Perfusion Preservation versus Static Preservation for Cardiac Transplantation: Effects on Myocardial Function and Metabolism

Nonischemic Donor Heart Preservation: New Milestone in Heart Transplantation History

Heart transplantation is considered the gold standard for the treatment of advanced end-stage heart failure. However, standard donors after brain death are decreasing, whereas patients on the heart transplant waitlist are constantly rising. The introduction of the ex vivo machine perfusion device has been a turning point; in fact, these systems are able to significantly reduce ischemic times and have a potential effect on ischemia-related damage reduction. From a clinical standpoint, these machines show emerging results in terms of heart donor pool expansion, making marginal donors and donor grafts after circulatory death suitable for donation. This article aims to review mechanisms and preclinical and clinical outcomes of currently available ex vivo perfusion systems, and to explore the future fields of application of these technologies.

Cold Oxygenated Machine Perfusion Improves Functional Survival of Slaughterhouse Porcine Hearts

The aim of our study was to explore the effect of cold oxygenated machine perfusion in slaughterhouse porcine hearts on functional myocardial survival compared to static cold storage (SCS). Seventeen hearts were harvested from Dutch Landrace Hybrid pigs, which were sacrificed for human consumption and randomly assigned to the 4 hours SCS group (N = 10) or the 4 hours cold oxygenated machine perfusion group (N = 7). Hearts were perfused with a homemade Heart Solution with a perfusion pressure of 20-25 mm Hg to achieve a coronary flow between 100 and 200 ml/minute. After 4 hours of preservation, all hearts were functionally assessed during 4 hours on a normothermic, oxygenated diluted whole blood (1:2) loaded heart model. Survival was defined by a cardiac output above 3 L with a mean aortic pressure above 60 mm Hg. Survival was significantly better in the cold oxygenated machine perfusion group, where 100% of the hearts reached the 4 hours end-point, as compared with 30% in the SCS group ( p = 0.006). Interestingly, warm ischemic time was inversely related to survival in the SCS group with a correlation coefficient of -0.754 ( p = 0.012). Cold oxygenated machine perfusion improves survival of the slaughterhouse porcine heart.

Cyclophilin D Regulates the Nuclear Translocation of AIF, Cardiac Endothelial Cell Necroptosis and Murine Cardiac Transplant Injury

Ischemia-reperfusion injury (IRI) is an inevitable consequence of organ transplant procedure and associated with acute and chronic organ rejection in transplantation. IRI leads to various forms of programmed cell death, which worsens tissue damage and accelerates transplant rejection. We recently demonstrated that necroptosis participates in murine cardiac microvascular endothelial cell (MVEC) death and murine cardiac transplant rejection. However, MVEC death under a more complex IRI model has not been studied. In this study, we found that simulating IRI conditions in vitro by hypoxia, reoxygenation and treatment with inflammatory cytokines induced necroptosis in MVECs. Interestingly, the apoptosis-inducing factor (AIF) translocated to the nucleus during MVEC necroptosis, which is regulated by the mitochondrial permeability molecule cyclophilin D (CypD). Furthermore, CypD deficiency in donor cardiac grafts inhibited AIF translocation and mitigated graft IRI and rejection (n = 7; p = 0.002). Our studies indicate that CypD and AIF play significant roles in MVEC necroptosis and cardiac transplant rejection following IRI. Targeting CypD and its downstream AIF may be a plausible approach to inhibit IRI-caused cardiac damage and improve transplant survival.

Myocardial Substrate Oxidation and Tricarboxylic Acid Cycle Intermediates During Hypothermic Machine Perfusion

BACKGROUND

The optimal substrate for hypothermic machine perfusion preservation of donor hearts is unknown. Fatty acids, acetate, and ketones are preferred substrates of the heart during normothermic perfusion, but cannot replete the tricarboxylic acid (TCA) cycle directly. Propionate, an anaplerotic substrate, can replenish TCA cycle intermediates and may affect cardiac metabolism. The purpose of this study was to determine myocardial substrate preferences during hypothermic machine perfusion and to assess if an anaplerotic substrate was required to maintain the TCA cycle intermediate pool in perfused hearts.

METHODS

Groups of rat hearts were perfused with carbon-13 (¹³C)-labeled substrates (acetate, β-hydroxybutyrate, octanoate, with and without propionate) at low and high concentrations. TCA cycle intermediate concentrations, substrate selection, and TCA cycle flux were determined by gas chromatography/mass spectroscopy and ¹³C magnetic resonance spectroscopy.

RESULTS

Acetate and octanoate were preferentially oxidized, whereas β-hydroxybutyrate was a minor substrate. TCA cycle intermediate concentrations except fumarate were higher in substrate-containing perfusion groups compared with either the no-substrate perfusion group or the no-ischemia control group.

