collected in a standard blood transfusion bag. (Right panel) Transfusion is initiated by the previously inserted aortic cardioplegic cannula with the aortic cross-clamp in place.
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Recipient operation
Preoperative sedation and anesthesia were similar to the donor protocol. In addition, a marginal ear vein was used for intravenous access and kept open with a 50 mL/hr 5% dextrose infusion. Continuous electrocardiographic monitoring was used and a carotid artery line was inserted to measure arterial pressure.
After sternotomy the heart and great vessels were exposed. Umbilical tapes were placed around the superior and inferior vena cava. Systemic anticoagulation was achieved by injecting heparin into the pump prime (10,000 U) in addition to an intravenous dose of 10,000 units. Ascending aortic and bicaval cannulation were used to place the recipient on cardiopulmonary bypass. Flow rates were adjusted to maintain systemic perfusion pressures above 50 mm Hg. No vasoactive medications were administered during cardiopulmonary bypass. Systemic perfusion was maintained at 37°C.
After the aorta was cross-clamped, the recipient heart was extracted maintaining a cuff of right and left atrium. The left hemiazygous vein was ligated at its insertion into the coronary sinus. The anastomotic margins were then inspected and trimmed in preparation for orthotopic transplantation using a standard atrial to atrial technique [13].
Donor blood perfusion of the allograft was stopped after 3 hours of hypothermic storage and an initial 350 mL blood cardioplegic dose infused in all groups at a flow rate of 100 mL/min. Cardioplegic protection consisted of a 2:1 mixture of blood:crystalloid and was delivered at 10°C after the completion of each atrial anastomosis. After completion of the pulmonary arterial anastomosis, 350 mL of blood cardioplegia was delivered at 37°C. Arterial and coronary sinus blood samples were obtained at each cardioplegic infusion, at the time of cross-clamp removal, and every 15 minutes during reperfusion. If ventricular fibrillation occurred during reperfusion, three attempts were made to defibrillate the heart. If unsuccessful, 100 mg lidocaine was delivered intravenously and defibrillation was attempted once again.
At the completion of 45 minutes of reperfusion, hemodynamic measurements were obtained. Preload was adjusted by transient venous occlusion. After completion of all measurements, the recipient was weaned off bypass if possible. In all hearts, calcium chloride (1 g) was given and if additional inotropic support was required an isoproterenol drip was established (0.4 mg/min). If the animal was not successful in maintaining a mean arterial pressure above 60 mm Hg for 30 minutes despite inotropic support, weaning was deemed to be unsuccessful. Ventricular pacing was used if necessary to maintain the heart rate more than 80 beats per minute. Thirty minutes after discontinuation of cardiopulmonary bypass, decannulation was performed and the animal sacrificed by intravenous potassium chloride injection.
Biochemical measurements
Arterial and coronary sinus blood samples were assayed for the partial pressure of oxygen (pO2), carbon dioxide (pCO2), pH, hemoglobin concentration (Hb) and oxygen saturation (SaO2). Oxygen content (O2Con) was calculated from the formula: 
. Blood samples for lactate determination were mixed with a measured volume of 6% perchloric acid. Lactate concentration was measured in the protein-free supernatant with a commercially available assay (Rapid Lactate Stat Pack, Calbiochem-Behring, La Jolla, CA).
Myocardial PDH activity was assessed in each group as previously described [20]. Left ventricular biopsies were obtained at the base line briefly, just before aortic cross-clamp release and after 45 minutes of normothermic reperfusion. Biopsies were flash frozen in liquid nitrogen and stored and -70°C for subsequent analysis. Specimens were then homogenized on ice and suspended in 250 µL of phosphate buffered saline. Seventy-five µL aliquots were then added to eppendorf tubes containing equal volumes of phosphate buffered saline with or without 5 mmol/L dichloroacetate. After 10 minutes of incubation at 37°C, PDH activity was stabilized with 25 mmol/L sodium fluoride. Tissue homogenates were then exposed to a reaction mixture containing 14C-pyruvate in the presence of benzothonium hydroxide to trap 14CO2. Following 10 minutes of normothermic incubation, the reaction was halted with 10% trichloroacetic acid and 14CO2 collected for 1 hour and counted in a ß-counter. The total native PDH activity was measured in the fraction exposed to dichloroacetate while the active fraction was determined from the unexposed homogenates. All counts were corrected for protein content and the results expressed as the percentage of active fraction to total native activity.
