Predicting survival among high-risk pediatric cardiac transplant recipients: An analysis of the United Network for Organ Sharing database

Pediatric risk to orthotopic heart transplant (PRO) score: Insights from United Network for Organ Sharing (UNOS) waitlist mortality findings

BACKGROUND

Pediatric heart transplant candidates on the waitlist have the highest mortality rate among all solid organ transplants. A risk score incorporating a candidate's individual risk factors may better predict mortality on the waitlist and optimize organ allocation to the sickest of those awaiting transplant.

METHODS

Using the United Network for Organ Sharing (UNOS) database, we evaluated a total of 5542 patients aged 0-18 years old on the waitlist for a single, first time, heart transplant from January 2010 to June 2019. We performed a univariate analysis on two-thirds (N = 3705) of these patients to derive the factors most associated with waitlist mortality or delisting secondary to deterioration within 1 year. Those with a p <0.2 underwent a multivariate analysis and the resulting factors were used to build a prediction model using the Fine-Grey model analysis. This predictive scoring model was then validated on the remaining one-third of the patients (N = 1852).

RESULTS

The Pediatric Risk to OHT (PRO) scoring model utilizes the following unique patient variables: blood type, diagnosis of congenital heart disease, weight, presence of ventilator support, presence of inotropic support, extracorporeal membrane oxygenation (ecmo) status, creatinine level, and region. A higher score indicates an increased risk of mortality. The PRO score had a predictive strength of 0.762 as measured by area under the ROC curve at 1 year.

CONCLUSION

The PRO score is an improved predictive model with the potential to better assess mortality for patients awaiting heart transplant.

International practice heterogeneity in pre-transplant management of pulmonary hypertension related to pediatric left heart disease

BACKGROUND

Elevated pulmonary vascular resistance (PVR) in the setting of left heart failure may contribute to poor outcomes after pediatric heart transplant (HTx), but peri-transplant management is variable.

METHODS

We sought to characterize international practice by surveying physicians at pediatric HTx centers.

RESULTS

We received 49 complete responses from 39 centers in 16 countries. Most respondents are pediatric cardiologists (90%), practice at centers offering heart (86%) and lung (55%) transplant, and perform pre-HTx acute vasoreactivity testing (AVT, 88%) in patients with elevated PVR. Half (51%) reported defining a PVR cutoff for HTx eligibility as ≤6 WU m² (56%) post-AVT (84%). The highest post-AVT PVR ever accepted for HTx ranged from 3-14.4 (median 6) WU m² . To treat elevated pre-transplant PVR, phosphodiesterase type 5 inhibitors are most common (65%) followed by oxygen (31%), nitric oxide (14%), endothelin receptor antagonists (11%), and prostacyclins (6%). Nearly a third (31%) do not routinely use pulmonary vasodilators without implantation of a left ventricular assist device (LVAD). Case scenarios highlight treatment variability: in a restrictive cardiomyopathy scenario, HTx listing with post-transplant vasodilator therapy was favored, whereas in a Shone's complex patient with fixed PVR, LVAD ± pulmonary vasodilators followed by repeat catheterization was most common. Management of dilated cardiomyopathy with reactive PVR was variable. Most continue vasodilator therapy until HTx (16%), PVR normalizes (16%) or ≤6 months.

CONCLUSIONS

Management of elevated PVR in children awaiting HTx is heterogenous. Evidence-based guidelines are needed to allow for longitudinal determination of optimal outcomes and standardized care.

External validation and comparison of risk score models in pediatric heart transplants

BACKGROUND

Pediatric heart transplant (PHT) patients have the highest waitlist mortality of solid organ transplants, yet more than 40% of viable hearts are unutilized. A tool for risk prediction could impact these outcomes. This study aimed to compare and validate the PHT risk score models (RSMs) in the literature.

METHODS

The literature was reviewed to identify RSMs published. The United Network for Organ Sharing (UNOS) registry was used to validate the published models identified in a pediatric cohort (<18 years) transplanted between 2017 and 2019 and compared against the Scientific Registry of Transplant Recipients (SRTR) 2021 model. Primary outcome was post-transplant 1-year mortality. Odds ratios were obtained to evaluate the association between risk score groups and 1-year mortality. Area under the curve (AUC) was used to compare the RSM scores on their goodness-of-fit, using Delong's test.

RESULTS

Six recipient and one donor RSMs published between 2008 and 2021 were included in the analysis. The validation cohort included 1,003 PHT. Low-risk groups had a significantly better survival than high-risk groups as predicted by Choudhry (OR = 4.59, 95% CI [2.36-8.93]) and Fraser III (3.17 [1.43-7.05]) models. Choudhry's and SRTR models achieved the best overall performance (AUC = 0.69 and 0.68, respectively). When adjusted for CHD and ventricular assist device support, all models reported better predictability [AUC > 0.6]. Choudhry (AUC = 0.69) and SRTR (AUC = 0.71) remained the best predicting RSMs even after adjustment.

CONCLUSION

Although the RSMs by SRTR and Choudhry provided the best prediction for 1-year mortality, none demonstrated a strong (AUC ≥ 0.8) concordance statistic. All published studies lacked advanced analytical approaches and were derived from an inherently limited dataset.

Evaluation of donor heart for transplantation

Cardiac transplantation is considered the gold-standard treatment option for patients suffering from end-stage heart failure refractory to maximum medical therapy. A major determinant of graft function and recipient survival is a comprehensive evaluation of the donor allograft. Challenges arise when designing and implementing an evidence-based donor evaluation protocol due to the number of influential donor-specific characteristics and the complex interactions that occur between them. Here, we present our systematic approach to donor evaluation by examining the impact that relevant donor variables have on graft function and recipient outcomes.

