Critical care therapies pre- and post-heart transplant and their impact: Analysis from the Pediatric Cardiac Critical Care Consortium.

BACKGROUND: Few studies highlighting the critical care management of patients after heart HTx (HTx) have been published to date. This analysis provides a contemporary representation of pre- and post-HTx critical care in various patient cohorts and outlines the impact of intensive care unit (ICU) therapies on outcomes. METHODS: Data from PC4 Collaborative Registry were analyzed for pediatric patients undergoing HTx between August 2014 and April 2022. RESULTS: A total of 1877 HTx in 1857 patients were reported from 42 centers; 56.5% had congenital heart disease (CHD). Patients with CHD were younger, smaller, more likely male, White race, and publicly insured. CHD patients had higher need for catheterization, increased likelihood of inotropic support and mechanical ventilation and lower VAD rates. Their operative courses were significant for longer bypass and cross-clamp times. Postoperatively, CHD patients required more CPR , utilized more ICU therapies and had higher hospital mortality (7.8% vs. 1.8% for non-CHD patients, p<0.0001). Longer cardiopulmonary bypass, longer deep hypothermic circulatory arrest times and delayed sternal closure were independent risk factors for hospital mortality. Lastly, center transplant volume but not surgical volume was associated with transplant outcomes. CONCLUSIONS: A diagnosis of CHD before HTx is associated with a greater use of ICU-specific therapies compared non-CHD cohort. Operative factors, particularly in patients with CHD, are independently associated with higher hospital mortality as was low transplant volume at the center. The study provides basis for further investigating ICU and operative factors that can be modified to improve transplant outcomes.

Novel tubing connectors reduce ECMO circuit thrombosis.

BACKGROUND: Thrombosis within extracorporeal membrane oxygenation (ECMO) circuits is a common complication that dominates clinical management of patients receiving mechanical circulatory support. Prior studies have identified that over 80% of circuit thrombosis can be attributed to tubing-connector junctions. METHODS: A novel connector was designed that reduces local regions of flow stagnation at the tubing-connector junction to eliminate a primary source of ECMO circuit thrombi. To compare clotting between the novel connectors and the traditional connectors, both in vitro loops and an in vivo caprine model of long-term (48 h) ECMO were used to generate tubing-connector junction clots. RESULTS: In vitro, the traditional connectors uniformly (9/9) formed large thrombi, while novel connectors formed a small thrombus in only one of nine (p < 0.0001). In the long-term goat ECMO circuits, the traditional connectors exhibited more thrombi (p < 0.04), and these thrombi were more likely to protrude into the lumen of the tubing (p < 0.001). CONCLUSION: Both in vitro and in vivo validation experiments successfully recreated circuit thrombosis and demonstrate that the adoption of novel connectors can reduce the burden of circuit thrombosis.

Evaluating threshold for donor fraction cell-free DNA using clinically available assay for rejection in pediatric and adult heart transplantation.

BACKGROUND: The aims of the study were to assess the performance of a clinically available cell-free DNA (cfDNA) assay in a large cohort of pediatric and adult heart transplant recipients and to evaluate performance at specific cut points in detection of rejection. METHODS: Observational, non-interventional, prospective study enrolled pediatric and adult heart transplant recipients from seven centers. Biopsy-associated plasma samples were used for cfDNA measurements. Pre-determined cut points were tested for analytic performance. RESULTS: A total of 487 samples from 160 subjects were used for the analysis. There were significant differences for df-cfDNA values between rejection [0.21% (IQR 0.12-0.69)] and healthy samples [0.05% (IQR 0.01-0.14), p < .0001]. The pediatric rejection group had a median df-cfDNA value of 0.93% (IQR 0.28-2.84) compared to 0.09% (IQR 0.04-0.23) for healthy samples, p = .005. Overall negative predictive value was 0.94 while it was 0.99 for pediatric patients. Cut points of 0.13% and 0.15% were tested for various types of rejection profiles and were appropriate to rule out rejection. CONCLUSION: The study suggests that pediatric patients with rejection show higher levels of circulating df-cfDNA compared to adults and supports the specific cut points for clinical use in pediatric and adult patients with overall acceptable performance.