CONCLUSIONS

The presence of an exogenous, oxidizable substrate is required to support metabolism in the cold perfused heart. An anaplerotic substrate is not essential to maintain the TCA cycle intermediate pool and support oxidative metabolism under these conditions.

The Role of Metabolomics in Current Concepts of Organ Preservation

In solid organ transplantation (Tx), both survival rates and quality of life have improved dramatically over the last few decades. Each year, the number of people on the wait list continues to increase, widening the gap between organ supply and demand. Therefore, the use of extended criteria donor grafts is growing, despite higher susceptibility to ischemia-reperfusion injury (IRI) and consecutive inferior Tx outcomes. Thus, tools to characterize organ quality prior to Tx are crucial components for Tx success. Innovative techniques of metabolic profiling revealed key pathways and mechanisms involved in IRI occurring during organ preservation. Although large-scale trials are needed, metabolomics appears to be a promising tool to characterize potential biomarkers, for the assessment of graft quality before Tx and evaluate graft-related outcomes. In this comprehensive review, we summarize the currently available literature on the use of metabolomics in solid organ Tx, with a special focus on metabolic profiling during graft preservation to assess organ quality prior to Tx.

A nonrandomized open-label phase 2 trial of nonischemic heart preservation for human heart transplantation

Pre-clinical heart transplantation studies have shown that ex vivo non-ischemic heart preservation (NIHP) can be safely used for 24 h. Here we perform a prospective, open-label, non-randomized phase II study comparing NIHP to static cold preservation (SCS), the current standard for adult heart transplantation. All adult recipients on waiting lists for heart transplantation were included in the study, unless they met any exclusion criteria. The same standard acceptance criteria for donor hearts were used in both study arms. NIHP was scheduled in advance based on availability of device and trained team members. The primary endpoint was a composite of survival free of severe primary graft dysfunction, free of ECMO use within 7 days, and free of acute cellular rejection ≥2R within 180 days. Secondary endpoints were I/R-tissue injury, immediate graft function, and adverse events. Of the 31 eligible patients, six were assigned to NIHP and 25 to SCS. The median preservation time was 223 min (IQR, 202–263) for NIHP and 194 min (IQR, 164–223) for SCS. Over the first six months, all of the patients assigned to NIHP achieved event-free survival, compared with 18 of those assigned to SCS (Kaplan-Meier estimate of event free survival 72.0% [95% CI 50.0–86.0%]). CK-MB assessed 6 ± 2 h after ending perfusion was 76 (IQR, 50–101) ng/mL for NIHP compared with 138 (IQR, 72–198) ng/mL for SCS. Four deaths within six months after transplantation and three cardiac-related adverse events were reported in the SCS group compared with no deaths or cardiac-related adverse events in the NIHP group. This first-in-human study shows the feasibility and safety of NIHP for clinical use in heart transplantation. ClinicalTrial.gov, number NCT03150147

Ischemia and reperfusion damage contribute to early graft dysfunction and recipient’s death. Here the authors show the feasibility and safety of a non-ischemic heart preservation method for heart transplantation in a non-randomized trial.

Cardiac donation after circulatory death

PURPOSE OF REVIEW

Increasing number of patients with end-stage heart failure and those with improved survivorship from selective utilization of implantable mechanical circulatory support devices have added further burden and complexity to the transplant waitlist and on the rate-limiting availability of donor hearts from the standard pathway of donation after brain death. Unlike this conventional route, the increasing clinical use of donation after circulatory death (DCD) donor hearts necessitates a closer understanding of the logistics involved in the DCD process as well as of the risks associated with the unique pathophysiological consequences in this setting.

RECENT FINDINGS

Notwithstanding a higher incidence of delayed graft function, the clinical utilization of DCD hearts for cardiac transplantation over the past five years has demonstrated this to be a well-tolerated and strategic alternative with excellent medium-term clinical outcomes.

SUMMARY

The uptake of DCD heart transplantation remains selective and currently confined to Australia, the United Kingdom, Belgium, and more recently the USA. A more significant adoption will only come about through: a concerted effort to resolve the ethical and clinical controversies; a better understanding of postconditioning strategies; continued resolve to reduce the obligatory period of warm ischemia; and from better extracorporeal platforms that permit functional viability assessment of the DCD donor heart.

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.

