Ex vivo cardiac allograft preservation by continuous perfusion techniques

The Challenges of O2 Detection in Biological Fluids: Classical Methods and Translation to Clinical Applications

Dissolved oxygen (DO) is deeply involved in preserving the life of cellular tissues and human beings due to its key role in cellular metabolism: its alterations may reflect important pathophysiological conditions. DO levels are measured to identify pathological conditions, explain pathophysiological mechanisms, and monitor the efficacy of therapeutic approaches. This is particularly relevant when the measurements are performed in vivo but also in contexts where a variety of biological and synthetic media are used, such as ex vivo organ perfusion. A reliable measurement of medium oxygenation ensures a high-quality process. It is crucial to provide a high-accuracy, real-time method for DO quantification, which could be robust towards different medium compositions and temperatures. In fact, biological fluids and synthetic clinical fluids represent a challenging environment where DO interacts with various compounds and can change continuously and dynamically, and further precaution is needed to obtain reliable results. This study aims to present and discuss the main oxygen detection and quantification methods, focusing on the technical needs for their translation to clinical practice. Firstly, we resumed all the main methodologies and advancements concerning dissolved oxygen determination. After identifying the main groups of all the available techniques for DO sensing based on their mechanisms and applicability, we focused on transferring the most promising approaches to a clinical in vivo/ex vivo setting.

Temperature-Related Effects of Myocardial Protection Strategies in Swine Hearts after Prolonged Warm Ischemia

Insufficient supply of cardiac grafts represents a severe obstacle in heart transplantation. Donation after circulatory death (DCD), in addition to conventional donation after brain death, is one promising option to overcome the organ shortage. However, DCD organs undergo an inevitably longer period of unprotected warm ischemia between circulatory arrest and graft procurement. In this scenario, we aim to improve heart preservation after a warm ischemic period of 20 min by testing different settings of myocardial protective strategies. Pig hearts were collected from a slaughterhouse and assigned to one of the five experimental groups: baseline (BL), cold cardioplegia (CC), cold cardioplegia + adenosine (CC-ADN), normothermic cardioplegia (NtC + CC) or normothermic cardioplegia + cold cardioplegia + adenosine (NtC-ADN + CC). After treatment, tissue biopsies were taken to assess mitochondrial morphology, antioxidant enzyme activity, lipid peroxidation and cytokine and chemokine expressions. NtC + CC treatment significantly prevented mitochondria swelling and mitochondrial cristae loss. Moreover, the antioxidant enzyme activity was lower in this group, as was lipid peroxidation, and the pro-inflammatory chemokine GM-CSF was diminished. Finally, we demonstrated that normothermic cardioplegia preserved mitochondria morphology, thus preventing oxidative stress and the subsequent inflammatory response. Therefore, normothermic cardioplegia is a better approach to preserve the heart after a warm ischemia period, with respect to cold cardioplegia, before transplantation.

Oxygenated machine perfusion at room temperature as an alternative for static cold storage in porcine donor hearts

Background

There is a continued interest in ex situ heart perfusion as an alternative strategy for donor heart preservation. We hypothesize that oxygenated machine perfusion of donor hearts at a temperature that avoids both normothermia and deep hypothermia offers adequate and safe preservation.

Methods

Cardioplegia‐arrested porcine donor hearts were randomly assigned to six hours of preservation using cold storage (CS, n = 5) or machine perfusion using an oxygenated acellular perfusate at 21°C (MP, n = 5). Subsequently, all grafts were evaluated using the Langendorff method for 120 min. Metabolic parameters and histology were analyzed. Systolic function was assessed by contractility and elastance. Diastolic function was assessed by lusitropy and stiffness.

Results

For both groups, in vivo baseline and post‐Langendorff biopsies were comparable, as were lactate difference and myocardial oxygen consumption. Injury markers gradually increased and were comparable. Significant weight gain was seen in MP (p = 0.008). Diastolic function was not impaired in MP, and lusitropy was superior from 30 min up to 90 min of reperfusion. Contractility was superior in MP during the first hour of evaluation.

Conclusion

We conclude that the initial functional outcome of MP‐preserved hearts was transiently superior compared to CS, with no histological injury post‐Langendorff. Our machine perfusion strategy could offer feasible and safe storage of hearts prior to transplantation. Future studies are warranted for further optimization.

Pathophysiology of severe primary graft dysfunction in orthotopic heart transplantation

BACKGROUND

A series of insults on the donor heart result in pathophysiological changes that manifest as primary graft dysfunction (PGD) post-orthotopic heart transplantation. The objectives of this study were: (i) describe the pathophysiology of severe PGD using an established cardiovascular model; and (ii) the evolution of the pathophysiology during recovery from severe PGD.