Impact of new allocation policy on waitlist and transplant outcomes of adult congenital heart patients supported with ECMO.

BACKGROUND: The use of ECMO as a bridge to heart transplantation has been growing rapidly in all heart transplant recipients since the implementation of the new UNOS allocation policy; however, the impact on adult congenital heart disease (ACHD) patients is not known. METHODS: We analyzed the UNOS data (2015-2021) for ACHD patients supported with extracorporeal membrane oxygenation (ECMO) during the waitlist, before and after October 2018, to assess the impact on the waitlist and posttransplant outcomes. We compared the characteristics and outcomes of ACHD patients with or without ECMO use during the waitlist and pre- and postpolicy changes. RESULTS: A total of 23 821 patients underwent heart transplantation, and only 918 (4%) had ACHD. Out of all ACHD patients undergoing heart transplants, 6% of patients in the prepolicy era and 7.6% in the postpolicy era were on ECMO at the time of listing. Those on ECMO were younger and sicker compared to the rest of the ACHD cohort. Those on ECMO had similar profiles pre- and postpolicy change; however, there was a very significant decrease in the waitlist time [136 days (IQR 29-384) vs. 38 days (IQR 11-108), p = 0.01]. There was no difference in waitlist mortality; however, competing risk analyses showed a higher likelihood of transplantation (51% vs. 29%) and a lower likelihood of death or deterioration (31% vs. 42%) postpolicy change. Long-term outcomes posttransplant for those supported with ECMO compared to the non-ECMO cohort are similar for ACHD patients, although there was higher attrition in the first year for the ECMO cohort. CONCLUSION: The new allocation policy has resulted in shorter waitlist times and a higher likelihood of transplantation for ACHD patients supported by ECMO. However, the appropriate use of ECMO and the underuse of durable circulatory support devices in this population need further exploration.

Paediatric heart transplantation: life-saving but not yet a cure.

In the 1980s, heart transplantation was the first successful treatment for infants born with hypoplastic left heart syndrome. Infants who have required heart transplantation benefit from immunologic "advantages," including long-term survival free from cardiac allograft vasculopathy. Currently ∼ 90% of children undergoing a heart transplant are reaching their first-year anniversary and the clinical practices of paediatric heart transplantation have dramatically improved. These successes are largely attributed to research sponsored by the Pediatric Heart Transplant Study Group, the International Society of Heart and Lung Transplantation and, more recently, the Non-profits Enduring Hearts and Additional Ventures. Despite these successes, the field is challenged to increase progress to achieve long-term survival into adulthood. The wait-list mortality, especially among infants, is unacceptably high often leading to palliative measures that can increase post-transplant mortality. Cardiac allograft vasculopathy remains a major cause for progressive graft loss of function and sudden death. The relative tolerance seen in immature recipients has not been translated to modifying older recipients' post-transplant outcomes. The modifiable cause(s) for the increased risks of transplantation in children of different ethnicities and races require definition. Addressing these challenges faces the reality that for-profit research favours funding adult recipients, with ∼ 10-fold greater numbers, and their more modest longevity goals. Advocacy for funding "incentives" such as the Orphan Drug rules in the United States and upholding principles of equity and inclusion are critical to addressing the challenges of paediatric heart transplant recipients worldwide.

Impact of the Pediatric ABO Policy Change on Listings, Transplants, and Outcomes for Children Younger Than 2 Years Listed for Heart Transplantation in the United States.

