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

Ex vivo heart perfusion: an updated systematic review

Due to the discrepancy between patients awaiting a heart transplant and the availability of donor hearts, strategies to expand the donor pool and improve the transplant's success are crucial. This review aims to summarize current knowledge on the ex vivo heart preservation (EVHP) experience as an alternative to standard cold static storage (CSS). EVHP techniques can improve the preservation of the donor's heart before transplantation and allow for pre-transplant organ evaluation.

Ex vivo lung perfusion and the Organ Care System: a review

With the increasing prevalence of heart failure and end-stage lung disease, there is a sustained interest in expanding the donor pool to alleviate the thoracic organ shortage crisis. Efforts to extend the standard donor criteria and to include donation after circulatory death have been made to increase the availability of suitable organs. Studies have demonstrated that outcomes with extended-criteria donors are comparable to those with standard-criteria donors. Another promising approach to augment the donor pool is the improvement of organ preservation techniques. Both ex vivo lung perfusion (EVLP) for the lungs and the Organ Care System (OCS, TransMedics) for the heart have shown encouraging results in preserving organs and extending ischemia time through the application of normothermic regional perfusion. EVLP has been effective in improving marginal or borderline lungs by preserving and reconditioning them. The use of OCS is associated with excellent short-term outcomes for cardiac allografts and has improved utilization rates of hearts from extended-criteria donors. While both EVLP and OCS have successfully transitioned from research to clinical practice, the costs associated with commercially available systems and consumables must be considered. The ex vivo perfusion platform, which includes both EVLP and OCS, holds the potential for diverse and innovative therapies, thereby transforming the landscape of thoracic organ transplantation.

Risk Index Predicts Pediatric Heart Allograft Non-Utilization

BACKGROUND

Children listed for heart transplantation face the highest waitlist mortality among all solid organ transplant patients (14%). Attempts at decreasing donor allograft non-utilization (41.5%) could potentially decrease waitlist mortality for pediatric heart transplant patients. Our aim was to quantify the non-utilization risk of pediatric donor heart allografts at the time of initial offering.

METHODS

Using the United Network of Organ Sharing (UNOS) database, we retrospectively analyzed 8823 deceased donors (≤18 years old) data through univariable and multivariable analysis and logistic regression models. These factors were divided into a training (n = 5882) and validation set (n = 2941). Donor clinical characteristics and laboratory values were used to predict non-utilization of donor hearts. The multivariable analysis used factors that were significant from the univariable analysis (p-value < .05), and the pediatric non-utilization risk index (pDRSI) included significant factors from the multivariable analysis, producing an overall risk score for non-utilization. With these data, we created a non-utilization risk index to predict likelihood of donor allograft non-utilization.

RESULTS

From the 24 potential factors that were identified from univariable analysis, 17 were significant predictors (p < .05) of pediatric heart non-utilization in the multivariable analysis. Low left ventricular ejection fraction (odds ratio (OR)-35.3), hepatitis C positive donor (OR-23.3), high left ventricular ejection fraction (OR-3.29), and hepatitis B positive donor (OR-3.27) were the most significant risk factors. The phDSRI has a C-statistic of 0.80 for the training set and 0.80 for the validation set.

CONCLUSION

Using over 8000 donors, the phDSRI uses 17 significant risk factors to predict risk of pediatric heart donor allograft non-utilization.

Donor Heart Preservation: Current Knowledge and the New Era of Machine Perfusion

Heart transplantation remains the conventional treatment in end-stage heart failure, with static cold storage (SCS) being the standard technique used for donor preservation. Nevertheless, prolonged cold ischemic storage is associated with the increased risk of early graft dysfunction attributed to residual ischemia, reperfusion, and rewarming damage. In addition, the demand for the use of marginal grafts requires the development of new methods for organ preservation and repair. In this review, we focus on current knowledge and novel methods of donor preservation in heart transplantation. Hypothermic or normothermic machine perfusion may be a promising novel method of donor preservation based on the administration of cardioprotective agents. Machine perfusion seems to be comparable to cold cardioplegia regarding donor preservation and allows potential repair treatments to be employed and the assessment of graft function before implantation. It is also a promising platform for using marginal organs and increasing donor pool. New pharmacological cardiac repair treatments, as well as cardioprotective interventions have emerged and could allow for the optimization of this modality, making it more practical and cost-effective for the real world of transplantation. Recently, the use of triiodothyronine during normothermic perfusion has shown a favorable profile on cardiac function and microvascular dysfunction, likely by suppressing pro-apoptotic signaling and increasing the expression of cardioprotective molecules.

