Competing Outcomes After Neonatal and Infant Wait-listing for Heart Transplantation

Pediatric urgent heart transplantation with age or weight mismatched donors: Reducing waiting time by enlarging donor criteria

BACKGROUND

Despite considerable progress in heart transplantation, pediatric waiting list mortality is still high, and often patients do not have enough time to wait. We hypothesized that extending the donor criteria regarding age and weight mismatch does not significantly affect the early follow-up.

METHODS

We retrospectively analyzed our pediatric heart transplantation patients operated on from 2014 to 2020 for high (>3.0) or low (<0.6) donor-recipient weight ratio (DRWR) or chronological age mismatches (donor organ >5 years older than recipient age). This patient cohort constituted "mismatched heart transplantations" (mHTX). We compared mHTX preoperative status, postoperative course, 1-year survival, and early clinical follow-up to standard pediatric heart transplantations (sHTX).

RESULTS

We performed 20 pediatric heart transplantations-10 mHTX and 10 sHTX. The minimum DRWR was 0.44, the maximum was 5.60, and the maximum age mismatch was 42.6 years. Median days in the intensive care unit (p = .436) and time-to-first-rejection episode (p = .925) were comparable. Nine patients in each group were alive after 1 year, two patients were operated within 1 year of follow-up. One mHTX patient developed cardiac allograft vasculopathy after 15 months and died 648 days after transplantation (p = .237). All other patients were alive at the end of follow-up and in good clinical conditions (median follow-up for mHTX was 732.5 days, 1149.5 days for sHTX).

CONCLUSION

Postoperative course and early follow-up after mHTX were comparable to sHTX. In urgent clinical situations, extended donor criteria may be considered an additional option for pediatric heart transplantation.

Ethical and practical dilemmas in cardiac transplantation in infants: a literature review

The waiting time in infants for a cardiac transplant remains high, due to the scarcity of donors. Consequently, waiting list morbidity and mortality are higher than those in other age groups. Therefore, the decision to list a small infant for cardiac transplantation is seen as an ethical dilemma by most physicians. This review aims to describe outcomes, limitations, and ethical considerations in infant heart transplantation. We used Medline and Embase as data sources. We searched for publications on infant (< 1 year) heart transplantation, bridge-to-transplant and long-term outcomes, and waiting list characteristics from January 2009 to March 2021. Outcome after cardiac transplant in infants is better than that in older children (1-year survival 88%), and complications are less frequent (25% CAV, 10% PTLD). The bridge-to-transplant period in infants is associated with increased mortality (32%) and decreased transplantation rate (43%). This is mainly due to MCS complications or the limited MCS options (with 51% mortality in infancy). Outcomes are worse for infants with CHD or in need of ECMO-support.Conclusion: Infants listed for cardiac transplantation have a high morbidity and mortality, especially in the period between diagnosis and transplantation. For those who receive cardiac transplant, the outlook is encouraging. Unfortunately, despite growing experience in VAD, mortality in children < 10 kg and children with CHD remains high. After transplantation, patients carry a psychological burden and there is a probability of re-transplantation later in life, with decreased outcomes compared to primary transplantation. These considerations are seen as an important ethical dilemma in many centers, when considering cardiac transplantation in infants (< 1 year). What is Known: • For infants, waitlist mortality remains high. In the pediatric population, MCS reduces the waiting list mortality. What is New: • Outcomes after infant cardiac transplantation are better than other age groups; however, MCS options remain limited, with persistently high waiting list mortality. • Future developments in MCS and alternative options to reduce waiting list mortality such as ABO-incompatible transplantation and pulmonary artery banding are encouraging and will improve ethical decision-making when an infant is in need of a cardiac transplant.

The Case for Cardiac Xenotransplantation in Neonates: Is Now the Time to Reconsider Xenotransplantation for Hypoplastic Left Heart Syndrome?