METHODS

Hemodynamic data from 20 consecutive patients with severe PGD (need for mechanical circulatory support, MCS) at baseline (T0), 6 h (T6) and "recovery" (explant of support), and 20 consecutive patients without severe PGD were used to model the pathophysiology using the cardiovascular model described by Burkhoff and Dickstein.

RESULTS

There was a progressive (from T0 to T6) up- and leftward shift in the diastolic pressure-volume relationship, especially of the right ventricle (RV), resulting in reduced capacitance. RV end-systolic elastance (Ees) was significantly elevated in severe PGD but preload-recruitable stroke work (PRSW) was significantly lower compared to patients without severe PGD. "Recovery" (after liberation from MCS) was associated with improvement in RV Ees, chamber capacitance and PRSW, although they remained significantly lower than patients without severe PGD.

CONCLUSION

Severe PGD of the dominant right heart failure phenotype is characterized by reduced chamber capacitance, increased "stiffness" and impaired contractility. Complete normalization was not required for successful weaning of MCS.

Effect of Shenfu Injection on Isolated Empty Beating Hearts from Miniature Pigs

OBJECTIVE

To investigate the effect of Shenfu (SF) injection on donor heart preservation.

METHODS

Twelve pigs were randomly divided into SF group (n=6) and control group (n=6). After eight hours of perfusion, the differences in hemoglobin, the expression of Bcl-2 and BAX, and changes in the myocardial ultrastructure were compared to illustrate the effects of SF injection in heart preservation.

RESULTS

The differences in free hemoglobin between the SF group and the control group were statistically significant (P=0.001), and there was significant interaction of groups with times (P=0.019), but the perfusion time may not be associated with the hemoglobin concentration (P=0.616). According to Western blotting analysis, the expression of Bcl-2 was higher in the SF group than in the control group, while the expression of BAX was not different between the two groups. As to ultrastructural changes, both groups exhibited mitochondrial swelling and myofilament lysis, but the degree of damage in the SF group was smaller.

CONCLUSION

Our study suggests that the application of SF injection for heart preservation may protect against cardiomyocytes and erythrocytes apoptosis, and Bcl-2 protein may play a role in these physiological processes.

New Strategies to Expand and Optimize Heart Donor Pool: Ex Vivo Heart Perfusion and Donation After Circulatory Death: A Review of Current Research and Future Trends

Heart transplantation remains the definitive management for end-stage heart failure refractory to medical therapy. While heart transplantation cases are increasing annually worldwide, there remains a deficiency in organ availability with significant patient mortality while on the waiting list. Attempts have therefore been made to expand the donor pool and improve access to available organs by recruiting donors who may not satisfy the standard criteria for organ donation because of donor pathology, anticipated organ ischemic time, or donation after circulatory death. "Ex vivo" heart perfusion (EVHP) is an emerging technique for the procurement of heart allografts. This technique provides mechanically supported warm circulation to a beating heart once removed from the donor and before implantation into the recipient. EVHP can be sustained for several hours, facilitate extended travel time, and enable administration of pharmacological agents to optimize cardiac recovery and function, as well as allow assessment of allograft function before implantation. In this article, we review recent advances in expanding the donor pool for cardiac transplantation. Current limitations of conventional donor criteria are outlined, including the determinants of organ suitability and assessment, involving transplantation of donation after circulatory death hearts, extended criteria donors, and EVHP-associated assessment, optimization, and transportation. Finally, ongoing research relating to organ optimization and functional ex vivo allograft assessment are reviewed.

Normothermic Ex Vivo Heart Perfusion: Effects of Live Animal Blood and Plasma Cross Circulation

Prolonged normothermic ex vivo heart perfusion could transform cardiac transplantation. To help identify perfusate components that might enable long-term perfusion, we evaluated the effects of cross-circulated whole blood and cross-circulated plasma from a live paracorporeal animal on donor porcine hearts preserved via normothermic ex vivo heart perfusion. Standard perfusion (SP; n = 40) utilized red blood cell/plasma perfusate and Langendorff technique for a goal of 12 hours. Cross-circulation groups used a similar circuit with the addition of cross-circulated venous whole blood (XC-blood; n = 6) or cross-circulated filtered plasma (XC-plasma; n = 7) between a live paracorporeal pig under anesthesia and the perfusate reservoir. Data included oxygen metabolism, vascular resistance, lactate production, left ventricular function, myocardial electrical impedance, and histopathologic injury score. All cross-circulation hearts were successfully perfused for 12 hours, compared with 22 of 40 SP hearts (55%; p = 0.002). Both cross-circulation groups demonstrated higher oxygen consumption and vascular resistance than standard hearts from hours 3-12. No significant differences were seen between XC-blood and XC-plasma hearts in any variable, including left ventricular dP/dT after 12 hours (1478 ± 700 mm Hg/s vs. 872 ± 500; p = 0.17). We conclude that cross circulation of whole blood or plasma from a live animal improves preservation of function of perfused hearts, and cross-circulated plasma performs similarly to cross-circulated whole blood.