Jacketed elastomeric tubes for passive self-regulation of pulsatile flow

Regulating pulsatile flow is important to achieve optimal separation and mixing and enhanced heat transfer in microfluidic devices, as well as maintaining homeostasis in biological systems. The human aorta, a composite and layered tube made (among others) of elastin and collagen, is an inspiration for researchers who seek an engineering solution for a self-regulation of pulsatile flow. Here, we present a bio-inspired approach showing that fabric-jacketed elastomeric tubes, manufactured using commercially available silicone rubber and knitted textiles, can be used to regulate pulsatile flow. Our tubes are evaluated via incorporation into a mock-circulatory 'flow loop' that replicates the pulsatile fluid flow conditions of an ex-vivo heart perfusion (EVHP) device, a machine used in heart transplants. Pressure waveforms measured near the elastomeric tubing clearly indicated an effective flow regulation. The 'dynamic stiffening' behavior of the tubes during deformation is analyzed quantitatively. Broadly, the fabric jackets allow for the tubes to experience greater magnitudes of pressure and distension without risk of asymmetric aneurysm within the expected operating time of an EVHP. Owing to its highly tunable nature, our design may serve as a basis for tubing systems that require passive self-regulation of pulsatile flow.

Introduction of machine perfusion of donor hearts in a single center in Germany

Introduction

Organ shortage, subsequent use of extended donor criteria organs and high-risk recipients needing redo-surgery are increasing the complexity of heart transplantation. Donor organ machine perfusion (MP) is an emerging technology allowing reduction of ischemia time as well as standardized evaluation of the organ. The aim of this study was to review the introduction of MP and analyze the results of heart transplantation after MP in our center.

Methods

In a retrospective single-center study, data from a prospectively collected database were analysed. From July 2018 to August 2021, fourteen hearts were retrieved and perfused using the Organ Care System (OCS), 12 hearts were transplanted. Criteria to use the OCS were based on donor/recipient characteristics. Primary objective was 30-day survival, secondary objectives were major cardiac adverse events, graft function, rejection episodes as well as overall survival in the follow-up and assessment of MP technical reliability.

Results

All patients survived the procedure and the postoperative 30-day interval. No MP related complications were noted. Graft ejection fraction beyond 14 days was ≥ 50% in all cases. Endomyocardial biopsy showed excellent results with no or mild rejection. Two donor hearts were rejected after OCS perfusion and evaluation.

Conclusion

Ex vivo normothermic MP during organ procurement is a safe and promising technique to expand the donor pool. Reduction of cold ischemic time while providing additional donor heart assessment and reconditioning options increased the number of acceptable donor hearts. Additional clinical trials are necessary to develop guidelines regarding the application of MP.

Normothermic ex vivo heart perfusion with NLRP3 inflammasome inhibitor Mcc950 treatment improves cardiac function of circulatory death hearts after transplantation

Background

The utilization of donation after circulatory death (DCD) hearts can enlarge the donor pool. However, DCD hearts suffer from serious ischemia/reperfusion injury (IRI). Recent studies found that the activation of NLRP3 inflammasome could play a significant role in organ IRI. Mcc950, which is a novel inhibitor of the NLRP3 inflammasome, can be applied to treat various kinds of cardiovascular diseases. Therefore, we hypothesized that the treatment of mcc950 could protect DCD hearts preserved with normothermic ex vivo heart perfusion (EVHP) against myocardial IRI via inhibiting NLRP3 inflammasome in a rat heart transplantation model of DCD.

Methods

Donor-heart rats were randomly divided into four groups: Control group; Vehicle group; MP-mcc950 group; and MP + PO-mcc950 group. Mcc950 was added into the perfusate of normothermic EVHP in the MP-mcc950 and MP + PO-mcc950 groups, and was injected into the left external jugular vein after heart transplantation in the MP + PO-mcc950 group. Cardiac functional assessment was performed. The level of oxidative stress, inflammatory response, apoptosis, and NLRP3 inflammasome-associated protein of donor hearts were evaluated.

Results

The treatment with mcc950 significantly increased the developed pressure (DP), dP/dtmax, and dP/dtmin of the left ventricular of DCD hearts at 90 min after heart transplantation in both MP-mcc950 and MP + PO-mcc950 groups. Furthermore, mcc950 added into perfusate and injected after transplantation in both MP-mcc950 and MP + PO-mcc950 groups significantly attenuated the level of oxidative stress, inflammatory response, apoptosis, and NLRP3 inflammasome compared with the vehicle group.

Conclusions

Normothermic EVHP combined with mcc950 treatment can be a promising and novel DCD heart preservation strategy, which can alleviate myocardial IRI via inhibiting NLRP3 inflammasome.