The influence of mechanical Circulatory support on post-transplant outcomes in pediatric patients: A multicenter study from the International Society for Heart and Lung Transplantation (ISHLT) Registry

BACKGROUND

Mechanical circulatory support (MCS) is increasingly being used as a bridge to transplant in pediatric patients. We compare outcomes in pediatric patients bridged to transplant with MCS from an international cohort.

METHODS

This retrospective cohort study of heart-transplant patients reported to the International Society for Heart and Lung Transplantation (ISHLT) registry from 2005-2017 includes 5,095 patients <18 years. Pretransplant MCS exposure and anatomic diagnosis were derived. Outcomes included mortality, renal failure, and stroke.

RESULTS

26% of patients received MCS prior to transplant: 240 (4.7%) on extracorporeal membrane oxygenation (ECMO), 1,030 (20.2%) on ventricular assist device (VAD), and 54 (1%) both. 29% of patients were <1 year, and 43.8% had congenital heart disease (CHD). After adjusting for clinical characteristics, compared to no-MCS and VAD, ECMO had higher mortality during their transplant hospitalization [OR 3.97 & 2.55; 95% CI 2.43-6.49 & 1.42-4.60] while VAD mortality was similar [OR 1.55; CI 0.99-2.45]. Outcomes of ECMO+VAD were similar to ECMO alone, including increased mortality during transplant hospitalization compared to no-MCS [OR 4.74; CI 1.81-12.36]. Patients with CHD on ECMO had increased 1 year, and 10 year mortality [HR 2.36; CI 1.65-3.39], [HR 1.82; CI 1.33-2.49]; there was no difference in survival in dilated cardiomyopathy (DCM) patients based on pretransplant MCS status.

CONCLUSION

Survival in CHD and DCM is similar in patients with no MCS or VAD prior to transplant, while pretransplant ECMO use is strongly associated with mortality after transplant particularly in children with CHD. In children with DCM, long term survival was equivalent regardless of MCS status.

Use of ECMO for Cardiogenic Shock in Pediatric Population

In children with severe advanced heart failure where medical management has failed, mechanical circulatory support in the form of veno-arterial extracorporeal membrane oxygenation (VA ECMO) or ventricular assist device represents life-sustaining therapy. This review provides an overview of VA ECMO used for cardiovascular support including medical and surgical heart disease. Indications, contraindications, and outcomes of VA ECMO in the pediatric population are discussed.VA ECMO provides biventricular and respiratory support and can be deployed in rapid fashion to rescue patient with failing physiology. There have been advances in conduct and technologic aspects of VA ECMO, but survival outcomes have not improved. Stringent selection and optimal timing of deployment are critical to improve mortality and morbidity of the patients supported with VA ECMO.

Diagnosis, Evaluation, and Treatment of Myocarditis in Children

Myocarditis in the pediatric population can be a challenging diagnosis to make and often requires utilization of multiple diagnostic modalities. The cause is often due to a viral infection with activation of the innate and acquired immune response with either recovery or disease progression. Laboratory testing often includes inflammatory markers, cardiac troponin levels, and natriuretic peptides. Noninvasive testing should include electrocardiogram, echocardiogram, and possibly an MRI. Treatment of myocarditis remains controversial with most providers using immune modulators with intravenous immunoglobulin and corticosteroids.

End-Stage Liver Disease Models and Outcomes in Pediatric Patients Supported With Short-Term Continuous-Flow Ventricular Assist Devices

Short-term continuous-flow ventricular assist devices (STCF-VADs) are increasingly being utilized in pediatrics. End-stage liver disease (ELD) models have been associated with outcomes in adult patients on mechanical circulatory support. We sought to determine the relationship between outcomes in children on STCF-VADs and three ELD models: model for end-stage liver disease-excluding international normalized ratio (MELD-XI; all) and MELD-XI (> 1 year), PELD, and a novel score, PedMELD-XI. All patients (< 19 years) supported with STCF-VADs, between June 2009 and December 2016 were included. The MELD-XI, PELD, and PedMELD-XI scores were calculated and their association with adverse events and a composite measure of death, major bleeding, and neurologic dysfunction was analyzed. Of 32 patients, median age was 0.57 years (interquartile range [IQR], 0.10-4.43), median weight was 7.15 kg (IQR, 3.68-16.53), 53.1% had congenital heart disease, and 53.1% were male. In total, 78.1% patients experienced an adverse event (78.1% a major bleed, 25.0% neurologic dysfunction, and 15.6% death). The median MELD-XI score was 11.17 (IQR, 9.44-30.01), MELD-XI (>1 year) 9.44 (IQR, 9.44-24.33), PELD 6.00 (IQR, 4.00-13.75), and PedMELD-XI -14.91 (IQR, -18.85 to -12.25). A higher MELD-XI for all ages (13.80 vs. 9.44, p = 0.037) and less negative PedMELD-XI (-14.16 vs. -19.34, p = 0.028) scores were significantly associated with bleeding and the composite outcome. PedMELD-XI was significantly associated with death (-12.87 vs. -16.84, p = 0.041) while a trend was seen for increased MELD-XI in all ages being associated with death (31.52 vs. 10.11, p = 0.051). Last, there was no association with the models and neurologic events. MELD-XI and PedMELD-XI were significantly associated with major bleeding and the composite endpoints with PedMELD-XI also being associated with death. These results suggest that ELD models can be used to predict outcomes in this specific patient population, however, further analysis in a larger population is required.

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.

The reality of limping to pediatric heart transplantation

OBJECTIVE

Improvements in surgical technique, critical care, and early repair for congenital heart disease (CHD) have led to improved outcomes with heart transplantation, often used as a salvage procedure after failed palliation, especially in infants. These patients, however, often have several risk factors for poor posttransplant survival. We aimed to identify the reality of survival after heart transplantation in patients "limping to transplant" with common risk factors.

