Steroids Limit Myocardial Edema During Ex Vivo Perfusion of Hearts Donated After Circulatory Death

Systemic Inflammation Differences in Brain-vs. Circulatory-Dead Donors: Impact on Lung Transplant Recipients

Brain death triggers a systemic inflammatory response. Whether systemic inflammation is different in lung donors after brain- (DBD) or circulatory-death (DCD) is unknown, but this may potentially increase the incidence of primary graft dysfunction (PGD) after lung transplantation. We compared the plasma levels of interleukin (IL)-6, IL-8, IL-10 and TNF-α in BDB and DCD and their respective recipients, as well as their relationship with PGD and mortality after LT. A prospective, observational, multicenter, comparative, cohort-nested study that included 40 DBD and 40 DCD lung donors matched and their respective recipients. Relevant clinical information and blood samples were collected before/during lung retrieval in donors and before/during/after (24, 48 and 72 h) LT in recipients. Incidence of PGD and short-term mortality after LT was recorded. Plasma levels of all determined cytokines were numerically higher in DBD than in DCD donors and reached statistical significance for IL-6, IL-10 and IL-8. In recipients with PGD the donor's plasma levels of TNF-α were higher. The post-operative mortality rate was very low and similar in both groups. DBD is associated with higher systemic inflammation than DCD donors, and higher TNF-α plasma levels in donors are associated with a higher incidence of PGD.

Metabolomic profiling during ex situ normothermic perfusion before heart transplantation defines patterns of substrate utilization and correlates with markers of allograft injury

BACKGROUND

Cardiac metabolism is altered in heart failure and ischemia-reperfusion injury states. We hypothesized that metabolomic profiling during ex situ normothermic perfusion before heart transplantation (HT) would lend insight into myocardial substrate utilization and report on subclinical and clinical allograft dysfunction risk.

METHODS

Metabolomic profiling was performed on serial samples of ex situ normothermic perfusate assaying biomarkers of myocardial injury in lactate and cardiac troponin I (TnI) as well as metabolites (66 acylcarnitines, 15 amino acids, nonesterified fatty acids [NEFA], ketones, and 3-hydroxybutyrate). We tested for change over time in injury biomarkers and metabolites, along with differential changes by recovery strategy (donation after circulatory death [DCD] vs donation after brain death [DBD]). We examined associations between metabolites, injury biomarkers, and primary graft dysfunction (PGD). Analyses were performed using linear mixed models adjusted for recovery strategy, assay batch, donor-predicted heart mass, and time.

RESULTS

A total of 176 samples from 92 ex situ perfusion runs were taken from donors with a mean age of 35 (standard deviation 11.3) years and a median total ex situ perfusion time of 234 (interquartile range 84) minutes. Lactate trends over time differed significantly by recovery strategy, while TnI increased during ex situ perfusion regardless of DCD vs DBD status. We found fuel substrates were rapidly depleted during ex situ perfusion, most notably the branched-chain amino acids leucine/isoleucine, as well as ketones, 3-hydroxybutyrate, and NEFA (least squares [LS] mean difference from the first to last time point -1.7 to -4.5, false discovery rate q < 0.001). Several long-chain acylcarnitines (LCAC), including C16, C18, C18:1, C18:2, C18:3, C20:3, and C20:4, increased during the perfusion run (LS mean difference 0.42-0.67, q < 0.001). Many LCACs were strongly associated with lactate and TnI. The change over time of many LCACs was significantly different for DCD vs DBD, suggesting differential trends in fuel substrate utilization by ischemic injury pattern. Changes in leucine/isoleucine, arginine, C12:1-OH/C10:1-DC, and C16-OH/C14-DC were associated with increased odds of moderate-severe PGD. Neither end-of-run nor change in lactate or TnI was associated with PGD.

CONCLUSIONS

Metabolomic profiling of ex situ normothermic perfusion solution reveals a pattern of fuel substrate utilization that correlates with subclinical and clinical allograft dysfunction. This study highlights a potential role for interventions focused on fuel substrate modification in allograft conditioning during ex situ perfusion to improve allograft outcomes.

