Donor predictors of allograft utilization for pediatric heart transplantation

Machine Learning for Predicting Waitlist Mortality in Pediatric Heart Transplantation

BACKGROUND

Waitlist mortality remains a critical issue for pediatric heart transplant (HTx) candidates, particularly for candidates with congenital heart disease. Listing center organ offer acceptance practices have been identified as a factor influencing waitlist outcomes. We utilized machine learning (ML) to identify factors associated with waitlist mortality, combining variables associated with institutional offer acceptance practices as well as candidate-specific risk factors.

METHODS

We analyzed the Organ Procurement and Transplantation Network database for pediatric HTx candidates listed between 2010 and 2020. Various statistical and ML models were employed to identify predictors of waitlist mortality or clinical deterioration leading to waitlist removal. The dataset was split into training (82%) and testing (18%), and the final model was selected based on predictive performance. SHAP values were used to assess variable importance.

RESULTS

Among 5523 pediatric candidates, overall waitlist mortality was 9.8%. The CatBoost model achieved the highest predictive performance with an AUC-ROC score of 0.74 and a recall score of 0.75. Key predictors included candidate diagnosis, age/size, ventilator use, eGFR, serum albumin, ECMO, and institutional factors such as high offer refusal rates and low transplant volume.

CONCLUSIONS

Institutional organ offer acceptance practices influence waitlist outcomes for pediatric HTx candidates. Centers with higher organ refusal rates are associated with worse outcomes, independent of candidate-specific risk factors, underscoring the need for standardizing organ acceptance criteria across institutions to reduce variability in decision-making and improve waitlist survival. Additionally, addressing modifiable risk factors such as malnutrition and renal dysfunction could further optimize patient outcomes.

Indications and Practical Considerations for Partial Heart Transplantation

Partial heart transplantation is a new approach to deliver growing heart valve substitutes for children. The rationale for partial heart transplantation is that the valves contained in heart transplants grow. Partial heart transplants differ from heart transplants because only the part of the heart containing the necessary valve is transplanted, while the native ventricles are preserved. Preserving the native ventricles eliminates the risk of graft ventricular dysfunction and allows for utilization of donor hearts with ventricular dysfunction. Here we outline practical considerations for partial heart transplantation, including indications, sources for donor hearts, graft procurement, graft preservation, implantation, recipient immunosuppression, and reimbursement. This invited expert review is intended to help clinical teams implement partial heart transplantation.

Organizational challenges for partial heart transplantation

Partial heart transplantation (PHT) has emerged as a new treatment strategy to correct unrepairable heart valve dysfunction in pediatric patients. PHT selectively replaces the dysfunctional components of the recipient's heart and spares the native ventricles. As a result, the transplant biology of PHTs differs from heart transplants. Notably, donor hearts that are unsuitable for whole heart transplantation can be used, graft preservation can be prolonged and immunosuppression levels can be lowered. These nuances of PHT transplant biology have important implications for organizational aspects of PHT clinical application.

"Take it or leave it": Analysis of pediatric heart offers for transplantation in Switzerland

BACKGROUND

There is a shortage of donor hearts in Switzerland, especially for pediatric recipients. However, the rate and reason for refusals of pediatric donor hearts offered in Switzerland has not been systematically analyzed.

METHODS

The national transplant database, Swiss Organ Allocation System, was searched for all hearts from Swiss and foreign donors younger than 16 years from 2015 to 2020. The numbers of accepted and refused hearts and early outcome were assessed, and the reasons for refusal were retrospectively analyzed.

RESULTS

A total of 136 organs were offered to the three Swiss pediatric heart centers and foreign donor procurement organizations. Of these, 26/136 (19%) organs were accepted and transplanted: 18 hearts were transplanted in Switzerland, and 13 of these were foreign. Reasons for refusal were (1) no compatible recipient due to blood group or weight mismatch, 89.4%; (2) medical, meaning organ too marginal for transplantation, 7.4%; (3) logistic, 1.4%; and (4) other, 1.8%. Five organs were refused in Switzerland by one center but later accepted and successfully transplanted by another center. Hearts from outside Switzerland were transplanted significantly less than Swiss hearts (n = 16/120 vs. 10/16, p < .001).

CONCLUSION

The most common reason for refusing a pediatric donor heart is lack of compatibility with the recipient. Few hearts are refused for medical reasons. A more generous acceptance seems to be justified in selected patients. Switzerland receives a high number of foreign offers, but their rate of acceptance is lower than that of Swiss donations.

Pediatric donor heart utilization variability among organ procurement organizations

BACKGROUND

Organ procurement organizations (OPOs) are responsible for the medical management of organ donors. Given the variability in pediatric donor heart utilization among OPOs, we examined factors that may explain this variability, including differences in donor medical management, organ quality, and candidate factors.

METHODS

The Organ Procurement and Transplant Network database was queried for pediatric (<18 years) heart donors and candidates receiving pediatric donor heart offers from 2010 to 2019. OPOs were stratified by pediatric donor heart utilization rate, and the top and bottom quintiles were compared based on donor management strategies and outcomes. A machine learning algorithm, combining 11 OPO, donor, candidate, and offer variables, was used to determine factors most predictive of whether a heart offer is accepted.

RESULTS

There was no clinically significant difference between the top and bottom quintile OPOs in baseline donor characteristics, distance between donor and listing center, management strategies, or organ quality. Machine learning modeling suggested neither OPO donor management nor cardiac function is the primary driver of whether an organ is accepted. Instead, number of prior donor offer refusals and individual listing center receiving the offer were two of the most predictive variables of organ acceptance.