Transplantation of Hearts Donated after Circulatory Death

Cardiac transplantation has become limited by a critical shortage of suitable organs from brain-dead donors. Reports describing the successful clinical transplantation of hearts donated after circulatory death (DCD) have recently emerged. Hearts from DCD donors suffer significant ischemic injury prior to organ procurement; therefore, the traditional approach to the transplantation of hearts from brain-dead donors is not applicable to the DCD context. Advances in our understanding of ischemic post-conditioning have facilitated the development of DCD heart resuscitation strategies that can be used to minimize ischemia-reperfusion injury at the time of organ procurement. The availability of a clinically approved ex situ heart perfusion device now allows DCD heart preservation in a normothermic beating state and minimizes exposure to incremental cold ischemia. This technology also facilitates assessments of organ viability to be undertaken prior to transplantation, thereby minimizing the risk of primary graft dysfunction. The application of a tailored approach to DCD heart transplantation that focuses on organ resuscitation at the time of procurement, ex situ preservation, and pre-transplant assessments of organ viability has facilitated the successful clinical application of DCD heart transplantation. The transplantation of hearts from DCD donors is now a clinical reality. Investigating ways to optimize the resuscitation, preservation, evaluation, and long-term outcomes is vital to ensure a broader application of DCD heart transplantation in the future.

Achieving 12 Hour Normothermic Ex Situ Heart Perfusion: An Experience of 40 Porcine Hearts

Although total body perfusion with extracorporeal life support (ECLS) can be maintained for weeks, individual organ perfusion beyond 12 hours has yet to be achieved clinically. Normothermic ex situ heart perfusion (ESHP) offers the potential for prolonged cardiac preservation. We developed an ESHP system to study the effect of perfusate variables on organ preservation, with the ultimate goal of extending organ perfusion for ≥24 hours. Forty porcine hearts were perfused for a target of 12 hours. Hearts that maintained electromechanical activity and had a <3× increase in vascular resistance were considered successful preservations. Perfusion variables, metabolic byproducts, and histopathology were monitored and sampled to identify factors associated with preservation failure. Twenty-two of 40 hearts were successfully preserved at 12 hours. Successful 12 hour experiments demonstrated lower potassium (4.3 ± 0.8 vs. 5.0 ± 1.2 mmol/L; p = 0.018) and lactate (3.5 ± 2.8 vs. 4.5 ± 2.9 mmol/L; p = 0.139) levels, and histopathology revealed less tissue damage (p = 0.003) and less weight gain (p = 0.072). Results of these early experiments suggest prolonged ESHP is feasible, and that elevated lactate and potassium levels are associated with organ failure. Further studies are necessary to identify the ideal perfusate for normothermic ESHP.

Successful transplantation in canines after long-term coronary sinus machine perfusion preservation of donor hearts

BACKGROUND

Machine perfusion is a promising strategy for donor heart preservation, but delivery of perfusate through the aorta may be limited by aortic valve incompetence. We hypothesized that retrograde machine perfusion preservation through the coronary sinus avoided this issue and allowed for recovery of donor hearts after long-term storage.

METHODS

Canine hearts were procured after arrest with 1 liter University of Wisconsin Machine Perfusion Solution (UWMPS) and preserved for 14 hours by static hypothermic storage (Static group, n = 5) or retrograde machine perfusion through the coronary sinus (RP group, n = 5). Myocardial oxygen consumption (MVo2) and lactate were monitored in perfused hearts. Hearts were implanted and reperfused for 6 hours. The pre-load recruitable stroke work was determined as a measure of myocardial function. Cardiac enzyme release was quantified. Cell death was evaluated by TUNEL (terminal deoxynucleotidyltransferase-mediated deoxy uridine triphosphate nick-end label).