Heart Transplant and Donors After Circulatory Death: A Clinical-Preclinical Systematic Review

INTRODUCTION

Heart transplantation is the treatment of choice for end-stage heart failure. There is a mismatch between the number of donor hearts available and the number of patients awaiting transplantation. Expanding the donor pool is critically important. The use of hearts donated following circulatory death is one approach to increasing the number of available donor hearts.

MATERIALS AND METHODS

A systematic review was performed according to the Preferred Reporting Items for Systematic reviews and Meta-Analyses (PRISMA) guidelines utilizing Pubmed/MEDLINE and Embase. Articles including adult human studies and preclinical animal studies of heart transplantation following donation after circulatory death were included. Studies of pediatric populations or including organs other than heart were excluded.

RESULTS

Clinical experience and preclinical studies are reviewed. Clinical experience with direct procurement, normothermic regional perfusion, and machine perfusion are included. Preclinical studies addressing organ function assessment and enhancement of performance of marginal organs through preischemic, procurement, preservation, and reperfusion maneuvers are included. Articles addressing the ethical considerations of thoracic transplantation following circulatory death are also reviewed.

CONCLUSIONS

Heart transplantation utilizing organs procured following circulatory death is a promising method to increase the donor pool and offer life-saving transplantation to patients on the waitlist living with end-stage heart failure. There is robust ongoing preclinical and clinical research to optimize this technique and improve organ yield. There are also ongoing ethical considerations that must be addressed by consensus before wide adoption of this approach.

Gene therapy during ex situ heart perfusion: a new frontier in cardiac regenerative medicine?

Ex situ organ preservation by machine perfusion can improve preservation of organs for transplantation. Furthermore, machine perfusion opens up the possibilities for selective immunomodulation, creation of tolerance to ischemia-reperfusion injury and/or correction of a pathogenic genetic defect. The application of gene modifying therapies to treat heart diseases caused by pathogenic mutations during ex situ heart perfusion seems promising, especially given the limitations related to delivery of vectors that were encountered during clinical trials using in vivo cardiac gene therapy. By isolating the heart in a metabolically and immunologically favorable environment and preventing off-target effects and dilution, it is possible to directly control factors that enhance the success rate of cardiac gene therapy. A literature search of PubMed and Embase databases was performed to identify all relevant studies regarding gene therapy during ex situ heart perfusion, aiming to highlight important lessons learned and discuss future clinical prospects of this promising approach.

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.

Thoracic organ machine perfusion: A review of concepts with a focus on reconditioning therapies

Thoracic organ transplantation, including lung, heart, and heart-lung transplants are highly regarded as gold standard treatments for patients suffering from heart failure or chronic end stage lung conditions. The relatively high prevalence of conditions necessitating thoracic organ transplants combined with the lack of available organs has resulted in many either dying or becoming too ill to receive a transplant while on the waiting list. There is a dire need to increase both the number of organs available and the utilization of such organs. Improved preservation techniques beyond static storage have shown great potential to lengthen the current period of viability of thoracic organs while outside the body, promising better utilization rates, increased donation distance, and improved matching of donors to recipients. Ex-situ organ perfusion (ESOP) can also make some novel therapeutic strategies viable, and the combination of the ESOP platform with such reconditioning therapies endeavors to better improve functional preservation of organs in addition to making more organs viable for transplantation. Given the abundance of clinical and pre-clinical studies surrounding reconditioning of thoracic organs in combination with ESOP, we summarize in this review important concepts and research regarding thoracic organ machine perfusion in combination with reconditioning therapies.

Donation After Circulatory Death in Heart Transplantation: History, Outcomes, Clinical Challenges, and Opportunities to Expand the Donor Pool

Heart transplantation remains the gold-standard therapy for end-stage heart failure; the expected median survival range is 12-13 years. More than 30,000 heart transplants have been performed globally in the past decade alone. With advances in medical and surgical therapies for heart failure, including durable left ventricular assist devices, an increasing number of patients are living with end-stage disease. Last year alone, more than 2500 patients were added to the heart-transplant waitlist in the United States. Despite recent efforts to expand the donor pool, including an increase in transplantation of hepatitis C-positive and extended-criteria donors, supply continues to fall short of demand. Donation after circulatory death (DCD), defined by irreversible cardiopulmonary arrest rather than donor brain death, is widely used in other solid-organ transplants, including kidney and liver, but has not been widely adopted in heart transplantation. However, resurging interest in DCD donation and the introduction of ex vivo perfusion technology has catalyzed recent clinical trials and the development of DCD heart-transplantation programs. Herein, we review the history of DCD heart transplantation, describe the currently used procurement protocols for it and examine clinical challenges and outcomes of such a procedure.