METHODS

All heart transplant recipients younger than 18 years were identified from the UNOS data set from 2000 to 2017. Modifiable risk factors (MRFs) of mechanical ventilation, renal dysfunction, and liver dysfunction at transplant and nonmodifiable risk factors of infancy at listing or CHD were examined. One-year posttransplant survival was analyzed with logistic regression.

RESULTS

Of 4101 transplants, 1459 patients (36%) had 1 or more MRFs. There was a decrease in 1-year survival with additional MRFs up to a 9.1-times increased risk of death in an infant with CHD. A noninfant without CHD and no MRFs had a 95% 1-year survival, in contrast to an intubated patient with CHD without other end-organ dysfunction, who had 1-year survival of 76%, which decreased to 58% if they were an infant and also had renal dysfunction.

CONCLUSIONS

Patients "limping to transplant" with multiple risk factors demonstrates decreasing early survival relative to those without other end-organ dysfunction. It is imperative that we have transparent discussions about expected outcomes with these families and identify ways to optimize patients' conditions through other supportive avenues to improve posttransplant outcomes.

Mechanical circulatory support in children: past, present and future

Rapid advances in the field of mechanical circulatory support (MCS) have dramatically changed the management of pediatric patients with heart failure. There is now emphasis on timely implantation of ventricular assist devices (VADs) to preserve or recover end-organ function, and increased focus on post-implant management to improve the stroke rate. Transplant waitlist mortality has significantly decreased in the era of VAD use. Devices approved for adults are being used off-label in children with excellent outcomes, allowing chronic therapy and discharge home to become part of pediatric VAD therapy.

Time for evidence-based, standardized donor size matching for pediatric heart transplantation

BACKGROUND

Accurately predicting cardiac size by other body parameters has long been problematic to determine whether a donor heart will serve a given waitlist candidate, yet hundreds of heart donors are turned down annually for size mismatch.

OBJECTIVES

We sought to describe how donor body weight parameters are currently utilized in cardiac transplantation and its influence on waitlist outcomes.

METHODS

From the United Network for Organ Sharing database, pediatric (age <18 years) heart transplant candidates were divided into lower quartile, interquartile, and upper quartile categories based on final maximum acceptable donor-candidate weight ratio (DCW), expressed as percentage. Baseline characteristics and waitlist outcomes, including monthly offers/candidate and survival were compared.

RESULTS

Overall median DCW was 200% (range, 159%-241%). Patients with congenital heart disease had higher DCW than those with cardiomyopathy (223% vs 203%; P < .001). Number of monthly offers/candidate (5.0, 5.6, and 7.2, respectively; P < .001) increased with quartile of DCW. Posttransplant survival was similar amongst the groups (log-rank P > .05). Subgroup analysis of critically ill children showed a waitlist survival advantage in those listed with a DCW ≥200% (P < .001).

CONCLUSIONS

Despite substantial practice variation in acceptable donor weight in pediatric heart transplantation, patients listed with variable DCW had similar posttransplant survival. However, in critically ill patients, higher DCW was associated with greater waitlist survival. Better understanding of the importance of donor weight could reduce practice variability and improve organ use and waitlist outcomes for pediatric cardiac transplant candidates.

Age-Dependent Impact of Pre-Transplant Intensive Care Unit Stay on Mortality in Heart Transplant Recipients

Background

Heart transplantation (HTx) is a treatment option for refractory end-stage heart failure. Severe illness requiring pre-transplant intensive care unit (ICU) stay may be a risk factor for diminished post-transplant survival, but this association is surprisingly inconsistent in recent studies. To clarify the significance of ICU stay as a risk factor for heart transplant outcomes, we aimed to define if patient age was a factor in which ICU stay was predictive of survival after HTx.

Methods

De-identified data were obtained on isolated first-time HTx performed during the years 2006 - 2015 from the UNOS Registry. Nine age groups were defined. The primary outcome was 1-year post-transplant mortality. Cox proportional hazard regression estimated unadjusted and adjusted hazard ratio (HR) associated with pre-transplant ICU stay in each age group.

Results

The analysis included 19,508 patients (9% deceased within 1 year). In the overall cohort, pre-transplant ICU stay was associated with increased hazard of 1-year mortality (HR = 1.3; 95% confidence interval (CI): 1.2 - 1.4; P < 0.001); but further univariate analysis showed a greater hazard of 1-year mortality associated with ICU stay in infants (HR = 2.2; 95% CI: 1.5 - 3.2; P < 0.001). However, the adjusted analysis found that adults ages 40 - 49 had the highest statistically significant hazard of 1-year mortality (HR = 1.5; 95% CI: 1.1 - 2.1; P = 0.011).

Conclusions

Our study established age variation in the association between ICU stay and survival after HTx, with this association being strongest among adults, 40 to 49 years of age, undergoing HTx. Previous data suggesting decreased survival in infants may be related to the increased use of extracorporeal membrane oxygenation as a mechanical cardiac assist rather than ventricular assist devices.

Prediction of mortality following pediatric heart transplant using machine learning algorithms

BACKGROUND

Optimizing transplant candidates' priority for donor organs depends on the accurate assessment of post-transplant outcomes. Due to the complexity of transplantation and the wide range of possible serious complications, recipient outcomes are difficult to predict accurately using conventional multivariable regression. Therefore, we evaluated the utility of 3 ML algorithms for predicting mortality after pediatric HTx.

METHODS

We identified patients <18 years of age receiving HTx in 2006-2015 in the UNOS Registry database. Mortality within 1, 3, or 5 years was predicted using classification and regression trees, RFs, and ANN. Each model was trained using cross-validation, then validated in a separate testing set. Model performance was primarily evaluated by the area under the receiver operating characteristic (AUC) curve.

RESULTS

The training set included 2802 patients, whereas 700 were included in the testing set. RF achieved the best fit to the training data with AUCs of 0.74, 0.68, and 0.64 for 1-, 3-, and 5-year mortality, respectively, and performed best in the testing data, with AUCs of 0.72, 0.61, and 0.60, respectively. Nevertheless, sensitivity was poor across models (training: 0.22-0.58; testing: 0.07-0.49).

