Donors after circulatory death heart trial

Revolutionizing Donor Heart Procurement: Innovations and Future Directions for Enhanced Transplantation Outcomes

Heart failure persists as a critical public health challenge, with heart transplantation esteemed as the optimal treatment for patients with end-stage heart failure. However, the limited availability of donor hearts presents a major obstacle to meeting patient needs. In recent years, the most groundbreaking progress in heart transplantation has been in donor heart procurement, significantly expanding the donor pool and enhancing clinical outcomes. This review comprehensively examines these advancements, including the resurgence of heart donation after circulatory death and innovative recovery and evaluation technologies such as normothermic machine perfusion and thoraco-abdominal normothermic regional perfusion. Additionally, novel preservation methods, including controlled hypothermic preservation and hypothermic oxygenated perfusion, are evaluated. The review also explores the use of extended-criteria donors, post-cardiopulmonary resuscitation donors, and high-risk donors, all contributing to increased donor availability without compromising outcomes. Future directions, such as xenotransplantation, biomarkers, and artificial intelligence in donor heart evaluation and procurement, are discussed. These innovations promise to address current limitations and optimize donor heart utilization, ultimately enhancing transplantation success. By identifying recent advancements and proposing future research directions, this review aims to provide insights into advancing heart transplantation and improving patient outcomes.

Open- vs. closed-chest pig models of donation after circulatory death

Background

During donation after circulatory death (DCD), cardiac grafts are exposed to potentially damaging conditions that can impact their quality and post-transplantation outcomes. In a clinical DCD setting, patients have closed chests in most cases, while many experimental models have used open-chest conditions. We therefore aimed to investigate and characterize differences in open- vs. closed-chest porcine models.

Methods

Withdrawal of life-sustaining therapy (WLST) was simulated in anesthetized juvenile male pigs by stopping mechanical ventilation following the administration of a neuromuscular block. Functional warm ischemic time (fWIT) was defined to start when systolic arterial pressure was <50 mmHg. Hemodynamic changes and blood chemistry were analyzed. Two experimental groups were compared: (i) an open-chest group with sternotomy prior to WLST and (ii) a closed-chest group with sternotomy after fWIT.

Results

Hemodynamic changes during the progression from WLST to fWIT were initiated by a rapid decline in blood oxygen saturation and a subsequent cardiovascular hyperdynamic (HD) period characterized by temporary elevations in heart rates and arterial pressures in both groups. Subsequently, heart rate and systolic arterial pressure decreased until fWIT was reached. Pigs in the open-chest group displayed a more rapid transition to the HD phase after WLST, with peak heart rate and peak rate-pressure product occurring significantly earlier. Furthermore, the HD phase duration tended to be shorter and less intense (lower peak rate-pressure product) in the open-chest group than in the closed-chest group.

Discussion

Progression from WLST to fWIT was more rapid, and the hemodynamic changes tended to be less pronounced in the open-chest group than in the closed-chest group. Our findings support clear differences between open- and closed-chest models of DCD. Therefore, recommendations for clinical DCD protocols based on findings in open-chest models must be interpreted with care.

NADPH oxidase overexpression and mitochondrial OxPhos impairment are more profound in human hearts donated after circulatory death than brain death