Inflammation and Oxidative Stress in the Context of Extracorporeal Cardiac and Pulmonary Support

Extracorporeal circulation (ECC) systems, including cardiopulmonary bypass, and extracorporeal membrane oxygenation have been an irreplaceable part of the cardiothoracic surgeries, and treatment of critically ill patients with respiratory and/or cardiac failure for more than half a century. During the recent decades, the concept of extracorporeal circulation has been extended to isolated machine perfusion of the donor organ including thoracic organs (ex-situ organ perfusion, ESOP) as a method for dynamic, semi-physiologic preservation, and potential improvement of the donor organs. The extracorporeal life support systems (ECLS) have been lifesaving and facilitating complex cardiothoracic surgeries, and the ESOP technology has the potential to increase the number of the transplantable donor organs, and to improve the outcomes of transplantation. However, these artificial circulation systems in general have been associated with activation of the inflammatory and oxidative stress responses in patients and/or in the exposed tissues and organs. The activation of these responses can negatively affect patient outcomes in ECLS, and may as well jeopardize the reliability of the organ viability assessment, and the outcomes of thoracic organ preservation and transplantation in ESOP. Both ECLS and ESOP consist of artificial circuit materials and components, which play a key role in the induction of these responses. However, while ECLS can lead to systemic inflammatory and oxidative stress responses negatively affecting various organs/systems of the body, in ESOP, the absence of the organs that play an important role in oxidant scavenging/antioxidative replenishment of the body, such as liver, may make the perfused organ more susceptible to inflammation and oxidative stress during extracorporeal circulation. In the present manuscript, we will review the activation of the inflammatory and oxidative stress responses during ECLP and ESOP, mechanisms involved, clinical implications, and the interventions for attenuating these responses in ECC.

Long-term normothermic machine preservation of human livers: what is needed to succeed?

Although short-term machine perfusion (≤24 h) allows for resuscitation and viability assessment of high-risk donor livers, the donor organ shortage might be further remedied by long-term perfusion machines. Extended preservation of injured donor livers may allow reconditioning, repairing, and regeneration. This review summarizes the necessary requirements and challenges for long-term liver machine preservation, which requires integrating multiple core physiological functions to mimic the physiological environment inside the body. A pump simulates the heart in the perfusion system, including automatically controlled adjustment of flow and pressure settings. Oxygenation and ventilation are required to account for the absence of the lungs combined with continuous blood gas analysis. To avoid pressure necrosis and achieve heterogenic tissue perfusion during preservation, diaphragm movement should be simulated. An artificial kidney is required to remove waste products and control the perfusion solution's composition. The perfusate requires an oxygen carrier, but will also be challenged by coagulation and activation of the immune system. The role of the pancreas can be mimicked through closed-loop control of glucose concentrations by automatic injection of insulin or glucagon. Nutrients and bile salts, generally transported from the intestine to the liver, have to be supplemented when preserving livers long term. Especially for long-term perfusion, the container should allow maintenance of sterility. In summary, the main challenge to develop a long-term perfusion machine is to maintain the liver's homeostasis in a sterile, carefully controlled environment. Long-term machine preservation of human livers may allow organ regeneration and repair, thereby ultimately solving the shortage of donor livers.

Ex vivo normothermic preservation of amputated limbs with a hemoglobin-based oxygen carrier perfusate

BACKGROUND

Ex vivo normothermic limb perfusion (EVNLP) preserves amputated limbs under near-physiologic conditions. Perfusates containing red blood cells (RBCs) have shown to improve outcomes during ex vivo normothermic organ perfusion, when compared with acellular perfusates. To avoid limitations associated with the use of blood-based products, we evaluated the feasibility of EVNLP using a polymerized hemoglobin-based oxygen carrier-201 (HBOC-201).

