Current Topics and Controversies in Pediatric Heart Transplantation: Proceedings of the Pediatric Heart Transplantation Summit 2017

Biomarkers from subcutaneous engineered tissues predict acute rejection of organ allografts

Invasive graft biopsies assess the efficacy of immunosuppression through lagging indicators of transplant rejection. We report on a microporous scaffold implant as a minimally invasive immunological niche to assay rejection before graft injury. Adoptive transfer of T cells into Rag2-/- mice with mismatched allografts induced acute cellular allograft rejection (ACAR), with subsequent validation in wild-type animals. Following murine heart or skin transplantation, scaffold implants accumulate predominantly innate immune cells. The scaffold enables frequent biopsy, and gene expression analyses identified biomarkers of ACAR before clinical signs of graft injury. This gene signature distinguishes ACAR and immunodeficient respiratory infection before injury onset, indicating the specificity of the biomarkers to differentiate ACAR from other inflammatory insult. Overall, this implantable scaffold enables remote evaluation of the early risk of rejection, which could potentially be used to reduce the frequency of routine graft biopsy, reduce toxicities by personalizing immunosuppression, and prolong transplant life.

Pulmonary Artery Banding for Dilated Cardiomyopathy in Children: Returning to the Bench from Bedside

Current treatment paradigms for end-stage dilated cardiomyopathy (DCM) in children include heart transplantation and mechanical support devices. However, waitlist mortality, shortage of smaller donors, time-limited durability of grafts, and thrombo-hemorrhagic events affect long-term outcomes. Moreover, both these options are noncurative and cannot preserve the native heart function. Pulmonary artery banding (PAB) has been reinvented as a possible “regenerative surgery” to retrain the decompensated left ventricle in children with DCM. The rationale is to promote positive ventricular–ventricular interactions that result in recovery of left ventricular function in one out of two children, allowing transplantation delisting. Although promising, global experience with this technique is still limited, and several surgical centers are reluctant to adopt PAB since its exact biological bases remain unknown. In the present review, we summarize the clinical, functional, and molecular known and supposed working mechanisms of PAB in children with DCM. From its proven efficacy in the clinical setting, we described the macroscopic geometrical and functional changes in biventricular performance promoted by PAB. We finally speculated on the possible underlying molecular pathways recruited by PAB. An evidence-based explanation of the working mechanisms of PAB is still awaited to support wider adoption of this surgical option for pediatric heart failure.

Pediatric heart transplantation in infants and small children under 3 years of age: Single center experience - "Early and long-term results"

OBJECTIVES

We analyzed the early and long-term survival after ABO-compatible heart transplantation in children under 3 years of age from 1991 to 2021 at our center. This retrospective and descriptive study aimed to identify serious adverse events associated with mortality after pediatric heart transplantation.

PATIENTS AND METHODS

46 patients with congenital heart failure (37%) in end-stage heart failure have undergone a pediatric heart transplantation. Primary outcome of interest was survival at follow-up time.

RESULTS

Median (IQR) follow-up time (y), age (y), body-weight (kg) and BMI (kg/cm²) were 13.2 (5.7-19.5), 0.9 (0.2-2.0), 6.8 (4.3-10.0) and 14.2 (12.3-15.7). Twenty-four (52%) patients were male. 15 patients (33%) had a single ventricle physiology. At 30- days survival rate was 94 ± 4%. Survival rate at 1, 5, 10 and 15 years post HTx was 87 ± 5%, 84 ± 6%, 79 ± 6% and 63 ± 8%. One child underwent re-transplantation after 4 years, and another one after 11 years - in both cases due to graft failure. Higher early mortality in patients under 3 months of age and in patients with single ventricle physiology. Transplant free survival at 15 years was in children with cardiomyopathy better (71 ± 10%) than in those with congenital heart disease (50 ± 13%). One or more previous heart surgeries prior to HTx (n = 21) were associated to more mortality.

CONCLUSION

Pediatric heart transplantation has acceptable long-term results and is still the best therapeutic option in children with end-stage cardiac failure. Underlying anomalies and single ventricle physiology, age below 3 months had a significant impact on survival.