RESULTS

MVo2 decreased initially then stabilized. Lactate accumulation was low in RP hearts. All RP hearts separated from cardiopulmonary bypass. All Static hearts required a return to bypass (p < .05). Pre-load recruitable stroke work in RP hearts was increased (55 ± 7 mm Hg) compared with Static (20 ± 11 mm Hg, p < .05) and did not differ from baseline values. Creatine kinase release was greater in Static group hearts (102 ± 16 IU/liter/g) than in RP hearts (51 ± 8 IU/liter/g, p < .05). The fraction of TUNEL-positive cells was higher in the Static group, but this difference was not significant.

CONCLUSIONS

Retrograde machine perfusion can preserve donor hearts for long intervals. Cardiac function after implantation suggested excellent myocardial protection. Retrograde machine perfusion appears promising for extending the donor ischemic interval and improving results of heart transplantation.

Avoidance of Profound Hypothermia During Initial Reperfusion Improves the Functional Recovery of Hearts Donated After Circulatory Death

The resuscitation of hearts donated after circulatory death (DCD) is gaining widespread interest; however, the method of initial reperfusion (IR) that optimizes functional recovery has not been elucidated. We sought to determine the impact of IR temperature on the recovery of myocardial function during ex vivo heart perfusion (EVHP). Eighteen pigs were anesthetized, mechanical ventilation was discontinued, and cardiac arrest ensued. A 15-min standoff period was observed and then hearts were reperfused for 3 min at three different temperatures (5°C; N = 6, 25°C; N = 5, and 35°C; N = 7) with a normokalemic adenosine-lidocaine crystalloid cardioplegia. Hearts then underwent normothermic EVHP for 6 h during which time myocardial function was assessed in a working mode. We found that IR coronary blood flow differed among treatment groups (5°C = 483 ± 53, 25°C = 722 ± 60, 35°C = 906 ± 36 mL/min, p < 0.01). During subsequent EVHP, less myocardial injury (troponin I: 5°C = 91 ± 6, 25°C = 64 ± 16, 35°C = 57 ± 7 pg/mL/g, p = 0.04) and greater preservation of endothelial cell integrity (electron microscopy injury score: 5°C = 3.2 ± 0.5, 25°C = 1.8 ± 0.2, 35°C = 1.7 ± 0.3, p = 0.01) were evident in hearts initially reperfused at warmer temperatures. IR under profoundly hypothermic conditions impaired the recovery of myocardial function (cardiac index: 5°C = 3.9 ± 0.8, 25°C = 6.2 ± 0.4, 35°C = 6.5 ± 0.6 mL/minute/g, p = 0.03) during EVHP. We conclude that the avoidance of profound hypothermia during IR minimizes injury and improves the functional recovery of DCD hearts.

Normothermic ex vivo perfusion provides superior organ preservation and enables viability assessment of hearts from DCD donors

The shortage of donors in cardiac transplantation may be alleviated by the use of allografts from donation after circulatory death (DCD) donors. We have previously shown that hearts exposed to 30 min warm ischemic time and then flushed with Celsior supplemented with agents that activate ischemic postconditioning pathways, show complete recovery on a blood-perfused ex vivo working heart apparatus. In this study, these findings were assessed in a porcine orthotopic heart transplant model. DCD hearts were preserved with either normothermic ex vivo perfusion (NEVP) using a clinically approved device, or with standard cold storage (CS) for 4 h. Orthotopic transplantation into recipient animals was subsequently undertaken. Five of six hearts preserved with NEVP demonstrated favorable lactate profiles during NEVP and all five could be weaned off cardiopulmonary bypass posttransplant, compared with 0 of 3 hearts preserved with CS (p < 0.05, Fisher's exact test). In conclusion, DCD hearts flushed with supplemented Celsior solution and preserved with NEVP display viability before and after transplantation. Viability studies of human DCD hearts using NEVP are warranted.

Addition of long-distance heart procurement promotes changes in heart transplant waiting list status

Objective

Evaluate the addition of long-distance heart procurement on a heart transplant program and the status of heart transplant recipients waiting list.

Methods

Between September 2006 and October 2012, 72 patients were listed as heart transplant recipients. Heart transplant was performed in 41 (57%), death on the waiting list occurred in 26 (36%) and heart recovery occurred in 5 (7%). Initially, all transplants were performed with local donors. Long-distance, interstate heart procurement initiated in February 2011. Thirty (73%) transplants were performed with local donors and 11 (27%) with long-distance donors (mean distance=792 km±397).