Solid Phase Microextraction—A Promising Tool for Graft Quality Monitoring in Solid Organ Transplantation

Solid organ transplantation is a life-saving intervention for patients suffering from end-stage organ failure. Although improvements in surgical techniques, standards of care, and immunosuppression have been observed over the last few decades, transplant centers have to face the problem of an insufficient number of organs for transplantation concerning the growing demand. An opportunity to increase the pool of organs intended for transplantation is the more frequent use of organs from extended criteria and the development of analytical methods allowing for a better assessment of the quality of organs to minimize the risk of post-transplant organ injury and rejection. Therefore, solid-phase microextraction (SPME) has been proposed in various studies as an effective tool for determining compounds of significance during graft function assessment or for the chemical profiling of grafts undergoing various preservation protocols. This review summarizes how SPME addresses the analytical challenges associated with different matrices utilized in the peri-transplant period and discusses its potential as a diagnostic tool in future work.

Review of Postoperative Care for Heart Transplant Recipients

The early postoperative management strategies after heart transplantation include optimizing the function of the denervated heart, correcting the causes of hemodynamic instability, and initiating and maintaining immunosuppressive therapy, allograft rejection surveillance, and prophylaxis against infections caused by immunosuppression. The course of postoperative support is influenced by the quality of allograft myocardial protection prior to implantation and reperfusion, donor-recipient heart size matching, surgical technique of orthotopic heart transplantation, and patient factors (eg, preoperative condition, immunologic compatibility, postoperative vasomotor tone, severity and reversibility of pulmonary vascular hypertension, pulmonary function, mediastinal blood loss, and end-organ perfusion). This review provides an overview of the early postoperative care of recipients and includes a brief description of the surgical techniques for orthotopic heart transplantation.

Is the Organ Care System (OCS) Still the First Choice With Emerging New Strategies for Donation After Circulatory Death (DCD) in Heart Transplant?

The scarcity of donor hearts continues to be a challenge in transplants for advanced heart failure patients. With an increasing number of patients on the waiting list for a heart transplant, the discrepancy in the number between donors and recipients is gradually increasing and poses a new challenge that plagues the healthcare systems when it comes to the heart. Several technologies have been developed to expand the donor pool in recent years. One such method is the organ care system (OCS). The standard method of organ preservation is the static cold storage (SCS) method which allows up to four hours of safe preservation of the heart. However, beyond four hours of cold ischemia, the incidence of primary graft dysfunction increases significantly. OCS keeps the heart perfused close to the physiological state beyond the four hours with superior results, which allows us to travel further and longer distances, leading to expansion in the donor pool. In this review, we discuss the OCS system, its advantages, and shortcomings.

Dynamic Metabolic Changes During Prolonged Ex Situ Heart Perfusion Are Associated With Myocardial Functional Decline

Ex situ heart perfusion (ESHP) was developed to preserve and evaluate donated hearts in a perfused beating state. However, myocardial function declines during ESHP, which limits the duration of perfusion and the potential to expand the donor pool. In this research, we combine a novel, minimally-invasive sampling approach with comparative global metabolite profiling to evaluate changes in the metabolomic patterns associated with declines in myocardial function during ESHP. Biocompatible solid-phase microextraction (SPME) microprobes serving as chemical biopsy were used to sample heart tissue and perfusate in a translational porcine ESHP model and a small cohort of clinical cases. In addition, six core-needle biopsies of the left ventricular wall were collected to compare the performance of our SPME sampling method against that of traditional tissue-collection. Our state-of-the-art metabolomics platform allowed us to identify a large number of significantly altered metabolites and lipid species that presented comparable profile of alterations to conventional biopsies. However, significant discrepancies in the pool of identified analytes using two sampling methods (SPME vs. biopsy) were also identified concerning mainly compounds susceptible to dynamic biotransformation and most likely being a result of low-invasive nature of SPME. Overall, our results revealed striking metabolic alterations during prolonged 8h-ESHP associated with uncontrolled inflammation not counterbalanced by resolution, endothelial injury, accelerated mitochondrial oxidative stress, the disruption of mitochondrial bioenergetics, and the accumulation of harmful lipid species. In conclusion, the combination of perfusion parameters and metabolomics can uncover various mechanisms of organ injury and recovery, which can help differentiate between donor hearts that are transplantable from those that should be discarded.