The donor heart and organ perfusion technology

Recent advancement in organ perfusion technology has led to increase clinical transplantation of marginal donor organs and allow for distant procurement of cardiac allograft beyond the time limitation of cold static storage. Ex-situ heart perfusion also provides essential nutrients to maintain cell integrity, thereby reducing the risk of ischaemic injury for functional preservation and provides a platform to assess organ viability and feasibility, with the potential for pharmacotherapy to recover these hearts. Notably, the use of NMP has led to the first distant procurement cardiac transplantation from a donation after circulatory death (DCD) in 2014, which resulted in the adoption of DCD heart transplantation in 4 centres between the United Kingdom and Australia. To date, over 100 DCD heart transplants have been performed utilising cardiac perfusion system with an estimated 10-15% increase in transplant activity in the individual units. This review aims to provide an overview of current experience and outcomes using cardiac perfusion technology, including future technologies and recent advancement within the field.

Machine perfusion of thoracic organs

This article summarizes recent knowledge and clinical advances in machine perfusion (MP) of thoracic organs. MP of thoracic organs has gained much attention during the last decade. Clinical studies are investigating the role of MP to preserve, resuscitate, and assess heart and lungs prior to transplantation. Currently, MP of the cardiac allograft is essential in all type DCD heart transplantation while MP of the pulmonary allograft is mandatory in uncontrolled DCD lung transplantation. MP of thoracic organs also offers an exciting platform to further investigate downregulation of the innate and adaptive immunity prior to reperfusion of the allograft in recipients. MP provides a promising technology that allows pre-transplant preservation, resuscitation, assessment, repair, and conditioning of cardiac and pulmonary allografts outside the body in a near physiologic state prior to planned transplantation. Results of ongoing clinical trials are awaited to estimate the true clinical value of this new technology in advancing the field of heart and lung transplantation by increasing the total number and the quality of available organs and by further improving recipient early and long-term outcome.

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.

Donor selection in the modern era

The growing disparity between the supply of donor hearts for transplantation and the demand for such organs has led to liberalization of the criteria for donor heart acceptance over the past few decades. The upper age limit and size restrictions for donor heart acceptance continue to be revised and hearts are being routinely used from donors with left ventricular dysfunction, left ventricular hypertrophy (LVH), cocaine use, multiple medical co-morbidities and after cardiopulmonary resuscitation. This article reviews recent data for use of such "expanded criteria" donor hearts and suggests ways to further increase the donor pool, including use of hearts from donors with hepatitis C and after circulatory determination of death. Donor biomarkers and risk scores may eventually aid in heart acceptance decisions, while ethical issues surrounding information sharing with transplant recipients remain a topic of great debate.

Blockade of Inflammation and Apoptosis Pathways by siRNA Prolongs Cold Preservation Time and Protects Donor Hearts in a Porcine Model

In donor hearts from mini pigs, overtime cold preservation and ischemia-reperfusion injury cause poor graft quality and impaired heart function. Blockage of complement, apoptosis, and inflammation is considered a strategy for attenuating ischemia-reperfusion injury and protecting cardiac function. Minipig donor hearts were perfused and preserved in Celsior solution or transfection reagent containing Celsior solution with scramble siRNA or siRNAs targeting complement 3, caspase-8, caspase-3, and nuclear factor κB-p65 genes at 4°C and subsequently hemo-reperfused ex vivo (38°C) or transplanted into recipients. The protective effect of the siRNA solution was evaluated by measuring cell apoptosis, structural alteration, protein markers for tissue damage and oxidative stress, and cardiac function. We found a reduction in cell apoptosis, myocardial damage, and tissue inflammation by reduced biochemistry and markers and protein expression of proinflammatory cytokines and improvement in cardiac function, as shown by the improved hemodynamic indices in 12-hr-preserved siRNA-treated hearts of both ex vivo and orthotopic transplantation models. These findings demonstrate that blockade of inflammation and apoptosis pathways using siRNA can prolong cold preservation time and better protect donor heart function in cardiac transplantation of large animals, which may be beneficial for human heart preservation.

(13)C glucose labelling studies using 2D NMR are a useful tool for determining ex vivo whole organ metabolism during hypothermic machine perfusion of kidneys

Background

The aim of this study is to determine the feasibility of using nuclear magnetic resonance (NMR) tracer studies (¹³C-enriched glucose) to detect ex vivo de novo metabolism in the perfusion fluid and cortical tissue of porcine kidneys during hypothermic machine perfusion (HMP).

Methods

Porcine kidneys (n = 6) were subjected to 24 h of HMP using the Organ Recovery Systems LifePort Kidney perfusion device. Glucose, uniformly enriched with the stable isotope ¹³C ([U-¹³C] glucose), was incorporated into KPS-1-like perfusion fluid at a concentration of 10 mM. Analysis of perfusate was performed using both 1D ¹H and 2D ¹H,¹³C heteronuclear single quantum coherence (HSQC) NMR spectroscopy. The metabolic activity was then studied by quantifying the proportion of key metabolites containing ¹³C in both perfusate and tissue samples.