Results

Patients submitted to interstate heart procurement had greater ischemic times (212 min ± 32 versus 90 min±18; P<0.0001). Primary graft dysfunction (distance 9.1% versus local 26.7%; P=0.23) and 1 month and 12 months actuarial survival (distance 90.1% and 90.1% versus local 90% and 86.2%; P=0.65 log rank) were similar among groups. There were marked incremental transplant center volume (64.4% versus 40.7%, P=0.05) with a tendency on less waiting list times (median 1.5 month versus 2.4 months, P=0.18). There was a tendency on reduced waiting list mortality (28.9% versus 48.2%, P=0.09).

Conclusion

Incorporation of long-distance heart procurement, despite being associated with longer ischemic times, does not increase morbidity and mortality rates after heart transplant. It enhances viable donor pool, and it may reduce waiting list recipient mortality as well as waiting time.

Preservation of donor hearts using hypothermic oxygenated perfusion

BACKGROUND

Hypothermic machine perfusion of donor hearts enables continuous aerobic metabolism and washout of toxic metabolic byproducts. We evaluated the effect of machine perfusion on cardiac myocyte integrity in hearts preserved for 4 h in a novel device that provides pulsatile oxygenated hypothermic perfusion (Paragonix Sherpa Perfusion™ Cardiac Transport System).

MATERIAL AND METHODS

Pig hearts were harvested and stored in Celsior® solution for 4 h using either conventional cold storage on ice (4-h CS, n=6) or the Sherpa device (4-h pulsatile perfusion (PP), n=6). After cold preservation, hearts were evaluated using a non-working heart Langendorff system. Controls (n=3) were reperfused immediately after organ harvest. Biopsies were taken from the apex of the left ventricle before storage, after storage, and after reperfusion to measure ATP content and endothelin-1 in the tissue. Ultrastructural analysis using electron microscopy was performed.

RESULTS

Four-hour CS, 4-h PP, and control group did not show any significant differences in systolic or diastolic function (+dP/dt, -dP/dt, EDP). Four-hour PP hearts showed significantly more weight gain than 4-h CS after preservation, which shows that machine perfusion led to myocardial edema. Four-hour CS led to higher endothelin-1 levels after preservation, suggesting more endothelial dysfunction compared to 4-h PP. Electron microscopy revealed endothelial cell rupture and damaged muscle fibers in the 4-h CS group after reperfusion, but the cell structures were preserved in the 4-h PP group.

CONCLUSIONS

Hypothermic pulsatile perfusion of donor hearts leads to a better-preserved cell structure compared to the conventional cold storage method. This may lead to less risk of primary graft failure after orthotopic heart transplantation.

Recovery of donor hearts after circulatory death with normothermic extracorporeal machine perfusion

OBJECTIVES

A severe donor organ shortage leads to the death of a substantial number of patients who are listed for transplantation. The use of hearts from donors after circulatory death could significantly expand the donor organ pool, but due to concerns about their viability, these are currently not used for transplantation. We propose short-term ex vivo normothermic machine perfusion (MP) to improve the viability of these ischaemic donor hearts.

METHODS

Hearts from male Lewis rats were subjected to 25 min of global in situ warm ischaemia (WI) (37°C), explanted, reconditioned for 60 min with normothermic (37°C) MP with diluted autologous blood and then stored for 4 h at 0-4°C in Custodiol cold preservation solution. Fresh and ischaemic hearts stored for 4 h in Custodiol were used as controls. Graft function was assessed in a blood-perfused Langendorff circuit.

RESULTS

During reconditioning, both the electrical activity and contractility of the ischaemic hearts recovered rapidly. Throughout the Langendorff reperfusion, the reconditioned ischaemic hearts had a higher average heart rate and better contractility compared with untreated ischaemic controls. Moreover, the reconditioned ischaemic hearts had higher tissue adenosine triphosphate levels and a trend towards improved tissue redox state. Perfusate levels of troponin T, creatine kinase and lactate dehydrogenase were not significantly lower than those of untreated ischaemic controls. The micro- and macroscopic appearance of the reconditioned ischaemic hearts were improved compared with ischaemic controls, but in both groups myocardial damage and oedema were evident.

CONCLUSIONS

Our results indicate that functional recovery from global WI is possible during short-term ex vivo reperfusion, allowing subsequent cold storage without compromising organ viability. We expect that once refined and validated, this approach may enable safe transplantation of hearts obtained from donation after circulatory death.

Metabolic characteristics of human hearts preserved for 12 hours by static storage, antegrade perfusion, or retrograde coronary sinus perfusion

OBJECTIVE

Machine perfusion of donor hearts is a promising strategy to increase the donor pool. Antegrade perfusion is effective but can lead to aortic valve incompetence and nonnutrient flow. Experience with retrograde coronary sinus perfusion of donor hearts has been limited. We tested the hypothesis that retrograde perfusion could support myocardial metabolism over an extended donor ischemic interval.