BACKGROUND: We assessed the impact of the liberalized ABO pediatric policy change on candidate characteristics and outcomes for children undergoing heart transplant (HT). METHODS AND RESULTS: Children <2 years undergoing HT with ABO strategy reported at listing and HT from December 2011 to November 2020 to the Scientific Registry of Transplant Recipients database were included. Characteristics at listing, HT, and outcomes during the waitlist and post-transplant were compared before the policy change (December 16, 2011 to July 6, 2016), and after the policy change (July 7, 2016 to November 30, 2020). The percentage of ABO-incompatible (ABOi) listings did not increase immediately after the policy change (P = .93); however, ABOi transplants increased by 18% (P < .0001). At listing, both before and after the policy change, ABOi candidates had higher urgency status, renal dysfunction, lower albumin, and required more cardiac support (intravenous inotropes, mechanical ventilation) than those listed ABO compatible (ABOc). On multivariable analysis, there were no differences in waitlist mortality between children listed as ABOi and ABOc before the policy change (adjusted hazard ratio [aHR] 0.80, 95% confidence interval [CI] 0.61-1.05, P = .10) or after the policy change (aHR 1.2, 95% CI 0.85-1.6, P = .33). Post-transplant graft survival was worse for ABOi transplanted children before the policy change (aHR 1.8, 95% CI 1.1-2.8, P = .014), but not significantly different after the policy change (aHR 0.94, 95% CI 0.61-1.4, P = .76). After the policy change, ABOi listed children had significantly shorter waitlist times (P < .05). CONCLUSIONS: The recent pediatric ABO policy change has significantly increased the percentage of ABOi transplantations and decreased waitlist times for children listed ABOi. This change in policy has resulted in broader applicability and actual performance of ABOi transplantation with equal access to ABOi or ABOc organs, and thus eliminated the potential disadvantage of only secondary allocation to ABOi recipients.

Research Gaps in Pediatric Heart Failure: Defining the Gaps and Then Closing Them Over the Next Decade.

Given the numerous opportunities and the wide knowledge gaps in pediatric heart failure, an international group of pediatric heart failure experts with diverse backgrounds were invited and tasked with identifying research gaps in each pediatric heart failure domain that scientists and funding agencies need to focus on over the next decade.

Perioperative Morbidity and Outcomes in Pediatric Patients Transitioned From Extracorporeal Membrane Oxygenation to Ventricular Assist Device Support: A Study of the Society of Thoracic Surgeons Congenital Heart Surgery Database.

As a bridge to transplant strategy, children transitioned from extracorporeal membrane oxygenation (ECMO) to ventricular assist device (VAD) have higher waitlist mortality compared with those who receive de novo VAD. However, the contribution of the immediate perioperative period and differences in the two groups are not well studied. We performed a nested case-control study between children receiving de novo VAD (group 1) and those transitioned from ECMO to VAD (group 2) between 2014 and 2019 using The Society of Thoracic Surgeons (STS) database. A total of 735 children underwent VAD placement with 498 in group 1 and 237 in group 2. Patients in group 2 were significantly younger, smaller, and significantly sicker, were twice as likely to transition to biventricular VAD and need unplanned reoperations. Overall mortality was 16% for group 1 and 34% for group 2 ( p < 0.01). Regression analysis showed that ECMO use (odds ratio [OR], 2.17 [1.3-3.4]), ventilator need (OR, 2.2 [1.3-3.9]), and cardiogenic shock (OR, 1.8 [1.2-2.8]) were all independent preoperative predictors of VAD mortality while dialysis need (OR, 25.5 [8.6-75.3]), stroke (OR, 6.2 [3.1-12.6]), and bleeding (OR, 1.9 [1.1-3.4]) were independent postoperative predictors of VAD mortality within 30 days (all p < 0.05). The study demonstrated significant baseline differences between the two cohorts, warranting avoidance of comparison. Early elective VAD placement in this cohort of patients should be sought to avoid interim ECMO and high post-VAD mortality.

Risk Factors for Extubation Failure After Pediatric Cardiac Surgery and Impact on Outcomes: A Multicenter Analysis.