This study investigated cardiac stress and mitochondrial oxidative phosphorylation (OxPhos) in human donation after circulatory death (DCD) hearts regarding warm ischemic time (WIT) and subsequent cold storage and compared them with that of human brain death donor (DBD) hearts. A total of 24 human hearts were procured for the research study-6 in the DBD group and 18 in the DCD group. DCD group was divided into three groups (n = 6) based on different WITs (20, 40, and 60 min). All hearts received del Nido cardioplegia before being placed in normal saline cold storage for 6 h. Left ventricular biopsies were performed at hours 0, 2, 4, and 6. Cardiac stress [nicotinamide adenine dinucleotide phosphate (NADPH) oxidase subunits: 47-kDa protein of phagocyte oxidase (p47phox), 91-kDa glycoprotein of phagocyte oxidase (gp91phox)] and mitochondrial oxidative phosphorylation [OxPhos, complex I (NADH dehydrogenase) subunit of ETC (CI)-complex V (ATP synthase) subunit of ETC (CV)] proteins were measured in cardiac tissue and mitochondria respectively. Modulation of cardiac stress and mitochondrial dysfunction were observed in both DCD and DBD hearts. However, DCD hearts suffered more cardiac stress (overexpressed NADPH oxidase subunits) and diminished mitochondrial OxPhos than DBD hearts. The severity of cardiac stress and impaired oxidative phosphorylation in DCD hearts correlated with the longer WIT and subsequent cold storage time. More drastic changes were evident in DCD hearts with a WIT of 60 min or more. Activation of NADPH oxidase via overproduction of p47phox and gp91phox proteins in cardiac tissue may be responsible for cardiac stress leading to diminished mitochondrial oxidative phosphorylation. These protein changes can be used as biomarkers for myocardium damage and might help assess DCD and DBD heart transplant suitability.NEW & NOTEWORTHY First human DCD heart research studied cardiac stress and mitochondrial dysfunction concerning WIT and the efficacy of del Nido cardioplegia as an organ procurement solution and subsequent cold storage. Mild to moderate cardiac stress and mitochondrial dysfunction were noticed in DCD hearts with WIT 20 and 40 min and cold storage for 4 and 2 h, respectively. These changes can serve as biomarkers, allowing interventions to preserve mitochondria and extend WIT in DCD hearts.

Beating Heart Transplants-Overview and Implications for Anesthesiologists

As the demand for heart allografts for transplantation continues to rise, ex vivo organ perfusion strategies are playing an increasingly important role in the preservation of organs from donation after circulatory death and extended-criteria donors. One such method uses the Organ Care System (TransMedics, Andover, MA). Traditionally, this technique of preservation requires 2 periods of warm ischemia and subsequent cardioplegic arrest. In a novel surgical technique pioneered at the authors' institution, heart allograft implantation no longer requires a second cardioplegic arrest. This article discusses the surgical approach for this procedure, the advantages and disadvantages of this approach, and analogs to current clinical practice to theorize what impact this may have on cardiac transplantation volumes in the future.

Graft function and incidence of cardiac allograft vasculopathy in donation after circulatory-determined death heart transplant recipients

Experience in donation after circulatory-determined death (DCD) heart transplantation (HTx) is expanding. There is limited information on the functional outcomes of DCD HTx recipients. We sought to evaluate functional outcomes in our cohort of DCD recipients. We performed a single-center, retrospective, observational cohort study comparing outcomes in consecutive DCD and donation after brain death (DBD) HTx recipients between 2015 and 2019. Primary outcome was allograft function by echocardiography at 12 and 24 months. Secondary outcomes included incidence of cardiac allograft vasculopathy, treated rejection, renal function, and survival. Seventy-seven DCD and 153 DBD recipients were included. There was no difference in left ventricular ejection fraction at 12 months (59% vs 59%, P = .57) and 24 months (58% vs 58%, P = .87). There was no significant difference in right ventricular function at 12 and 24 months. Unadjusted survival between DCD and DBD recipients at 5 years (85.7% DCD and 81% DBD recipients; P = .45) was similar. There were no significant differences in incidence of cardiac allograft vasculopathy (odds ratio 1.59, P = .21, 95% confidence interval 0.77-3.3) or treated rejection (odds ratio 0.60, P = .12, 95% confidence interval 0.32-1.15) between DBD and DCD recipients. Post-transplant renal function was similar at 1 and 2 years. In conclusion, cardiac allografts from DCD donors perform similarly to a contemporary population of DBD allografts in the medium term.

Heart transplantation using donation after circulatory death in the United States

OBJECTIVES

Heart donation after circulatory death was recently reintroduced in the United States with hopes of increasing donor heart availability. We examined its national use and outcomes.

METHODS

The United Network for Organ Sharing database was used to identify validated adult patients undergoing heart transplantation using donation after circulatory death donors (n = 266) and donation after brain death donors (n = 5998) between December 1, 2019, and December 31, 2021, after excluding heart-lung transplants. Propensity score matching was used to create more balanced groups for comparison.