Neonatal cardiac transplantation for hypoplastic left heart syndrome (HLHS) is associated with excellent long-term survival compared to older recipients. However, heart transplantation for neonates is greatly limited by the critical shortage of donor hearts, and by the associated mortality of the long pre-transplant waiting period. This led to the development of staged surgical palliation as the first-line surgical therapy for HLHS. Recent advances in genetic engineering and xenotransplantation have provided the potential to replicate the excellent results of neonatal cardiac allotransplantation while eliminating wait-list-associated mortality through genetically modified pig-to-human neonatal cardiac xenotransplantation. The elimination of the major pig antigens in addition to the immature B-cell response in neonates allows for the potential to induce B-cell tolerance. Additionally, the relatively mature neonatal T-cell response could be reduced by thymectomy at the time of operation combined with donor-specific pig thymus transplantation to "reprogram" the host's T-cells to recognize the xenograft as host tissue. In light of the recent significantly increased graft survival of genetically-engineered pig-to-baboon cardiac xenotransplantation, we propose that now is the time to consider devoting research to advance the potential clinical application of cardiac xenotransplantation as a treatment option for patients with HLHS. Employing cardiac xenotransplantation could revolutionize therapy for complex congenital heart defects and open a new chapter in the field of pediatric cardiac transplantation.

Impact of Heart Transplantation on the Functional Status of US Children With End-Stage Heart Failure

Background:

There are limited data describing the functional status (FS) of children after heart transplant (HT). We sought to describe the FS of children surviving at least 1 year after HT, to evaluate the impact of HT on FS, and to identify factors associated with abnormal FS post-HT.

Methods:

Organ Procurement and Transplantation Network data were used to identify all US children <21 years of age surviving ≥1 year post-HT from 2005 to 2014 with a functional status score (FSS) available at 3 time points (listing, transplant, ≥1 year post-HT). Logistic regression and generalized estimating equations were used to identify factors associated with abnormal FS (FSS≤8) post-HT.

Results:

A total of 1633 children met study criteria. At the 1-year assessment, 64% were “fully active/no limitations” (FSS=10), 21% had “minor limitations with strenuous activity” (FSS=9); and 15% scored ≤8. In comparison with listing FS, FS at 1 year post-HT increased in 91% and declined/remained unchanged in 9%. A stepwise regression procedure selected the following variables for association with abnormal FS at 1 year post-HT: ≥18 years of age (odds ratio [OR], 1.8; 95% confidence interval [CI], 1.2–2.7), black race (OR, 1.5; 95% CI, 1.1–2.0), support with ≥inotropes at HT (OR, 1.7; 95% CI, 1.2–2.5), hospitalization status at HT (OR, 1.5; 95% CI, 1.0–2.19), chronic steroid use at HT (OR, 1.5; 95% CI, 1.0–2.2), and treatment for early rejection (OR, 2.0; 95% CI, 1.5–2.7).

Conclusion:

Among US children who survive at least 1 year after HT, FS is excellent for the majority of patients. HT is associated with substantial improvement in FS for most children. Early rejection, older age, black race, chronic steroid use, hemodynamic support at HT, and being hospitalized at HT are associated with abnormal FS post-HT.

ABO-incompatible heart transplantation

PURPOSE OF REVIEW

ABO-incompatible (ABOi) heart transplantation (HTx) in young children has evolved from an experimental approach to a standard allocation option in many countries. Clinical and immunological research in ABOi transplantation has revealed insight into the immature immune system and its role in superior graft acceptance in childhood and antigen-specific tolerance.

RECENT FINDINGS

Multicenter experience has confirmed equal actuarial survival, freedom from rejection, and graft vasculopathy comparing ABOi with ABO-compatible HTx. Observations of reduced antibody production and B-cell immunity toward the donor blood group have been confirmed in long-term follow-up. Mechanisms contributing to tolerance in this setting involve the interplay between B-cells and the complement system and the development of B-cell memory. Better characterization of the ABH polysaccharide antigens has improved diagnostic methods and clinical assessment of blood group antibodies. Boundaries regarding age, immune maturity, and therapeutic interventions to extend the applicability of ABOi HTx have been explored and resulted in data that may be useful for HTx patients beyond infancy and ABOi transplantation of other organs. Tolerance of ABH antigens possibly extends to HLA response.