Statistical analysis
Statistical analysis was performed using the SAS statistical software program (SAS Institute, Cary, NC). Categorical data were analyzed by 
-squared or two-tailed Fischer’s exact test where appropriate. Continuous data are expressed as the mean ± standard deviation and were analyzed by two-way repeated measures of analysis of variance evaluating the main effects of group and time as well as the interactive effect (group–time). Duncan’s multiple range test was performed to specify differences between groups at p less than 0.05.
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Results
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Table 1 provides experimental data describing the total volume of blood perfusate harvested from the chest of the donor and subsequently perfused during allograft storage. Approximately 3,000 mL of blood was successfully harvested in each group. There were no differences in the total volume of blood perfused or in the average coronary flow rate. Similarly, there were no differences in the total time to initial blood cardioplegic perfusion before organ implantation (storage time) or in the total ischemic time. The composition of the donor blood perfusate was similar in both groups and represents a mixture of arterial and venous blood as well as crystalloid cardioplegic solution.
Recovery of myocardial metabolism
Figure 2 illustrates myocardial lactate flux during the experimental protocol. There was no interactive effect between group and time (group–time effect, p = 0.894). Myocardial lactate release increased significantly after cross-clamp removal in both groups suggesting a washout of lactate from underperfused myocardium (time effect, p < 0.0001). Myocardial lactate release remained greater than base line even after 45 minutes of reperfusion suggesting persistent anaerobic metabolism in both groups. There were no differences in myocardial lactate release between groups at any time point (group effect, p = 0.685).
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Fig 2. Myocardial lactate flux during the experimental protocol. Myocardial lactate release increased significantly after cross-clamp removal in both groups suggesting a washout of lactate from underperfused myocardium (time effect, p < 0.0001). There were no differences in myocardial lactate release between groups at any time point (group effect, p = 0.685). (Sampling time depicted on x-axis: PRE = base line; PLEG = initial cardioplegic infusion after completion of left atrial (LA), right atrial (RA), pulmonary arterial (PA) anastamosis. Removal of aortic cross-clamp (XCL); 15, 30, and 45 minutes of reperfusion. NS = not significant.)
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Figure 3 illustrates myocardial acid release during the experimental protocol. There was no interactive effect between group and time (group–time effect, p = 0.587). Myocardial acid release increased significantly after the initial cardioplegic infusion in both groups and then returned to base line levels during reperfusion (time effect, p < 0.0001). There were no differences in myocardial acid release between groups at any time point (group effect, p = 0.787).
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Fig 3. Myocardial acid release (arterial-coronary sinus pH difference) during the experimental protocol. Myocardial acid release increased significantly after the initial cardioplegic infusion in both groups and then returned to base line levels during reperfusion (time effect, p < 0.0001). There were no differences in myocardial acid release between groups at any time point (group effect, p = 0.787). (Sampling time depicted on x-axis: PRE = base line; PLEG = initial cardioplegic infusion after completion of left atrial (LA), right atrial (RA), pulmonary arterial (PA) anastamosis. Removal of aortic cross-clamp (XCL); 15, 30, and 45 minutes of reperfusion. NS = not significant.)
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Figure 4 illustrates myocardial oxygen extraction during the experimental protocol. There was no interactive effect between group and time (group–time effect, p = 0.609). Myocardial oxygen extraction recovered earlier in the insulin group (group effect, p = 0.013), but remained depressed in both groups compared to base line (time effect, p < 0.0001). Duncan’s multiple range test specified higher oxygen extraction in the insulin group after the completion of the pulmonary arterial anastomosis (2.2 ± 0.2 mL/dL vs 0.94 ± 0.4 mL/dL, p = 0.019).
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Fig 4. Myocardial oxygen extraction during the experimental protocol. There was no interactive effect between group and time (group–time effect, p = 0.609). Myocardial oxygen extraction recovered earlier in the insulin group (group effect, p = 0.013), but remained depressed in both groups compared to base line (time effect, p < 0.0001). (Sampling time depicted on x-axis: PRE = base line; PLEG = initial cardioplegic infusion after completion of left atrial (LA), right atrial (RA), pulmonary arterial (PA) anastamosis. Removal of aortic cross-clamp (XCL); 15, 30, and 45 minutes of reperfusion.)