RESULTS

The monthly percentage of donation after circulatory death heart transplant increased from 2.5% in December 2019 to 6.8% in December 2021 (P < .001). Twenty-two centers performed donation after circulatory death heart transplants, ranging from 1 to 75 transplants per center. Four centers performed 70% of the national volume. Recipients of donation after circulatory death hearts were more likely to be clinically stable (80.4% vs 41.1% in status 3-6, P < .001), to have type O blood (58.3% vs 39.9%, P < .001), and to wait longer after listing (55, interquartile range, 15-180 days vs 32, interquartile range, 9-160 days, P = .003). Six-month survival was 92.1% (95% confidence interval, 91.3-92.8) after donation after brain death heart transplants and 92.6% (95% confidence interval, 88.1-95.4) after donation after circulatory death heart transplants (hazard ratio, 0.94, 95% confidence interval, 0.57-1.54, P = .79). Outcomes in propensity-matched patients were similar except for higher rates of treated acute rejection in donation after circulatory death transplants before discharge (14.4% vs 8.8%, P = .01). In donation after circulatory death heart recipients, outcomes did not differ based on the procurement technique (normothermic regional perfusion vs direct procurement and perfusion).

CONCLUSIONS

Heart transplantation with donation after circulatory death donors has short-term survival comparable to donation after brain death transplants. Broader implementation could substantially increase donor organ availability.

The ethics of donation after circulatory death organ recovery: an overview of new considerations arising from procurement practice and policy changes

PURPOSE OF REVIEW

The aim of this study is to examine ethical issues raised by organ recovery from donors after circulatory death (DCD).

RECENT FINDINGS

Recent technological developments and policy modifications have implications for evolving ethical issues related to DCD organ procurement and donation. We identify four such changes and discuss the most significant ethical issues raised by each: the use of cardiac perfusion machines and the need to develop criteria to allow prioritization for organ preservation in joint thoracic-abdominal procurements, normothermic regional perfusion and the irreversibility criterion in the definition of death, practice variability in DCD withdrawal of care and death declarations, and equitable access to donation, and changes in organ procurement organization evaluation metrics and transplant system resource utilization.

SUMMARY

The evolution of DCD donation raises new ethical concerns that require further analysis to ensure that deceased donors, donor families and transplant recipients are treated respectfully and equitably.

American Society of Transplant Surgeons recommendations on best practices in donation after circulatory death organ procurement

The American Society of Transplant Surgeons supports efforts to increase the number of organs that are critically needed for patients desperately awaiting transplantation. In the United States, transplantation using organs procured from donation after circulatory death (DCD) donors has continued to increase in number. Despite these increases, substantial variability in the utilization and practices of DCD transplantation still exists. To improve DCD organ utilization, it is important to create a set of best practices for DCD recovery. The following recommendations aim to provide guidance on contemporary issues surrounding DCD organ procurement in the United States. A work group was composed of members of the American Society of Transplant Surgeon Scientific Studies Committee and the Thoracic Organ Transplantation Committee. The following topics were identified by the group either as controversial or lacking standardization: prewithdrawal preparation, definition of donor warm ischemia time, DCD surgical technique, combined thoracic and abdominal procurements, and normothermic regional perfusion. The proposed recommendations were classified on the basis of the grade of available evidence and the strength of the recommendation. This information should be valuable for transplant programs as well as for organ procurement organizations and donor hospitals as they develop robust DCD donor procurement protocols.

Prediction Model for Contractile Function of Circulatory Death Donor Hearts Based on Microvascular Flow Shifts During Ex Situ Hypothermic Cardioplegic Machine Perfusion