Results

There was significant enrichment of ¹³C in a number of central metabolites present in both the perfusate and tissue extracts and was most pronounced for lactate and alanine. The total amount of enriched lactate (per sample) in perfusion fluid increased during HMP (31.1 ± 12.2 nmol at 6 h vs 93.4 ± 25.6 nmol at 24 h p < 0.01). The total amount of enriched alanine increased in a similar fashion (1.73 ± 0.89 nmol at 6 h vs 6.80 ± 2.56 nmol at 24 h p < 0.05). In addition, small amounts of enriched acetate and glutamic acid were evident in some samples.

Conclusions

This study conclusively demonstrates that de novo metabolism occurs during HMP and highlights active metabolic pathways in this hypothermic, hypoxic environment. Whilst the majority of the ¹³C-enriched glucose is metabolised into glycolytic endpoint metabolites such as lactate, the presence of non-glycolytic pathway derivatives suggests that metabolism during HMP is more complex than previously thought. Isotopic labelled ex vivo organ perfusion studies using 2D NMR are feasible and informative.

Safe orthotopic transplantation of hearts harvested 24 hours after brain death and preserved for 24 hours

Objectives. The aim of this study was to demonstrate safe orthotopic transplantation of porcine donor hearts harvested 24 hours after brain death and preserved for 24 hours before transplantation. Design. Circulatory normalization of brain dead (decapitated) pigs was obtained using a new pharmacological regimen (n = 10). The donor hearts were perfused at 8 °C in cycles of 15 min perfusion followed by 60 min without perfusion. The perfusate consisted of an albumin-containing hyperoncotic cardioplegic nutrition solution with hormones and erythrocytes. Orthotopic transplantation was done in 10 recipient pigs after 24 hours’ preservation. Transplanted pigs were monitored for 24 hours, then an adrenaline stress test was done. Results. All transplanted pigs were stable throughout the 24-hour observation period with mean aortic pressure around 80 mmHg and normal urine production. Mean right and left atrial pressures were in the range of 3–6 and 5–10 mmHg, respectively. Blood gases at 24 hours did not differ from baseline values. The adrenaline test showed a dose dependent response, with aortic pressure increasing from 98/70 to 220/150 mmHg and heart rate from 110 to 185 beats/min. Conclusion. Orthotopic transplantation of porcine hearts harvested 24 hours after brain death and preserved for 24 hours can be done safely.

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.

Hypothermic continuous machine perfusion enables preservation of energy charge and functional recovery of heart grafts in an ex vivo model of donation following circulatory death

OBJECTIVES

Cardiac transplantation using hearts from donors after circulatory death (DCD) is critically limited by the unavoidable warm ischaemia and its related unpredictable graft function. Inasmuch as hypothermic machine perfusion (MP) has been shown to improve heart preservation, we hypothesized that MP could enable the use of DCD hearts for transplantation.

METHODS

We recovered 16 pig hearts following anoxia-induced cardiac arrest and cardioplegia. Grafts were randomly assigned to two different groups of 4-h preservation using either static cold storage (CS) or MP (Modified LifePort© System, Organ Recovery Systems©, Itasca, Il). After preservation, the grafts were reperfused ex vivo using the Langendorff method for 60 min. Energetic charge was quantified at baseline, post-preservation and post-reperfusion by measuring lactate and high-energy phosphate levels. Left ventricular contractility parameters were assessed both in vivo prior to ischaemia and ex vivo during reperfusion.

RESULTS

Following preservation, the hearts that were preserved using CS exhibited higher lactate levels (57.1 ± 23.7 vs 21.4 ± 12.2 µmol/g; P < 0.001), increased adenosine monophosphate/adenosine triphosphate ratio (0.53 ± 0.25 vs 0.11 ± 0.11; P < 0.001) and lower phosphocreatine/creatine ratio (9.7 ± 5.3 vs 25.2 ± 11; P < 0.001) in comparison with the MP hearts. Coronary flow was similar in both groups during reperfusion (107 ± 9 vs 125 ± 9 ml/100 g/min heart; P = ns). Contractility decreased in the CS group, yet remained well preserved in the MP group.

CONCLUSION

MP preservation of DCD hearts results in improved preservation of the energy and improved functional recovery of heart grafts compared with CS.

Subzero 12-hour Nonfreezing Cryopreservation of Porcine Heart in a Variable Magnetic Field

BACKGROUND

A novel subzero nonfreezing heart preservation method has been developed. It uses a refrigerating device that generates a variable magnetic field, allowing the whole organ to be cooled simultaneously to a supercooled state without the use of cryoprotectant. As a fundamental experiment for heart preservation, we verified whether this novel method is able to suppress anaerobic metabolism and reduce damage in the hearts of large animals.

