Current approaches in retrieval and heart preservation

Protective effects of mesenchymal stem cells-derived extracellular vesicles against ischemia-reperfusion injury of hearts donated after circulatory death: Preliminary study in a pig model

INTRODUCTION

Insufficient supply of cardiac grafts represents a severe obstacle in heart transplantation. Donation after Circulatory Death (DCD), in addition to conventional donation after brain death, is one promising option to overcome the organ shortage. However, DCD organs undergo an inevitable more extended period of warm unprotected ischemia between circulatory arrest and graft procurement. Mesenchymal stromal cell-derived extracellular vesicles (MSC-EVs) have shown remarkable protective effects against ischemia-reperfusion injury. Thus, we aimed to enhance grafts preservation from DCD donors, through treatment with MSC-EVs.

METHODS

Female pigs were euthanized by barbiturate overdose and after 20 min of a flat EKG, the chest was opened, the heart harvested and subsequently connected to an extracorporeal perfusion machine. MSC-EVs, isolated by ion exchange chromatography, were added to the perfusion solution (1×1011 particles) and the heart was perfused for 2 h. Then, heart tissue biopsies were taken to assess histological changes, mitochondrial morphology, antioxidant enzyme activity and inflammation mediators' expression. Biochemical parameters of myocardial viability were assessed in the perfusate.

RESULTS

The treatment with MSC-EVs significantly prevented mitochondria swelling, mitochondrial cristae loss and oxidative stress in cardiac tissue. The protective effect of MSC-EVs was confirmed by the delayed increase of the cardiac-specific enzymes CK and TnC in the perfusate and the reduction of caspase-3+ cells in tissue sections.

CONCLUSION

MSC-EVs improve graft quality by preserving the mitochondrial ultrastructure protecting the myocardium against oxidative stress, reducing apoptosis of cardiac cells and preventing the increase of pro-inflammatory cytokines.

Supercooled preservation of cultured primary rat hepatocyte monolayers

Supercooled preservation (SCP) is a technology that involves cooling a substance below its freezing point without initiating ice crystal formation. It is a promising alternative to prolong the preservation time of cells, tissues, engineered tissue products, and organs compared to the current practices of hypothermic storage. Two-dimensional (2D) engineered tissues are extensively used in in vitro research for drug screening and development and investigation of disease progression. Despite their widespread application, there is a lack of research on the SCP of 2D-engineered tissues. In this study, we presented the effects of SCP at -2 and -6°C on primary rat hepatocyte (PRH) monolayers for the first time and compared cell viability and functionality with cold storage (CS, + 4°C). We preserved PRH monolayers in two different commercially available solutions: Hypothermosol-FRS (HTS-FRS) and the University of Wisconsin (UW) with and without supplements (i.e., polyethylene glycol (PEG) and 3-O-Methyl-Α-D-Glucopyranose (3-OMG)). Our findings revealed that UW with and without supplements were inadequate for the short-term preservation of PRH monolayers for both SCP and CS with high viability, functionality, and monolayer integrity. The combination of supplements (PEG and 3-OMG) in the HTS-FRS solution outperformed the other groups and yielded the highest viability and functional capacity. Notably, PRH monolayers exhibited superior viability and functionality when stored at -2°C through SCP for up to 3 days compared to CS. Overall, our results demonstrated that SCP is a feasible approach to improving the short-term preservation of PRH monolayers and enables readily available 2D-engineered tissues to advance in vitro research. Furthermore, our findings provide insights into preservation outcomes across various biological levels, from cells to tissues and organs, contributing to the advancement of bioengineering and biotechnology.

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.

Heart graft preservation technics and limits: an update and perspectives

Heart transplantation, the gold standard treatment for end-stage heart failure, is limited by heart graft shortage, justifying expansion of the donor pool. Currently, static cold storage (SCS) of hearts from donations after brainstem death remains the standard practice, but it is usually limited to 240 min. Prolonged cold ischemia and ischemia-reperfusion injury (IRI) have been recognized as major causes of post-transplant graft failure. Continuous ex situ perfusion is a new approach for donor organ management to expand the donor pool and/or increase the utilization rate. Continuous ex situ machine perfusion (MP) can satisfy the metabolic needs of the myocardium, minimizing irreversible ischemic cell damage and cell death. Several hypothermic or normothermic MP methods have been developed and studied, particularly in the preclinical setting, but whether MP is superior to SCS remains controversial. Other approaches seem to be interesting for extending the pool of heart graft donors, such as blocking the paths of apoptosis and necrosis, extracellular vesicle therapy, or donor heart-specific gene therapy. In this systematic review, we summarize the mechanisms involved in IRI during heart transplantation and existing targeting therapies. We also critically evaluate all available data on continuous ex situ perfusion devices for adult donor hearts, highlighting its therapeutic potential and current limitations and shortcomings.