DISCUSSION

ML algorithms demonstrated fair predictive utility in both training and testing data, but the sensitivity of these algorithms was generally poor. With the registry missing data on many determinants of long-term survival, the ability of ML methods to predict mortality after pediatric HTx may be fundamentally limited.

Practice Variation, Costs and Outcomes Associated with the Use of Inhaled Nitric Oxide in Pediatric Heart Transplant Recipients

Right ventricular (RV) failure is a potentially fatal complication following heart transplantation (HTx). Inhaled nitric oxide (iNO) is a selective pulmonary vasodilator that is used to decrease pulmonary vascular resistance immediately post-HTx to reduce the risk of RV failure. The aim of this study was to describe utilization patterns, costs, and outcomes associated with post-transplant iNO use in children. All pediatric HTx recipients (2002-2016) were identified from a unique linked PHIS/SRTR dataset. Post-HTx iNO use was determined based on hospital billing data. Utilization patterns and associated costs were described. The association of iNO support with post-HTx survival was assessed using the Kaplan-Meier method and a multivariable Cox proportional hazards model was used to adjust for risk factors. A total of 2833 pediatric HTx recipients from 28 centers were identified with 1057 (36.5%) receiving iNO post-HTx. Post-HTx iNO use showed significant increase overall (17.2-54.7%, p < 0.001) and wide variation among centers (9-100%, p < 0.001). Patients with congenital heart disease (aOR 1.4, 95% CI 1.2, 1.6), requiring mechanical ventilation at HTx (aOR 1.3, 95% CI 1.1, 1.6), and pre-transplant iNO (aOR 9.3, 95% CI 5.4, 16) were more likely to receive iNO post-HTx. The median daily cost of iNO was $2617 (IQR $1843-$3646). Patients who required > 5 days of iNO post-HTx demonstrated inferior 1-year post-HTx survival (p < 0.001) and iNO use > 5 days was independently associated with worse post-HTx survival (AHR 1.6, 95% CI 1.2, 2.1; p < 0.001). There is wide variation in iNO use among centers following pediatric HTx with use increasing over time despite significant incremental cost. Prolonged iNO use post-HTx is associated with worse survival, likely serving as a marker of residual illness severity. Further research is needed to define the populations that derive the greatest benefit from this costly therapy.

Cumulative Effect of Preoperative Risk Factors on Mortality After Pediatric Heart Transplantation

BACKGROUND

Risk assessment in heart transplantation is critical for candidate selection, but current models inadequately assess individual risk of postoperative mortality. We sought to identify risk factors and develop a scoring system to predict mortality after heart transplantation in children.

METHODS

The records of patients undergoing heart transplantation at our institution from 2010 through 2016 were reviewed. Clinical characteristics were recorded and compared between survivors and nonsurvivors. We used Cox proportional hazard modeling of factors associated with postoperative mortality to develop a risk factor score.

RESULTS

There were 74 patients who underwent heart transplantation at a mean age of 8.8 ± 6.6 years. Congenital heart disease was the most common indication, comprising 48.6% of the cohort. Overall mortality was 18.9%, with 10 of 14 dying within 30 days of the operation or during the initial postoperative admission (early mortality). Preoperative factors associated with overall mortality were single-ventricle congenital heart disease (hazard ratio [HR], 3.2; p = 0.042), biventricular assist device (HR, 4.8; p = 0.043), history of four or more sternotomies (HR, 3.9; p = 0.023), panel reactive antibody exceeding 10% (HR, 4.4; p = 0.013), any previous operation at another institution (HR, 3.2; p = 0.038), and pulmonary vein disease (HR, 4.7; p = 0.045). Each risk factor was assigned a point value, based on similar magnitude of the HRs. A score of 4 or higher predicted mortality with 57% sensitivity and 90% specificity.

CONCLUSIONS

In this single-center pediatric cohort, postheart transplantation mortality could be predicted using patient-specific risk factors. The cumulative effect of these risk factors predicted mortality with high specificity.

Prelisting predictions of early postoperative survival in infant heart transplantation using classification and regression tree analysis

Infants listed for heart transplantation experience high waitlist and early post-transplant mortality, and thus, optimal allocation of scarce donor organs is required. Unfortunately, the creation and validation of multivariable regression models to identify risk factors and generate individual-level predictions are challenging. We sought to explore the use of data mining methods to generate a prediction model. CART analysis was used to create a model which, at the time of listing, would predict which infants listed for heart transplantation would survive at least 3 months post-transplantation. A total of 48 infants were included; 13 died while waiting, and six died within 3 months of heart transplant. CART analysis identified RRT, blood urea nitrogen, and hematocrit as terminal nodes with alanine transaminase as an intermediate node predicting death. No patients listed on RRT (n = 10) survived and only three of 12 (25%) patients listed on ECLS survived >3 months post-transplant. CART analysis overall accuracy was 83%, with sensitivity of 95% and specificity 76%. This study shows that CART analysis can be used to generate accurate prediction models in small patient populations. Model validation will be necessary before incorporation into decision-making algorithms used to determine transplant candidacy.

Identifiable Risk Factors and Miscalculations During Listing for Pediatric Heart Transplantation

The objective of this study is to describe identifiable risk factors, complications, and pitfalls while listing pediatric patients for heart transplantation, which is the standard of care for end-stage heart disease in children. Since the introduction of cyclosporine in the 1980s, the management in pediatric heart transplantation has shown consistent improvement, mainly because of technological advances and the integration of multidisciplinary teams in the field. However, the complexity of this patient population makes medical providers vulnerable to complications as a result of undesirable mistakes. Transplant survival is impacted negatively when mistakes from health-care providers compound the high-risk status of the patient. The identification of multiple risk factors and undesirable miscalculations may help transplant teams make decisions before allocating organs, intervene or minimize morbidity, and provide the best quality of life to recipients.