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Figure 5 illustrates myocardial pyruvate dehydrogenase activity at base line, after storage and implantation and after 45 minutes of reperfusion. There appeared to be lower PDH activity after storage and reperfusion (time effect, p = 0.17); however, there was no significant effect of insulin over time (time– group effect, p = 0.75).
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Fig 5. Myocardial pyruvate dehydrogenase (PDH) activity at base line (PRE), after cross-clamp removal (OFF), and after 45 minutes of reperfusion (REP). There was a trend towards lower PDH activity after storage and reperfusion (time effect: p = 0.17); however, there was no significant effect of insulin over time (time–group effect: p = 0.75).
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Recovery of myocardial function
All hearts were successfully weaned from cardiopulmonary bypass. Three hearts in each group required inotropic support to maintain adequate systemic pressures after weaning from cardiopulmonary bypass. Two hearts in the insulin group required ventricular pacing to wean from cardiopulmonary bypass compared to one heart in the blood group (p = 0.552). Ventricular fibrillation requiring lidocaine therapy occurred in six hearts in the insulin group compared to five hearts in the blood group (p = 0.552).
Figure 6 represents the recovery of developed pressure in each group at a left ventricular end-diastolic pressure of 2 mm Hg and 10 mm Hg. Compared to base line measurements, hearts in the insulin group recovered 91% ± 19% of their left ventricular developed pressure compared to only 73% ± 2% in the blood group (p = 0.042). There were no differences in rate-pressure products either before (blood 8856 ± 1552 vs insulin 8550 ± 1445, p = 0.72) or after transplantation (blood 7430 ± 1818 vs insulin 6452 ± 971, p = 0.31). The recovery in rate-pressure product was similar in both groups (insulin 82% ± 22% vs blood 84% ± 16%, p = 0.863). However, the maximal positive derivative of the systolic pressure curve (+dP/dT) was improved in the insulin group (base line: blood 481 ± 75 mm Hg/sec vs insulin 464 ± 64 mm Hg/sec, p = 0.77; posttransplant: blood 465 ± 80 mm Hg/sec vs insulin 512 ± 72 mm Hg/sec, p = 0.05).
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Fig 6. Recovery of developed pressure following orthotopic transplantation at left ventricular end-diastolic pressures (LVEDP) of 2 mm Hg and 10 mm Hg. The recovery of developed pressure improved in the insulin group (p = 0.042). (PRE = base line; POST = posttransplant.)
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Comment
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Nonspecific primary graft dysfunction remains the predominant cause of early mortality after isolated orthotopic cardiac transplantation [2]. Furthermore, endothelial damage sustained during allograft preservation may increase antigen expression and lead to the development of immunologically mediated late allograft coronary vasculopathy [21, 22]. Therefore, improved methods of myocardial preservation during organ storage are required to improve the early and potentially, the late survival after cardiac transplantation.
Several investigators have reported excellent results with continuous perfusion systems using either blood or crystalloid preparations [3–12]. Unfortunately, no one system has become widely adopted due to the cost, complexity, or lack of portability of the device. We previously reported that a simple, cost-effective, and portable perfusion system could be used to improve the recovery of myocardial function after transplantation [13]. We used shed mediastinal blood from the chest of the donor to perfuse the allograft during 3 hours of hypothermic storage. The advantages of this system are numerous: (1) the simplicity of the perfusion apparatus permits its use in even the most remote procurement areas, (2) the use of autologous blood perfusion prevents endothelial damage that may occur with pure crystalloid perfusion [23], and (3) the perfusate can be enhanced with numerous cardioplegic additives to further improve myocardial tolerance to ischemia. Unfortunately, continuous unmodified donor blood perfusion during organ storage did not prevent the inhibition of aerobic metabolism that occurs early during reperfusion. Myocardial contractility has been demonstrated to be dependent upon aerobically produced ATP [16]. Therefore, improving the transition from anaerobic to aerobic myocardial metabolism after hypothermic storage should lead to improved recovery of systolic function.
In a previous study using isolated human cardiomyocytes, we demonstrated that exposure to 10 IU/L of insulin resulted in a stimulation of PDH activity, a reduction of extracellular lactate release and an improvement in ATP preservation [20]. We hypothesized that supplementing the donor blood perfusate with insulin would stimulate myocardial pyruvate dehydrogenase [17–20] and lead to improved recovery of left ventricular function [23].