Surgical strategies for the management of end-stage heart failure in infants and children: A 15-year experience with a patient-tailored approach

End‐stage heart failure (ESHF) in pediatric age is an ongoing challenge. Heart transplantation is the final option, but its long‐term outcomes are still suboptimal in children. An alternative patient‐tailored surgical protocol to manage ESHF in children is described. Retrospective, single‐center analysis of pediatric patients admitted to our institution between April 2004 and February 2021 for ESHF. Our current protocol is as follows: (a) Patients <1 year with isolated left ventricular dysfunction due to dilated cardiomyopathy underwent pulmonary artery banding (PAB). (b) Patients <10 years and <20 kg, who did not meet previous criteria were managed with Berlin Heart EXCOR. (c) Patients >10 years or >20 kg, underwent placement of intracorporeal Heartware. Primary outcomes were survival, transplant incidence, and postoperative adverse events. A total of 24 patients (mean age 5.3 ± 5.9 years) underwent 26 procedures: PAB in 6 patients, Berlin Heart in 11, and Heartware in 7. Two patients shifted from PAB to Berlin Heart. Overall survival at 1‐year follow‐up and 5‐year follow‐up was 78.7% (95%CI = 62%‐95.4%) and 74.1% (95%CI = 56.1%‐92.1%), respectively. Berlin Heart was adopted in higher‐risk settings showing inferior outcomes, whereas a PAB enabled 67% of patients to avoid transplantation, with no mortality. An integrated, patient‐tailored surgical strategy, comprehensive of PAB and different types of ventricular assist devices, can provide satisfactory medium‐term results for bridging to transplant or recovery. The early postoperative period is critical and requires strict clinical vigilance. Selected infants can benefit from PAB that has demonstrated to be a safe bridge to recovery.

A 4D flow MRI evaluation of the impact of shear-dependent fluid viscosity on in vitro Fontan circulation flow

The Fontan procedure for univentricular heart defects creates a nonphysiologic circulation where systemic venous blood drains directly into the pulmonary arteries, leading to multiorgan dysfunction secondary to chronic low-shear nonpulsatile pulmonary blood flow and central venous hypertension. Although blood viscosity increases exponentially in this low-shear environment, the role of shear-dependent ("non-Newtonian") blood viscosity in this pathophysiology is unclear. We studied three-dimensional (3D)-printed Fontan models in an in vitro flow loop with a Philips 3-T magnetic resonance imaging (MRI) scanner. A 4D flow phase-contrast sequence was used to acquire a time-varying 3D velocity field for each experimental condition. On the basis of blood viscosity of a cohort of patients who had undergone the Fontan procedure, it was decided to use 0.04% xanthan gum as a non-Newtonian blood analog; 45% glycerol was used as a Newtonian control fluid. MRI data were analyzed using GTFlow and MATLAB software. The primary outcome, power loss, was significantly higher with the Newtonian fluid [14.8 (13.3, 16.4) vs. 8.1 (6.4, 9.8)%, medians with 95% confidence interval, P < 0.0001]. The Newtonian fluid also demonstrated marginally higher right pulmonary artery flow, marginally lower shear stress, and a trend toward higher caval flow mixing. Outcomes were modulated by Fontan model complexity, cardiac output, and caval flow ratio. Vortexes, helical flow, and stagnant flow were more prevalent with the non-Newtonian fluid. Our data demonstrate that shear-dependent viscosity significantly alters qualitative flow patterns, power loss, pulmonary flow distribution, shear stress, and caval flow mixing in synthetic models of the Fontan circulation. Potential clinical implications include effects on exercise capacity, ventilation-perfusion matching, risk of pulmonary arteriovenous malformations, and risk of thromboembolism.NEW & NOTEWORTHY Although blood viscosity increases exponentially in low-shear environments, the role of shear-dependent ("non-Newtonian") blood viscosity in the pathophysiology of the low-shear Fontan circulation is unclear. We demonstrate that shear-dependent viscosity significantly alters qualitative flow patterns, power loss, pulmonary flow distribution, shear stress, and caval flow mixing in synthetic models of the Fontan circulation. Potential clinical implications include effects on exercise capacity, ventilation-perfusion matching, risk of pulmonary arteriovenous malformations, and risk of thromboembolism.