Prolonged Ischemic Times for Heart Transplantation: Impact of the 2018 Allocation Change

Severe primary graft dysfunction in heart transplant recipients using donor hearts after circulatory death: United States experience

OBJECTIVE

This study compares the incidence of severe Primary Graft Dysfunction (PGD) in a contemporaneous cohort of donors after circulatory death (DCD) and brain death (DBD) heart transplant recipients.

METHOD

The United Network for Organ Sharing database was queried for isolated adult heart transplant recipients from 9/2023 to 6/2024. Heart recipients were stratified based on the organ donation type (DCD vs DBD). DCD heart recipients were further categorized based on the procurement method: time between circulatory death to cross-clamp: ≤ 30 minutes (Direct Procurement and Preservation, DPP), >30 minutes (Normothermic Regional Perfusion, NRP). Outcomes of interest included: severe PGD (Left/Bi-Ventricular; LV/BiV) at 24 hours and Severe Graft Dysfunction at 72 hours (patients with severe PGD at 24 hours that remain on mechanical support at 72 hours).

RESULTS

A total of 2590 adult heart transplant recipients were identified, of which 17.1% underwent DCD heart transplantation. DCD heart recipients were less likely to be on inotrope (36.7% vs 41.6%, p=0.046) and ECMO (4.1% vs 9.9%, p<0.001) prior to transplant than DBD heart recipients. DCD heart recipients were more likely than DBD heart recipients to develop severe PGD (LV/BiV) at 24 hours (9.5% vs 5.1%, p<0.001). The Severe Graft Dysfunction at 72 hours (2.3% vs 2.9%, p=0.67) and 30-day mortality were similar between the 2 groups. Recipients of DCD heart procured with DPP or NRP had similar severe PGD (LV/BiV) at 24 hours (9.4% vs 9.7%, p=0.93).

CONCLUSION

Severe PGD at 24 hours is higher among the DCD than DBD heart recipients, but Graft Dysfunction improves by 72 hours.

Effects of ex vivo machine perfusion on preservation time and donor age in donation after brain death heart transplantation

With encouraging early experience, ex vivo machine perfusion (MP) systems are increasingly employed in heart transplantation. In this study, utilizing a national registry database, 2 separate analyses were performed to evaluate the effects of MP on graft preservation time (total n = 22,794; n = 308 with MP) and donor age (total n = 22,581; n = 95 with MP) in donation after brain death (DBD) heart transplantation. The cohort was stratified based on total preservation time (<4 and ≥4 hours) and donor age (<45 and ≥45 years). During the study period, the use of MP in isolated DBD heart transplantation significantly increased. Utilization of MP was associated with improved 90-day post-transplant survival among the recipients with preservation times ≥4 hours or donor age ≥45 years, compared to cases where MP was not utilized. These findings positively highlight the potential utility of ex vivo MP in DBD heart transplantation involving longer graft preservation times and in older donors.

Correlation Between the Distance From Donors and Ischemic Time in Heart Transplantation of Korea and Its Clinical Impact

BACKGROUND

The heart donor allocation system in South Korea is divided into three regions, with priority given to recipients within the same region over those in other regions of the same tier. It is commonly believed that heart transplantation (HT) within the same region can reduce ischemic time (IT), although its clinical impact remains unclear. The purpose of this study is to compare the characteristics and outcomes of intra-region HT and inter-region HT.

METHODS

From 2014 to 2022, a total of 115 adult patients underwent isolated HT at a tertiary hospital. Of these, 58 recipients (54.5 ± 10.3 years, female, 36.2%) underwent intra-region HT and 57 recipients (53.9 ± 14.1 years, female, 31.6%) underwent inter-region HT. Extracorporeal membrane oxygenation-bridged HTs accounted for 50.0% and 54.4% of cases, respectively (P = 0.638). There were no differences in preoperative characteristics between the two groups.