Pediatric cardiac transplantation

Heart transplantation in pediatric patients generally arises as a treatment option of last resort, that is, the indication is for patients with heart failure of various etiologies, with potential or actual end-organ dysfunction, in whom there are no reasonable, long-term options for life-prolonging therapy. The concept of heart failure is complex in a pediatric population, particularly those with congenital heart disease. While heart failure may refer simply to systolic dysfunction leading to low cardiac output, it can also encompass: diastolic dysfunction in restrictive cardiomyopathy; single ventricle physiology without an option for stable palliation. A good candidate should have a predicted life expectancy less than the median lifetime of a transplanted heart. Significant improvement in survival has been observed over time with 1- and 5-year survival approximately 90% and 80% in the contemporary era.

Favorable Waitlist and Posttransplant Outcomes in Children and Adolescent Patients Supported With Durable Continuous-Flow Ventricular Assist Devices

Pediatric centers are implanting durable adult continuous-flow ventricular assist devices (CFVADs) in children who are smaller than the industry-recommended size. Waitlist and posttransplant outcomes data in pediatric patients supported with CFVADs as a bridge to transplant are limited. We analyzed the United Network of Organ Sharing and Organ Procurement and Transplantation Network registry to identify patients aged ≤18 years with a CFVAD at the time of listing or transplantation. Patients were stratified by body surface area (BSA; >1.5 vs. ≤1.5 m(2) ) at time of listing. We identified 138 patients with a durable CFVAD during the listing period (100 with BSA >1.5 m(2) , 38 with BSA ≤1.5 m(2) ). Patients with BSA ≤1.5 m(2) were more likely to have a noncardiomyopathy diagnosis (18% vs. 4%, p = 0.007) and to be implanted with a centrifugal-flow rather than an axial-flow device (74% vs. 30%, p = 0.001). There was no difference in failure-free waitlist survival between BSA groups (p = 0.99) among patients with a CFVAD at listing. Posttransplantation survival was 100% and 88% at 1 and 5 years, respectively, for the entire cohort and did not differ by BSA group (p = 0.99). Consequently, waitlist and posttransplant outcomes are favorable for pediatric CFVAD recipients. Small patients (≤1.5 m(2) ) had pre- and posttransplant outcomes similar to those of larger patients that met the industry-recommended size for implantation.

Is Myocarditis an Independent Risk Factor for Post-Transplant Mortality in Pediatric Heart Transplant Recipients?

BACKGROUND

Previous studies suggest that children with myocarditis who receive heart transplantation (HT) may be at higher risk of post-transplant mortality compared with children who are transplanted for idiopathic dilated cardiomyopathy. We hypothesized that these differences are because of more severe heart failure at HT in children with myocarditis.

METHODS AND RESULTS

We identified 221 children with myocarditis and 1583 with idiopathic dilated cardiomyopathy who were <18 years old and listed for HT in the United States between July 2004 and December 2013 using the Organ Procurement and Transplant Network database. We compared baseline characteristics at listing and at HT and used Cox models to determine whether myocarditis is independently associated with wait-list mortality (or becoming too sick to transplant) or post-transplant graft loss (death/re-HT). Children with myocarditis were more likely to be listed while on assisted ventilation, mechanical circulatory support and with renal dysfunction. Overall, 137 children with myocarditis and 1249 with idiopathic dilated cardiomyopathy received HT. In unadjusted analysis, children with myocarditis were at higher risk of wait-list mortality (hazard ratio 2.1; 95% confidence interval 1.5-3.0) and showed a trend toward increased risk of post-transplant graft loss (hazard ratio 1.4; 95% confidence interval 1.0-2.2). However, in adjusted analysis, myocarditis was not associated with wait-list mortality (hazard ratio 1.3, 95% confidence interval 0.9-1.9) or post-transplant graft loss (hazard ratio 1.3, 95% confidence interval 0.9-2.0).

CONCLUSIONS

Among children listed for HT, those with myocarditis have more severe heart failure than children with idiopathic dilated cardiomyopathy. After adjustment for severity of illness, myocarditis does not confer additional risk for wait-list or post-transplant mortality.

Elevated pretransplant pulmonary vascular resistance index does not predict mortality after isolated orthotopic heart transplantation in children: A retrospective analysis of the UNOS database

OHT is the definitive therapy in end-stage heart failure. Elevated PVRI is considered a relative contraindication to isolated OHT; this assumption is re-evaluated using data from the UNOS database. A retrospective review of de-identified data from the UNOS dataset was performed. There were 1943 pediatric OHT recipients between 10/87 and 12/11 with sufficient data for analysis. Cox regression was performed to examine the effect of baseline characteristics on post-transplant survival. Patients were propensity matched, and Kaplan-Meier survival analysis was performed comparing cohorts of patients using thresholds of 6 and 9 WU × m(2) . PVRI was not a significant predictor of post-transplant outcomes in either univariate or multivariate Cox regression. Kaplan-Meier analysis revealed no difference in survival between both unmatched and propensity-matched OHT recipients. In conclusion, elevated PVRI was not associated with post-transplant mortality in pediatric OHT recipients. A prospective study assessing the current use of PVRI ≥6 as a threshold to contraindicate isolated OHT should be undertaken. Removing this potentially unnecessary restriction on transplant candidacy may make this life-saving therapy available to a greater number of patients.

Predicting graft loss by 1 year in pediatric heart transplantation candidates: an analysis of the Pediatric Heart Transplant Study database

BACKGROUND

Pediatric data on the impact of pre-heart transplantation (HTx) risk factors on early post-HTx outcomes remain inconclusive. Thus, among patients with previous congenital heart disease or cardiomyopathy, disease-specific risk models for graft loss were developed with the use pre-HTx recipient and donor characteristics.