IMPORTANCE: Extubation failure (EF) after pediatric cardiac surgery is associated with increased morbidity and mortality. OBJECTIVES: We sought to describe the risk factors associated with early (< 48 hr) and late (48 hr ≤ 168 hr) EF after pediatric cardiac surgery and the clinical implications of these two types of EF. DESIGN SETTING AND PARTICIPANTS: Retrospective cohort study using prospectively collected clinical data for the Pediatric Cardiac Critical Care Consortium (PC4) Registry. Pediatric patients undergoing Society of Thoracic Surgeons benchmark operation or heart transplant between 2013 and 2018 available in the PC4 Registry were included. MAIN OUTCOMES AND MEASURES: We analyzed demographics and risk factors associated with EFs (primary outcome) including by type of surgery. We identified potentially modifiable risk factors. Clinical outcomes of mortality and length of stay (LOS) were reported. RESULTS: Overall 18,278 extubations were analyzed. Unplanned extubations were excluded from the analysis. The rate of early EF was 5.2% (948) and late EF was 2.5% (461). Cardiopulmonary bypass time, ventilator duration, airway anomaly, genetic abnormalities, pleural effusion, and diaphragm paralysis contributed to both early and late EF. Extubation during day remote from shift change and nasotracheal route of initial intubation was associated with decreased risk of early EF. Extubation in the operating room was associated with an increased risk of early EF but with decreased risk of late EF. Across all operations except arterial switch, EF portrayed an increased burden of LOS and mortality. CONCLUSION AND RELEVANCE: Both early and late EF are associated with significant increase in LOS and mortality. Study provides potential benchmarking data by type of surgery. Modifiable risk factors such as route of intubation, time of extubation as well as treatment of potential contributors such as diaphragm paralysis or pleural effusion can serve as focus areas for reducing EFs.

Impact of Antegrade Pulmonary Blood Flow as Patients Progress Through Single-Ventricle Palliations.

BACKGROUND: The impact of antegrade pulmonary blood flow (APBF) during single-ventricle (SV) palliation continues to be debated. We sought to assess its impact on the hemodynamic profile and the short- and long-term outcomes of patients progressing through stages of SV palliation. METHODS: A retrospective single-center study was conducted of SV patients who underwent surgery between January 2010 and December 2020. Patients with APBF were matched to those with no APBF by a propensity score based on body surface area, sex, and type of systemic ventricle. Analysis was performed using appropriate statistics with a significance level of P = .05. RESULTS: Sixty-three patients with APBF were matched with 95 patients with no APBF. At the pre-stage 2 catheterization, APBF patients had a larger left pulmonary artery diameter (z score, 0.1 vs -0.8; P < .042). Patients with APBF had shorter cardiopulmonary bypass time (57.0 vs 79.0 minutes), shorter duration of mechanical ventilation (14.1 vs 17.4 hours), and shorter hospital length of stay (5.0 vs 7.0 days) at stage 2 palliation (P < .05). In the multivariable Cox regression analysis, patients with hypoplastic pulmonary arteries (z scores < -2; adjusted hazard ratio, 9.17) and patients with chromosomal abnormalities/genetic syndrome (adjusted hazard ratio, 4.03) were at increased risk for poor outcomes (P < .05). During the follow-up period, there was no significant difference in risk of the composite poor outcome and long-term survival between groups. CONCLUSIONS: SV patients with APBF had shorter cardiopulmonary bypass time, duration of mechanical ventilation, and hospital length of stay after stage 2 palliation. Patients with hypoplastic pulmonary arteries or chromosomal abnormalities/genetic syndromes had increased risk for poor outcomes. Maintaining APBF has better short-term outcomes, but there are no long-term hemodynamic or survival benefits.

Elective and non-elective endomyocardial biopsy in heart transplant patients and procedural outcomes: An IMPACT registry analysis.

BACKGROUND: Endomyocardial biopsies are standard of care for transplant surveillance, however the procedural risks are not well established, especially in children. The purpose of the study was therefore to assess procedural risks and outcomes associated with elective (surveillance) biopsies and non-elective (clinically indicated) biopsies. METHODS: We used the NCDR IMPACT registry database for this retrospective analysis. Patients undergoing an endomyocardial biopsy were identified using the procedural code, with a diagnosis of heart transplantation required. Data regarding indication, hemodynamics, adverse events and outcomes was gathered and analyzed. RESULTS: A total of 32 547 endomyocardial biopsies were performed between 2012-2020; 31 298 (96.5%) elective and 1133 (3.5%) were non-elective biopsies. Non-elective biopsy was more commonly performed in infants and in those above 18 years of age, in female and in Black race patients and in those with non-private insurance (all p < .05) and showed hemodynamic derangements. Overall rate of complications was low. Combined major adverse events were more common in non-elective patients, with sicker patient profile, use of general anesthesia and femoral access with overall decline in these events over time. CONCLUSIONS: This large-scale analysis shows safety of surveillance biopsies and that non-elective biopsies carry a small but significant risk of major adverse event. Patient profile impacts the safety of the procedure. These data may serve as important comparison point for newer non-invasive tests and for bench marking, especially in children.