CONCLUSIONS

OPO clinical practice variation does not seem to account for the discrepancy in pediatric donor heart utilization rates among OPOs. Listing center acceptance practice and prior number of donor refusals seem to be the important drivers of heart utilization and may at least partially account for the variation in OPO heart utilization rates given the regional association between OPOs and listing centers.

Risk Index Predicts Pediatric Heart Allograft Non-Utilization

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSION

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

Pediatric donor heart acceptance practices in the United States: What is really being considered?

BACKGROUND

Recent studies demonstrate high offer decline and organ non-utilization rates are associated with increased pediatric heart transplant waitlist mortality. We sought to determine which donor, candidate, and offer specific variables most importantly influenced these decisions using only data available at the time of each offer.

METHODS

Retrospective review of pediatric (<18 years) heart donor offers made to pediatric candidates in the United States between 2010 and 2020. In addition to standard donor, candidate, and offer data available in UNOS, we extracted objective and qualitative valvar and myocardial function data from all available donor echocardiogram reports.

RESULTS

During the study period, 5625 pediatric donor hearts produced 30 156 offers to 4905 unique candidates, of which 88.7% of all offers were declined and 39.2% of organs were not utilized by pediatric waitlisted candidates. Of the 60.8% utilized hearts, 89.7% had a 'cumulatively' normal echocardiogram at the time of offer acceptance; 62.9% of hearts not utilized for a pediatric candidate also had a cumulatively normal final echocardiogram. Random forest and logistic regression modeling demonstrated good predictive performance (AUROC ≥0.83) of likelihood to accept when utilizing donor, candidate, and offer specific variables. SHAP variable importance scores demonstrated number of prior offer declines and candidate institution's prior year acceptance rates as the two most important variables influencing offer decisions.

CONCLUSIONS

Behavioral economics appear to play a significant role in pediatric heart transplant candidate institutions' acceptance practices, even when considering the arguably healthier pediatric donor population. Removal of prior institution's decisions from DonorNet may help increase donor utilization.

Pediatric heart transplantation: Looking forward after five decades of learning

Heart transplantation has become the standard of care for pediatric patients with end-stage heart disease throughout the world. Since the first transplant was performed in 1967, the number of transplants has grown dramatically with 13 449 pediatric heart transplants being reported to The International Society of Heart and Lung Transplant (ISHLT) between January 1992 and June 30, 2018. Outcomes have consistently improved over the last few decades, specifically short-term outcomes. Most recent survival data demonstrate that recipients who survive to 1-year post-transplant have excellent long-term survival with more than 60% of those who were transplanted as infants being alive 25 years later. Nonetheless, the rates of graft loss beyond the first year have remained relatively constant over time; driven primarily by our poor understanding and lack of treatments for chronic allograft vasculopathy (CAV). Acute rejection, CAV, graft failure, and infection continue to be the major causes of death within the first 5 years post-transplant. In addition, renal dysfunction, malignancy, and the need for re-transplantation remain as significant issues that require close follow-up. Looking forward, key challenges include improving donor utilization rates (including donation after cardiac death (DCD) and the use of ex vivo perfusion devices), the development of non-invasive biomarkers for rejection, efforts to mitigate the long-term effects of immunosuppression, and prevention of CAV. It is not possible to cover the entire evolution of pediatric heart transplantation over the last five decades, but in this review, we hope to touch on key observations, lessons learned, and practice changes that have advanced the field, as well as glance ahead to the next decade.

The Impact of Ex Situ Heart Perfusion in Pediatric Transplantation: An Analysis of the OPTN Database

Ex situ heart perfusion (ESHP) has increased the pool of donors in adults. However, this is not true in pediatrics due to lack of devices. Therefore, we sought to understand organ refusal in pediatrics and estimate donor heart usage with ESHP. Donor hearts offered to pediatrics were identified from the Organ Procurement and Transplantation Network Database (2000-2019). A linear regression model was built to predict average travel speed, and the extended maximum permitted distance with ESHP was calculated. This extended distance was compared with the policy for maximum travel distance. There were 33,708 donor offers (n = 10,807 hearts) to pediatric programs [24.1% (n = 2,604) transplanted]. Six percent of the offers (n = 1,832) (n = 771 hearts) were turned down due to distance, with 676 of the hearts never transplanted. Based on the modeling and using an ESHP time of 5.5 hours, 84% (n = 570/676) of hearts turned down due to distance could be utilized by pediatric programs. This proportion increased to 100% with 10 hours of support time. By addressing prolonged ischemic time due to distance, ESHP has the potential to increase the number of donors utilized in pediatric candidates. Although no device exists for pediatrics, this analysis lends support to the importance of developing this technology.

Optimal Donor Allograft Function: The Search for the Lowest Acceptable Donor Left Ventricular Ejection Fraction in Pediatric Heart Transplantation

BACKGROUND

The availability of heart donors is limited by organ shortage. Due to concerns of reduced survival, donors with depressed left ventricular ejection fraction (LVEF <50%) have been cautiously used in pediatric heart transplantation. One strategy to expand the donor pool is to re-evaluate whether lower donor LVEF may be acceptable for transplantation.

METHODS

We performed a multicenter retrospective cohort study of patients <18 y receiving heart transplants from April 2007 to September 2021 using the United Network of Organ Sharing dataset. We excluded retransplants and multiorgan transplants. Cut-point analyses of LVEF was performed and Kaplan-Meier method was used to compare 1-y survival for new cut-points and the standard (LVEF >50%).