METHODS

Twelve porcine hearts were collected and preserved for 12 hours using a simple immersion method. The hearts were divided into 2 groups: 6 underwent nonfreezing preservation at -3°C in a variable magnetic field (subzero group), and 6 underwent conventional preservation at 4°C (conventional group). The quantity of anaerobic metabolism and the degree of ultrastructural change in the 2 groups were evaluated and compared.

RESULTS

The concentration of adenosine triphosphate in the myocardial tissue was significantly greater in the subzero group than in the conventional group (21.06±5.87 μmol/g vs 5.96±3.41 μmol/g; P < 0.05). The accumulated lactate concentration was significantly lower in the subzero group than in the conventional group (6.58±2.28 μmol/g vs 11.15±3.74 μmol/g; P < 0.05). The Flameng score, an index of ultrastructural changes to the mitochondria, was significantly lower in the subzero group than in the conventional group (1.28±0.40 vs 2.73±0.30; P < 0.05).

CONCLUSIONS

Subzero nonfreezing preservation using a variable magnetic field resulted in a remarkable suppression of anaerobic metabolism and myocardial protection in porcine hearts.

Changing paradigms in organ preservation and resuscitation

PURPOSE OF REVIEW

Shortage of donor organs has increased consideration for use of historically excluded grafts. Ex-vivo machine perfusion is an emerging technology that holds the potential for organ resuscitation and reconditioning, potentially increasing the quality and number of organs available for transplantation. This article aims to review the recent advances in machine perfusion and organ preservation solutions.

RECENT FINDINGS

Flow and pressure-based machine perfusion has shown improved kidney graft function and survival, especially among expanded criteria donors. Pressure-based machine perfusion is demonstrating promising results in preservation and resuscitation of liver, pancreas, heart, and also lung grafts. August 2014 marked Food and Drug Administration approval of XPS XVIVO Perfusion System (XVIVO Perfusion Inc., Englewood, Colorado, USA), a device for preserving and resuscitating lung allografts initially considered unsuitable for transplantation. Although there is no consensus among physicians about the optimal preservation solution, adding antiapoptotic and cell protective agents to preservation solutions is an interesting research area that offers potential to improve preservation.

SUMMARY

Ex-vivo machine perfusion of solid organs is a promising method that provides the opportunity for resuscitation and reconditioning of suboptimal grafts, expanding the number and quality of donor organs.

Preservation of the donor heart: from basic science to clinical studies

The methods of donor heart preservation are aimed at minimizing graft dysfunction caused by ischaemia-reperfusion injury (IRI) which inevitably occurs during the ex vivo transport interval. At present, the standard technique of heart preservation is cardiac arrest followed by static cold storage in a crystalloid heart preservation solution (HPS). This technique ensures an acceptable level of heart protection against IRI for <6 h. In clinical trials, comparable levels of myocardial protection against IRI were provided by various HPSs. The growing shortage of donor hearts is one of the major factors stimulating the development of new techniques of heart preservation. Here, we summarize new HPS formulations and provide a focus for optimization of the composition of existing HPSs. Such methods of donor heart preservation as machine perfusion, preservation at sub-zero temperature and oxygen persufflation are also discussed. Furthermore, we review experimental data showing that pre- and post-conditioning of the cardiac graft can improve its function when used in combination with cold storage. The evidence on the feasibility of cardiac donation after circulatory death, as well as the techniques of heart reconditioning after a period of warm ischaemia, is presented. The implementation of new techniques of donor heart preservation may contribute to the use of hearts from extended criteria donors, thereby expanding the total donor pool.

Hypothermic continuous machine perfusion improves metabolic preservation and functional recovery in heart grafts

The number of heart transplants is decreasing due to organ shortage, yet the donor pool could be enlarged by improving graft preservation. Hypothermic machine perfusion (MP) has been shown to improve kidney, liver, or lung graft preservation. Sixteen pig hearts were recovered following cardioplegia and randomized to two different groups of 4-hour preservation using either static cold storage (CS) or MP (Modified LifePort© System, Organ Recovery Systems, Itasca, Il). The grafts then underwent reperfusion on a Langendorff for 60 min. Energetic metabolism was quantified at baseline, postpreservation, and postreperfusion by measuring lactate and high-energy phosphates. The contractility index (CI) was assessed both in vivo prior to cardioplegia and during reperfusion. Following reperfusion, the hearts preserved using CS exhibited higher lactate levels (56.63 ± 23.57 vs. 11.25 ± 3.92 μmol/g; P < 0.001), increased adenosine monophosphate/adenosine triphosphate (AMP/ATP) ratio (0.4 ± 0.23 vs. 0.04 ± 0.04; P < 0.001), and lower phosphocreatine/creatine (PCr/Cr) ratio (33.5 ± 12.6 vs. 55.3 ± 5.8; P <0.001). Coronary flow was similar in both groups during reperfusion (107 ± 9 vs. 125 + /-9 ml/100 g/min heart; P = ns). CI decreased in the CS group, yet being well-preserved in the MP group. Compared with CS, MP resulted in improved preservation of the energy state and more successful functional recovery of heart graft.