Immediate major dynamic changes in the T- and NK-cell subset composition after cardiac transplantation

Early kinetics of lymphocyte subsets involved in tolerance and rejection following heart transplantation (HTx) are barely defined. Here, we aimed to delineate the early alloimmune response immediately after HTx. Therefore, blood samples from 23 heart-transplanted patients were collected before (pre-), immediately (T0), 24 hours (T24), and 3 weeks (3 wks) after HTx. Immunophenotyping was performed using flow cytometry. A significant increase was detected for terminally differentiated (TEMRA) CD4+ or CD8+ T cells and CD56dim CD16+ NK cells immediately after HTx linked to a decrease in naïve CD8+ and CM CD4+ T as well as CD56bright CD16- NK cells, returning to baseline levels at T24. More detailed analyses revealed increased CD69+ CD25- and diminished CD69- CD25- CD4+ or CD8+ T-cell proportions at T0 associated with decreasing S1PR1 expression. Passenger T and NK cells were found at low frequencies only in several patients at T0 and did not correlate with lymphocyte alterations. Collectively, these results suggest an immediate, transient shift toward memory T and NK cells following HTx. Opposite migratory properties of naïve versus memory T and NK cells occurring in the early phase after HTx could underlie these observations and may impinge on the development of allo-specific immune responses.

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.

Left ventricular assist device mode: Co-pulse left ventricular unloading in a working mode of ex vivo heart perfusion

BACKGROUND

For normothermic ex vivo heart perfusion (EVHP), a resting mode and working mode have been proposed. We newly developed a left ventricular assist device (LVAD) mode that supports heart contraction by co-pulse synchronized LVAD.

METHODS

Following resting mode during time 0 to 1 hour, pig hearts (n = 18) were perfused in either resting, working, or LVAD mode during time 1 to 5 hour, and then myocardial function was evaluated in working mode at 6 hour. The preservation ratio was defined as the myocardial mechanical function at 330 minute divided by the function at 75 minute. In LVAD mode, LVAD unloaded the pressure and the volume in the left ventricle in the systolic phase.

RESULTS

The LVAD group was significantly associated with higher preservation ratios in cardiac output (resting, 33 ± 3; working, 35 ± 5; LVAD, 76% ± 5%; p < 0.001), stroke work, dP/dt maximum, and dP/dt minimum compared with the other groups. Glucose consumption was significantly reduced in the resting group. The LVAD group was significantly associated with higher myocardial oxygen consumption (resting, 2.2 ± 0.3; working; 4.6 ± 0.5; LVAD, 6.1 ± 0.5 mL O₂/min/100 g, p < 0.001) and higher adenosine triphosphate (ATP) levels (resting, 1.1 ± 0.1; working, 0.7 ± 0.1; LVAD, 1.6 ± 0.2 μmol/g, p = 0.001) compared with the others.

CONCLUSION

These data suggest that myocardial mechanical function was better preserved in LVAD mode than in resting and working modes. Although our data suggested similar glycolysis activity in the LVAD and working groups, the higher final ATP in the LVAD group might be explained by reduced external work in LVAD.

Donation After Circulatory Death: A New Frontier

PURPOSE OF REVIEW

To highlight the current global experience with DCD heart transplantation and explore the evolution of, and compare preservation strategies; examine early clinical outcomes, and discuss the growing use of DCD donors as a new frontier in heart transplantation.

RECENT FINDINGS

The two strategies of DCD heart preservation include NMP using the OCS Heart and TA-NRP followed by either: NMP or CSS. Better understanding the limits of cold ischaemia following TA-NRP will aid in distant procurement. Asystolic warm ischaemia plays an important role in determining immediate post-operative graft function and potential need for mechanical support. Large volume DCD heart transplant units show no difference in survival between DCD and DBD donor heart transplants. In a previously non-utilised source of donor hearts, often viewed as an "unknown frontier" in heart transplantation, DCD hearts are a suitable alternative to brain-dead donor hearts and are likely to remain a permanent part of the heart transplantation landscape. Global uptake is currently increasing, and as understanding of preservation strategies and tolerable ischaemic times improve, utilisation of DCD hearts will continue to grow.

Coronary angiography of the ex-situ beating donor heart in a portable organ care system

OBJECTIVES

To determine safety and feasibility of ex-situ coronary angiography.

BACKGROUND

To cater for the perpetually growing demand for heart donors, interest in donation following circulatory death (DCD) has been rekindled. Further pursuit of donor pool expansion has led to eligibility extension to "marginal" donors who are at higher risk of coronary artery disease (CAD). Excluding CAD in potentially eligible DCD donors, for whom ante-mortem angiography is commonly not permitted, is therefore challenging. Ex-situ coronary angiography serves as an ethical and feasible diagnostic tool to assess for preclusive CAD.

METHODS

We undertook a systematic review of the published literature and institutional retrospective review of case experience with ex-situ coronary angiography of donor hearts, supported by a portable organ care system.

RESULTS

Combined literature and institutional case review yielded nine total cases of ex-situ coronary angiography of donor human hearts plus one experimental porcine model. Of the eight cases of ex-situ coronary angiography performed at our institute, all were conducted without complication or injury to the allograft. Two thirds of reported human cases have proceeded to successful transplantation.

CONCLUSIONS

Diagnostic coronary angiography of the ex-situ beating donor heart is safe, feasible, and demonstrates novel clinical utility in mitigating subsequent transplantation of unsuitable allografts. In the setting of suspected coronary atherosclerosis of the donor heart, which may preclude favorable transplantation outcomes, ex-situ coronary angiography should be considered at eligible transplant centers.