RESULTS

The analytic sample consisted of 5255 patients. Recipients receiving hearts with lower LVEFs were more likely to be on ventilator and extracorporeal membrane oxygenation support. Recipients did not differ in waitlist times or transplant status. Cut-point analysis identified LVEF 45% as a potentially new cutoff. One-year survival of recipients of donors with LVEF ≥45% (92.1%; 95% confidence interval [CI], 91.3%-92.8%) was similar to that of LVEF >50% (92.1%; CI, 91.4%-92.9%). Survival for the LVEF 45%-49% (88.8%; CI, 72.9%-95.7%) cohort was slightly lower than the ≥50% cohort, albeit nonsignificant.

CONCLUSIONS

One-year survival among pediatric heart transplants using a donor heart LVEF threshold of 45% or 40% was similar to a threshold of 50%. However, the finding is based on a small number of patients with LVEF <50%, and future larger prospective studies are warranted to confirm the findings of this study before a lower LVEF threshold is considered.

Do vasoactive medications impact donor hearts clinical outcomes in pediatric heart transplantation?

OBJECTIVES

There is limited data examining donor vasopressor and/or inotrope medications (vasoactives) on pediatric orthotopic heart transplant (OHT) outcomes. We aim to evaluate the effects of vasoactives on pediatric OHT outcomes.

METHODS

The United Network for Organ Sharing database was retrospectively reviewed from January 2000 to March 2018 for donor hearts. Exclusion criteria included multiorgan transplants and recipient age >18. Donors receiving vasoactives at the time of procurement were compared to donors not on vasoactives, including the number of vasoactives and the type. End-points of interest were survival at 30 days and 1 year as well as post-transplant rejection at 1 year. Logistic and Cox models were used to quantify survival end-points.

RESULTS

Of 6462 donors, 3187 (49.3%) were receiving at least one vasoactive. Comparing any vasoactive medication versus none, there was no difference in 30-day survival (p = .27), 1 year survival (p = .89), overall survival (p = .68), or post-transplant rejection (p = .98). There was no difference in 30-day survival for donors receiving 2 or more vasoactive infusions (p = .89), 1 year survival (p = .53), overall survival (p = .75), or post-transplant rejection at 1 year (p = .87). Vasopressin was associated with decreased 30-day mortality (OR = 0.22; p = .028), dobutamine with decreased 1-year mortality (OR = 0.37; p = .036), overall survival (HR = 0.51; p = .003), and decreased post-transplant rejection (HR = 0.63; p = .012).

CONCLUSIONS

There is no difference in pediatric OHT outcomes when the cardiac donor is treated with vasoactive infusions at procurement. Vasopressin and dobutamine were associated with improved outcomes. This information can be used to guide medical management and donor selection.

The Impact of Ex Situ Heart Perfusion in Pediatric Transplantation: An Analysis of the United Network for Organ Sharing Registry

Ex situ heart perfusion (ESHP) has increased the pool of donors in adults. However, this is not true in pediatrics due to lack of devices. Therefore, we sought to understand organ refusal in pediatrics and estimate donor heart usage with ESHP. Donor hearts offered to pediatrics were identified from the United Network for Organ Sharing (UNOS) Database (2000-2019). A linear regression model was built to predict average travel speed, and the extended maximum permitted distance with ESHP was calculated. This extended distance was compared with the policy for maximum travel distance. There were 33,708 donor offers (n = 10,807 hearts) to pediatric programs (24.1% [n = 2,604] transplanted). Six percent of the offers (n = 1,832) (n = 771 hearts) were turned down due to distance, with 676 of the hearts never transplanted. Based on the modeling and using an ESHP time of 5.5 hours, 84% (n = 570/676) of hearts turned down as distance could be utilized by pediatric programs. This proportion increased to 100% with 10 hours of support time. By addressing prolonged ischemic time due to distance, ESHP has the potential to increase the number of donors utilized in pediatric candidates. While no device exists for pediatrics, this analysis lends support to the importance of developing this technology.

Barriers and misconceptions of ex situ heart perfusion in pediatric donation

BACKGROUND

Despite efforts, pediatric HTx candidates continue to have high waitlist mortality due to limited donor availability. However, there is a significant number of offered hearts not used due to concerns of viability. ESHP is a method for continuous perfusion of the donor heart that allows assessment and extended out-of-body time. It is imperative to understand healthcare stakeholders' perspectives on ESHP for implementation. Therefore, the aims of this qualitative study were to: (1) Explore pediatric stakeholders' perspectives toward ESHP; and (2) Identify barriers to widespread adoption of this technology.

METHODS

Virtual focus groups were completed with pediatric HTx healthcare professional stakeholders. Following transcription of audio-recordings, the material was analyzed using content analysis.

RESULTS

Four focus groups were completed with 17 participants, representing 12 institutions and three countries. Focus groups revealed varied understanding of both current and potential uses of ESHP. Participants did see the potential benefits of extending out-of-body time for and the ability to evaluate donor heart quality. However, concerns were expressed relating to patient selection, wait-list times, post-HTx outcomes, adverse events, and technical issues. These were felt to be important to understand in order to justify the costs of ESHP and impact on the healthcare system.

CONCLUSIONS

This project represents the first qualitative formative evaluation of ESHP in pediatrics. The knowledge gained from stakeholders will form the basis for education initiatives, clinical trial design, and roll-out of new ESHP technologies designed for pediatrics.

Association of Donors With US Public Health Service Risk Criteria and Outcomes After Adult vs Pediatric Cardiac Transplant

Importance

The United Network for Organ Sharing (UNOS) evaluates donor risk for acute transmission of HIV, hepatitis B, or hepatitis C based on US Public Health Services (PHS)-specific criteria. However, recent data regarding use and outcomes of those donors with PHS risk criteria among pediatric and adult heart transplant recipients are lacking.