Ex vivo approach to treat failing organs: expanding the limits

BACKGROUND

Advanced organ failure is often classified as an end-stage disease where the treatment options are limited only to transplantation. As an alternative, different attempts have been undertaken to improve the outcome of the treatment of failing organs by using targeted ex vivo approaches. This may solve the issue of organ shortage by treating the donor organs before transplantation and the number of patients requiring transplantation may also be reduced by applying extensive ex vivo treatment followed by autotransplantation.

METHODS

We performed a literature review of PubMed and included articles published between 1962 and 2013. The following keywords were used (and; or): ex vivo, therapy, surgery, organ perfusion and autotransplantation. This review includes specific methods and attempts related to ex vivo organ perfusion and preservation, temporary life support systems, surgical and other therapeutic approaches, and diagnostic methods applied ex vivo to an isolated organ.

RESULTS

For the practical clinical use of ex vivo therapies, we could identify three major directions: (1) ex vivo pretransplant organ reconditioning, (2) ex vivo surgery and (3) ex vivo medical treatment. Different attempts have been made worldwide in the above-mentioned areas focusing on ex vivo organ preservation and treatment. We summarize in the present review the developments in the field of ex vivo organ recovery and evaluate the possibilities of combining and applying different technologies such as organ perfusion and storage, ex vivo exact topographical diagnosis, ex vivo locoregional medical treatment and ex vivo surgical correction.

CONCLUSION

Ex vivo therapies open new horizons in the treatment of end-stage organ pathologies.

Comparative analysis of preservation method and intermittent perfusion volume on the expression of endothelial and inflammatory markers by coronal artery and myocardium in porcine donor hearts

Although continuous perfusion of donor hearts for preservation during transportation has been widely applied, intermittent perfusion has been suggested as an alternative. The aim of this study was to identify the optimal intermittent perfusion protocol by investigating the effects of perfusion volume on endothelial and inflammatory marker expression by the coronary artery. Donor porcine hearts were perfused with various volumes of Celsior solution supplemented with diazoxide (50, 100, 150, 200, and 250 ml) every 2 h for 30 min each for a 10 h period. The effects on cardiomyocytes and vascular endothelial cell morphology and marker expression were compared to the immersion control group. Whereas an incomplete endothelial cell layer with disorganized connective tissue was observed in the control and 50, 100, and 150 ml intermittent perfusion groups, transmission electron microscopic analysis revealed a complete endothelial cell layer in the intima with an organized subendothelium. A perfusion volume-dependent increase in eNOS expression that coincided with a decrease in ET-1, ICAM-1, vWF, and P-selectin expression was detected (all p < 0.01). Intermittent perfusion with 200 ml of Celsior solution every 2 h conferred protective effects simultaneously to the coronary arteries and myocardium on the porcine donor heart over a clinically relevant preservation period.

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.

Functional evaluation of human donation after cardiac death donor hearts using a continuous isolated myocardial perfusion technique: Potential for expansion of the cardiac donor population

OBJECTIVE

To investigate the resuscitation potential and contractile function in adult human donation after cardiac death (DCD) hearts by ex vivo perfusion.

METHODS

With institutional review board approval and under the DCD protocol at the University of Wisconsin (UW) Organ Procurement Organization, 5 brain dead (BD) and 5 DCD donor hearts were evaluated. All BD hearts were declined for clinical transplantation because of coronary artery disease, advanced age, or social history. All hearts were preserved by flushing and cold storage with UW solution. By using our ex vivo perfusion system, the left ventricular end systolic pressure-volume relationship (LV-ESPVR) was assessed for 2 hours of oxygenated blood reperfusion.

RESULTS

All BD (n = 5) and 4 DCD hearts were successfully resuscitated. One DCD heart was unable to be resuscitated due to prolonged warm ischemic time (WIT; 174 minutes). Mean WIT for resuscitated DCD hearts (from extubation to flushing with cold UW solution) was 34 ± 3 minutes (range, 26 to 40 minutes); mean cold ischemic time for BD donors was 211 ± 31 minutes compared with 177 ± 64 minutes for DCD donors. The calculated LV-ESPVRs for BD hearts after 1 and 2 hours of reperfusion were 6.9 ± 0.7 and 5.7 ± 1.0 mm Hg/mL, respectively; LV-ESPVRs for DCD hearts after 1 and 2 hours of reperfusion were 5.6 ± 1.5 (P = .45) and 3.0 ± 0.7 mm Hg/mL (P = .07), respectively.