Outcomes of Cardiac Transplantation in Western Australia - A Contemporary Single Centre Experience

BACKGROUND

Cardiac transplantation remains the gold standard therapy for select patients with end-stage heart failure and outcomes have improved significantly over the past few decades. We report the 5-year contemporary experience of cardiac transplantation in Western Australia, one of the most remote transplant centres worldwide.

METHODS

Patients undergoing isolated cardiac transplant at Fiona Stanley Hospital (FSH) from February 2015 until April 2021 were included. Donor details were collected using donor electronic records (Donate Life, Australia). Recipient data was collated from electronic medical records at FSH and the Australia and New Zealand Society of Cardiothoracic Surgery database. The primary outcome measure was all-cause mortality. Secondary outcome measures included postoperative intensive care and total hospital length of stay and rates of acute kidney injury, rejection, serious infections, and cardiac allograft vasculopathy. Frailty indices were also assessed.

RESULTS

A total of 60 patients were included (mean age 53±14 yrs, 66.7% male). The commonest indication for transplant was a non-ischaemic cardiomyopathy (46.7%). Mean donor age was 35±12 years and median donor ischaemia time was 171 minutes (IQR=138-240). After median follow-up of 3.7 years, there were no mortalities. Postoperative renal failure occurred in 21 (35.0%) patients, pneumonia in four (6.7%), deep sternal wound infection in three (5.1%), acute rejection in 17 (28.3%) and cardiac allograft vasculopathy (CAV) in 23 (38.3%).

CONCLUSION

With recipient and donor criteria comparable to national and international standards, compounded by the challenges of geographic isolation, we report the first published data on contemporary outcomes post isolated cardiac transplantation in Western Australia.

Normothermic Ex Vivo Heart Perfusion with Mesenchymal Stem Cell-Derived Conditioned Medium Improves Myocardial Tissue Protection in Rat Donation after Circulatory Death Hearts

Objective. Adopting hearts from donation after circulatory death (DCD) is a promising approach to enlarge the donor pool. Nevertheless, DCD hearts experience severe warm ischemia/reperfusion (I/R) injury. Recent studies have demonstrated that conditioned medium (CM) derived from bone marrow mesenchymal stem cells (BMSCs) has the potential of reducing organ I/R injury. Therefore, we investigated whether DCD heart preservation with normothermic ex vivo heart perfusion (EVHP) and BMSCs-CM treatment could alleviate myocardial warm I/R injury in the DCD hearts. Methods. We randomly divided donor rats into two groups: (1) DCD-Control group and (2) DCD-CM group. Before DCD heart preservation with the normothermic EVHP system for 105 minutes, rats suffered from a 25-minute warm ischemia injury in the DCD procedure. Vehicle or CM (300 μl) was added to the perfusate at the beginning of the perfusion process. The cardiac function of DCD hearts in the DCD-Control and DCD-CM groups was measured every 30 minutes. Besides, non-DCD hearts were harvested from the beating-heart rats. Results. The antibody array demonstrated that the CM contained 14 bioactive factors involved in apoptosis, inflammation, and oxidative stress. Warm ischemia injury resulted in a significant increase in the level of oxidative stress, inflammation, and apoptosis in the DCD hearts of DCD-Control group. Furthermore, compared with the DCD-Control group, CM treatment increased the developed pressure, $\text{dP}/\text{d}{\text{t}}_{\max }$ and $\text{dP}/\text{d}{\text{t}}_{\min }$ of the left ventricular in the DCD hearts during a 90-minute EVHP. Moreover, the administration of CM attenuated the level of oxidative stress, inflammation, and apoptosis in the DCD hearts of the DCD-CM group. Conclusions. Normothermic EVHP combined with CM treatment can alleviate warm I/R injury in the DCD hearts by decreasing the level of oxidative stress, inflammatory response, and apoptosis, which might alleviate the shortage of donor hearts by adopting DCD hearts.

Strategies for Expanding Donors Pool in Heart Transplantation

Heart transplant remains the criterion standard treatment for patients in end-stage heart failure. Improvement in the post-heart transplant outcomes in the last decade has contributed to increased demand for organs. Worldwide each year, more than 5000 heart transplants are performed and 50,000 people become candidates for heart transplant. In the last 50 years, there have been several attempts to expand donor criteria to increase the donor pool. Despite making hepatitis C virus, opioid overdose death, old age allowable and changing the allocation system, the gap between supply and demand is widening and unfortunately, thousands die every year waiting due to the critical shortage of organs. New technologies for heart donation after circulatory death have emerged, particularly normothermic regional organ perfusion and ex-vivo heart perfusion using organ care systems. However, these technologies still do not fill the gap. Continuous advancements in areas such as regenerative medicine and xenotransplantation, among others, are needed to overcome the shortage of heart donors for 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.