RESULTS

The median inter-hospital distance (38.0 [32.0-112.0] km vs. 351.0 [300.0-390.5] km, P < 0.001) and total IT (153 [123-170] minute vs. 265 [243-298] minute, P < 0.001) were longer in the inter-region group than intra-region group. Despite these differences, both groups showed similar clinical outcomes. The 30-day mortality rates were 5.2% and 5.3% (P < 0.99), respectively. There were no differences in postoperative cardiac index, early adverse outcomes, or long-term survival between the two groups. The inter-hospital distance and cold IT showed a strong positive correlation (time [minute] = 39.462 + 0.410 × distance [km]).

CONCLUSION

Despite the difference in IT, there was no difference in postoperative outcomes between the two groups. Based on these findings, the effect of donor location on the outcomes of HT in South Korea is not considered significant.

The Year in Cardiothoracic Transplant Anesthesia: Selected Highlights From 2022 Part II: Cardiac Transplantation

These highlights focus on research published in the year 2022 and is divided into preoperative, intraoperative, and postoperative sections. The preoperative section includes research on the assessment and optimization of candidates for heart transplantation; donor optimization and the use of extended donors; organ protection systems; donation after circulatory death allografts; recipient factors including cannabis use, sex, race, and comorbidities such as obesity, diabetes mellitus, and peripartum cardiomyopathy; the effects of the 2018 heart allocation policy change on waitlist and postoperative mortality; updates on heart transplantation in patients with coronavirus disease 2019; in pediatric patients; and those who require a bridge to transplant. The intraoperative section includes the use of a multidisciplinary team, a proposed transfusion algorithm, bench surgery on the allograft, and size matching. The postoperative section focuses on the research on the development and management of tricuspid regurgitation, echocardiography, arrhythmia management, and, finally, xenotransplantation.

Effects of Nighttime Procurement and Transplantation on Outcomes Following Heart Transplantation

BACKGROUND

This study evaluates the effects of nighttime procurement and transplantation on outcomes following heart transplantation.

METHODS

The UNOS registry was queried to analyze adult recipients who underwent isolated orthotopic heart transplantation between January 1, 2010, and September 30, 2022. The cohort was stratified into daytime (4 am-8 pm) and nighttime (8 pm-4 am) transplant groups. The primary outcome was 1-year survival. Propensity score-matching was performed. Risk adjustment was performed using multivariable Cox regression. Restricted cubic spline was used to model the association between the time of transplantation and the likelihood of 1-year mortality. Sub-analysis was performed to evaluate the impact of nighttime procurement.

RESULTS

Altogether 30 426 recipients were analyzed, where 10 807 recipients (35.5%) underwent nighttime transplantation. The nighttime recipients had reduced 1-year post-transplant survival compared to the daytime recipients (90.6% vs. 91.5%, p = 0.019), and this lower survival persisted in the propensity score-matched comparison. After adjusting for established predictors for post-transplant mortality, nighttime transplantation continued to have a significantly increased risk of 1-year mortality (hazard ratio [HR] 1.12, 95% confidence interval [CI] 1.03-1.21, p = 0.005). The spline model demonstrated increased odds of 1-year mortality between 5 pm and 4 am, with the highest odds at 11 pm (odds ratio [OR] 1.25, 95% CI 1.07-1.47), compared to the reference transplantation time of 7 am. When assessing the impact of procurement timing, nighttime procurement negatively impacted 1-year post-transplant survival among the daytime recipients.

CONCLUSION

This study demonstrates the adverse impact of nighttime heart procurement and transplantation on early post-transplant survival. With emerging organ perfusion and thermal protection systems, additional studies are warranted to assess the safety of extending the heart preservation period to optimize the timing of transplantation.

Bridge to Transplantation: Policies Impact Practices

Since the development of the first heart allocation system in 1988 to the most recent heart allocation system in 2018, the road to heart transplantation has continued to evolve. Policies were shaped with advances in temporary and durable left ventricular assist devices as well as prioritization of patients based on degree of illness. Herein, we review the changes in the heart allocation system over the past several decades and the impact of practice patterns across the United States.