METHODS

Twenty-four porcine forelimbs were procured from Yorkshire pigs. Six forelimbs underwent EVNLP with an HBOC-201-based perfusate, six with an RBC-based perfusate, and 12 served as static cold storage (SCS) controls. Ex vivo normothermic limb perfusion was terminated in the presence of systolic arterial pressure of 115 mm Hg or greater, fullness of compartments, or drop of tissue oxygen saturation by 20%. Limb contractility, weight change, compartment pressure, tissue oxygen saturation, oxygen uptake rates (OURs) were assessed. Perfusate fluid-dynamics, gases, electrolytes, metabolites, methemoglobin, creatine kinase, and myoglobin concentration were measured. Uniformity of skin perfusion was assessed with indocyanine green angiography and infrared thermography.

RESULTS

Warm ischemia time before EVNLP was 35.50 ± 8.62 minutes (HBOC-201), 30.17 ± 8.03 minutes (RBC) and 37.82 ± 10.45 (SCS) (p = 0.09). Ex vivo normothermic limb perfusion duration was 22.5 ± 1.7 hours (HBOC-201) and 28.2 ± 7.3 hours (RBC) (p = 0.04). Vascular flow (325 ± 25 mL·min-1 vs. 444.7 ± 50.6 mL·min-1; p = 0.39), OUR (2.0 ± 1.45 mL O2·min-1·g-1 vs. 1.3 ± 0.92 mL O2·min-1·g-1 of tissue; p = 0.80), lactate (14.66 ± 4.26 mmol·L-1 vs. 13.11 ± 6.68 mmol·L-1; p = 0.32), perfusate pH (7.53 ± 0.25 HBOC-201; 7.50 ± 0.23 RBC; p = 0.82), flexor (28.3 ± 22.0 vs. 27.5 ± 10.6; p = 0.99), and extensor (31.5 ± 22.9 vs. 28.8 ± 14.5; p = 0.82) compartment pressures, and weight changes (23.1 ± 3.0% vs. 13.2 ± 22.7; p = 0.07) were not significantly different between HBOC-201 and RBC groups, respectively. In HBOC-201 perfused limbs, methemoglobin levels increased, reaching 47.8 ± 12.1% at endpoint. Methemoglobin saturation did not affect OUR (ρ = -0.15, r2 = 0.022; p = 0.45). A significantly greater number of necrotic myocytes was found in the SCS group at endpoint (SCS, 127 ± 17 cells; HBOC-201, 72 ± 30 cells; RBC-based, 56 ± 40 cells; vs. p = 0.003).

CONCLUSION

HBOC-201- and RBC-based perfusates similarly support isolated limb physiology, metabolism, and function.

The Position of the Heart During Normothermic Ex Situ Heart Perfusion is an Important Factor in Preservation and Recovery of Myocardial Function

Ex situ heart perfusion (ESHP) is being investigated as a method for the continuous preservation of the myocardium in a semiphysiologic state for subsequent transplantation. Most methods of ESHP position the isolated heart in a hanging (H) state, representing a considerable departure from the in vivo anatomical positioning of the heart and may negatively affect the functional preservation of the heart. In the current study, cardiac functional and metabolic parameters were assessed in healthy pig hearts, perfused for 12 hours, in either an H, or supported (S) position, either in nonworking mode (NWM) or working mode (WM). The cardiac function was best preserved in the S position hearts in WM (median 11 hour cardiac index (CI)/1 hour CI%: working mode perfusion in supported position = 94.77% versus nonworking mode perfusion in supported position = 62.80%, working mode perfusion in H position = 36.18%, nonworking mode perfusion in H position = 9.75%; p < 0.001). Delivery of pyruvate bolus significantly improved the function in S groups, however, only partially reversed myocardial dysfunction in the H heart groups. The hearts perfused ex situ in a semianatomical S position and in physiologic WM had better functional preservation and recovery than the H hearts in non-S position. Optimizing the positional support for the ex situ-perfused hearts may improve myocardial preservation during ESHP.

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.