METHODS

Human hearts from donors that were rejected or not offered for transplantation were preserved for 12 hours in University of Wisconsin Machine Perfusion Solution by: (1) static hypothermic storage; (2) hypothermic antegrade machine perfusion; or (3) hypothermic retrograde machine perfusion. Myocardial oxygen consumption (MVO2), and lactate accumulation were measured. Ventricular tissue was collected for proton and phosphorus 31 magnetic resonance spectroscopy (MRS) to evaluate the metabolic state of the myocardium. Myocardial water content was determined at the end of the experiment.

RESULTS

Stable perfusion parameters were maintained throughout the perfusion period with both perfusion techniques. Lactate/alanine ratios were lower in perfused hearts compared with static hearts (P<.001). Lactate accumulation (antegrade 2.0±0.7 mM, retrograde 1.7±0.1 mM) and MVO2 (antegrade 0.25±0.2 mL, retrograde 0.26±0.3 mL O2/min/100 g) were similar in machine-perfused groups. High-energy phosphates were better preserved in both perfused groups (P<.05). Left ventricular myocardial water content was increased in retrograde perfused hearts (80.2±0.8%) compared with both antegrade perfused hearts (76.6±0.8%, P=.02) and static storage hearts (76.7±1%, P=.02).

CONCLUSIONS

Machine perfusion by either the antegrade or the retrograde technique can support myocardial metabolism over long intervals. Machine perfusion seems promising for long-term preservation of human donor hearts.

Heart transplantation outcomes from cardiac arrest-resuscitated donors

BACKGROUND

The aim of this study was to compare the outcomes of heart transplantation from cardiopulmonary-resuscitated donors (CPR(+)) to those who received hearts from donors who did not require cardiopulmonary resuscitation (CPR(-)).

METHODS

This investigation was a retrospective analysis of UNOS adult heart transplantation donor and recipient data from May 1994 through July 2012. Discrete variables were compared using the chi-square test. Continuous variables were compared using the t-test. Patient and graft survival rates were calculated using the actuarial method and compared using Wilcoxon's test.

RESULTS

Of the 29,242 adult heart transplantations performed in USA during the study period, 1,396 patients (4.7%) received hearts from CPR(+) donors. The patients in the CPR(+) group were younger (25.5 ± 15 years vs 28.5 ± 14 years; p < 0.0001) and more likely to be female (31% vs 27%; p = 0.001). Mean duration of CPR in these donors was 20 minutes. UNOS listing status at the time of transplantation was Status 1A for 54.3% of those in the CPR(+) group and 46.9% in the CPR(-) group (p < 0.0001). More recipients were hospitalized and were in the intensive care unit at transplantation in the CPR(+) group (56% vs 51%; p = 0.0008). Recipient survival at 30 days, 1 year and 5 years was 95.2%, 88.2% and 72.9% in CPR(+) group, and 94.7%, 87.7% and 74.4% in the CPR(-) group, respectively. Similarly, graft survival at 30 days, 1 year and 5 years was 94.7%, 87.6% and 71.9% in the CPR(+) donor hearts, and 94.4%, 87.3% and 73.2% in the CPR(-) donor hearts, respectively.

CONCLUSIONS

This large, multicenter adult heart transplant database from across the USA did not show inferior outcomes in recipients of heart transplantation from selected CPR(+) donors. Recipient and graft survival were similar over 5 years of follow-up.

Ex vivo perfusion of the swine heart as a method for pre-transplant assessment

We describe a cost-effective, reproducible circuit in a porcine, ex vivo, continuous warm-blood, bi-ventricular, working heart model that has future possibilities for pre-transplant assessment of marginal hearts donated from brain stem dead donors and hearts donated after circulatory determination of death (DCDD). In five consecutive experiments over five days, pressure volume loops were performed. During working mode, the left ventricular end systolic pressure volume relationship (LV ESPVR) was 23.1±11.1 mmHg/ml and the LV preload recruitable stroke work (PRSW) was 67.8±7.2. (Standard PVAN analysis software) (Millar Instruments, Houston, TX, USA) All five hearts were perfused for 219±64 minutes and regained normal cardiac function on the perfusion system.They displayed a significant upward and leftward shift of the end systolic pressure volume relationship, a significant increase in preload recruitable stroke work and minimal stiffness. These hearts could potentially be considered for transplantation. The circuit was effective during reperfusion and working modes whilst proving to be successful in maintaining cardiac function in excess of four hours. Using an autologous prime of approximately 20% haematocrit (Hct), electrolytes and blood gases were easy to control within this period using standard perfusion techniques.