A novel nonlinear afterload for ex vivo heart evaluation: porcine experimental results

Background

Existing working heart models for ex vivo functional evaluation of donor hearts often use cardiac afterloads made up of discrete resistive and compliant elements. This approach limits the practicality of independently controlling systolic and diastolic aortic pressure to safely test the heart under multiple loading conditions. We present and investigate a novel afterload concept designed to enable such control.

Methods

Six ∼70 kg pig hearts were evaluated in vivo, then ex vivo in left‐ventricular working mode using the presented afterload. Both in vivo and ex vivo, the hearts were evaluated at two exertion levels: at rest and following a 20 μg adrenaline bolus, while measuring aortic pressure and flow, left ventricular pressure and volume, and left atrial pressure.

Results

The afterload gave aortic pressure waveforms that matched the general shape of the in vivo measurements. A wide range of physiological systolic pressures (93 to 160 mm Hg) and diastolic pressures (73 to 113 mm Hg) were generated by the afterload.

Conclusions

With the presented afterload concept, multiple physiological loading conditions could be tested ex vivo, and compared with the corresponding in vivo data. An additional control loop from the set pressure limits to the measured systolic and diastolic aortic pressure is proposed to address discrepancies observed between the set limits and the measured pressures.

Successful heart transplantation from a donor with bacterial and fungal bloodstream infection: Case report of donor optimization strategy

Donor optimization is vital to increase donor hearts utilized for transplantation. We report a case of a 34-year-old female with end-stage cardiomyopathy that was admitted to the intensive care unit on inotropic support with progressive decline (INTERMACS-2). She was offered a donor heart from a 14-year male that was found to have Klebsiella pneumoniae bacteremia and candidemia co-infection. The donor was transferred to our hospital and optimized hemodynamically and biochemically. Targeted antimicrobial and antifungal therapy based on the susceptibility testing was established in the donor till blood cultures were negative. The recipient received similar prophylactic therapy for 2-week course starting 24-h before transplantation. The patient was transplanted with no clinical consequences. She was discharged home in 4 weeks post-transplantation. Her 3-month follow-up was completely uneventful.

Application of Mesenchymal Stem Cells During Machine Perfusion: An Emerging Novel Strategy for Organ Preservation

Although solid organ transplantation remains the definitive management for patients with end-stage organ failure, this ultimate treatment has been limited by the number of acceptable donor organs. Therefore, efforts have been made to expand the donor pool by utilizing marginal organs from donation after circulatory death or extended criteria donors. However, marginal organs are susceptible to ischemia-reperfusion injury (IRI) and entail higher requirements for organ preservation. Recently, machine perfusion has emerged as a novel preservation strategy for marginal grafts. This technique continually perfuses the organs to mimic the physiologic condition, allows the evaluation of pretransplant graft function, and more excitingly facilitates organ reconditioning during perfusion with pharmacological, gene, and stem cell therapy. As mesenchymal stem cells (MSCs) have anti-oxidative, immunomodulatory, and regenerative properties, mounting studies have demonstrated the therapeutic effects of MSCs on organ IRI and solid organ transplantation. Therefore, MSCs are promising candidates for organ reconditioning during machine perfusion. This review provides an overview of the application of MSCs combined with machine perfusion for lung, kidney, liver, and heart preservation and reconditioning. Promising preclinical results highlight the potential clinical translation of this innovative strategy to improve the quality of marginal grafts.

Ex Vivo Delivery of Viral Vectors by Organ Perfusion for Cardiac Transplantation Gene Therapy

Recent advances in ex vivo perfusion have enabled an extended preservation time for solid organs prior to transplantation allowing for possible resuscitation of the donor organ during the preservation period. Opportunities to provide viral vector-mediated gene therapy to the entire cardiac graft during this extended preservation period may lead to improvements in cardiac transplantation outcomes. Here we describe how to achieve successful gene delivery using viral vectors to an entire cardiac graft by normothermic, ex vivo perfusion. This protocol has been confirmed with the most highly utilized viral vector types in gene therapy clinical studies (adenoviral [Ad] and adeno-associated viral vector [AAV]).

Normothermic ex vivo Heart Perfusion Combined With Melatonin Enhances Myocardial Protection in Rat Donation After Circulatory Death Hearts via Inhibiting NLRP3 Inflammasome-Mediated Pyroptosis

Objective

The adoption of hearts from donation after circulatory death (DCD) is a promising approach for the shortage of suitable organs in heart transplantation. However, DCD hearts suffer from serious ischemia/reperfusion injury (IRI). Recent studies demonstrate that nucleotide-binding oligomerization domain-like receptor family pyrin domain-containing 3 (NLRP3) inflammasome-mediated pyroptosis is a novel target to ameliorate myocardial IRI. Melatonin is shown to inhibit NLRP3 inflammasome-mediated pyroptosis. Therefore, this study is designed to verify the hypothesis that melatonin can protect the heart graft preserved with ex vivo heart perfusion (EVHP) against myocardial IRI via inhibiting NLRP3 inflammasome-mediated pyroptosis in a rat model of DCD.