Ex vivo normothermic perfusion in heart transplantation: a review of the TransMedics® Organ Care System

Cardiac transplantation is the gold standard for treatment for select patients with end-stage heart failure, yet donor supply is limited. Ex vivo machine perfusion is an emerging technology capable of safely preserving organs and expanding the viable donor pool. The TransMedics^® Organ Care System™ is an investigational device which mimics physiologic conditions while maintaining the heart in a warm, beating state rather than cold storage. The use of Organ Care System allows increased opportunities for using organs from marginal donors, distant procurement sites, donation after cardiac death, and in recipients with complex anatomy. In the future, bioengineering technologies including use of mesenchymal stem cells, viral vector delivery of gene therapy, and alternate devices may further broaden the field of ex vivo machine perfusion.

Heart transplantation following donation after circulatory death: Expanding the donor pool

Heart transplantation from donation after circulatory death (DCD) donors is a rapidly expanding practice. In this review, we describe the history and challenges of DCD heart transplantation and overview the procurement protocols and methods of limiting ischemic injury, current outcomes, and future directions. There are now at least three protocols that permit resuscitation and viability assessment of the DCD heart either in situ or ex situ. While the retrieval protocol for hearts from DCD donors will depend on local regulations, the outcomes of DCD heart transplant recipients reported to date are excellent regardless of the retrieval protocol and are comparable to the outcomes of heart transplant recipients from donation after brain death (DBD) donors. In the two centers with the largest published experience, DCD heart transplantation now accounts for one third of their heart transplant activity. With international trends indicating that there is an increasing utilisation of the DCD pathway, it is expected that DCD donors will become a major source of heart donation worldwide.

Organ Preservation Solutions in Transplantation: A Literature Review

OBJECTIVES

Renal transplant with ABO-incompatible donors expands the donor pool. Earlier studies have focused the use of protocol biopsies in ABOincompatible transplant patients. Our study described outcomes of indication (for cause) renal biopsies and clinical outcomes in patients with ABO-incompatible renal transplant.

MATERIALS AND METHODS

This retrospective study included 164 patients from January 2012 to June 2019. Biochemical parameters, serial immunoglobulin G anti-ABO titers, and class I and II donor-specific antibody findings were obtained from hospital records, and renal graft biopsies were reviewed according to the Banff 2017 update.

RESULTS

We analyzed the results of 65 biopsies from 54 patients. Biopsy-proven acute antibody-mediated rejection (12.8%) was found to be more prevalent than acute cellular rejection (1.8%). Patients with antibodymediated rejection all had microvascular inflammation (g+ptc score of 2 or more, where g+ptc is the sum of the glomerulitis and peritubular capillaritis scores) and were positive for C4d. Acute tubular injury per se was seen in 10.3% of patients; 65% of these patients had C4d positivity in peritubular capillaries, and only 1 patient developed chronic active antibody-mediated rejection on follow-up. Patient and death-censored graft survival rates were 92% and 98% at 1 year after transplant and 88% and 91% at 3 years, respectively. Patients with an episode of antibody-mediated rejection had lower rates of patient (76.5%) and deathcensored graft survival (84.6%) at 1 year.

CONCLUSIONS

The microvascular inflammation score (g+ptc score of 2 or higher) is more reliable than diffuse C4d positivity to determine antibody-mediated rejection in ABO-incompatible transplants because diffuse C4d positivity may also be seen in etiologies unrelated to antibody-mediated rejection. Acute tubular injury with C4d positivity without microvascular injury does not confirm antibody-mediated rejection. We suggest that Banff classification be updated in ABOincompatible transplants to include diagnostic criteria for the diagnosis of antibody-mediated rejection.

A Multi-Mode System for Myocardial Functional and Physiological Assessment during Ex Situ Heart Perfusion