Objective

To compare use and outcomes of graft from donors with PHS risk criteria vs those with a standard-risk donor (SRD) in children vs adults in a contemporary cohort.

Design, Setting, and Participants

This cohort was a nationwide analysis of heart transplants in the US that used data from the UNOS database. Participants were children (<18 years old) and adults (≥18 years old) who received a heart transplant from January 1, 2010, to December 31, 2021.

Exposures

UNOS-defined donor risk status.

Main Outcomes and Measures

Trend analysis compared changes in PHS risk criteria use among children and adults. Patient survival was analyzed using Kaplan-Meier curves with log rank and Cox proportional hazards to compare PHS risk-criteria outcomes vs SRD-criteria outcomes in children and adult heart transplant recipients. Additional analysis was performed among adults who received a PHS-risk criteria graft that was previously declined for pediatric recipients.

Results

Of 5115 pediatric transplant recipients (donor without PHS risk median [IQR] age, 5 [0-13] years and donor with PHS risk median [IQR] age, 8 [0-14] years) and 30 289 adult heart transplant recipients (donor without PHS risk median [IQR] age, 56 [46-63] years and donor with PHS risk median [IQR] age, 57 [47-63] years), PHS risk criteria comprised 8% in children vs 25% in adults. PHS criteria are being increasingly used over the past decade with the proportion of recipients transplanted with PHS risk-criteria donors being approximately 3 times greater among adult recipients than children recipients. Pediatric recipients of a PHS risk-criteria donor had greater pretransplant ventilatory support, whereas adult recipients of a PHS risk-criteria donor had greater pretransplant extracorporeal membrane oxygenation use. Patient survival was similar between pediatric recipients of PHS risk-criteria grafts vs SRD-criteria grafts and slightly higher among adult recipients of PHS risk-criteria grafts vs SRD-criteria grafts. The 1778 adult recipients who received a PHS criteria-risk donor that was previously declined for pediatric recipients had similar patient survival recipients compared with SRD-criteria donors (HR, 0.92; 95% CI, 0.81-1.03; P = .18).

Conclusions and Relevance

In the current era, a 3-fold greater proportion of adult recipients receive a PHS risk-criteria graft compared with children despite similar posttransplant patient survival. The ongoing organ donor shortage underscores the need for consideration of PHS risk criteria where these donors remain underused.

Outcomes following use of pediatric and young adult donor hearts with bicuspid aortic valves: A single-center case series

BACKGROUND

Valvular disease in pediatric and young adult donor hearts may be a relative contraindication to graft use. Outcomes following the use of donor hearts with bicuspid aortic valve (BAV) have not been previously reported in children. We describe 4 cases of pediatric heart transplantation (HTx) utilizing a donor heart with a BAV.

CASE SERIES

Of the 469 HTx included in this study, 4 utilized a donor heart with a BAV. All recipients were female; median age was 11 years (range 0.3 to 19 years). In all cases, the BAV was not discovered until after HTx. All donors were less than 30 years old. The patients were followed for a median of 6 years (range 2 to 9 years) with all patients alive at last follow-up. Two patients have transitioned to adult care, and 2 patients continue to follow in our clinic. In follow-up, no patient has required an aortic valve intervention or had infective endocarditis. At last review, no patient had greater than mild aortic insufficiency or more than mild aortic stenosis. Three patients developed mild-to-moderate left ventricular hypertrophy in the first year post-transplant that improved over time. One patient experienced a peri-operative embolic stroke at time of transplant unrelated to the BAV.

CONCLUSION

On short- and intermediate-term follow-up, pediatric and young adult donor hearts with BAV demonstrated acceptable graft longevity and valvular function. A functionally normal BAV in a pediatric heart transplant donor should not be a contraindication to organ acceptance.

Don't Throw Your Heart Away: Increased Transparency of Donor Utilization Practices in Transplant Center Report Cards Alters How Center Performance Is Evaluated

BACKGROUND

Publicly available report cards for transplant centers emphasize posttransplant survival and obscure the fact that some centers reject many of the donor organs they are offered (reflecting a conservative donor acceptance strategy), while others accept a broader range of donor offers (reflecting an open donor acceptance strategy).

OBJECTIVE

We assessed how the provision of salient information about donor acceptance practices and waitlist survival rates affected evaluation judgments of hospital report cards given by laypeople and medical trainees.

METHODS

We tested 5 different report card formats across 4 online randomized experiments (n1 = 1,003, n2 = 105, n3 = 123, n4 = 807) in the same hypothetical decision. The primary outcome variable was a binary choice between transplant hospitals (one with an open donor acceptance strategy and the other with a conservative donor acceptance strategy).

RESULTS

Report cards featuring salient information about donor organ utilization rates (transplant outcomes categorized by quality of donor offers accepted) or overall survival rates (outcomes from both waitlist and transplanted patients) led lay participants (studies 1, 3, and 4) and medical trainees (study 2) to evaluate transplant centers with open donor acceptance strategies more favorably than centers with conservative strategies.

LIMITATIONS

Due to the nature of the decision, a hypothetical scenario was necessary for both ethical and practical reasons. Results may not generalize to transplant clinicians or patients faced with the decision of where to join the transplant waitlist.

CONCLUSIONS

These findings suggest that performance evaluations for transplant centers may vary significantly based not only on what outcome information is presented in report cards but also how the information is displayed.

Decline of increased risk donor offers increases waitlist mortality in paediatric heart transplantation

BACKGROUND

Increased risk donors in paediatric heart transplantation have characteristics that may increase the risk of infectious disease transmission despite negative serologic testing. However, the risk of disease transmission is low, and refusing an IRD offer may increase waitlist mortality. We sought to determine the risks of declining an initial IRD organ offer.