SUMMARY

The review provides insight into the clinical evolution of ABOi HTx and associated immunologic discoveries. Current experiences and boundaries are discussed together with recent and potential future developments for utilization in other patient and age groups.

Pediatric heart allocation and transplantation in Eurotransplant

Pediatric heart allocation in Eurotransplant (ET) has evolved over the past decades to better serve patients and improve utilization. Pediatric heart transplants (HT) account for 6% of the annual transplant volume in ET. Death rates on the pediatric heart transplant waiting list have decreased over the years, from 25% in 1997 to 18% in 2011. Within the first year after listing, 32% of all infants (<12 months), 20% of all children aged 1-10 years, and 15% of all children aged 11-15 years died without having received a heart transplant. Survival after transplantation improved over the years, and in almost a decade, the 1-year survival went from 83% to 89%, and the 3-year rates increased from 81% to 85%. Improved medical management of heart failure patients and the availability of mechanical support for children have significantly improved the prospects for children on the heart transplant waiting list.

C3d plasma levels and CD21 expressing B-cells in children after ABO-incompatible heart transplantation: Alterations associated with blood group tolerance

BACKGROUND

Most children transplanted with ABO-incompatible (ABOi) hearts develop selective tolerance to donor A/B antigens, whereas anti-A/B antibodies typically re-accumulate in adults after ABOi kidney transplantation. Deficiency of essential factors linking innate and adaptive immunity in early childhood may promote development of tolerance, specifically interactions between complement split product C3d and its ligand CD21 on B cells, considering their role in augmenting "T-independent" B-cell activation.

METHODS

Blood and clinical data were analyzed from children after ABOi or ABO-compatible (ABOc) heart transplantation (HTx). Plasma C3d levels were quantified by enzyme-linked immunoassay. Peripheral blood mononuclear cells (PBMC) were phenotyped by flow cytometry; expression of B-cell co-receptor components CD21 and CD81 was quantified.

RESULTS

Fifty-five samples from pediatric HTx recipients (median age at transplant: 4.2 [range 0.03 to 20.4] months; age at sample collection: 14.6 [0.04 to 51.3] months; 53% ABOi) and 21 controls were studied. CD21-expressing B cells increased in trend with age (p = 0.079); longitudinal measures in individual patients showed a strong correlation with age. CD21 expression intensity in B-cells was not age-dependent. Plasma C3d levels did not correlate with age. Comparing ABOc vs ABOi HTx, CD21-expressing cell proportions were similar; however, serum C3d levels were significantly lower after ABOi HTx (p < 0.05).

CONCLUSIONS

In children, including HTx patients, CD21-expressing B-cells show a trend to increase with age, corresponding with improved responsiveness to polysaccharide antigens. This does not differ in patients with ABOi grafts developing tolerance to donor ABO antigens. C3d levels are not age-dependent, but reduced C3d levels after ABOi HTx suggest altered complement metabolism contributing to ABO tolerance.

Risk factors for mortality or delisting of patients from the pediatric heart transplant waiting list

OBJECTIVE

Current literature assessing factors associated with outcomes of patients waiting for pediatric heart transplants has focused on survival to transplant and mortality. Our aim was to determine risk factors associated with the outcomes of delisting, transplant, or death while waiting.

METHODS

In this single-center, retrospective study of patients listed for heart transplants, competing risk analysis was used to model survival from listing to 4 competing outcomes (transplant, death, delisting for clinical deterioration, delisting for clinical improvement or surgical intervention).

RESULTS

There were 308 listing episodes in 280 patients. In competing risk analysis, 11% remained listed at 6 months (transplant 62%, dead 13%, delisted worse 6%, delisted improved 8%). Extracorporeal membrane oxygenation and ventricular assist devices were associated both with higher probability of transplant (hazard ratio [HR], 2.8; P < .001) and delisting for clinical deterioration (HR, 2.7; P = .06). Younger age at listing and complex congenital heart disease were shared risk factors for mortality (HR, 1.07; P = .05; HR, 2.9; P = .003) and delisting because of clinical deterioration (HR, 1.17; P = .01; HR, 2.8; P = .02). Younger age at listing and fetal listing were associated with delisting for clinical improvement or surgical intervention (HR, 1.13; P = .01; HR, 2.9; P = .02).