Methods

Donor-heart rats were randomly divided into three groups: (1) Control group: non-DCD hearts were harvested from heart-beating rats and immediately preserved with allogenic blood-based perfusate at constant flow for 105 min in the normothermic EVHP system; (2) DCD-vehicle group; and (3) DCD-melatonin group: rats were subjected to the DCD procedure with 25 min of warm ischemia injury and preserved by the normothermic EVHP system for 105 min. Melatonin (200 μmol/L) or vehicle was perfused in the cardioplegia and throughout the whole EVHP period. Cardiac functional assessment was performed every 30 min during EVHP. The level of oxidative stress, inflammatory response, apoptosis, and NLRP3 inflammasome-mediated pyroptosis of heart grafts submitted to EVHP were evaluated.

Results

Twenty five-minute warm ischemia injury resulted in a significant decrease in the developed pressure (DP), dP/dt _max , and dP/dt _min of left ventricular of the DCD hearts, while the treatment with melatonin significantly increased the DP, dP/dt _max of the left ventricular of DCD hearts compared with DCD-vehicle group. Furthermore, warm ischemia injury led to a significant increase in the level of oxidative stress, inflammatory response, apoptosis, and NLRP3 inflammasome-mediated pyroptosis in the hearts preserved with EVHP. However, melatonin added in the cardioplegia and throughout the EVHP period significantly attenuated the level of oxidative stress, inflammatory response, apoptosis, and NLRP3 inflammasome-mediated pyroptosis compared with DCD-vehicle group.

Conclusion

EVHP combined with melatonin post-conditioning attenuates myocardial IRI in DCD hearts by inhibiting NLRP3 inflammasome-mediated pyroptosis, which might expand the donor pool by the adoption of transplantable DCD hearts.

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.

EXPANDing the Donor Pool: Quantifying the Potential Impact of a Portable Organ-Care System for Expanded Criteria Heart Donation

The recently concluded prospective Portable Organ Care System (OCS) Heart trial to Evaluate the Safety and Effectiveness of The Portable Organ Care System Heart for Preserving and Assessing Expanded Criteria Donor Hearts for Transplantation (EXPAND) demonstrated that the use of ex vivo perfusion for expanded-criteria hearts may be a viable method for increasing the use of donor hearts. We sought to estimate the potential impact of ex vivo expanded-criteria heart perfusion on the donor pool in the United States by using a large national transplant registry. After applying the inclusion criteria of EXPAND, 8637 potentially eligible donors were identified in the U.S. between January 1, 2015, and June 30, 2019, representing a substantial potential increase in the donor pool.

Impact of center donor acceptance patterns on utilization of extended-criteria donors and outcomes

BACKGROUND

This study investigated the impact of transplanting center donor acceptance patterns on usage of extended-criteria donors (ECDs) and posttransplant outcomes following orthotopic heart transplantation (OHT).

METHODS

The Scientific Registry of Transplant Recipients was queried to identify heart donor offers and adult, isolated OHT recipients in the United States from January 1, 2013 to October 17, 2018. Centers were stratified into three equal-size terciles based on donor heart acceptance rates (<13.7%, 13.7%-20.2%, >20.2%). Overall survival was compared between recipients of ECDs (≥40 years, left ventricular ejection fraction [LVEF] <60%, distance ≥500 miles, hepatitis B virus [HBV], hepatitis C virus [HCV], or human immunodeficiency virus [HIV], or ≥50 refusals) and recipients of traditional-criteria donors, and among transplanting terciles.

RESULTS

A total of 85,505 donor heart offers were made to 133 centers with 15,264 (17.9%) accepted for OHT. High-acceptance programs (>20.2%) more frequently accepted donors with LVEF <60%, HIV, HCV, and/or HBV, ≥50 offers, or distance >500 miles from the transplanting center (each p < .001). Posttransplant survival was comparable across all three terciles (p = .11). One- and five-year survival were also similar across terciles when examining recipients of all five ECD factors. Acceptance tier and increasing acceptance rate were not found to have any impact on mortality in multivariable modeling. Of ECD factors, only age ≥40 years was found to have increased hazards for mortality (hazard ratio, 1.33; 95% confidence interval [CI], 1.22-1.46; p < .001).