Continuous perfusion of donor hearts with oxygenated blood cardioplegia improves graft function

Donor hearts cannot be preserved beyond 6h using cold storage (CS). Improving preservation methods may permit prolonged storage of donor heart. We compared graft function in large animal model after prolonged preservation (8h) using continuous perfusion (CP) and CS method. Twenty-four miniature pigs were used as donors and recipients. Donor hearts were either stored in University of Wisconsin solution (UW solution) for 8h at 0-4°C (CS group, n=6) or were continuously perfused with oxygenated blood cardioplegia at 26°C for 8h (CP group, n=6). After preservation, hearts were transplanted into recipients and reperfused for 3h. Left ventricular (LV) function, cardiac output (CO), malondialdehyde (MDA) and adenosine triphosphate (ATP) levels, and water content were measured. Although water content of CP hearts was higher than that of CS, LV contractility and diastolic function of CP hearts were superior to those of CS. In addition, CP hearts performed better than CS hearts on CO in working heart state. ATP was better preserved and MDA levels were lower in CP hearts compared with those of CS (P<0.0001). Donor hearts can be preserved longer using continuous perfusion with oxygenated blood cardioplegia and this method prevents time-dependent ischemic injury.

Myocardial perfusion characteristics during machine perfusion for heart transplantation

BACKGROUND

Optimal parameters for machine perfusion preservation of hearts prior to transplantation have not been determined. We sought to define regional myocardial perfusion characteristics of a machine perfusion device over a range of conditions in a large animal model.

METHODS

Dog hearts were connected to a perfusion device (LifeCradle, Organ Transport Systems, Inc, Frisco, TX) and cold perfused at differing flow rates (1) at initial device startup and (2) over the storage interval. Myocardial perfusion was determined by entrapment of colored microspheres. Myocardial oxygen consumption (MVO(2)) was estimated from inflow and outflow oxygen differences. Intra-myocardial lactate was determined by (1)H magnetic resonance spectroscopy.

RESULTS

MVO(2) and tissue perfusion increased up to flows of 15 mL/100 g/min, and the ratio of epicardial:endocardial perfusion remained near 1:1. Perfusion at lower flow rates and when low rates were applied during startup resulted in decreased capillary flow and greater non-nutrient flow. Increased tissue perfusion correlated with lower myocardial lactate accumulation but greater edema.

CONCLUSIONS

Myocardial perfusion is influenced by flow rates during device startup and during the preservation interval. Relative declines in nutrient flow at low flow rates may reflect greater aortic insufficiency. These factors may need to be considered in clinical transplant protocols using machine perfusion.

Intermittent antegrade cardioplegia: isolated heart preservation with the Asporto heart preservation device

BACKGROUND

A major problem in procurement of donor hearts is the limited time a donor heart remains viable. After cardiectomy, ischemic hypoxia is the main cause of donor heart degradation. The global myocardial ischemia causes a cascade of oxygen radical formation that cumulates in an elevation in hydrogen ions (decrease in pH), irreversible cellular injury, and potential microvascular changes in perfusion.

OBJECTIVE

To determine the changes of prolonged storage times on donor heart microvasculature and the effects of intermittent antegrade perfusion.

MATERIALS AND METHODS

Using porcine hearts flushed with a Ribosol-based cardioplegic solution, we examined how storage time affects microvascular myocardial perfusion by using contrast-enhanced magnetic resonance imaging at a mean (SD) of 6.1 (0.6) hours (n = 13) or 15.6 (0.6) hours (n = 11) after cardiectomy. Finally, to determine if administration of cardioplegic solution affects pH and microvascular perfusion, isolated hearts (group 1, n = 9) given a single antegrade dose, were compared with hearts (group 2, n = 8) given intermittent antegrade cardioplegia (150 mL, every 30 min, 150 mL/min) by a heart preservation device. Khuri pH probes in left and right ventricular tissue continuously measured hydrogen ion levels, and perfusion intensity on magnetic resonance images was plotted against time.

RESULTS

Myocardial perfusion measured via magnetic resonance imaging at 6.1 hours was significantly greater than at 15.6 hours (67% vs 30%, P = .00008). In group 1 hearts, the mean (SD) for pH at the end of 6 hours decreased to 6.2 (0.2). In group 2, hearts that received intermittent antegrade cardioplegia, pH at the end of 6 hours was higher at 6.7 (0.3) (P = .0005). Magnetic resonance imaging showed no significant differences between the 2 groups in contrast enhancement (group 1, 62%; group 2, 40%) or in the wet/dry weight ratio.