CONCLUSIONS

Overall survival to transplant depends on risk factors including age at listing, cardiac diagnosis, and mechanical circulatory support. Knowledge of risk factors for death and delisting for clinical deterioration or improvement can assist patient selection and timing of transplant listing.

ABO-incompatible heart transplantation: analysis of the Pediatric Heart Transplant Study (PHTS) database

BACKGROUND

ABO incompatible (ABOi) heart transplantation is an accepted approach to increasing organ availability for young patients. Previous studies have suggested that early survival for ABOi transplants is similar to ABO compatible (ABOc) transplants. We analyzed the Pediatric Heart Transplant Study (PHTS) database from 1/96 to 12/08 to further assess this strategy.

METHODS

We analyzed the numbers of ABOi and ABOc done at the PHTS centers. We then compared the clinical characteristics, and short-term freedom from death, rejection and infection in the ABOi patients with the patients that had an ABOc heart transplant during the same period. All patients were less than or equal to 15 months of age at listing (the age of the oldest ABOi patient). We adjusted for co-variates shown to increase risk for mortality (age less than 1 month, extracorporeal membrane oxygenation (ECMO), ventilator, previous sternotomy, and congenital heart disease).

RESULTS

There were 931 total transplants done at 34 PHTS centers during the 12 year time period in patients ≤15 months of age. Of these, 502 transplants were performed at 20 PHTS centers that did at least one ABOi heart transplant. Eighty-five of the 502 (17%) were ABOi. At time of transplant, ABOi recipients compared with ABOc were more likely to be on a ventilator (49.4% vs 36.5%, p=0.025), and more often supported with ECMO (23.5% vs 13.4%, p=0.018). There was similar survival at 12 months (82% vs 84%, p=0.7). In risk adjusted analysis ABOi status was not associated with 1 year mortality (HR 0.85, 95% CI 0.45-1.6, p=0.61). The ABOi patients had greater freedom from rejection when compared with ABOc patients for all 34 centers (75% vs 62%, p=0.016), but the difference was not significant when limited only to the 20 centers doing ABOi transplants (75% vs 69%, p=0.4). The ABOi cohort had lower infection rates (23.5% vs 37.9%, p = 0.013). This difference remained after adjusting for center and other covariates.

CONCLUSIONS

In center and risk adjusted analysis, young children who received an ABOi transplant had equivalent one-year survival and freedom from rejection compared with those who received an ABOc transplant. In spite of the favorable outcome for ABOi recipients, many centers appear to reserve ABOi transplantation for sicker patients. These data mandate reexamination of the current United Network for Organ Sharing (UNOS) policy that gives priority to ABOc over ABOi transplantation in the United States.

Development of donor-specific isohemagglutinins following pediatric ABO-incompatible heart transplantation

Graft acceptance following pediatric ABO-incompatible heart transplantation has been associated with a deficiency of donor-specific isohemagglutinins (DSI) due to B-cell elimination. Recent observations suggest that some of these patients do produce DSI. The purpose of this study was to examine the pattern of, risk factors for development and clinical impact of DSI. All children who underwent an ABO-incompatible heart transplant (1996-2009) were included. Serial postheart transplantation DSI titers and clinical outcomes were reviewed. DSI were produced in 27% of the patients (n = 11/41). Anti-A production was significantly greater in "at risk" patients than Anti-B (39% vs. 8%; p = 0.04). Risk factors associated with the development of DSI included: older age at transplantation (HR: 1.15/month, p = 0.04), pretransplant Anti-B level ≥ 1:8 (HR: 9.61, p = 0.004) and HLA sensitization (HR: 2.80, p = 0.11). The presence of DSI did increase the risk of cellular rejection but not antibody-mediated rejection, allograft vasculopathy, graft loss or death. Although these antibodies do not result in any significant clinical consequences, their presence suggests that B-cell tolerance is not the sole mechanism of graft acceptance.