Background Hearts procured from circulatory death donors (DCD) are predominantly maintained by machine perfusion (MP) with normothermic donor blood. Currently, DCD heart function is evaluated by lactate and visual inspection. We have shown that MP with the cardioplegic, crystalloid Custodiol-N solution is superior to blood perfusion to maintain porcine DCD hearts. However, no method has been developed yet to predict the contractility of DCD hearts after cardioplegic MP. We hypothesize that the shift of microvascular flow during continuous MP with a cardioplegic preservation solution predicts the contractility of DCD hearts. Methods and Results In a pig model, DCD hearts were harvested and maintained by MP with hypothermic, oxygenated Custodiol-N for 4 hours while myocardial microvascular flow was measured by Laser Doppler Flow (LDF) technology. Subsequently, hearts were perfused with blood for 2 hours, and left ventricular contractility was measured after 30 and 120 minutes. Various novel parameters which represent the LDF shift were computed. We used 2 combined LDF shift parameters to identify bivariate prediction models. Using the new prediction models based on LDF shifts, highest r² for end-systolic pressure was 0.77 (P=0.027), for maximal slope of pressure increment was 0.73 (P=0.037), and for maximal slope of pressure decrement was 0.75 (P=0.032) after 30 minutes of reperfusion. After 120 minutes of reperfusion, highest r² for end-systolic pressure was 0.81 (P=0.016), for maximal slope of pressure increment was 0.90 (P=0.004), and for maximal slope of pressure decrement was 0.58 (P=0.115). Identical prediction models were identified for maximal slope of pressure increment and for maximal slope of pressure decrement at both time points. Lactate remained constant and therefore was unsuitable for prediction. Conclusions Contractility of DCD hearts after continuous MP with a cardioplegic preservation solution can be predicted by the shift of LDF during MP.

Early Outcomes of Heart Transplantation Using Donation After Circulatory Death Donors in the United States

BACKGROUND

Limited donor availability and evolution in procurement techniques have renewed interest in heart transplantation (HT) with donation after circulatory death (DCD). The aim of this study is to evaluate outcomes of HT using DCD in the United States.

METHODS

The United Network for Organ Sharing registry was used to identify adult HT recipients from 2019 to 2021. Recipients were stratified between DCD and donation after brain death. Propensity-score matching was performed. Cox proportional hazards was used to identify independent predictors of 1-year mortality. Kaplan-Meier analysis was used to estimate 1-year survival.

RESULTS

Of 7496 HTs, 229 DCD and 7267 donation after brain death recipients were analyzed. The frequency of DCD HT increased from 0.2% of all HT in 2019 to 6.4% in 2021 (P<0.001), and the number of centers performing DCD HT increased from 3 of 120 centers to 20 of 121 centers (P<0.001). DCD donors were more likely to be younger, male, and White. After propensity matching, 1-year survival was 92.5% for DCD versus 90.3% for donation after brain death (hazard ratio, 0.80 [95% CI, 0.44-1.43]; P=0.44). Among DCD HTs, increasing recipient age and waitlist time predicted 1-year mortality on univariable analysis.

CONCLUSIONS

Rates of DCD HT in the United States are increasing. This practice appears safe and feasible as mortality outcomes are comparable to donation after brain death. Although this study represents early adopting centers, outcomes of the experience for DCD HT in the United States is consistent with existing international data and encourages broader utilization of this practice.

Expanding Donor Heart Utilization Through Machine Perfusion Technologies

Purpose of Review

Recent advances in donor heart preservation have allowed the utilization of hearts that would typically be discarded due to prolonged ischemic times or donation via the circulatory death pathway. This review will discuss recent advances in donor heart preservation including optimization of machine perfusion technologies and future strategies of potential benefit for the donor heart and transplant outcomes.

Recent Findings

Improvements in organ preservation strategies have enabled retrieval of donor hearts that were not ideal for static cold storage. Machine perfusion (normothermic and hypothermic) and normothermic regional perfusion have ultimately expanded the donor pool for adult heart transplantation. Xenotransplantation has also incorporated machine perfusion for porcine donor heart preservation.

Summary

Traditional static cold storage is feasible for non-complex donors and transplants. Machine perfusion has enabled increased donor heart utilization however optimal preservation strategies are dependent on the donor criteria, predicted ischemic times and surgical complexity.

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

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

Appraisal of Donation After Circulatory Death: How Far Could We Expand the Heart Donor Pool?

BACKGROUND

the incidence of organ donation after circulatory death (DCD) is increasing; however, heart use has lagged behind other solid organs. Ex vivo perfusion devices are under United States Food and Drug Administration review for use in DCD heart recovery. This study sought to measure the potential increase in the donor pool if DCD heart donation becomes widely adopted.