Influence of Body Mass Index in Donor-Recipient Size Mismatch in Pediatric Heart Transplantation.

BACKGROUND: Body weight is the traditional metric for matching donor and recipient size for pediatric heart transplantation (pHT). We hypothesized that mismatch in body mass index (BMI) or body surface area (BSA) rather than weight is better associated with outcomes of transplantation and therefore should be used for donor-recipient size matching. METHODS: Analysis of the United Network for Organ Sharing database limited to pHT recipients was performed. Donor and recipient mismatch groups were created for weight, BMI, and BSA ratios. Differences in recipient characteristics between each cohort and the impact of mismatch on outcomes were statistically analyzed. RESULTS: A total of 4,465 patients were included in the analysis of which 43% had congenital heart disease (CHD). There were significant differences in patient characteristics by matching, independent of the matching parameter. Multivariable regression analysis showed that a low donor-recipient BMI ratio (compared to normal) (CHD OR 1.70; non-CHD 2.78) was a predictor of one-year mortality (all P < .001) in both CHD and non-CHD cohorts. Low BMI ratio was also associated with worse long-term survival in non-CHD groups, but not in the CHD cohort. Weight and BSA ratio did not predict one year or long-term survival. CONCLUSION: The use of low BMI donors compared to recipient may predict poor early and long-term survival and therefore should be avoided in pHT. The use of BMI matching may improve donor-recipient matching in pHT.

Extracorporeal Membrane Oxygenation Cannulation Timing in the Pediatric Myocarditis Population: An Exploratory Analysis From the Extracorporeal Life Support Organization Registry.

Children presenting with acute myocarditis may experience rapid clinical deterioration requiring extracorporeal membrane oxygenation (ECMO); however, our understanding of best practices and timing of ECMO initiation are lacking. We explored the relationships between pre-cannulation factors and survival in this high-acuity patient population. DESIGN: Retrospective review of a large international registry. Primary outcome was survival to hospital discharge, stratified by incident cardiac arrest (CA) prior to ECMO and time to cannulation after intubation. SETTING AND SUBJECTS: The Extracorporeal Life Support Organization registry was queried for patients less than or equal to 18 years old receiving ECMO support for myocarditis between 2007 and 2018. Exclusion criteria included being nonindex runs, non-venoarterial ECMO or missing data points for main variables studied. INTERVENTIONS: None. MEASUREMENTS AND MAIN RESULTS: Population characteristics and survival were compared using t test, Wilcoxon rank-sum test, or Fisher exact test. Multivariable logistic regression was used for significant factors in the unadjusted logistic regression. Among 506 index ECMO runs in pediatric patients with myocarditis, survival for the cohort was 72%, with no difference between early and late eras (2007-2012 vs 2013-2018; p = 0.69). Survivors demonstrated higher pre-ECMO pH levels as well as shorter intubation-to-cannulation (ITC) times (3 hr [interquartile range (IQR)], 1-14 hr vs 6 hr [IQR, 2-20 hr]; p = 0.021). CA occurred within 24 hours prior to ECMO cannulation, including extracorporeal cardiopulmonary resuscitation, in 54% of ECMO runs (n = 273). Accounting for the interaction between pre-ECMO CA occurrence and ITC time, longer ITC time remained associated with lower survival for patients who did not experience a CA prior to ECMO, with adjusted odds ratio of 0.09 (IQR, 0.02-0.40; p = 0.002) for ITC time greater than or equal to 18 hours. CONCLUSIONS: The results of this multicenter analysis of ECMO utilization and outcomes for pediatric myocarditis suggest that patients approaching ECMO cannulation who have not experienced CA may have better survival outcomes if cannulated onto ECMO early after intubation.

Validation of donor fraction cell-free DNA with biopsy-proven cardiac allograft rejection in children and adults.