Transplantation of a beating heart: A first in man

BACKGROUND

In the current practice, graft ischaemia and reperfusion injury (IRI) is considered an inevitable component in organ transplantation, contributes to compromised organ quality, inferior graft survival and limitations in organ availability. Among all the donor organs, the heart is most vulnerable to IRI and the tolerated ischaemic time is the shortest.

METHODS

By combining adapted surgical techniques and normothermic machine perfusion (NMP), we performed the first case of ischaemia-free beating heart transplantation (IFBHT) in man. The donor heart was procured after an in situ NMP circuit was established, then underwent ex situ NMP and implanted under NMP support. The post-transplant graft function was monitored.

FINDINGS

The donor heart was procured, preserved, and implanted under a continuously perfused, normothermic, oxygenated, beating state. During ex situ NMP, the donor heart beat with sinus rhythm and adequate ventricular contraction, consumed oxygen and lactate, suggesting a good cardiac function. The dynamic electrocardiogram demonstrated an absence of ischaemic injury of the donor heart during the entire procedure. The echocardiogram showed an immediate graft function with a left ventricle ejection fraction (LVEF) of 70%. The patient was discharged on post-transplantation day 20 and was followed up for 8 months with normal cardiac function and life.

INTERPRETATION

This study shows the feasibility of IFBHT procedure, which might be able to completely avoid graft IRI, has thus the potential to improve transplant outcome while increasing organ utilization.

FUNDING

This study was funded by National Natural Science Foundation of China, Guangdong Provincial Key Laboratory Construction Projection on Organ Donation and Transplant Immunology, and Guangdong Provincial International Cooperation Base of Science and Technology.

Ex-Vivo Preservation with the Organ Care System in High Risk Heart Transplantation

Objective: Ex vivo organ perfusion is an advanced preservation technique that allows graft assessment and extended ex situ intervals. We hypothesized that its properties might be especially beneficial for high-risk recipients and/or donors with extended criteria. Methods: We reviewed the outcomes of 119 consecutive heart transplant patients, which were divided into two groups: A (OCS) vs. B (conventional). Ex vivo organ perfusion was performed using the Organ Care System (OCS). Indications for OCS-usage were expected ischemic time of >4 h or >2 h plus given extended donor criteria. Results: Both groups included mostly redo cases (A: 89.7% vs. B: 78.4%; p = 0.121). Incidences of donors with previous cardiac arrest (%) (A: 32.4 vs. B: 22.2; p < 0.05) or LV-hypertrophy (%) (A: 19.1 vs. B: 8.3; p = 0.119) were also increased in Group A. Ex situ time (min) was significantly longer in Group A (A: 381 (74) vs. B: 228 (43); p < 0.05). Ventilation time (days) (A: 10.0 (19.9) vs. B: 24.3 (43.2); p = 0.057), postoperative need for ECLS (%) (A: 25.0 vs. B: 39.2; p = 0.112) and postoperative dialysis (chronic) (%) (A: 4.4 vs. B: 27.5; p < 0.001) were numerically better in the OCS group, without any difference in the occurrence of early graft rejection. The 30-d-survival (A: 92.4% vs. B: 90.2%; p = 0.745) and mid-term survival were statistically not different between both groups. Conclusions: OCS heart allowed safe transplantation of surgically complex recipients with excellent one-year outcomes, despite long preservation times and unfavourable donor characteristics. Furthermore, we observed trends towards decreased ventilation times and fewer ECLS treatments. In times of reduced organ availability and increasing recipient complexity, OCS heart is a valuable instrument that enables otherwise infeasible allocations and contributes to increase surgical safety.

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 Donation From Donors After Controlled Circulatory Death

The gold-standard therapy for advanced-stage heart failure is cardiac transplantation. Since the first heart transplant in 1967, the majority of hearts transplanted came from brain death donors. Nevertheless, in recent years, the option of donation after circulatory death (DCD) is gaining importance to increase donor pool. Currently, heart-transplant programs using controlled donation after circulatory death (cDCD) have been implemented in the United Kingdom, Belgium, Australia, United States of America, and, recently, in Spain. In this article, we performed a concise review of the literature in heart cDCD; we summarize the pathophysiology involved in ischemia and reperfusion injury during this process, the different techniques of heart retrieval in cDCD donors, and the strategies that can be used to minimize the damage during retrieval and until transplantation. Heart transplant using DCD hearts is in continuous improvement and must be implemented in experienced cardiac transplant centers.

3D bioprinting of cardiac tissue: current challenges and perspectives

Demand for donor hearts has increased globally due to cardiovascular diseases. Recently, three-dimensional (3D) bioprinting technology has been aimed at creating clinically viable cardiac constructs for the management of myocardial infarction (MI) and associated complications. Advances in 3D bioprinting show promise in aiding cardiac tissue repair following injury/infarction and offer an alternative to organ transplantation. This article summarizes the basic principles of 3D bioprinting and recent attempts at reconstructing functional adult native cardiac tissue with a focus on current challenges and prospective strategies.

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.