We used a porcine model of orthotopic cardiac transplantation for several reasons: (1) the circulating blood volume and the mediastinal cavity of a 50 kg Yorkshire pig closely approximates that of a 70 kg adult human, (2) the porcine heart has been demonstrated to be extremely sensitive to global ischemia [13, 24], which may increase its sensitivity to subtle metabolic interventions such as insulin, and (3) the coronary anatomy of the porcine heart more closely resembles that of humans compared to canine or rat models.
In these studies we found that the donor blood perfusate represented a mixture of arterial and venous blood in addition to the crystalloid solution used to achieve cardioplegic arrest. The composition of this perfusate (Table 1) is similar to that obtained in previous studies and has been shown to provide superior protection to simple static storage [13]. The addition of insulin to the perfusate did not affect its pH or oxygen carrying capacity.
Supplementing the blood perfusate with insulin did not affect myocardial acid or lactate release. Stimulating myocardial PDH should increase lactate extraction by the heart and lead to less lactate release in the venous effluent [20]. Maintaining hypothermia (10°C) during storage and implantation may have prevented PDH stimulation by insulin. Due to the small sample size, we were unable to demonstrate a significant effect of insulin on myocardial PDH activity. Furthermore, we obtained our final reperfusion biopsy 45 minutes after cross-clamp release. Previous studies have suggested that PDH inhibition occurs shortly after reperfusion and returns to base line within 30 to 60 minutes. Therefore, potential differences in PDH activity during early reperfusion may not have been detected in this protocol. However, there appeared to be lower PDH activity in both groups over time, again suggesting a detrimental effect of hypothermic storage. Interestingly, the only metabolic difference between the two groups occurred in myocardial oxygen extraction following completion of the pulmonary arterial anastomosis. At this time point, all hearts received a normothermic infusion of blood cardioplegia. In both groups, a depression in myocardial oxygen extraction was observed at 30 minutes of reperfusion compared with values obtained immediately after cross-clamp removal.
The earlier recovery of myocardial oxygen extraction observed in the insulin group may be responsible for the improved preservation of left ventricular systolic function. Other metabolic effects of insulin exposure also may have contributed to the improved recovery of myocardial contractility. We did not measure myocardial levels of high energy phosphates such as ATP or creatine phosphate. However, we have previously demonstrated in isolated human ventricular cardiomyocytes that a similar insulin exposure improved pyruvate dehydrogenase activity and led to higher ATP levels after normothermic ischemia and reperfusion [20].
Another possible cause of the depression in myocardial metabolic and functional recovery may be the use of profound hypothermia. In clinical studies involving patients undergoing coronary artery bypass operations, we found that normothermic blood cardioplegia preserved myocardial metabolism and function compared to hypothermic blood cardioplegia [25]. The optimal temperature for allograft storage remains controversial. Sakaguchi and colleagues [26] found that myocardial storage at subzero nonfreezing temperatures (-1°C) improved myocardial preservation. These authors reasoned that reducing the temperature of storage from 4 to -1°C would reduce myocardial metabolism by two to threefold leading to less accumulation of toxic metabolites. However, these authors used a static storage method. The use of continuous perfusion, as in this study, may also prevent the accumulation of toxic metabolites. Allowing persistent metabolism by increasing the storage temperature may allow for higher ATP production and lead to improved recovery of myocardial function. We are currently investigating this hypothesis.
In summary, the harvesting of shed mediastinal blood from the chest cavity of a donor animal provides an acceptable perfusate for myocardial protection during hypothermic storage. The addition of insulin to this perfusate appears to improve the recovery of aerobic myocardial metabolism and leads to improved systolic function following hypothermic storage. Additional studies are required to further improve the transition from anaerobic to aerobic metabolism following prolonged ischemia. Improved methods of allograft preservation may lead to improved early and late survival after cardiac transplantation.
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Acknowledgments
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The authors appreciate the assistance of Frank Merante, PhD, Molly Mohabeer, and Laura C. Tumiati for analysis of biochemical specimens.
Supported by the Heart and Stroke Foundation (HSFO) of Canada (Grant NA4033). Richard D. Weisel, MD, is a Career Investigator of the HSFO.
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Abstract
Introduction