Ex situ heart perfusion (ESHP) has proven to be an important and valuable step toward better preservation of donor hearts for heart transplantation. Currently, few ESHP systems allow for a convenient functional and physiological evaluation of the heart. We sought to establish a simple system that provides functional and physiological assessment of the heart during ESHP. The ESHP circuit consists of an oxygenator, a heart-lung machine, a heater-cooler unit, an anesthesia gas blender, and a collection funnel. Female Yorkshire pig hearts (n = 10) had del Nido cardioplegia (4°C) administered, excised, and attached to the perfusion system. Hearts were perfused retrogradely into the aortic root for 2 hours before converting the system to an isovolumic mode or a working mode for further 2 hours. Blood samples were analyzed to measure metabolic parameters. During the isovolumic mode (n = 5), a balloon inserted in the left ventricular (LV) cavity was inflated so that an end-diastolic pressure of 6-8 mmHg was reached. During the working mode (n = 5), perfusion in the aortic root was redirected into left atrium (LA) using a compliance chamber which maintained an LA pressure of 6-8 mmHg. Another compliance chamber was used to provide an afterload of 40-50 mmHg. Hemodynamic and metabolic conditions remained stable and consistent for a period of 4 hours of ESHP in both isovolumic mode (LV developed pressure: 101.0 ± 3.5 vs. 99.7 ± 6.8 mmHg, p = .979, at 2 and 4 hours, respectively) and working mode (LV developed pressure: 91.0 ± 2.6 vs. 90.7 ± 2.5 mmHg, p = .942, at 2 and 4 hours, respectively). The present study proposed a novel ESHP system that enables comprehensive functional and metabolic assessment of large mammalian hearts. This system allowed for stable myocardial function for up to 4 hours of perfusion, which would offer great potential for the development of translational therapeutic protocols to improve dysfunctional donated hearts.

Ex situ heart perfusion: The past, the present, and the future

Despite the advancements in medical treatment, mechanical support, and stem cell therapy, heart transplantation remains the most effective treatment for selected patients with advanced heart failure. However, with an increase in heart failure prevalence worldwide, the gap between donor hearts and patients on the transplant waiting list keeps widening. Ex situ machine perfusion has played a key role in augmenting heart transplant activities in recent years by enabling the usage of donation after circulatory death hearts, allowing longer interval between procurement and implantation, and permitting the safe use of some extended-criteria donation after brainstem death hearts. This exciting field is at a hinge point, with 1 commercially available heart perfusion machine, which has been used in hundreds of heart transplantations, and a number of devices being tested in the pre-clinical and Phase 1 clinical trial stage. However, no consensus has been reached over the optimal preservation temperature, perfusate composition, and perfusion parameters. In addition, there is a lack of objective measurement for allograft quality and viability. This review aims to comprehensively summarize the lessons about ex situ heart perfusion as a platform to preserve, assess, and repair donor hearts, which we have learned from the pre-clinical studies and clinical applications, and explore its exciting potential of revolutionizing heart transplantation.

Immunity and Stress Responses Are Induced During Ex Situ Heart Perfusion

BACKGROUND

Ex situ heart perfusion (ESHP) preserves the donated heart in a perfused, beating condition preventing cold storage-related ischemia and provides a platform to evaluate myocardial viability during preservation. However, myocardial function declines gradually during ESHP. Extracorporeal circulation systems are associated with the induction of systemic inflammatory and stress responses. Our aim was to evaluate the incidence of inflammation and induction of endoplasmic reticulum stress responses during an extended period of ESHP.

METHODS

Cardiac function, myocardial tissue injury, markers of inflammation, oxidative stress, and endoplasmic reticulum stress were assessed in healthy pig hearts, perfused for 12 hours either in nonworking mode (non-WM=7) or working mode (WM, n=6).

RESULTS

Cardiac function declined during ESHP but was significantly better preserved in the hearts perfused in WM (median 11-hour cardiac index/1-hour cardiac index: WM=27% versus non-WM=9.5%, P=0.022). Myocardial markers of endoplasmic reticulum stress were expressed higher in ESHP hearts compared with in vivo samples. The proinflammatory cytokines and oxidized low-density lipoprotein significantly increased in the perfusate throughout the perfusion in both perfusion groups. The left ventricular expression of the cytokines and malondialdehyde was induced in non-WM, whereas it was not different between WM and in vivo.

CONCLUSIONS

Myocardial function declines during ESHP regardless of perfusion mode. However, ESHP in WM may lead to superior preservation of myocardial function and viability. Both inflammation and endoplasmic reticulum stress responses are significantly induced during ESHP and may contribute to the myocardial functional decline, representing a potential therapeutic target to improve the clinical donor heart preservation.