Outcomes of heart transplantation in patients bridged with Impella 5.0: Comparison with native chest transplanted patients without preoperative mechanical circulatory support

The Impella (Abiomed, Danvers, MA, USA) has become an important adjunct treatment modality in bridging patients with end-stage heart failure to recovery or orthotopic heart transplantation (HTx). We compared the outcome of patients directly bridged to HTx with the Impella 5.0 versus patients without mechanical circulatory support (MCS). Patients with no previous sternotomy or MCS, who were transplanted between September 2014 and March 2019 were included in this retrospective analysis. Impella 5.0 was implanted using surgical access and transesophageal echocardiography guidance. Forty-two out of 155 transplanted patients fulfilled the insertion criteria. Eight (19%) were bridged with Impella 5.0 to HTx. Recipient and donor baseline characteristics were comparable in both groups. There were no significant differences in survival between the groups at 30-day (94% no MCS vs. 87.5% Impella group, P = .47) or 6 months (94% vs. 87.5%, P = .51). Patients on Impella 5.0 showed a significant recovery of hemodynamic parameters and end-organ function. Average duration of support to HTx was 16 ± 17 days. Impella 5.0, when used in suitable patients in a timely fashion can be a good strategy for bridging patients to HTx. The axillary approach allows for early extubation and mobilization. Outcomes of patients bridged to HTx with Impella 5.0 in acute cardiogenic shock are comparable to those of patients with no MCS.

Mitigating the Impact of Using Female Donor Hearts in Male Recipients Using BMI Difference

BACKGROUND

Heart transplantation is limited by the supply of donor organs. Previous studies have associated female donor to male recipient with decreased posttransplant survival. We wanted to evaluate whether this risk can be mitigated using higher donor than recipient body mass index (BMI).

METHODS

We performed a retrospective analysis of the Organ Procurement and Transplantation Network/United Network of Organ Sharing registry encompassing years 2005 to 2018 for all male adult recipients (>18 years of age) who underwent isolated heart transplantation with grafts from female donors. The association between donor and recipient BMI difference and recipient survival was evaluated using adjusted Cox proportional hazards modeling.

RESULTS

A total of 3788 male recipients who received female donor hearts met inclusion criteria for analysis. Maximally selected rank statistics identified donor minus recipient BMI of 1.5 kg/m² as a meaningful cutoff point in the analysis of recipient survival. Multivariable Cox proportional hazards analysis demonstrated that increasing donor BMI relative to recipient BMI up to this cutoff point was associated with improved survival (hazard ratio per 5-unit difference, 0.87; 95% confidence interval, 0.77-0.99). Above this cutoff point, increasing donor BMI relative to the recipient did not improve survival more than what was achieved by adding 1.5 of BMI difference (hazard ratio per 5-unit difference, 0.97; 95% confidence interval, 0.90-1.04).

CONCLUSIONS

Increasing donor BMI relative to recipient BMI up to 1.5 kg/m² greater than recipient BMI was associated with improved survival. BMI difference may be useful as a simple surrogate for predicted heart mass difference to help mitigate the impact of sex mismatch in heart transplantation.

Development of a pro-arrhythmic ex vivo intact human and porcine model: cardiac electrophysiological changes associated with cellular uncoupling

We describe a human and large animal Langendorff experimental apparatus for live electrophysiological studies and measure the electrophysiological changes due to gap junction uncoupling in human and porcine hearts. The resultant ex vivo intact human and porcine model can bridge the translational gap between smaller simple laboratory models and clinical research. In particular, electrophysiological models would benefit from the greater myocardial mass of a large heart due to its effects on far-field signal, electrode contact issues and motion artefacts, consequently more closely mimicking the clinical setting. Porcine (n = 9) and human (n = 4) donor hearts were perfused on a custom-designed Langendorff apparatus. Epicardial electrograms were collected at 16 sites across the left atrium and left ventricle. A total of 1 mM of carbenoxolone was administered at 5 ml/min to induce cellular uncoupling, and then recordings were repeated at the same sites. Changes in electrogram characteristics were analysed. We demonstrate the viability of a controlled ex vivo model of intact porcine and human hearts for electrophysiology with pharmacological modulation. Carbenoxolone reduces cellular coupling and changes contact electrogram features. The time from stimulus artefact to (-dV/dt)_max increased between baseline and carbenoxolone (47.9 ± 4.1–67.2 ± 2.7 ms) indicating conduction slowing. The features with the largest percentage change between baseline and carbenoxolone were fractionation + 185.3%, endpoint amplitude − 106.9%, S-endpoint gradient + 54.9%, S point − 39.4%, RS ratio + 38.6% and (-dV/dt)_max − 20.9%. The physiological relevance of this methodological tool is that it provides a model to further investigate pharmacologically induced pro-arrhythmic substrates.