METHODS AND RESULTS

We performed a retrospective analysis of candidates waitlisted for isolated PHT using 20072017 United Network of Organ Sharing datasets. Match runs identified candidates receiving IRD offers. Competing risks analysis was used to determine mortality risk for those that declined an initial IRD offer with stratified Cox regression to estimate the survival benefit associated with accepting initial IRD offers. Overall, 238/1067 (22.3%) initial IRD offers were accepted. Candidates accepting an IRD offer were younger (7.2 versus 9.8 years, p < 0.001), more often female (50 versus 41%, p = 0.021), more often listed status 1A (75.6 versus 61.9%, p < 0.001), and less likely to require mechanical bridge to PHT (16% versus 23%, p = 0.036). At 1- and 5-year follow-up, cumulative mortality was significantly lower for candidates who accepted compared to those that declined (6% versus 13% 1-year mortality and 15% versus 25% 5-year mortality, p = 0.0033). Decline of an IRD offer was associated with an adjusted hazard ratio for mortality of 1.87 (95% CI 1.24, 2.81, p < 0.003).

CONCLUSIONS

IRD organ acceptance is associated with a substantial survival benefit. Increasing acceptance of IRD organs may provide a targetable opportunity to decrease waitlist mortality in PHT.

Pediatric heart transplant

Pediatric heart transplantation has additional and unique aspects from standard pediatric heart surgery and adult heart transplantation. The purpose of this article is to review pediatric heart transplantation and special surgical considerations. The methods used by the authors involved reviewing the literature and surgical techniques surrounding this patient population and procedure. The article presents a general review of the topic including the history, current state, surgical approaches, post-operative management, and outcomes in this patient population.

A coordinated approach to improving pediatric heart transplant waitlist outcomes: A summary of the ACTION November 2019 waitlist outcomes committee meeting

The number of children needing heart transplantation continues to rise. Although improvements in heart failure therapy, particularly durable mechanical support, have reduced waitlist mortality, the number of children who die while waiting for a suitable donor organ remains unacceptably high. Roughly, 13% of children and 25% of infants on the heart transplant waitlist will not survive to transplantation. With this in mind, the Advanced Cardiac Therapies Improving Outcomes Collaborative Learning Network (ACTION), through its Waitlist Outcomes Committee, convened a 2-day symposium in Ann Arbor, Michigan, from 2-3 November 2019, to better understand the factors that contribute to pediatric heart transplant waitlist mortality and to focus future efforts on improving the organ allocation rates for children needing heart transplantation. Using improvement science methodology, the heart failure-transplant trajectory was broken down into six key steps, after which modes of failure and opportunities for improvement at each step were discussed. As a result, several projects aimed at reducing waitlist mortality were initiated.

Pediatric donor heart allocation in the United States, 2006-2017: Current patterns and potential for improvement

OBJECTIVE

To understand current donor heart allocation practices for pediatric transplantation.

BACKGROUND

Despite high waitlist mortality rates among pediatric patients awaiting transplant, a substantial proportion of donor hearts go unused. Analysis of UNOS match run data may identify opportunities to optimize organ utilization.

METHODS

Using UNOS/OPTN data, we evaluated all match runs for pediatric (<18 years) donor hearts from 1/1/2006 to 3/31/2017. We assessed final disposition of donor hearts, reasons for donor refusal, and other match run characteristics. Variation in total offers made per organ, and refusal rates by OPOs were also evaluated.

RESULTS

Of 7585 pediatric potential donor hearts, 2226 (29.3%) were refused. Hearts accepted underwent a median of 2 offers (IQR: 1-5), compared to 11 (IQR: 5-24) for refused donor hearts. Organ refusal rates decreased from 36.9% in 2006-2009 to 22.3% in 2014-2017 (P < .001). Reasons for refusal included quality (80.9%), size mismatch (57.5%), and known/suspected crossmatch positivity (39.1%). Among 1800 hearts deemed "poor quality" by ≥1 transplant program, less than half (46.6%) were coded "poor quality" by multiple refusing programs. Organ refusal rates ranged from 13.5% to 83.3% across OPOs, and there was no correlation between refusal rates and median number of offers made by the OPO.

CONCLUSION

Although more organs are being used over time, 1 in 5 available pediatric donor hearts are still discarded. The lack of donor evaluation consensus and wide variability in donor refusal rates indicates a need for standardization of donor assessment and match run processes across OPOs.

A comprehensive strategy in donor acceptance: Impact on pediatric waitlist and heart transplant outcomes

Significant inter- and intra-center practice variability is present in pediatric donor heart acceptability. This may contribute to variation in the donor refusal rate and may impact waitlist time, morbidity, mortality, and transplant rates. In order to reduce practice variability, our center developed and implemented a comprehensive strategy regarding donor acceptance in September 2017. The aim of this study was to assess the impact of this strategy on waitlist time and outcomes as well as early post-transplant outcomes. We performed a single-center, retrospective analysis of all pediatric (<18 years) patients listed for single-organ heart transplant at our center from September 2015 to September 2018. Patients were divided into those listed before (Group 1) and after implementation of the comprehensive strategy (Group 2). The primary end-point was waitlist time. Secondary end-points included waitlist removal due to death or clinical deterioration, donor refusals per listed patient, early post-transplant outcomes (graft failure, mechanical ventilation time, inotropic support, length of hospital stay) and 1-year post-transplant survival. Of 78 listed patients, 54 were transplanted (29 in Group 1), 9 were removed due to death or clinical deterioration (7 in Group 1) and 15 were removed due to clinical improvement (12 in Group 1). The waitlist time was significantly shorter in Group 2 (17 days, IQR 7-53) vs Group 1 (90 days, IQR 14-162); P = .006. The number of donor refusals was lower in Group 2 (1, IQR 0-2.2) vs Group 1 (4, IQR 2-19); P < .001. The percentage of refused donors with normal function (Left ventricular ejection fraction > 50%) was lower in Group 2 vs Group 1 (53% vs 84%; P < .001). Difference in removal from the waitlist for death or deterioration in Group 2 vs Group 1 (n = 2, 7% vs n = 7, 20%, P = .18) did not reach statistical significance. There was no difference in post-transplant outcomes between groups. The waitlist time and donor refusals significantly decreased after implementation of a comprehensive donor acceptance strategy without impacting transplant outcomes. This analysis supports the need for a comprehensive approach to donor organ acceptance within a pediatric transplant center.