Pyruvate Carboxylase Attenuates Myocardial Ischemia-Reperfusion Injury in Heart Transplantation via Wnt/β-Catenin-Mediated Glutamine Metabolism

The ischemia-reperfusion process of a donor heart during heart transplantation leads to severe mitochondrial dysfunction, which may be the main cause of donor heart dysfunction after heart transplantation. Pyruvate carboxylase (PC), an enzyme found in mitochondria, is said to play a role in the control of oxidative stress and the function of mitochondria. This research examined the function of PC and discovered the signaling pathways controlled by PC in myocardial IRI. We induced IRI using a murine heterotopic heart transplantation model in vivo and a hypoxia-reoxygenation cell model in vitro and evaluated inflammatory responses, oxidative stress levels, mitochondrial function, and cardiomyocyte apoptosis. In both in vivo and in vitro settings, we observed a significant decrease in PC expression during myocardial IRI. PC knockdown aggravated IRI by increasing MDA content, LDH activity, TUNEL-positive cells, serum cTnI level, Bax protein expression, and the level of inflammatory cytokines and decreasing SOD activity, GPX activity, and Bcl-2 protein expression. PC overexpression yielded the opposite findings. Additional research indicated that reducing PC levels could block the Wnt/β-catenin pathway and glutamine metabolism by hindering the movement of β-catenin to the nucleus and reducing the activity of complex I and complex II, as well as ATP levels, while elevating the ratios of NADP+/NADPH and GSSG/GSH. Overall, the findings indicated that PC therapy can shield the heart from IRI during heart transplantation by regulating glutamine metabolism through the Wnt/β-catenin pathway.

Non-inferior outcomes in lower urgency patients transplanted with extended criteria donor hearts

BACKGROUND

Recent work has suggested that outcomes among heart transplant patients listed at the lower-urgency (United Network for Organ Sharing Status 4 or 6) status may not be significantly impacted by donor comorbidities. The purpose of this study was to investigate outcomes of extended criteria donors (ECD) in lower versus higher urgency patients undergoing heart transplantation.

METHODS

The United Network for Organ Sharing (UNOS) database was queried for all adult patients undergoing heart transplantation from October 18, 2018 through December 31, 2021. Patients were stratified by degree of urgency (higher urgency: UNOS 1 or 2 vs lower urgency: UNOS 4 or 6) and receipt of ECD hearts, as defined by donor hearts failing to meet established acceptable use criteria. Outcomes were compared using propensity score matched cohorts.

RESULTS

Among 9,160 patients included, 2,320 (25.4%) were low urgency. ECD hearts were used in 35.5% of higher urgency (HU) patients and 39.2% of lower urgency (LU) patients. While ECD hearts had an impact on survival among high-urgency patients (p < 0.01), there was no difference in 1- and 2-year survival (p > 0.05) found among low urgency patients receiving ECD versus standard hearts. Neither ECDs nor individual ECD criteria were independently associated with mortality in low urgency patients (p > 0.05).

CONCLUSIONS

Post-transplant outcomes among low urgency patients are not adversely affected by receipt of ECD vs. standard hearts. Expanding the available donor pool by optimizing use of ECDs in this population may increase transplant frequency, decrease waitlist morbidity, and improve postoperative outcomes for the transplant community at large.

Impact of new allocation system on length of stay following heart transplantation in the United States

BACKGROUND

United Network for Organ Sharing (UNOS) allocation criteria changed in 2018 to accommodate the increased prevalence of ventricular assist device use as a bridge to heart transplant, which consequently prioritized sicker patients. We aimed to assess the impact of this new allocation policy on the length of stay following heart transplantation. Secondary outcomes include other risk factors for prolonged hospitalization and its effect on mortality and postoperative complications.