Attitudes and practices of cardiologists and surgeons who manage HLHS

OBJECTIVE

We conducted a survey to determine which management options pediatric cardiologists and cardiac surgeons in North America discuss and recommend when counseling parents after the diagnosis of hypoplastic left heart syndrome (HLHS).

METHODS

Pediatric cardiologists and cardiac surgeons across North America were asked to complete an anonymous, Internet-based survey about their attitudes and practices regarding the management of HLHS.

RESULTS

We contacted 1621 pediatric cardiologists and surgeons, of whom 749 (46%) completed the survey. When counseling parents of newborns with HLHS, 99.7% of respondents discussed staged palliative surgery, 67% discussed cardiac transplantation, and 62.2% discussed compassionate care without surgery. Only a minority (14.9%) discussed all of those options. Staged palliative surgery was recommended over cardiac transplantation or compassionate care without surgery by 76.2% of respondents. When counseling parents after prenatal diagnosis of HLHS, 98.8% of respondents discussed continuation of pregnancy with staged palliative surgery after birth, 53.5% discussed continuation of pregnancy with cardiac transplantation after birth, 56.9% discussed continuation of pregnancy with compassionate care after birth, and 74.3% discussed termination of pregnancy. Only 36.5% discussed all of those options. Continuation of pregnancy with staged palliative surgery after birth was recommended over the other options by 56% of respondents.

CONCLUSIONS

Virtually all North American pediatric cardiologists and cardiac surgeons surveyed discuss a surgical intervention when counseling parents about the care of their child or fetus with HLHS. However, only a minority discuss all options. Most physicians recommend staged palliative surgery for management of HLHS.

Equivalent outcomes for pediatric heart transplantation recipients: ABO-blood group incompatible versus ABO-compatible

ABO-blood group incompatible infant heart transplantation has had excellent short-term outcomes. Uncertainties about long-term outcomes have been a barrier to the adoption of this strategy worldwide. We report a nonrandomized comparison of clinical outcomes over 10 years of the largest cohort of ABO-incompatible recipients. ABO-incompatible (n = 35) and ABO-compatible (n = 45) infant heart transplantation recipients (< or =14 months old, 1996-2006) showed no important differences in pretransplantation characteristics. There was no difference in incidence of and time to moderate acute cellular rejection. Despite either the presence (seven patients) or development (eight patients) of donor-specific antibodies against blood group antigens, in only two ABO-incompatible patients were these antibodies implicated in antibody-mediated rejection (which occurred early posttransplantation, was easily managed and did not recur in follow-up). Occurrence of graft vasculopathy (11%), malignancy (11%) and freedom from severe renal dysfunction were identical in both groups. Survival was identical (74% at 7 years posttransplantation). ABO-blood group incompatible heart transplantation has excellent outcomes that are indistinguishable from those of the ABO-compatible population and there is no clinical justification for withholding this lifesaving strategy from all infants listed for heart transplantation. Further studies into observed differing responses in the development of donor-specific isohemagglutinins and the implications for graft accommodation are warranted.

Incidence and risk factors for mortality in infants awaiting heart transplantation in the USA

BACKGROUND

Infants awaiting heart transplantation (HT) face the highest wait-list mortality among all children and adults listed for HT in the USA. We sought to determine the risk of death for infants <12 months old while awaiting HT in the current era, and to identify the principle risk factors associated with wait-list mortality.

METHODS

We analyzed outcomes for all infants listed for HT in the USA from January 1999 to July 2006, using data reported to the U.S. Scientific Registry of Transplant Recipients.

RESULTS

Of the 1,133 listed infants, 61% were <3 months of age, 80% were listed as Status 1A, 64% had a congenital heart disease (CHD) and 31% had cardiomyopathy. Of 724 infants with CHD, 25% were on prostaglandin (PG) and 27% had a history of prior surgery. By 6 months after listing, 23% died on the wait-list and 54% were transplanted. Multivariate factors associated with wait-list mortality were weight <3 kg (hazard ratio [HR] 1.4, 95% confidence interval [CI] 1.0 to 1.9), extracorporeal membrane oxygenation (ECMO) support (HR 5.6, CI 4.0 to 7.9), ventilator support (HR 2.1, 95% CI 1.6 to 2.8), CHD with PG support (HR 2.8, 95% CI 1.8 to 4.3), CHD without prior surgery (HR 2.8, 95% CI 1.9 to 3.9) and non-white race/ethnicity (HR 1.8, 95% CI 1.4 to 2.3).