Cold-inducible RNA binding protein agonist enhances the cardioprotective effect of UW solution during extended heart preservation

In heart transplantation, time restriction is an unavoidable thorny problem during cardiac transport. Cold storage is an important organ preservation method in donor heart transport. Cold-inducible RNA binding protein (CIRBP) has been proven to play a protective role under cold stress. In this study, we investigated the role of CIRBP in hypothermic cardioprotection during heart preservation in UW solution and explored a new approach to extend the heart preservation time. Cirbp-knockout (Cirbp^-/- ), Cirbp-transgenic (Cirbp-Tg), and wild-type rats were, respectively, randomized into two groups based on various heart preservation times (6 or 12-hour group) (n = 8 per group). After preservation in UW solution, all hearts were mounted on a Langendorff apparatus and underwent measurement of cardiac parameters, histological analysis, and molecular study. Within the 6-hour preservation group, no significant difference was found in cardiac functions and histological changes between different rat species. However, after 12 hours of preservation, Cirbp^-/- rat hearts showed more apoptosis and worse cardiac function, but less apoptosis and better cardiac function were observed in Cirbp-Tg rat hearts. Furthermore, we found CIRBP-mediated cardiac ubiquinone (CoQ₁₀ ) biosynthesis plays an important role in extending heart preservation, and ubiquinone biosynthesis protein COQ9 was an essential down-stream regulator during this process. Finally, we found that zr17-2, a CIRBP agonist, could enhance the expression of CIRBP, which further enhances the synthesis of CoQ₁₀ and promotes scavenging of reactive oxygen species and ATP production to extend heart preservation. This study demonstrated that CIRBP-enhanced CoQ₁₀ biosynthesis during hypothermic heart preservation and zr17-2-supplemented UW solution could be a promising approach to ameliorate heart damage and extend heart preservation during cardiac transport.

Heart transplantation after SynCardia® total artificial heart implantation

Background

The SynCardia total artificial heart (TAH)^® is the only approved TAH device. This report summarizes our single-center experience with the SynCardia TAH^® with particular focus on the outcome after subsequent heart transplantation.

Methods

We retrospectively analysed the outcome of all transplanted SynCardia TAH^® patients at our center between 2001 and 2019 in comparison to transplanted left ventricular assist device (LVAD) and biventricular assist device (BVAD) patients and to transplanted patients without prior durable mechanical circulatory support (non-MCS).

Results

Only a fraction (n=69; 37.3%) of all SynCardia TAH^® patients (n=193) were transplanted. The majority (81.2%) of those were in high-urgency status at the time of transplantation. Survival in transplanted SynCardia TAH^® patients was significantly poorer when compared to LVAD-, BVAD- and non-MCS patients (P=0.008).

Conclusions

Heart transplantation in SynCardia TAH^® patients requires distinct risk stratification to improve outcomes.

Portable Normothermic Cardiac Perfusion System in Donation After Cardiocirculatory Death: A Health Technology Assessment

BACKGROUND

Heart transplantation is the most effective treatment for people experiencing end-stage heart failure whose quality of life and life expectancy are unacceptable. However, there is a chronic shortage of donor hearts to meet the demand, so it is essential to expand the donor pool and increase supply. Heart donation mainly occurs after brain death (neurological determination of death [NDD]), but it may also be feasible after cardiocirculatory death (when the heart has stopped beating and there is no longer blood flow or a pulse), provided specialized preservation techniques are used. An investigational device, a portable normothermic cardiac perfusion system, could make it possible to procure, preserve, and transport hearts donated after cardiocirculatory death (DCD). We conducted a health technology assessment of a portable normothermic cardiac perfusion system for the preservation and transportation of DCD hearts for adult transplantation. This included an evaluation of the effectiveness, safety, value for money, and budget impact of publicly funding this system, as well as an evaluation of patient preferences and values.

METHODS

We performed a systematic review of the clinical literature published since 1998 that examined the clinical safety and effectiveness of a portable normothermic cardiac perfusion system for DCD heart transplantation. We assessed the risk of bias of each included study and the quality of the body of evidence according to the Grading of Recommendations Assessment, Development, and Evaluation (GRADE) Working Group criteria. We also reviewed the economic evidence published during the same time period for the cost-effectiveness of a portable normothermic cardiac perfusion system for DCD hearts compared with cold storage for NDD hearts. We further estimated the 5-year net budget impact of publicly funding a normothermic cardiac perfusion system for DCD heart transplantation for adults on Ontario's waitlist. To contextualize the potential value of a portable normothermic cardiac perfusion system, we spoke with people waiting for a heart transplant, people who had received a heart transplant, and family members of organ donors.

RESULTS

We screened 2,386 clinical citations. One study and two case reports met the inclusion criteria. The survival of recipients of DCD hearts procured with a portable normothermic cardiac perfusion system did not differ significantly from the survival of recipients of hearts donated after NDD at 30 days or 90 days, nor was there a significant difference in cumulative survival at 1 year post-transplant (GRADE: Very Low). The occurrence of rejection and graft failure also did not significantly differ between the groups (GRADE: Very Low). Cardiac function in the early post-operative period was better in DCD hearts than NDD hearts (GRADE: Very Low). There were no differences in outcomes between DCD procurement techniques.The economic literature search yielded 62 citations. One report met the inclusion criteria but was not directly applicable to the Ontario context. Given the lack of clinical and economic evidence on long-term outcomes, we did not conduct a primary economic evaluation. In the budget impact analysis, based on the number of DCD donors under 40 years of age in the last 5 years, we estimated that the increased availability of donor hearts made possible by the technology would result in an additional seven transplants in year 1, increasing to 12 in year 5. The annual net budget impact of publicly funding a normothermic cardiac perfusion system for the transplantation of DCD hearts in Ontario over the next 5 years is about $2.0 million in the first year and about $0.9 million in each of years 2 through 5, yielding a total net budget impact of about $5.6 million. This number increases to about $10.3 million if the transplant volume increases to 18 hearts in year 1 (meaning a subsequent increase of up to 21 hearts in year 5). If transplantation were limited to people who do not qualify for a ventricular assistive device or who qualify but do not wish to receive one, the total 5-year net budget impact would be about $7.9 million.People waiting for a heart transplant or who had received a heart transplant and family members of organ donors expressed no substantial concerns about the potential use of a portable normothermic cardiac perfusion system. They hope that it may increase the number of donor hearts available for transplant. For family members of organ donors, a perfusion system may provide comfort and value if it can increase the successful procurement of donor hearts.