METHODS AND RESULTS

Patients enrolled in the Pediatric Heart Transplant Study (PHTS) from 1996 to 2006 were stratified by pre-HTx diagnosis into cardiomyopathy and congenital heart disease cohorts. Logistic regression identified independent, pre-HTx risk factors. Risk models were constructed for 1-year post-HTx graft loss. Donor factors were added for model refinement. The models were validated with the use of patients transplanted from 2007 to 2009. Risk factors for graft loss were identified in patients with cardiomyopathy (n=896) and congenital heart disease (n=965). For cardiomyopathy, independent risk factors were earlier year of transplantation, nonwhite race, female sex, diagnosis other than dilated cardiomyopathy, higher blood urea nitrogen, and panel reactive antibody >10%. The recipient characteristic risk model had good accuracy in the validation cohort, with predicted versus actual survival of 97.5% versus 95.3% (C statistic, 0.73). For patients with congenital heart disease, independent risk factors were nonwhite race, history of Fontan, ventilator dependence, higher blood urea nitrogen, panel reactive antibody >10%, and lower body surface area. The risk model was less accurate, with 86.6% predicted versus 92.4% actual survival, in the validation cohort (C statistic, 0.63). Donor characteristics did not enhance model precision.

CONCLUSIONS

Risk factors for 1-year post-HTx graft loss differ on the basis of pre-HTx cardiac diagnosis. Modeling effectively stratifies the risk of graft loss in patients with cardiomyopathy and may be an adjunctive tool in allocation policies and center performance metrics.

Heart transplantation in children for end-stage congenital heart disease

Heart transplantation (HT) as primary therapy for children with congenital heart disease (CHD) has become unusual. With improved early results of reconstructive surgery, the population of children and adults surviving with CHD is expanding. End-stage CHD related to myocardial dysfunction or circulation failure after prior surgery is becoming more common as an indication for HT. This heterogeneous group of CHD recipients referred for HT presents unique decision-making, technical, and physiologic challenges. Historically, a diagnosis of CHD has been a major risk factor for early mortality after HT. Rescue HT, especially in the setting of failing Fontan physiology, has the worst outcome. Early referral (before end-organ damage), proper selection, and optimization of recipients, as well as meticulous intra- and postoperative management are crucial to improving early outcomes of HT in this population. Beyond the early post-HT period, children with end-stage CHD experience long-term survival comparable to most other non-CHD recipients.

Creation of a quantitative score to predict the need for mechanical support in children awaiting heart transplant

BACKGROUND

Due to the availability of new devices, the use of ventricular assist devices (VADs) in children has been increasing; however, patient selection and optimal timing of device implantation in this population remains uncertain.

METHODS

A retrospective review of the United Network for Organ Sharing dataset identified 5,200 listings without mechanical circulatory support (MCS) for isolated pediatric heart transplant, 1995 to 2012. Patients were randomly divided into a derivation and validation cohort. A multivariable logistic regression model predicting the likelihood of death or need for MCS within 60 days was built using the derivation cohort and tested in the validation cohort. A simplified score (PedsMCS score) was developed and evaluated for accuracy.

RESULTS

The predictive model consisted of variables present at listing (age, albumin level, creatinine clearance, serum bilirubin, mechanical ventilation, and inotropic support). It had good predictive ability (C statistic 0.7304) within the validation cohort. The simplified PedsMCS score was also predictive (C statistic 0.7217) and there was a strong correlation between predicted and expected outcomes (r=0.91, p<0.0001). Patients with PedsMCS score 16 or greater had a significantly higher risk of death or MCS within 2 months (36.6%) than those with low scores (<6) (1.5%, p<0.0001). A single point increase in PedsMCS score was associated with a 16.7% increase in the risk of death or MCS with 2 months (p<0.0001).

CONCLUSIONS

We have developed and validated a simplified score to predict the need for MCS based on risk factors present at listing. This will provide more accurate prognostication in children awaiting heart transplant, and may improve patient selection.

Ventricular assist devices as a bridge-to-transplant improve early post-transplant outcomes in children

BACKGROUND

The use of ventricular assist devices (VADs) to bridge pediatric patients to transplant or recovery has been expanding. There are few current pediatric data assessing the impact of VAD support on post-transplant survival.

METHODS

We performed a retrospective review of all pediatric (≤18 years old, n = 4,028) transplants performed between 1995 and 2011 and contained within the United Network for Organ Sharing data set. Transplants were divided into three eras: early (1995 to 2002, n = 1,450); intermediate (2003 to 2007, n = 1,138); and recent (2008 to 2011, n = 1,440). VADs were present at transplant in 398 patients (9.8%). Outcomes among patients with and without VADs were assessed and compared across eras.

RESULTS

The use of VADs for bridge to transplant has increased (early 1.1%, intermediate 10.5%, recent 17.9%; p < 0.0001). Mean weight among VAD-supported patients (early 63.5 kg, intermediate 42.3 kg, recent 28.8 kg; p < 0.0001) has decreased during this period. VAD patients <10 kg had an increased risk of stroke (odds ratio [OR] = 4.9, 95% confidence interval [CI] 2.1 to 10.8) compared with non-mechanical support patients. In multivariable analyses, extracorporeal VADs were the only type of VAD associated with higher post-transplant mortality (OR = 3.0, 95% CI 0.8 to 10.6). Other types of VAD had lower mortality (OR = 0.5, 95% CI 0.2 to 1.0). Long-term survival was unaffected by the use of a VAD pre-transplant.

CONCLUSIONS

Pediatric patients bridged to transplantation with VADs are increasingly younger and smaller. Complication rates remain high among patients <10 kg. Early post-transplant survival among intracorporeal and paracorporeal VAD patients is excellent and better when compared with unsupported patients. The use of short-term support devices is associated with higher post-transplant mortality. Long-term survival is unaffected by VAD use.