CONCLUSION

Intermittent perfusion maintains a significantly higher myocardial pH than does a conventional single antegrade dose. This difference may translate into an improved quality of donor hearts procured for transplantation, allowing longer distance procurement, tissue matching, improved outcomes for transplant recipients, and ideally a decrease in transplant-related costs.

Intermittent Antegrade Cardioplegia: Isolated Heart Preservation with the Asporto Heart Preservation Device

Background

A major problem in procurement of donor hearts is the limited time a donor heart remains viable. After cardiectomy, ischemic hypoxia is the main cause of donor heart degradation. The global myocardial ischemia causes a cascade of oxygen radical formation that cumulates in an elevation in hydrogen ions (decrease in pH), irreversible cellular injury, and potential microvascular changes in perfusion.

Objective

To determine the changes of prolonged storage times on donor heart microvasculature and the effects of intermittent antegrade perfusion.

Materials and Methods

Using porcine hearts flushed with a Ribosol-based cardioplegic solution, we examined how storage time affects microvascular myocardial perfusion by using contrast-enhanced magnetic resonance imaging at a mean (SD) of 6.1 (0.6) hours (n=13) or 15.6 (0.6) hours (n=11) after cardiectomy. Finally, to determine if administration of cardioplegic solution affects pH and microvascular perfusion, isolated hearts (group 1, n=9) given a single antegrade dose, were compared with hearts (group 2, n=8) given intermittent antegrade cardioplegia (150 mL, every 30 min, 150 mL/min) by a heart preservation device. Khuri pH probes in left and right ventricular tissue continuously measured hydrogen ion levels, and perfusion intensity on magnetic resonance images was plotted against time.

Results

Myocardial perfusion measured via magnetic resonance imaging at 6.1 hours was significantly greater than at 15.6 hours (67% vs 30%, P=.00008). In group 1 hearts, the mean (SD) for pH at the end of 6 hours decreased to 6.2 (0.2). In group 2, hearts that received intermittent antegrade cardioplegia, pH at the end of 6 hours was higher at 6.7 (0.3) ( P=.0005). Magnetic resonance imaging showed no significant differences between the 2 groups in contrast enhancement (group 1, 62%; group 2, 40%) or in the wet/dry weight ratio.

Conclusion

Intermittent perfusion maintains a significantly higher myocardial pH than does a conventional single antegrade dose. This difference may translate into an improved quality of donor hearts procured for transplantation, allowing longer distance procurement, tissue matching, improved outcomes for transplant recipients, and ideally a decrease in transplant-related costs.

Perfusion preservation maintains myocardial ATP levels and reduces apoptosis in an ex vivo rat heart transplantation model

BACKGROUND

Machine perfusion preservation improves reperfusion function of many solid organs, compared with conventional storage, but has received limited clinical attention in preserving hearts for transplantation. We evaluated representative extracellular (Celsior) and intracellular (University of Wisconsion) storage solutions using static and perfusion protective strategies over a clinically relevant preservation period.

METHODS

Rat hearts were preserved for 200 minutes by either static storage or perfusion preservation in Celsior or University of Wisconsin solutions. Three conditions were studied: conventional static storage; static storage using either solution with 5.5 mmol/L glucose added; and perfusion preservation using either solution with 5.5 mmol/L glucose added. Glucose was provided as U-13C-labeled glucose, and glycolysis and oxidative metabolism during preservation were quantified from incorporation of (13)C into glycolytic and tricarboxylic acid cycle intermediates. Adenosine triphosphate levels after preservation, and apoptosis and cardiac function after reperfusion were measured.

RESULTS

Both perfusion preservation groups had higher myocardial oxygen consumption during storage and better early graft function, compared with static preservation groups (P < .05). Adenosine triphosphate levels were higher after storage in the perfusion groups (P < .01). Apoptosis was reduced in the perfusion groups (P < .01). Comparing perfusion groups, hearts preserved with Celsior had higher myocardial oxygen consumption and glucose utilization during perfusion storage and exhibited decreased reperfusion coronary vascular resistance and myocardial water content, compared with the UW perfusion group (P < .05).

CONCLUSIONS

Perfusion preservation results in greater metabolism during storage and superior cardiac function with improved myocyte survival, compared with static storage. Extracellular preservation solutions appear more effective for perfusion preservation, possibly by augmenting cellular metabolism.