CONCLUSIONS

Based on very low quality of evidence, the outcomes for recipients of DCD hearts preserved using a portable normothermic cardiac perfusion system appear to be similar to outcomes for recipients of NDD hearts. Owing to a lack of evidence relevant to the Ontario context, we were unable to determine whether a portable normothermic perfusion system may be cost-effective. We estimate that publicly funding a portable normothermic cardiac perfusion system for DCD heart transplantation over the next 5 years will cost about $5.6 million. The people we spoke with believe that the system may increase the number of hearts available for transplant and therefore increase the number of heart transplants that can be done.

Mimicking "J-Shaped" and Anisotropic Stress-Strain Behavior of Human and Porcine Aorta by Fabric-Reinforced Elastomer Composites

An ex vivo heart perfusion device preserves the donor heart in a warm beating state during transfer between extraction and implantation surgeries. One of the current challenges includes the use of rigid and noncompliant plastic tubes, which causes injuries to the heart at the junction between the tissue and the tube. The compliant and rapidly strain-stiffening mechanical property that generates a "J-shaped" stress-strain behavior is necessary for producing the Windkessel effect, which ensures continuous flow of blood through the aorta. In this study, we mimic the J-shaped and anisotropic stress-strain behavior of human aorta in synthetic elastomers to replace the problematic noncompliant plastic tube. First, we assess the mechanical properties of human (n = 1) and porcine aorta (n = 14) to quantify the nonlinear and anisotropic behavior under uniaxial tensile stress from five different regions of the aorta. Second, fabric-reinforced elastomer composites were prepared by reinforcing silicone elastomers with embedded fabrics in a trilayer geometry. The knitted structures of the fabric provide strain-stiffening as well as anisotropic mechanical properties of the resulting composite in a deterministic manner. By optimizing the combination between different elastomers and fabrics, the resulting composites matched the J-shaped and anisotropic stress-strain behavior of natural human and porcine aorta. Finally, improved analytical constitutive models based on Gent's and Mooney-Rivlin's constitutive model (to describe the elastomer matrix) combined with Holzapfel-Gasser-Ogden's model (to represent the stiffer fabrics) were developed to describe the J-shaped behavior of the natural aortas and the fabric-reinforced composites. We anticipate that the suggested fabric-reinforced silicone elastomer composite design concept can be used to develop complex soft biomaterials, as well as in emerging engineering fields such as soft robotics and microfluidics, where the Windkessel effect can be useful in regulating the flow of fluids.

Heart Transplantation Survival and the Use of Traumatically Brain-Injured Donors: UNOS Registry Propensity-Matched Analysis

Background

The transplantation of hearts from traumatically brain‐injured (TBI) donors has been associated with inferior long‐term survival in single‐center analyses. However, in a more recent analysis, death caused by cerebrovascular accident was associated with worse posttransplant survival in recipients. The purpose of this study was to explore the outcomes of heart transplantation in recipients receiving donor hearts from TBI and non‐TBI donors in a large national registry.

Methods and Results

We performed a retrospective cohort analysis of the UNOS (United Network of Organ Sharing) Registry Organ Procurement and Transplantation Network between 2006 and 2018 for adult candidates wait‐listed for isolated heart transplantation. Recipients were stratified into 2 groups, TBI and non‐TBI donors. Propensity score matching was performed. Kaplan‐Meier analysis was used to estimate survival posttransplant. A total of 24 894 candidates met inclusion criteria. TBI was the leading cause of death in the donor population. Recipients of TBI donor hearts (N=13 07) were younger (median age, 55 versus 57 years; P<0.001) and less likely women (21.6% versus 29.8%; P<0.001). At 10 years, the TBI group had better long‐term survival compared with the non‐TBI group (62.8% versus 59.9%; P<0.001). After propensity group matching, the 10‐year survival was similar between groups.

Conclusions

In the largest analysis of heart transplants and their survival, according to the type of donor injury (TBI versus non‐TBI), we found similar survival in heart transplant recipients. Future studies should address specific subpopulations (eg, hemorrhagic stroke) in the non‐TBI group to address concerns about reduced posttransplant survival.

Comparison of Custodiol vs warm blood cardioplegia and conditioning of donor hearts during transportation with the organ care system

Objectives

Cold crystalloid cardioplegia for donor heart harvesting and cold ischemic storage conditions during the transportation is the standard of care during heart transplantation procedure. Organ care system (OCS) was introduced for more prolonged and reliable ex vivo organ management. This study evaluated the two different techniques used for myocardial preservation during the procurement and transportation of the heart using the OCS.