OBJECTIVES: Donor-specific cell-free DNA shows promise as a noninvasive marker for allograft rejection, but as yet has not been validated in both adult and pediatric recipients. The study objective was to validate donor fraction cell-free DNA as a noninvasive test to assess for risk of acute cellular rejection and antibody-mediated rejection after heart transplantation in pediatric and adult recipients. METHODS: Pediatric and adult heart transplant recipients were enrolled from 7 participating sites and followed for 12 months or more with plasma samples collected immediately before all endomyocardial biopsies. Donor fraction cell-free DNA was extracted, and quantitative genotyping was performed. Blinded donor fraction cell-free DNA and clinical data were analyzed and compared with a previously determined threshold of 0.14%. Sensitivity, specificity, negative predictive value, positive predictive value, and receiver operating characteristic curves were calculated. RESULTS: A total of 987 samples from 144 subjects were collected. After applying predefined clinical and technical exclusions, 745 samples from 130 subjects produced 54 rejection samples associated with the composite outcome of acute cellular rejection grade 2R or greater and pathologic antibody-mediated rejection 2 or greater and 323 healthy samples. For all participants, donor fraction cell-free DNA at a threshold of 0.14% had a sensitivity of 67%, a specificity of 79%, a positive predictive value of 34%, and a negative predictive value of 94% with an area under the curve of 0.78 for detecting rejection. When analyzed independently, these results held true for both pediatric and adult cohorts at the same threshold of 0.14% (negative predictive value 92% and 95%, respectively). CONCLUSIONS: Donor fraction cell-free DNA at a threshold of 0.14% can be used to assess for risk of rejection after heart transplantation in both pediatric and adult patients with excellent negative predictive value.

Clinical approach to acute cellular rejection from the pediatric heart transplant society.

BACKGROUND: Early detection of cardiac allograft rejection is crucial for post-transplant graft survival. Despite the progress made in immunosuppression strategies, acute cellular rejection remains a serious complication during and after the first post-transplant year, and there is a continued lack of consensus regarding its treatment, especially in pediatric transplant patients. METHODS: An open request was placed via the listserv to the membership of the Pediatric Heart Transplant Society (PHTS). Along with a broad literature search, numerous institutional protocols were pooled, analyzed and consolidated. A clinical approach document was generated highlighting areas of consensus and practice variation. RESULTS: The clinical approach document divides cellular rejection by International Society for Heart and Lung Transplantation grades and provides management strategies for each, including persistent cellular rejection. CONCLUSIONS: Cellular rejection treatment can be tailored to the clinical status, graft function, and the grade of cellular rejection. A case of mild and asymptomatic rejection may not require treatment, whereas a higher-grade rejection or rejection with graft dysfunction or hemodynamic compromise may require aggressive intravenous therapies, changes to maintenance immunosuppression therapy and augmented surveillance.

Relationship between donor fraction cell-free DNA and clinical rejection in heart transplantation.

BACKGROUND: Clinical rejection (CR) defined as decision to treat clinically suspected rejection with change in immunotherapy based on clinical presentation with or without diagnostic biopsy findings is an important part of care in heart transplantation. We sought to assess the utility of donor fraction cell-free DNA (DF cfDNA) in CR and the utility of serial DF cfDNA in CR patients in predicting outcomes of clinical interest. METHODS: Patients with heart transplantation were enrolled in two sequential, multi-center, prospective observational studies. Blood samples were collected for surveillance or clinical events. Clinicians were blinded to the results of DF cfDNA. RESULTS: A total of 835 samples from 269 subjects (57% pediatric) were included for this analysis, including 28 samples associated with CR were analyzed. Median DF cfDNA was 0.43 (IQR 0.15, 1.36)% for CR and 0.10 (IQR 0.07, 0.16)% for healthy controls (p < .0001). At cutoff value of 0.13%, the area under curve (AUC) was 0.82, sensitivity of 0.86, specificity of 0.67, and negative predictive value of 0.99. There was serial decline in DF cfDNA post-therapy, however, those with cardiovascular events (cardiac arrest, need for mechanical support or death) showed significantly higher levels of DF cfDNA on Day 0 (2.11 vs 0.31%) and Day 14 (0.51 vs 0.22%) compared to those who did not have such an event (p < .0001). CONCLUSION: DF cfDNA has excellent agreement with clinical rejection and, importantly, serial measurement of DF cfDNA predict clinically significant outcomes post treatment for rejection in these patients.