Pediatric donor management to optimize donor heart utilization

Optimal management of pediatric cardiac donors is essential in order to maximize donor heart utilization and minimize the rate of discarded organs. This review was performed after a systematic literature review and gives a detailed overview on current practices and guidelines. The review focuses on optimal monitoring of pediatric donors, donor workup, hormonal replacement, and obliterating the adverse effects of brain death. The current evidence on catecholamine support and thyroid hormone replacement is also discussed. Recognizing and addressing this shall help in a standardized approach toward donor management and optimal utilization of pediatric heart donors organs.

Review of interactions between high-risk pediatric heart transplant recipients and marginal donors including utilization of risk score models

BACKGROUND

Donor organ acceptance practices vary among pediatric heart transplant professionals. We sought to understand what is known about the interactions between the "high-risk" recipient and the "marginal donor," and how donor risk scores can impact this discussion.

METHODS

A systematic review of published literature on pediatric HTx was undertaken with the assistance of a medical librarian. Two authors independently assessed search results, and papers were reviewed for inclusion.

RESULTS

We found that there are a large number of individual factors, and clusters of factors, that have been used to label individual recipients "high-risk" and individual donors "marginal." The terms "high-risk recipient" and "marginal donor" have been used broadly in the literature making it virtually impossible to make comparisons between publications. In general, the data support that patients who could be easily agreed to be "sicker recipients" are at more risk compared to those who are clearly "healthier," albeit still "sick enough" to need transplantation. Given this variability in the literature, we were unable to define how being a "high-risk" recipient interplays with accepting a "marginal donor." Existing risk scores are described, but none were felt to adequately predict outcomes from factors available at the time of offer acceptance.

CONCLUSIONS

We could not determine what makes a donor "marginal," a recipient "high-risk," or how these factors interplay within the specific recipient-donor pair to determine outcomes. Until there are better risk scores predicting outcomes at the time of organ acceptance, programs should continue to evaluate each organ and recipient individually.

Effects of donor cause of death, ischemia time, inotrope exposure, troponin values, cardiopulmonary resuscitation, electrocardiographic and echocardiographic data on recipient outcomes: A review of the literature

BACKGROUND

Heart transplantation has become standard of care for pediatric patients with either end-stage heart failure or inoperable congenital heart defects. Despite increasing surgical complexity and overall volume, however, annual transplant rates remain largely unchanged. Data demonstrating pediatric donor heart refusal rates of 50% suggest optimizing donor utilization is critical. This review evaluated the impact of donor characteristics surrounding the time of death on pediatric heart transplant recipient outcomes.

METHODS

An extensive literature review was performed to identify articles focused on donor characteristics surrounding the time of death and their impact on pediatric heart transplant recipient outcomes.

RESULTS

Potential pediatric heart transplant recipient institutions commonly receive data from seven different donor death-related categories with which to determine organ acceptance: cause of death, need for CPR, serum troponin, inotrope exposure, projected donor ischemia time, electrocardiographic, and echocardiographic results. Although DITs up to 8 hours have been reported with comparable recipient outcomes, most data support minimizing this period to <4 hours. CVA as a cause of death may be associated with decreased recipient survival but is rare in the pediatric population. Otherwise, however, in the setting of an acceptable donor heart with a normal echocardiogram, none of the other data categories surrounding donor death negatively impact pediatric heart transplant recipient survival.

CONCLUSIONS

Echocardiographic evaluation is the most important donor clinical information following declaration of brain death provided to potential recipient institutions. Considering its relative importance, every effort should be made to allow direct image visualization.

Pediatric cardiac waitlist mortality-Still too high

Cardiac transplantation for children with end-stage cardiac disease with no other medical or surgical options is now standard. The number of children in need of cardiac transplant continues to exceed the number of donors considered "acceptable." Therefore, there is an urgent need to understand which recipients are in greatest need of transplant before becoming "too ill" and which "marginal" donors are acceptable in order to reduce waitlist mortality. This article reviewed primarily pediatric studies reported over the last 15 years on waitlist mortality around the world for the various subgroups of children awaiting heart transplant and discusses strategies to try to reduce the cardiac waitlist mortality.

Behavioral economics-A framework for donor organ decision-making in pediatric heart transplantation

The high discard rate of pediatric donor hearts presents a major challenge for children awaiting heart transplantation. Recent literature identifies several factors that contribute to the disparities in pediatric donor heart usage, including regulatory oversight, the absence of guidelines on pediatric donor heart acceptance, and variation among transplant programs. However, a likely additional contributor to this issue are the behavioral factors influencing transplant team decisions in donor offer scenarios, a topic that has not yet been studied in detail. Behavioral economics and decision psychology provide an excellent foundation for investigating decision-making in the pediatric transplant setting, offering key insights into the behavior of transplant professionals. We conducted a systematic review of published literature in pediatric heart transplant related to behavioral economics and the psychology of decision-making. In this review, we draw on paradigms from these two domains in order to examine how existing aspects of the transplant environment, including regulatory oversight, programmatic variation, and allocation systems, may precipitate potential biases surrounding donor offer decisions. Recognizing how human decision behavior influences donor acceptance is a first step toward improving utilization of potentially viable pediatric donor hearts.