Vasoactive-inotropic score after pediatric heart transplant: a marker of adverse outcome

VIS, a quantitative index of pressor support, has been shown to be a predictor of morbidity and mortality in infants younger than six months who underwent CPB. Data on its prognostic utility following pediatric OHT are lacking. This study compared clinical outcomes in children with differential VIS after pediatric OHT. A retrospective cohort study of 51 consecutive heart transplants from 2004 to 2011 was performed at a pediatric tertiary care facility. Peak VIS was computed within initial 24 and 48 h after OHT and was weighted for peak dose and administration of any or all of six pressors. Patients with peak VIS ≥ 15 constituted high VIS group. Children who persistently required a higher magnitude of pressor support for the first 48 h after OHT, as reflected by high peak VIS, had significantly longer ICU stay (30.2 vs. 15.9 days, p = 0.01), pressor (11.4 vs. 6.8 days, p = 0.02) and ventilatory durations (12.4 vs. 5.9 days, p = 0.05), and higher rates of short-term morbidities. Patients with longer CPB (213 vs. 153 min, p = 0.005) time have higher peak VIS. High peak VIS at 48 h is an effective, yet simple clinical marker for adverse outcomes in pediatric OHT recipients.

Regional variation in survival before and after pediatric heart transplantation--an analysis of the UNOS database

Geographic variation occurs in a variety of health outcomes. Regional influences on outcomes before and after listing for pediatric heart transplantation have not been assessed. Review of the UNOS dataset identified 5398 pediatric (≤ 18 years) patients listed for heart transplantation 2000-2011. Patients were stratified based on the region of listing. Regional-level variables were correlated with individual risk-adjusted outcomes. Mean time spent on the waitlist varied from 91.0 ± 163 days (Region 6 [R6]) to 248.1 ± 493 days (R4, p < 0.0001). Regions with more transplant centers (p < 0.0001) and fewer transplants (p = 0.0015) had higher waitlist mortality. Risk-adjusted individual waitlist mortality varied from 6.9% (R1, CI 6.2-7.8) to 19.2% (R5, CI 18.0-20.6). Waitlist mortality was higher for individuals awaiting transplant in regions with more listings per center (OR 1.04, CI 1.01-1.08) and lower in regions with more donors per center (OR 0.95, CI 0.90-0.99 per donor). Posttransplant risk-adjusted survival varied across regions (R4: 5.4%, CI 4.2-7.4; R7: 18.0%, CI 12.4-32.5), but regional variables were not correlated with outcomes. Outcomes among children undergoing heart transplantation vary by region. Factors leading to increased competition for donor allografts are associated with poorer waitlist survival. Equitable allocation of cardiac allografts requires further investigation of these findings.

Postoperative care of the transplanted patient

The successful delivery of optimal peri-operative care to pediatric heart transplant recipients is a vital determinant of their overall outcomes. The practitioner caring for these patients must be familiar with and treat multiple simultaneous issues in a patient who may have been critically ill preoperatively. In addition to the complexities involved in treating any child following cardiac surgery, caretakers of newly transplanted patients encounter multiple transplant-specific issues. This chapter details peri-operative management strategies, frequently encountered early morbidities, initiation of immunosuppression including induction, and short-term outcomes.

Using the UNOS/SRTR and PHTS Databases to Improve Quality in Pediatric Cardiac Transplantation

Data collection and dissemination have been a part of the US transplant experience since its earliest days. As part of this process, the United Network for Organ Sharing (UNOS) has provided open access to its data. In addition, multiinstitutional groups such as the Pediatric Heart Transplant Study (PHTS) have collected data of particular interest to pediatric and congenital transplants. This wealth of data enables quality improvement along several pathways including individual program assessment and improvement and development of both structure and process measures for ongoing improvement. Extensive literature exists utilizing these data, but must be read critically, recognizing the limitations presented by missing variables (whether uncollected or collected but left blank), reproducibility, and small sample sizes among pediatric patients. However, despite these limitations, opportunity continues to exist to apply these data sets to ongoing questions of quality and optimize organ allocation and long-term survival among pediatric patients with heart failure.

A risk-prediction model for in-hospital mortality after heart transplantation in US children

We sought to develop and validate a quantitative risk-prediction model for predicting the risk of posttransplant in-hospital mortality in pediatric heart transplantation (HT). Children <18 years of age who underwent primary HT in the United States during 1999-2008 (n = 2707) were identified using Organ Procurement and Transplant Network data. A risk-prediction model was developed using two-thirds of the cohort (random sample), internally validated in the remaining one-third, and independently validated in a cohort of 338 children transplanted during 2009-2010. The best predictive model had four categorical variables: hemodynamic support (ECMO, ventilator support, VAD support vs. medical therapy), cardiac diagnosis (repaired congenital heart disease [CHD], unrepaired CHD vs. cardiomyopathy), renal dysfunction (severe, mild-moderate vs. normal) and total bilirubin (≥ 2.0, 0.6 to <2.0 vs. <0.6 mg/dL). The C-statistic (0.78) and the Hosmer-Lemeshow goodness-of-fit (p = 0.89) in the model-development cohort were replicated in the internal validation and independent validation cohorts (C-statistic 0.75, 0.81 and the Hosmer-Lemeshow goodness-of-fit p = 0.49, 0.53, respectively) suggesting acceptable prediction for posttransplant in-hospital mortality. We conclude that this risk-prediction model using four factors at the time of transplant has good prediction characteristics for posttransplant in-hospital mortality in children and may be useful to guide decision-making around patient listing for transplant and timing of mechanical support.