CONCLUSIONS

We successfully resuscitated and measured ex vivo cardiac function in human DCD and BD donor hearts. Resuscitation potential in DCD hearts was achieved when the WIT was less than 40 minutes. Contractile performance in DCD hearts tended to be lower compared with BD hearts. Further investigation with longer reperfusion periods seems warranted.

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.

A cardioprotective preservation strategy employing ex vivo heart perfusion facilitates successful transplant of donor hearts after cardiocirculatory death

BACKGROUND

Ex vivo heart perfusion (EVHP) has been proposed as a means to facilitate the resuscitation of donor hearts after cardiocirculatory death (DCD) and increase the donor pool. However, the current approach to clinical EVHP may exacerbate myocardial injury and impair function after transplant. Therefore, we sought to determine if a cardioprotective EVHP strategy that eliminates myocardial exposure to hypothermic hyperkalemia cardioplegia and minimizes cold ischemia could facilitate successful DCD heart transplantation.

METHODS

Anesthetized pigs sustained a hypoxic cardiac arrest and a 15-minute warm ischemic standoff period. Strategy 1 hearts (S1, n = 9) underwent initial reperfusion with a cold hyperkalemic cardioplegia, normothermic EVHP, and transplantation after a cold hyperkalemic cardioplegic arrest (current EVHP strategy). Strategy 2 hearts (S2, n = 8) underwent initial reperfusion with a tepid adenosine-lidocaine cardioplegia, normothermic EVHP, and transplantation with continuous myocardial perfusion (cardioprotective EVHP strategy).

RESULTS

At completion of EVHP, S2 hearts exhibited less weight gain (9.7 ± 6.7 [S2] vs 21.2 ± 6.7 [S1] g/hour, p = 0.008) and less troponin-I release into the coronary sinus effluent (4.2 ± 1.3 [S2] vs 6.3 ± 1.5 [S1] ng/ml; p = 0.014). Mass spectrometry analysis of oxidized pleural in post-transplant myocardium revealed less oxidative stress in S2 hearts. At 30 minutes after wean from cardiopulmonary bypass, post-transplant systolic (pre-load recruitable stroke work: 33.5 ± 1.3 [S2] vs 19.7 ± 10.9 [S1], p = 0.043) and diastolic (isovolumic relaxation constant: 42.9 ± 6.7 [S2] vs 65.2 ± 21.1 [S1], p = 0.020) function were superior in S2 hearts.

CONCLUSION

In this experimental model of DCD, an EVHP strategy using initial reperfusion with a tepid adenosine-lidocaine cardioplegia and continuous myocardial perfusion minimizes myocardial injury and improves short-term post-transplant function compared with the current EVHP strategy using cold hyperkalemic cardioplegia before organ procurement and transplantation.

Keeping donor hearts in completely beating status with normothermic blood perfusion for transplants

BACKGROUND

Previously, we reported the preservation method of donor hearts in an empty beating status with mild hypothermic perfusion. To completely avoid cardiac arrest and myocardial ischemia, we performed the beating preservation technique from procurement of hearts to transplants and assessed its efficacy for long-term preservation and feasibility for heart transplantation.

METHODS

Thirty-two swine donor hearts were preserved in beating status (group A, n = 8 pairs, perfused continuously with normothermic blood) or in static cold storage (group B, n = 8 pairs, stored in 4°C histidine-tryptophan-ketoglutarate solutions) for 8 hours. Then the donor hearts were implanted either in beating or static status. During transplantation, the incidence of arrhythmia, duration of anastomosis and cardiopulmonary bypass, and dosage of inotropic drugs were recorded. Hemodynamics of left ventricle and serum level of creatine kinase-MB were measured during transplantation. Myocardial ultrastructure was observed.

RESULTS

Compared with group B, in group A the anastomotic time was significantly longer, the cardiopulmonary bypass time was significantly shorter, the cardiac output was larger, and the incidence of arrhythmia, dosage of cardiovascular-active drugs, and serum level of creatine kinase-MB were lower. After declamping for 2 hours and 3.5 hours, the left ventricular hemodynamics of group A was significantly better than that of group B. The myocardial ultrastructure of group A was superior to that of group B.

CONCLUSIONS

Preservation of donor hearts in beating status with continuous, normothermic, blood perfusion is an effective approach for long-term preservation and is appropriate for heart transplantation.