CONCLUSIONS

Of recipients of ECD hearts, outcomes are similar across center-acceptance terciles. Educating less aggressive programs to increase donor acceptance and ECD utilization may yield higher national rates of OHT without major impact on outcomes.

A Novel Rat Model of Cardiac Donation After Circulatory Death Combined With Normothermic ex situ Heart Perfusion

Background: In heart transplantation, the adoption of hearts from donation after circulatory death (DCD) is considered to be a promising approach to expanding the donor pool. Normothermic ex situ heart perfusion (ESHP) is emerging as a novel preservation strategy for DCD hearts. Therefore, pre-clinical animal models of ESHP are essential to address some key issues before efficient clinical translation. We aim to develop a novel, reproducible, and economical rat model of DCD protocol combined with normothermic ESHP.

Methods: Circulatory death of the anesthetized rats in the DCD group was declared when systolic blood pressure below 30 mmHg or asystole was observed after asphyxiation. Additional 15 min of standoff period was allowed to elapse. After perfusion of cold cardioplegia, the DCD hearts were excised and perfused with allogenic blood-based perfusate at constant flow for 90 min in the normothermic ESHP system. Functional assessment and blood gas analysis were performed every 30 min during ESHP. The alteration of DCD hearts submitted to different durations of ESHP (30, 60, and 90 min) in oxidative stress, apoptosis, tissue energy state, inflammatory response, histopathology, cell swelling, and myocardial infarction during ESHP was evaluated. Rats in the non-DCD group were treated similarly but not exposed to warm ischemia and preserved by the normothermic ESHP system for 90 min.

Results: The DCD hearts showed compromised function at the beginning of ESHP and recovered over time, while non-DCD hearts presented better cardiac function during ESHP. The alteration of DCD hearts in oxidative stress, apoptosis, tissue energy state, histopathological changes, cell swelling, and inflammatory response didn't differ among different durations of ESHP. At the end of 90-min ESHP, DCD, and non-DCD hearts presented similarly in apoptosis, oxidative stress, inflammatory response, myocardial infarction, and histopathological changes. Moreover, the DCD hearts had lower energy storage and more evident cell swelling compared to the non-DCD hearts.

Conclusion: We established a reproducible, clinically relevant, and economical rat model of DCD protocol combined with normothermic ESHP, where the DCD hearts can maintain a stable state during 90-min ESHP.

Mending hearts: A further strategy to improve cardiac donors availability

Patients listed for heart transplantation are increasing annually worldwide, but the limited number of available donor hearts restricts this treatment to a small fraction of potential recipients. Attempts have, therefore, been made to expand the donor pool by recruiting donors who may not satisfy the standard criteria for organ donation. We reviewed our early experience by using three donor hearts which were successfully transplanted either after correction or not of pre-existing defects (Case #1: Coronary fistula; Case #2: Takayasu syndrome; Case #3: Percutaneously repaired atrial septal defect), demonstrating that structural cardiac abnormalities might not always be an absolute contraindication to donation candidacy.

Zebrafish as a New Tool in Heart Preservation Research

Heart transplantation became a reality at the end of the 1960s as a life-saving option for patients with end-stage heart failure. Static cold storage (SCS) at 4-6 °C has remained the standard for heart preservation for decades. However, SCS only allows for short-term storage that precludes optimal matching programs, requires emergency surgeries, and results in the unnecessary discard of organs. Among the alternatives seeking to extend ex vivo lifespan and mitigate the shortage of organs are sub-zero or machine perfusion modalities. Sub-zero approaches aim to prolong cold ischemia tolerance by deepening metabolic stasis, while machine perfusion aims to support metabolism through the continuous delivery of oxygen and nutrients. Each of these approaches hold promise; however, complex barriers must be overcome before their potential can be fully realized. We suggest that one barrier facing all experimental efforts to extend ex vivo lifespan are limited research tools. Mammalian models are usually the first choice due to translational aspects, yet experimentation can be restricted by expertise, time, and resources. Instead, there are instances when smaller vertebrate models, like the zebrafish, could fill critical experimental gaps in the field. Taken together, this review provides a summary of the current gold standard for heart preservation as well as new technologies in ex vivo lifespan extension. Furthermore, we describe how existing tools in zebrafish research, including isolated organ, cell specific and functional assays, as well as molecular tools, could complement and elevate heart preservation research.

Consistent improvements in short- and long-term survival following heart transplantation over the past three decades

BACKGROUND

Despite noted improvements in short-term survival outcomes following orthotopic heart transplantation (OHT), review of the relevant literature suggests little improvement in long-term outcomes for patients surviving beyond 1 year.