Heart Transplantation With Donation After Circulatory Death

Heart transplantation remains the preferred option for improving quality of life and survival for patients suffering from end-stage heart failure. Unfortunately, insufficient supply of cardiac grafts has become an obstacle. Increasing organ availability with donation after circulatory death (DCD) may be a promising option to overcome the organ shortage. Unlike conventional donation after brain death, DCD organs undergo a period of warm, global ischemia between circulatory arrest and graft procurement, which raises concerns for graft quality. Nonetheless, the potential of DCD heart transplantation is being reconsidered, after reports of more than 70 cases in Australia and the United Kingdom over the past 3 years. Ensuring optimal patient outcomes and generalized adoption of DCD in heart transplantation, however, requires further development of clinical protocols, which in turn require a better understanding of cardiac ischemia-reperfusion injury and the various possibilities to limit its adverse effects. Thus, we aim to provide an overview of the knowledge obtained with preclinical studies in animal models of DCD heart transplantation, to facilitate and promote the most effective and efficient advancement in preclinical research. A literature search of the PubMed database was performed to identify all relevant preclinical studies in DCD heart transplantation. Specific aspects relevant for DCD heart transplantation were analyzed, including animal models, graft procurement and storage conditions, cardioprotective approaches, and graft evaluation strategies. Several potential therapeutic strategies for optimizing graft quality are identified, and recommendations for further preclinical research are provided.

Hurdles to Cardioprotection in the Critically Ill

Cardiovascular disease is the largest contributor to worldwide mortality, and the deleterious impact of heart failure (HF) is projected to grow exponentially in the future. As heart transplantation (HTx) is the only effective treatment for end-stage HF, development of mechanical circulatory support (MCS) technology has unveiled additional therapeutic options for refractory cardiac disease. Unfortunately, despite both MCS and HTx being quintessential treatments for significant cardiac impairment, associated morbidity and mortality remain high. MCS technology continues to evolve, but is associated with numerous disturbances to cardiac function (e.g., oxidative damage, arrhythmias). Following MCS intervention, HTx is frequently the destination option for survival of critically ill cardiac patients. While effective, donor hearts are scarce, thus limiting HTx to few qualifying patients, and HTx remains correlated with substantial post-HTx complications. While MCS and HTx are vital to survival of critically ill cardiac patients, cardioprotective strategies to improve outcomes from these treatments are highly desirable. Accordingly, this review summarizes the current status of MCS and HTx in the clinic, and the associated cardiac complications inherent to these treatments. Furthermore, we detail current research being undertaken to improve cardiac outcomes following MCS/HTx, and important considerations for reducing the significant morbidity and mortality associated with these necessary treatment strategies.

Myocardial Functional Decline During Prolonged Ex Situ Heart Perfusion

BACKGROUND

Myocardial function declines in a time-dependent fashion during ex situ heart perfusion. Cell death and metabolic alterations may contribute to this phenomenon, limiting the safe perfusion period and the potential of ex situ heart perfusion to expand the donor pool. Our aim was to investigate the etiology of myocardial functional decline in ex situ perfused hearts.

METHODS

Cardiac function, apoptosis, effectors and markers of cell death, and metabolic function were assessed in healthy pig hearts perfused for 12 hours. These hearts were perfused in nonworking mode or working mode.

RESULTS

Cardiac function declined during ex situ heart perfusion regardless of perfusion mode but was significantly better preserved in the hearts perfused in working mode (11-hour cardiac index/1-hour cardiac index: working mode, 33%; nonworking mode, 10%; p = 0.025). The rate of apoptosis was higher in the ex situ perfused hearts compared with in vivo samples (apoptotic cells: in vivo, 0.13%; working mode, 0.54%; nonworking mode, 0.88%; p < 0.001), but the absolute values were low and out of proportion to the decline in function in either group. Myocardial dysfunction at the end of the perfusion interval was partially rescued by delivery of a pyruvate bolus.

CONCLUSIONS

A significant decline in myocardial function occurs over time in hearts preserved ex situ that is out of proportion to the magnitude of myocyte cell death present in dysfunctional hearts. Alterations in myocardial substrate utilization during prolonged ex situ heart perfusion may contribute to this phenomenon and represent an avenue to improve donor heart preservation.

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.