ISHLT consensus statement on donor organ acceptability and management in pediatric heart transplantation

The number of potential pediatric heart transplant recipients continues to exceed the number of donors, and consequently the waitlist mortality remains significant. Despite this, around 40% of all donated organs are not used and are discarded. This document (62 authors from 53 institutions in 17 countries) evaluates factors responsible for discarding donor hearts and makes recommendations regarding donor heart acceptance. The aim of this statement is to ensure that no usable donor heart is discarded, waitlist mortality is reduced, and post-transplant survival is not adversely impacted.

Donor and Recipient Characteristics in Heart Transplantation Are Associated with Altered Myocardial Tissue Structure and Cardiac Function

PURPOSE

To use structure-function cardiac MRI in the evaluation of relationships between donor and heart transplantation (HTx) recipient characteristics and changes in cardiac tissue structure and function. HTx candidates and donor hearts are evaluated for donor-recipient matches to improve survival, but the impact of donor and recipient characteristics on changes in myocardial tissue and function in the transplanted heart is not fully understood.

MATERIALS AND METHODS

Cardiac MRI at 1.5 T was performed from August 2014 to June 2017 in 58 HTx recipients (mean age, 51.1 years ± 12.6 [standard deviation], 26 female patients) and included T2 mapping (to evaluate edematous and/or inflammatory changes), precontrast and postcontrast T1 mapping (allowing the calculation of extracellular volume fraction [ECV] to estimate interstitial expansion), and tissue phase mapping (allowing the calculation of myocardial velocities and twist). Donor and recipient demographics (age, sex, height, weight, and body mass index [BMI]) and comorbidities (hypertension, diabetes, and smoking history) were evaluated for relationships with cardiac MRI measures.

RESULTS

Sex-influenced cardiac MRI measures of myocardial tissue and function are as follows: Female HTx recipients demonstrated increased precontrast T1 (P = .002) and reduced systolic peak long-axis velocities (P = .015). Increased age of the donor heart was associated with elevated T2 (r = 0.32; P < .05) and ECV (r = 0.47; P < .01), indicating increased edema and interstitial expansion, as well as impaired diastolic peak long-axis velocities (r = 0.41; P < .01). Recipient-donor differences in age, weight, and BMI were significantly associated with elevated ECV (r = 0.36-0.48; P < .05). Hypertension in donors resulted in increased ECV (31.0% ± 4.2 vs 26.0% ± 3.3; P = .001).

CONCLUSION

Donor and HTx recipient characteristics were significantly associated with cardiac MRI-derived measures of myocardial tissue structure and function.© RSNA, 2019.

Utilizing increased risk for disease transmission (IRD) kidneys for pediatric renal transplant recipients

BACKGROUND

Strategies to expand numbers of deceased donor kidneys suitable for pediatric recipients are urgently needed to prevent long-term dialysis-associated morbidity and mortality. Donors designated as increased risk of disease transmission (IRD) are infrequently used in pediatric recipients. We examined outcomes of these kidneys in pediatric patients and the potential to increase the donor pool.

METHODS

The United Network for Organ Sharing (UNOS) database records presence of IRD in all deceased donors since 2004. All pediatric kidney transplant recipients from 2004 to 2017 were identified and stratified by IRD status, and outcomes were examined.

RESULTS

Four hundred seventy-three pediatric kidney transplant recipients received an IRD allograft. IRD donors had lower kidney donor profile index (KDPI); were more likely to be younger, male, and Caucasian; and were more likely to have used drugs. IRD kidneys were more likely to have been biopsied and placed on pulsatile perfusion. Other than an older recipient age, demographic data were not different between groups. Allograft and patient survivals were similar, as were rejection and delayed graft function rates. Compared with adult recipients and adult IRD recipients, pediatric recipients were more likely to have a younger donor, receive a kidney with a lower creatinine, and were less likely to have delayed graft function (p < 0.05). There were no recorded disease transmissions in IRD group.

CONCLUSIONS

Patient and allograft survivals are similar in IRD and non-IRD kidneys. High-quality IRD organs used in adults represent a large number of donors with excellent outcomes. IRD allografts have a potential to increase transplant volume and should be considered for pediatric patients.

Variability in donor selection among pediatric heart transplant providers: Results from an international survey

There is considerable variability in donor acceptance practices among adult heart transplant providers; however, pediatric data are lacking. The aim of this study was to assess donor acceptance practices among pediatric heart transplant professionals. The authors generated a survey to investigate clinicians' donor acceptance practices. This survey was distributed to all members of the ISHLT Pediatric Council in April 2018. A total of 130 providers responded from 17 different countries. There was a wide range of acceptable criteria for potential donors. These included optimal donor-to-recipient weight ratio (lower limit: 50%-150%, upper limit: 120%-350%), maximum donor age (25-75 years), and minimum acceptable left ventricular EF (30%-60%). Non-US centers demonstrated less restrictive donor selection criteria and were willing to accept older donors (50 vs 35 years, P < 0.001), greater size discrepancy (upper limit weight ratio 250% vs 200%, P = 0.009), and donors with a lower EF (45% vs 50%, P < 0.001). Recipient factors were most influential in the decision to accept marginal donors including recipients requiring ECMO support, ventilator support, and highly sensitized patients with a negative XM. However, programmatic factors impacted the decision to decline marginal donors including recent programmatic mortalities and concerns for programmatic restrictions from regulatory bodies. There is significant variation in donor acceptance practices among pediatric heart transplant professionals. Standardization of donor acceptance practices through the development of a consensus statement may help to improve donor utilization and reduce waitlist mortality.