METHODS

All OHT cases performed between 1989 and 2019 within the United Network for Organ Sharing (UNOS) database were reviewed. Adults who underwent isolated OHT were included in a 1-year survival analysis. Those who survived at least 1 year post-transplant were included in a long-term survival analysis. Demographic factors were assessed using Students' t test and chi-square analysis. Survival trends and risk factors were assessed using the Kaplan-Meier and the Cox regression analysis, respectively.

RESULTS

A total of 53 265 and 46 372 recipients were included in the short-term and long-term cohorts, respectively. In an adjusted analysis, the reference implant era 2014-2019 had significantly better short-term survival outcomes when compared with earlier implant eras: 1989-1993 (HR: 2.92), 1994-1998 (HR: 1.53), 1999-2003 (HR: 1.27), 2004-2008 (HR: 1.11), and 2009-2013 (HR: 1.02). The same trend was recognized for long-term outcomes: 1989-1993 (HR: 1.87), 1994-1998 (HR: 1.27), 1999-2003 (HR: 1.09), and 2004-2008 (HR: 1.03).

CONCLUSIONS

Despite increases in multiple traditional risk factors, both short-term and long-term survival outcomes have consistently improved over the past 30 years, suggesting other factors are contributing to improved outcomes in recent eras.

Anesthetic Considerations During Heart Transplantation Using Donation After Circulatory Death

Worldwide, the majority of heart transplant organs are from donation after brain death. However, the shortage of suitable donors places severe limitations on this route. One option to increase the donor pool is to use organs from donation after circulatory death (DCD). Transplant centers for solid organs have been using DCD organs for years. At this time, 40% of solid organ transplantation in the United Kingdom uses organs from DCD. Use of DCD for solid organ transplants in Canada is also rising. Recently, there has been interest in using DCD organs for heart transplantation. The authors will discuss their experience of 4 heart transplants with organs from DCD donors after normothermic regional perfusion (NRP). The authors' first heart transplant using a DCD organ was in January 2020, and the fourth was in March 2020, just before the coronavirus disease 2019 (COVID-19) pandemic. The authors' protocol using NRP allows adequate evaluation of the donor heart to confidently determine organ acceptance. The co-location of the donor and the recipient in neighboring operating rooms limits ischemic times. Avoidance of an expensive ex vivo organ perfusion machine is an additional benefit for programs that may not have the resources required to purchase and maintain the machine. Some hospitals may not have the resources and space to be able to co-locate both the donor and recipient. Use of cold storage may be an option to transport the procured organ, similar to donation after brain death organs. The authors hope that this technique of NRP in DCD donors can help further increase the donor pool for heart transplantation in the United States.

Comparing Donor Heart Assessment Strategies During Ex Situ Heart Perfusion to Better Estimate Posttransplant Cardiac Function

BACKGROUND

Ex situ heart perfusion (ESHP) limits ischemic periods and enables continuous monitoring of donated hearts; however, a validated assessment method to predict cardiac performance has yet to be established. We compare biventricular contractile and metabolic parameters measured during ESHP to determine the best evaluation strategy to estimate cardiac function following transplantation.

METHODS

Donor pigs were assigned to undergo beating-heart donation (n = 9) or donation after circulatory death (n = 8) induced by hypoxia. Hearts were preserved for 4 hours with ESHP while invasive and noninvasive (NI) biventricular contractile, and metabolic assessments were performed. Following transplantation, hearts were evaluated at 3 hours of reperfusion. Spearman correlation was used to determine the relationship between ESHP parameters and posttransplant function.

RESULTS

We performed 17 transplants; 14 successfully weaned from bypass (beating-heart donation versus donation after circulatory death; P = 0.580). Left ventricular invasive preload recruitable stroke work (PRSW) (r = 0.770; P = 0.009), NI PRSW (r = 0.730; P = 0.001), and NI maximum elastance (r = 0.706; P = 0.002) strongly correlated with cardiac index (CI) following transplantation. Right ventricular NI PRSW moderately correlated to CI following transplantation (r = 0.688; P = 0.003). Lactate levels were weakly correlated with CI following transplantation (r = -0.495; P = 0.043). None of the echocardiography measurements correlated with cardiac function following transplantation.

CONCLUSIONS

Left ventricular functional parameters, especially ventricular work and reserve, provided the best estimation of myocardial performance following transplantation. Furthermore, simple NI estimates of ventricular function proved useful in this setting. Right ventricular and metabolic measurements were limited in their ability to correlate with myocardial recovery. This emphasizes the need for an ESHP platform capable of assessing myocardial contractility and suggests that metabolic parameters alone do not provide a reliable evaluation.