METHODS

The UNOS Registry was queried to identify patients who underwent isolated heart transplants in the United States between 2001 and 2023. Patients were divided into quartiles according to their respective length of stay.

RESULTS

A total of 57 020 patients were included, 15 357 of which were allocated with the new system. The median hospital length of stay was 15 days (mean 22.7 days). Length of stay was longer in the new allocation era (25 ± 30 vs. 22 ± 27 days, p < .001). The longer length of stay was associated with increased 5-year mortality in the new allocation system (aHR: 1.18; 95% CI: 1.15, 1.20; p-value: < .001).

CONCLUSION

Longer hospital stays and associated observed increased risk for mortality in the era after the allocation criteria change reflect the rationale of this shift which was to prioritize heart transplants for sicker patients. Further studies are needed to track the progress of surgical and perioperative management of these studies over time.

Cinnamaldehyde protects donor heart from cold ischemia-reperfusion injury via the PI3K/AKT/mTOR pathway

With the growing shortage of organs, improvements in donor organ protection are needed to meet the increasing demands for transplantation. Here, the aim was to investigate the protective effect of cinnamaldehyde against ischemia-reperfusion injury (IRI) in donor hearts exposed to prolonged cold ischemia. Donor hearts were harvested from rats pretreated with or without cinnamaldehyde, then subjected to 24 h of cold preservation and 1 h of ex vivo perfusion. Hemodynamic changes, myocardial inflammation, oxidative stress, and myocardial apoptosis were evaluated. The PI3K/AKT/mTOR pathway involved in the cardioprotective effects of cinnamaldehyde was explored through RNA sequencing and western blot analysis. Intriguingly, cinnamaldehyde pretreatment remarkably improved cardiac function through increasing coronary flow, left ventricular systolic pressure, +dp/dtmax, and -dp/dtmax, decreasing coronary vascular resistance and left ventricular end-diastolic pressure. Moreover, our findings indicated that cinnamaldehyde pretreatment protected the heart from IRI by alleviating myocardial inflammation, attenuating oxidative stress, and reducing myocardial apoptosis. Further studies showed that the PI3K/AKT/mTOR pathway was activated after cinnamaldehyde treatment during IRI. The protective effects of cinnamaldehyde were abolished by LY294002. In conclusion, cinnamaldehyde pretreatment alleviated IRI in donor hearts suffering from prolonged cold ischemia. Cinnamaldehyde exerted cardioprotective effects through the activation of the PI3K/AKT/mTOR pathway.

The Year in Cardiothoracic Transplant Anesthesia: Selected Highlights From 2021 Part II: Cardiac Transplantation

This article spotlights the research highlights of this year that specifically pertain to the specialty of anesthesia for heart transplantation. This includes the research on recent developments in the selection and optimization of donors and recipients, including the use of donation after cardiorespiratory death and extended criteria donors, the use of mechanical circulatory support and nonmechanical circulatory support as bridges to transplantation, the effect of COVID-19 on heart transplantation candidates and recipients, and new advances in the perioperative management of these patients, including the use of echocardiography and postoperative outcomes, focusing on renal and cerebral outcomes.

Impact of the 2018 UNOS Heart Transplant Policy Changes on Patient Outcomes

In 2018, the United Network for Organ Sharing implemented a 6-tier allocation policy to replace the prior 3-tier system. Given increasing listings of critically ill candidates for heart transplantation and lengthening waitlist times, the new policy aimed to better stratify candidates by waitlist mortality, shorten waiting times for high priority candidates, add objective criteria for common cardiac conditions, and further broaden sharing of donor hearts. There have been significant shifts in cardiac transplantation practices and patient outcomes following the implementation of the new policy, including changes in listing practices, waitlist time and mortality, transplant donor characteristics, post-transplantation outcomes, and mechanical circulatory support use. This review aims to highlight emerging trends in United States heart transplantation practice and outcomes following the implementation of the 2018 United Network for Organ Sharing heart allocation policy and to address areas for future modification.