Pediatric heart transplantation from an influenza B-positive donor

As heart transplantation demand is increasing without subsequent growth of the donor pool, need for expansion of acceptance criteria is paramount, particularly when considering critically ill, highly sensitized patients. We present a case report of a pediatric heart transplant recipient of an organ refused by 197 prior potential recipients due to the donor being infected with influenza virus. We perform a literature review of recent solid organ transplant cases from influenza-positive donors and conclude that the donor pool may be expandable by allowing donors with treatable infections to be included.

Alternative methods for virtual heart transplant-Size matching for pediatric heart transplantation with and without donor medical images available

BACKGROUND

Listed pediatric heart transplant patients have the highest solid-organ waitlist mortality rate. The donor-recipient body weight (DRBW) ratio is the clinical standard for allograft size matching but may unnecessarily limit a patient's donor pool. To overcome DRBW ratio limitations, two methods of performing virtual heart transplant fit assessments were developed that account for patient-specific nuances. Method 1 uses an allograft total cardiac volume (TCV) prediction model informed by patient data wherein a matched allograft 3-D reconstruction is selected from a virtual library for assessment. Method 2 uses donor images for a direct virtual transplant assessment.

METHODS

Assessments were performed in medical image reconstruction software. The allograft model was developed using allometric/isometric scaling assumptions and cross-validation.

RESULTS

The final predictive model included gender, height, and weight. The 25th-, 50th-, and 75th-percentiles for TCV percentage errors were -13% (over-prediction), -1%, and 8% (under-prediction), respectively. Two examples illustrating the potential of virtual assessments are presented.

CONCLUSION

Transplant centers can apply these methods to perform their virtual assessments using existing technology. These techniques have potential to improve organ allocation. With additional experience and refinement, virtual transplants may become standard of care for determining suitability of donor organ size for an identified recipient.

Pediatric marginal donor hearts: Trends in US national use, 2005-2014

Pediatric patients awaiting heart transplant face high mortality rates due to donor organ shortages, including non-use of marginal donor hearts. We examined national trends in pediatric marginal donor heart use over time. UNOS data were queried for heart donors <18 years from 2005 to 2014. The proportion of donor hearts considered marginal was determined using previously cited marginal characteristics: left ventricular ejection fraction (LVEF) <50%, use of ≥2 inotropes, cerebrovascular death, CDC high-risk status, and eGFR < 30 mL/min/1.73 m² . Disposition of donor hearts was determined and stratified by marginal donor status. Of 6778 pediatric hearts offered from 2005 to 2014, 2373 (35.0%) were considered marginal. Non-use of marginal donor hearts was significantly higher than that of donor hearts without any marginal characteristics (59.5% vs 20.3%, P < .001). In particular, LVEF < 50% and donor inotropes were associated with high rates of organ non-use among pediatric donors. Yet, non-use of marginal donor organs decreased from 67% to 48% from 2005 to 2014 (P < .001). Although the proportion of pediatric donor hearts used for pediatric patients has increased, more than half of donor hearts are declined for use in pediatric recipients due, in part, to perceived marginal status.

Is there an optimal organ acceptance rate for pediatric heart transplantation: "A sweet spot"?

Despite a limited supply of donors, potential donor hearts are often declined for subjective concerns regarding organ quality. This analysis will investigate the relationship between donor heart AR and patient outcome at pediatric transplant centers. The UNOS database was used to identify all match runs for pediatric candidates (age < 18 years) from 2008 through March 2015 in which a heart offer was ultimately placed. Centers which received ≥10 offers/y were included (10 634 offers, 38 centers). Transplant centers were stratified based on their AR: low (<20%, n = 13), medium (20%-40%, n = 16), or high (>40%, n = 9). Low AR centers experienced worse negative WL outcome compared with medium (P = .022) and high (P = .004) AR centers. Low AR centers had similar post-transplant graft survival to medium (P = .311) or high (P = .393) AR centers; however, medium AR centers had better post-transplant graft survival than high AR centers (P = .037). E-F survival from listing regardless of transplant was worse for low AR centers compared with medium (P < .001) or high (P = .001) AR centers. Low AR centers experience worse WL outcomes without improvement in post-transplant outcomes. High AR centers experience higher post-transplant graft failure than medium AR centers. AR of 20%-40% appears to have optimal WL and post-transplant outcomes.

Efficient method to create integration-free, virus-free, Myc and Lin28-free human induced pluripotent stem cells from adherent cells

AIM

Nonviral induced pluripotent stem cell (IPSC) reprogramming is not efficient without the oncogenes, Myc and Lin28. We describe a robust Myc and Lin28-free IPSC reprogramming approach using reprogramming molecules.

METHODS

IPSC colony formation was compared in the presence and absence of Myc and Lin28 by the mixture of reprogramming molecules and episomal vectors.

RESULTS

While more colonies were observed in cultures transfected with the aforementioned oncogenes, the Myc and Lin28-free method achieved the same reprogramming efficiency as reports that used these oncogenes. Further, all colonies were fully reprogrammed based on expression of SSEA4, even in the absence of Myc and Lin28.

CONCLUSION

This approach satisfies an important regulatory pathway for developing IPSC cell therapies with lower clinical risk.