Novel heat shock protein 90 inhibitor improves cardiac recovery in a rodent model of donation after circulatory death

OBJECTIVE

Organ donation after circulatory death (DCD) is a potential solution for the shortage of suitable organs for transplant. Heart transplantation using DCD donors is not frequently performed due to the potential myocardial damage following warm ischemia. Heat shock protein (HSP) 90 has recently been investigated as a novel target to reduce ischemia/reperfusion injury. The objective of this study is to evaluate an innovative HSP90 inhibitor (HSP90i) as a cardioprotective agent in a model of DCD heart.

METHODS

A DCD protocol was initiated in anesthetized Lewis rats by discontinuation of ventilation and confirmation of circulatory death by invasive monitoring. Following 15 minutes of warm ischemia, cardioplegia was perfused for 5 minutes at physiological pressure. DCD hearts were mounted on a Langendorff ex vivo heart perfusion system for reconditioning and functional assessment (60 minutes). HSP90i (0.01 μmol/L) or vehicle was perfused in the cardioplegia and during the first 10 minutes of ex vivo heart perfusion reperfusion. Following assessment, pro-survival pathway signaling was evaluated by western blot or polymerase chain reaction.

RESULTS

Treatment with HSP90i preserved left ventricular contractility (maximum + dP/dt, 2385 ± 249 vs 1745 ± 150 mm Hg/s), relaxation (minimum -dP/dt, -1437 ± 97 vs 1125 ± 85 mm Hg/s), and developed pressure (60.7 ± 5.6 vs 43.9 ± 4.0 mm Hg), when compared with control DCD hearts (All P = .001). Treatment abrogates ischemic injury as demonstrated by a significant reduction of infarct size (2,3,5-triphenyl-tetrazolium chloride staining) of 7 ± 3% versus 19 ± 4% (P = .03), troponin T release, and mRNA expression of Bax/Bcl-2 (P < .05).

CONCLUSIONS

The cardioprotective effects of HSP90i when used following circulatory death might improve transplant organ availability by expanding the use of DCD hearts.

New Techniques for Optimization of Donor Lungs/Hearts

Injuries sustained by donor heart and lung allografts during the transplantation process are multiple and cumulative. Optimization of allograft function plays an essential role in short- and long-term outcomes after transplantation. Therapeutic targets to prevent or attenuate injury are present in the donor, the preservation process, during transplantation, and in postoperative management of the recipient. The newest and most promising methods of optimizing donor heart and lung allografts are found in alternative preservation strategies, which enable functional assessment of donor organs and provide a modality to initiate therapies for injured allografts or prevent injury during reperfusion in recipients.

The implementation of physiological afterload during ex situ heart perfusion augments prediction of posttransplant function

Ex situ heart perfusion (ex situ heart perfusion) is an emerging technique that aims to increase the number of organs available for transplantation by augmenting both donor heart preservation and evaluation. Traditionally, ex situ heart perfusion has been performed in an unloaded Langendorff mode, though more recently groups have begun to use pump-supported working mode (PSWM) and passive afterload working mode (PAWM) to enable contractile evaluation during ex situ heart perfusion. To this point, however, neither the predictive effectiveness of the two working modes nor the predictive power of individual contractile parameters has been analyzed. In this article, we use our previously described system to analyze the predictive relevance of a multitude of contractile parameters measured in each working mode. Ten porcine hearts were excised and perfused ex situ in Langendorff mode for 4 h, evaluated using pressure-volume catheterization in both PSWM and PAWM, and transplanted into size-matched recipient pigs. After 3 h, hearts were weaned from cardiopulmonary bypass and evaluated. When correlating posttransplant measurements to their ex situ counterparts, we report that parameters measured in both modes show sufficient power (Spearman rank coefficient > 0.7) in predicting global posttransplant function, characterized by cardiac index and preload recruitable stroke work. For the prediction of specific posttransplant systolic and diastolic function, however, a large discrepancy between the two working modes was observed. With 9 of 10 measured posttransplant parameters showing stronger correlation with counterparts measured in PAWM, it is concluded that PAWM allows for a more detailed and nuanced prediction of posttransplant function than can be made in PSWM.NEW & NOTEWORTHY Ex situ heart perfusion has been proposed as a means to augment the organ donor pool by improving organ preservation and evaluation between donation and transplantation. Using our multimodal perfusion system, we analyzed the impact of using a "passive afterload working mode" for functional evaluation as compared with the more traditional "pump-supported working mode." Our data suggests that passive afterload working mode allows for a more nuanced prediction of posttransplant function in porcine hearts.