METHODS

DCD donor data were obtained from Organ Procurement and Transplantation Network database. Selection criteria included donor age 18 to 49 years, donors meeting Maastricht III criteria, warm ischemia time ≤30 minutes, and donation between 2015 and 2020. Exclusion criteria were coronary disease, prior myocardial infarction, ejection fraction <0.50, significant valve disease, bacteremia, pulmonary capillary wedge pressure >15 mm Hg, and history of HIV/hepatitis C virus infections.

RESULTS

There were 12 813 DCD donors during this period, of which 3528 met study criteria, and 70 hearts (2%) were transplanted. The use of DCD hearts would represent an additional 48 heart transplants per month, which corresponds to a 21% (3458 of 16 521) increase across the country. Median warm ischemia was 23 minutes, with no difference between hearts that were or were not transplanted (23 vs 22.5 minutes, P = .97). The frequency with which other organs were successfully transplanted was kidney, 92%; liver, 44%; lung, 7%; intestine, 0%; and pancreas, 2%.

CONCLUSIONS

Wide adoption of DCD heart transplantation could yield a substantial increase in the donor pool size, with approximately 580 additional organs being available each year across the United States. This would represent the largest increase in the donor pool in the modern era of heart transplantation.

Donation after cardiac death in heart transplantation: is there an ethical dilemma?

PURPOSE OF REVIEW

In an attempt to address the organ shortages in heart transplantation, USA centres have begun utilizing donation after cardiac death (DCD) as an alternative to traditional donation after brain death (DBD). As this paradigm continues to expand, there is a need to address the medico-legal and ethical aspects of DCD donation, which is the focus of the current review.

RECENT FINDINGS

Current protocols use criteria established by the Uniform Determination of Death Act (UDDA), which is explicit in defining the irreversibility of circulation and brain function in determining death. By the nature of DCD, the patient may not meet death criteria from a biological systems perspective of irreversibility, and thus, the moral dilemma ensues on whether removing vital organs violates our legal and moral obligations to the patient.

SUMMARY

In the current article, we review the ethical issues raised with DCD and define DCD protocols and their ability to comply with established regulatory guidelines while respecting the wishes of patients and their surrogates through informed decisions making about organ donation and end-of-life care.

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.

The Stanford experience of heart transplantation over five decades

AIMS 

Since 1968, heart transplantation has become the definitive treatment for patients with end-stage heart failure. We aimed to summarize our experience in heart transplantation at Stanford University since the first transplantation performed over 50 years ago.

METHODS AND RESULTS 

From 6 January 1968 to 30 November 2020, 2671 patients presented to Stanford University for heart transplantation, of which 1958 were adult heart transplantations. Descriptive analyses were performed for patients in 1968-95 (n = 639). Stabilized inverse probability weighting was applied to compare patients in 1996-2006 (n = 356) vs. 2007-19 (n = 515). Follow-up data were updated through 2020. The primary endpoint was all-cause mortality. Prior to weighting, recipients in 2007-19 vs. those in 1996-2006 were older and had heavier burden of chronic diseases. After the application of stabilized inverse probability weighting, the distance organ travelled increased from 84.2 ± 111.1 miles to 159.3 ± 169.9 miles from 1996-2006 to 2007-19. Total allograft ischaemia time also increased over time (199.6 ± 52.7 vs. 225.3 ± 50.0 min). Patients in 2007-19 showed superior survival than those in 1996-2006 with a median survival of 12.1 vs. 11.1 years.

CONCLUSION 

In this half-century retrospective descriptive study from one of the largest heart transplant programmes in the USA, long-term survival after heart transplantation has improved over time despite increased recipient and donor age, worsening comorbidities, increased technical complexity, and prolonged total allograft ischaemia time. Further investigation is warranted to delineate factors associated with the excellent outcomes observed in this study.

Primary Graft Dysfunction after Heart Transplantation - Unravelling the Enigma

Primary graft dysfunction (PGD) remains the main cause of early mortality following heart transplantation despite several advances in donor preservation techniques and therapeutic strategies for PGD. With that aim of establishing the aetiopathogenesis of PGD and the preferred management strategies, the new consensus definition has paved the way for multiple contemporaneous studies to be undertaken and accurately compared. This review aims to provide a broad-based understanding of the pathophysiology, clinical presentation and management of PGD.

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

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