CONCLUSIONS

One in four infants listed for HT in the USA die before a donor heart can be identified. Wait-list mortality is associated with weight <3 kg, level of invasive support and CHD, but not listing status, which captures medical urgency poorly. Measures to expand infant organ donation, especially among neonates, are urgently needed.

Outcome of pediatric patients with dilated cardiomyopathy listed for transplant: a multi-institutional study

BACKGROUND

The course of dilated cardiomyopathy (DCM) leading to heart failure in children varies; survival with conventional treatment is 64% at 5 years. Heart transplantation (HTx) enables improved survival; however, outcomes from listing for transplant are not well described. This study reports survival of patients with DCM from listing with the availability of mechanical bridge to transplant.

METHODS

Patients with a primary diagnosis of DCM (n = 1,098) were identified from a multi-institutional, prospective, registry of patients aged < 18 years listed for HTx from January 1, 1993, to December 31, 2006.

RESULTS

Characteristics of DCM patients at listing included a mean age of 7.3 years; 51% male, 64% white ethnicity, 77% United Network for Organ Sharing status I, 66% on inotropic support, 28% mechanically ventilated, and 15% on mechanical support. Waitlist mortality was 11%, and 75% underwent HTx at 2 years after listing. Overall 10-year survival after listing was 72%, with higher risk of death associated with arrhythmias, mechanical ventilation, and extracorporeal membrane oxygenation (ECMO) support, but not ventricular assist device (VAD) support. Survival at 10 years post-HTx was 72%, with a higher risk of death associated with black race, older age, mechanical ventilation, longer ischemic time, and earlier era of transplant.

CONCLUSIONS

Transplantation for DCM in the pediatric population offers enhanced survival compared with the natural history. Overall waitlist mortality for DCM is low, with the exception of patients on ECMO, mechanically ventilated, or with arrhythmias. DCM patients fared well after transplant, making HTx a key therapeutic intervention.

Waiting list mortality among children listed for heart transplantation in the United States

BACKGROUND

Children listed for heart transplantation face the highest waiting list mortality in solid-organ transplantation medicine. We examined waiting list mortality since the pediatric heart allocation system was revised in 1999 to determine whether the revised allocation system is prioritizing patients optimally and to identify specific high-risk populations that may benefit from emerging pediatric cardiac assist devices.

METHODS AND RESULTS

We conducted a multicenter cohort study using the US Scientific Registry of Transplant Recipients. All children <18 years of age who were listed for a heart transplant between 1999 and 2006 were included. Among 3098 children, the median age was 2 years (interquartile range 0.3 to 12 years), and median weight was 12.3 kg (interquartile range 5 to 38 kg); 1294 (42%) were nonwhite; and 1874 (60%) were listed as status 1A (of whom 30% were ventilated and 18% were on extracorporeal membrane oxygenation). Overall, 533 (17%) died, 1943 (63%) received transplants, and 252 (8%) recovered; 370 (12%) remained listed. Multivariate predictors of waiting list mortality include extracorporeal membrane oxygenation support (hazard ratio [HR] 3.1, 95% confidence interval [CI] 2.4 to 3.9), ventilator support (HR 1.9, 95% CI 1.6 to 2.4), listing status 1A (HR 2.2, 95% CI 1.7 to 2.7), congenital heart disease (HR 2.2, 95% CI 1.8 to 2.6), dialysis support (HR 1.9, 95% CI 1.2 to 3.0), and nonwhite race/ethnicity (HR 1.7, 95% CI 1.4 to 2.0).

CONCLUSIONS

US waiting list mortality for pediatric heart transplantation remains unacceptably high in the current era. Specific high-risk subgroups can be identified that may benefit from emerging pediatric cardiac assist technologies. The current pediatric heart-allocation system captures medical urgency poorly. Further research is needed to define the optimal organ-allocation system for pediatric heart transplantation.