Organizational structure and processes in pediatric heart transplantation: a survey of practices

Despite emerging literature on pediatric heart transplantation, there continues to be variation in current practices. The degree of variability among heart transplant programs has not been previously characterized. The purpose of this study was to evaluate organizational structure and practices of pediatric heart transplant programs. The UNOS database was queried to identify institutions according to volume. Coordinators from 50 institutions were invited to participate with a 70% response rate. Centers were grouped by volume into four categories. Some institutional practices were dominated by clear volume trends. Ninety-five percent of larger centers routinely transplant patients with known antibody sensitization and report a broader range and acuity of recipients. Ninety-four percent report problems with non-adherence. Sixty-nine percent of centers routinely require prospective crossmatches. There was dramatic variation in the use of steroids across all centers. Sixty-five percent of centers transition adolescents to an adult program. Prophylaxis protocols were also highly inconsistent. This survey provided a comprehensive insight into current practices at pediatric heart transplant programs. The results delineated remarkably variable strategies for routine aspects of care. Analysis of divergence along with uniformity across protocols is a valuable exercise and may serve as a stepping-stone toward ongoing cooperation and clarity for evidence-based practice protocols.

Multiple risk factors before pediatric cardiac transplantation are associated with increased graft loss

Identification of heart transplant recipients at highest risk for a poor outcome could lead to improved posttransplantation survival. A chart review of primary heart transplantations from 1993 to 2006 was performed. Analysis was performed to evaluate the risk of graft loss for those with a transplantation age less than 1 year, congenital heart disease (CHD), elevated pulmonary vascular resistance (index > 6), positive panel reactive antibody or crossmatch, liver or renal dysfunction, mechanical ventilation, or mechanical circulatory support (MCS). Primary transplantation was performed for 189 patients. Among these patients, 37% had CHD, 23% had mechanical ventilation, and 6% had renal dysfunction. Overall graft survival was 82% at 1 year and 68% at 5 years. The univariate risk factors for graft loss included mechanical ventilation (hazard ratio [HR], 1.9; 95% confidence interval [CI], 1.15-3.18), CHD (HR, 1.68; 95% CI, 1.04-2.70), and renal dysfunction (HR, 3.05; 95% CI, 1.34-6.70). The multivariate predictors of graft loss were CHD (HR, 1.8; 95% CI, 1.02-2.64), mechanical ventilation (HR, 1.9; 95% CI, 1.13-3.10), and the presence of two or more statistically significant univariate risk factors (SRF) (HR, 3.8; 95% CI, 2.00-7.32). Mechanical ventilation, CHD, and the presence of two or more SRFs identify pediatric patients at higher risk for graft loss and should be considered in the management of children with end-stage heart failure.

Association of graft ischemic time with survival after heart transplant among children in the United States

BACKGROUND

Previous studies have found no association between graft ischemic time (IT) and survival in pediatric heart transplant (HTx) recipients. However, previous studies were small or analyzed risk only at the extremes of IT, where observations are few. We sought to determine whether graft IT is independently associated with graft survival in a large cohort of children with no a priori assumptions about where the risk threshold may lie.

METHODS

All children aged <18 years in the U.S. undergoing primary HTx (1987 to 2008) were included. The primary end point was graft loss (death or retransplant) within 6 months. Multivariate analysis was performed to analyze the association between graft IT and graft loss within 6 months after transplant. A secondary end point of longer-term graft loss was assessed among recipients who survived the first 6 months after transplant.

RESULTS

Of 4,716 pediatric HTxs performed, the median IT was 3.5 hours (interquartile range, 2.7-4.3 hours). Adjusted analysis showed that children with an IT > 3.5 hours were at increased risk of graft loss within 6 months after transplant (hazard ratio, 1.3; 95% confidence interval, 1.1-1.5; p = 0.002). Among 6-month survivors, IT was not associated with longer-term graft loss.

CONCLUSIONS

IT beyond 3.5 hours is associated with a 30% increase in risk of graft loss within 6 months in pediatric HT recipients. Although the magnitude of risk associated with IT is small compared with the risk associated with recipient factors, these findings may be important during donor assessment for high-risk transplant candidates.

Factors associated with in-hospital mortality in infants undergoing heart transplantation in the United States

OBJECTIVE

Infants undergoing heart transplantation have the highest early posttransplant mortality of any age group. We sought to determine the pretransplantation factors associated with in-hospital mortality in transplanted infants in the current era.

METHODS

All infants under 12 months of age who underwent primary heart transplantation during a recent 10-year period (1999-2009) in the United States were identified using the Organ Procurement and Transplant Network database. Multivariable logistic regression was used to identify independent pretransplantation factors associated with in-hospital mortality.

RESULTS

Of 730 infants in the study (median age 3.8 months), 462 (63%) had congenital heart disease, 282 (39%) were supported by a ventilator, 94 (13%) with extracorporeal membrane oxygenation, and 22 (3%) with a ventricular assist device at the time of transplantation. Overall, 82 (11.2%) infants died before their initial hospital discharge. In adjusted analysis, in-hospital mortality was associated with repaired congenital heart disease (odds ratio [OR], 3.6; 95% confidence interval [CI], 1.8, 7.2), unrepaired congenital heart disease not on prostaglandin E (OR, 2.8; CI, 1.3, 6.1), extracorporeal membrane oxygenator support (OR, 6.1; CI, 2.8, 13.4), ventilator support (OR, 4.4; CI, 2.3, 8.3), creatinine clearance less than 40 mL·min(-1)·1.73 m(-2) (OR, 3.1; CI, 1.7, 5.3), and dialysis (OR, 6.2; CI, 2.1, 18.3) at transplantation.

CONCLUSIONS

One in 9 infants undergoing heart transplantation dies before hospital discharge. Pretranplantation factors associated with early mortality include congenital heart disease, extracorporeal membrane oxygenator support, mechanical ventilation, and renal failure. Risk stratification for early posttransplant mortality among infants listed for heart transplantation may improve decision-making for transplant eligibility, organ allocation, and posttransplant interventions to reduce mortality.

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.