Methods

We performed prospective analysis of 43 patients with heart failure undergoing heart transplantation and using the OCS for donor organ transport. Donor hearts were arrested using blood cardioplegia and conditioning (n = 30) or standard Custodiol (SC) solution ( n = 13). Perfusion and cardiac function parameters were continuously monitored while the donor hearts were perfused in the OCS. Impact of preservation techniques on biochemical parameters and clinical outcomes were evaluated.

Results

All donor hearts had stable perfusion and lactate characteristics in the OCS, with similar measures between the two groups at the beginning of the ex vivo perfusion. Ex vivo heart perfusion mean ending concentration of Interleukin (IL)‐6 and IL‐8 was significantly lower in the blood cardioplegia group compared to the standard care group. Clinical outcomes were comparable between the two groups of patients.

Conclusions

The use of blood cardioplegia and conditioning could be a safe method for myocardial protection in distant procurement and preservation of donor hearts in the OCS.

Bioengineering approaches to organ preservation ex vivo

IMPACT STATEMENT

Over the past several decades, ex vivo perfusion has emerged as a promising technology for the assessment, preservation, and recovery of donor organs. Many exciting pre-clinical findings have now been translated to clinical use, and successful transplantation following ex vivo perfusion has been achieved for heart, lung, and liver. While machine perfusion provides distinct advantages over traditional cold preservation, many challenges remain, including that of long-term (multi-day) ex vivo support. Here, we provide an overview of the current status of ex vivo machine perfusion in the pre-clinical and clinical setting and share our perspective on the future direction of the field.

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.

The Biocompatibility Challenges in the Total Artificial Heart Evolution

There are limited therapeutic options for final treatment of end-stage heart failure. Among them, implantation of a total artificial heart (TAH) is an acceptable strategy when suitable donors are not available. TAH development began in the 1930s, followed by a dramatic evolution of the actuation mechanisms operating the mechanical pumps. Nevertheless, the performance of TAHs has not yet been optimized, mainly because of the low biocompatibility of the blood-contacting surfaces. Low hemocompatibility, calcification, and sensitivity to infections seriously affect the success of TAHs. These unsolved issues have led to the withdrawal of many prototypes during preclinical phases of testing. This review offers a comprehensive analysis of the pathophysiological events that may occur in the materials that compose TAHs developed to date. In addition, this review illustrates bioengineering strategies to prevent these events and describes the most significant steps toward the achievement of a fully biocompatible TAH.

Antiarrhythmic effect of sevoflurane as an additive to HTK solution on reperfusion arrhythmias induced by hypothermia and ischaemia is associated with the phosphorylation of connexin 43 at serine 368

Background

Reperfusion ventricular arrhythmia (RA) associated with hypothermic ischaemic storage is increasingly recognized as a substantial contributor to adverse consequences after heart transplantation. Ischemia- or hypothermia-induced gap junction (GJ) remodelling is closely linked to RA. Reducing GJ remodelling contributes to RA attenuation and is important in heart transplantation. However, sevoflurane has an antiarrhythmic effect associated with the connexin 43 (Cx43) protein that has not yet been fully established.

Methods

Hearts were divided into two groups according to a random number table: all hearts were arrested by an infusion of histidine-tryptophan-ketoglutarate (HTK) solution (4 °C) followed by (1) storage in HTK solution (4 °C) alone for 6 h (n = 8, Control group) or (2) storage in HTK solution supplemented with sevoflurane (2.5%) (4 °C) for 6 h (n = 8, Sevo-HTK group). First, the total Cx43 level and the phosphorylation of Cx43 at Ser368 (Cx43-pS368) were assessed by Western blotting, and the distribution of Cx43 was assessed by immunohistochemistry. Second, programmed electrical stimulation (PES) and monophasic action potential (MAP) recording were used to analyse the MAP duration (MAPD), conduction velocity (CV) and transmural repolarization dispersion (TDR). In addition, haematoxylin and eosin (HE) and terminal deoxynucleotidyl transferase-dUTP nick end labelling (TUNEL) staining were individually used to investigate the degree of myocardial pathological damage and cell apoptosis. Finally, bipolar electrograms were used to record the graft re-beating time and monitor RA during reperfusion for 15 to 30 min.

Results

Sevo-HTK solution relatively increased the total Cx43 (P < 0.01) and Cx43-pS368 (P < 0.01) levels and prevented Cx43 redistribution (P < 0.05) and CV slowing (P < 0.001) but did not change TDR (P > 0.05). Additionally, the Cx43-pS368/total Cx43 ratio (P>0.05) was similar in the two groups. However, with Sevo-HTK solution, the graft re-beating times were shortened, myocardial pathological damage was ameliorated, and the number of apoptotic cells was markedly decreased.

Conclusion

The reduction in hypothermia and ischaemia-induced reperfusion arrhythmias by the addition of sevoflurane to HTK solution may be related to the phosphorylation of Cx43 at serine 368.