Machine perfusion in organ transplantation: a tool for ex-vivo graft conditioning with mesenchymal stem cells?

PURPOSE OF REVIEW

Machine perfusion has emerged as a tool to evaluate pretransplant graft function more objectively during preservation. Machine perfusion also offers the possibility to recondition questionable organs and to 'immunomodulate' allografts ex vivo. This article aims to review the current knowledge on machine perfusion of the various solid thoracic and abdominal organs, and to discuss the new possibility of conditioning and treating grafts with mesenchymal stem cells (MSCs) during machine perfusion.

RECENT FINDINGS

Different methods of machine perfusion have been described varying among organs in temperature and composition of perfusate. Commercial devices have recently become available for machine perfusion of all organs, with the largest clinical experience acquired in kidney and lung transplantation. Clinical studies are ongoing for liver, heart, and pancreas. MSC therapy in organ transplantation is now emerging with clinical studies set up to investigate its potential to attenuate ischemia/reperfusion injury (innate immunity) and to downregulate the alloimmune response (adaptive immunity) and promote engraftment after transplantation. We hypothesize that delivery of MSCs directly into the machine perfusion circuit may provide a unique opportunity to treat and immunomodulate organs prior to transplantation. To our knowledge, no study on ex-vivo delivery of MSCs during machine perfusion has been reported.

SUMMARY

Machine perfusion of solid organs has regained much attention during the last decade. It provides a new promising tool that may allow pretransplant ex-vivo assessment, preservation, repair, and conditioning of grafts. Experimental research and clinical trials testing the administration of MSCs during machine perfusion are warranted to explore the potential benefit and mechanisms of this approach.

Low-flow perfusion preservation versus static preservation for isolated rat heart: effects on recovery of myocardial function

BACKGROUND

Clinically, donor hearts cannot be preserved for >6 hours between explantation and recipient implantation. A better approach is needed to preserve donor hearts for a longer time. We tested whether low-flow perfusion (LFP) could satisfactorily preserve isolated rat hearts with histidine-tryptophan-ketoglutarate (HTK) solution or Fuwai modified (FWM) solution.

METHODS

We divided 32 male Sprague-Dawley rats randomly into 4 groups (n = 8): H1, H2, F1, and F2. The Langendorff heart model immersed isolated hearts in the H1 and F1 groups in HTK or FWM solution for 8 hours at 4 °C. Isolated hearts in the H2 and F2 groups were low-flow perfused with HTK solution and FWM solution for 8 hours at a pressure of 10 cmH(2)O at 4 °C. After 60 minutes reperfusion, we measured recovery of cardiac function, myocardial water content, and leakage of myocardial enzymes.

RESULTS

After reperfusion, no cardiac rebeating was observed among F1 group hearts; in addition, they showed significantly higher myocardial water content and lactate dehydrogenase leakage compared with the other 3 groups (P < .05). The recovery rates of cardiac function among H2 hearts were better than the other 3 groups (P < .05); their myocardial water content and enzyme leakage were less than the other 3 groups (P < .05).

CONCLUSIONS

Hypothermic LFP was better than static storage to preserve isolated rat hearts. HTK solution afforded better myocardial protection than FWM.

Innovations in organ donation

The growing disparity between organ availability for transplantation and the number of patients in need has challenged the donation and transplantation community of practice to develop innovative processes, ideas, and techniques to bridge the gaps. Advances in the sharing of best practices in the donation community have contributed greatly over the last 8 years. Broader sharing of updated guidelines for declaration of brain death in conjunction with improvements in deceased donor management have increased opportunities for organ donation. New techniques for organ preservation and organ resuscitation have allowed for better utilization of the potential donor pool. This review will highlight processes, ideas, and techniques in organ donation.

Machine perfusion or cold storage in organ transplantation: indication, mechanisms, and future perspectives

Most organs are currently preserved by cold storage (CS) prior to transplantation. However, as more so called marginal donor organs are utilized, machine perfusion has regained clinical interest. Recent studies have demonstrated advantages of pulsatile perfusion over CS preservation for kidney transplantation. However, it remains unclear whether there is a significant benefit of one preservation method over the other in general, or, whether the utilization of particular preservation approaches needs to be linked to organ characteristics. Proposed protective mechanisms of pulsatile perfusion remain largely obscure. It can be speculated that pulsatile perfusion may not only provide nutrition and facilitate the elimination of toxins but also trigger protective mechanisms leading to the amelioration of innate immune responses. Those aspects may be of particular relevance when utilizing grafts with suboptimal quality which may have an increased vulnerability to ischemia/reperfusion injury and compromised repair mechanisms. This review aims to enunciate the principles of organ perfusion and preservation as they relate to indication, aspects of organ protection and to highlight future developments.

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.