Abstract

Purpose
We previously identified a population of clonally expanded, cytotoxic CD8+ T cells in the airways of transplant recipients with chronic lung allograft dysfunction. Importantly, these cells upregulated KLRK1, the gene for the co-stimulatory peptide, NKG2D. NKG2D is a co-receptor found on both natural killer (NK) cells and cytotoxic CD8+ T cells. We set out to determine the impact of systemic NKG2D blockade on chronic rejection using a single antigen-mismatch murine model of orthotopic lung transplantation.

Methods
C57Bl/6 (B6) mice underwent orthotopic single left-lung transplantation; donor lungs came from C57BL/6-Mcph1^{Tg(HLA-A2.1)1Enge}/J (HLA) mice. Either 150 micrograms of NKG2D blockade (clone CX5) or 100 microliters of phosphate-buffered saline was administered intraperitoneally on day 14 and 21 post-transplantation. On day 28, pulmonary function testing was performed on all mice followed by either obtaining single cell suspension after mechanical and enzymatic digestion for flow cytometry analysis, or formalin-fixation and paraffin embedding for analysis by trichrome staining and immunofluorescence imaging.

Results
We found a significant decrease in elastance and increase in inspiratory capacity in mice treatment with systemic NKG2D blockade (Fig A). Peribronchiolar fibrosis, identified via connective tissue deposition on trichrome staining, was also reduced following NKG2D blockade. Immunofluorescence images of lung allografts with CD8a and NK1.1 staining were quantitatively analyzed. Mice treated with NKG2D blockade had similar quantity of NK cells but significantly reduced quantity of allograft-infiltrating CD8+ T cells (Fig B,C).

Conclusion
Systemic administration of NKG2D blockade contributes to reduce airway remodeling and diminished CD8+ T cell accumulation in allografts following orthotropic lung transplantation. Further study is needed to explore the impact of NKG2D blockade on both NK and CD8+ T cell responses.

Abstract

Purpose
Chronic lung allograft dysfunction (CLAD) represents the primary cause of late-stage mortality in lung transplant recipients beyond the first post-transplant year. In this study, we examined the relationship between CLAD progression and the development of leukocyte-mediated transplant arteriosclerosis (TA) utilizing a humanized mouse model to explore underlying immunological mechanisms.

Methods
The pericardiophrenic artery was obtained from surplus donor lung tissue (n = 31) transplanted in our clinical program between 2012 and 2020. These arteries were implanted into the abdominal aorta of immune-deficient mice. Outcomes were compared between patients who developed CLAD (PBMC CLAD+ group) and those who did not (PBMC CLAD- group), with a follow-up period of 71 ± 26 months. Allogeneic human peripheral blood mononuclear cells (PBMCs) were collected from the respective recipients one day after lung transplantation. TA in mice was assessed 28 days post-implantation using histology.

Results
During the study period, 31 lung transplant recipients were included. Of these, 11 patients (35.4%) developed CLAD at 67 ± 30 months post-transplant, while the remaining 20 patients in the PBMC CLAD- group (64.5%) did not develop CLAD within 43 ± 30 months. In the mouse experiments, the PBMC CLAD+ group exhibited significantly more severe TA than the PBMC CLAD- group (41.9% ± 12% vs. 15.9% ± 4% intimal thickening, P = .0089). Mortality within 8 years was 41.94% (13 patients).

Conclusion
The findings indicate that lung transplant recipients who eventually develop CLAD possess peripheral leukocytes with a proinflammatory phenotype at the time of transplantation. When introduced into a humanized mouse model, these leukocytes contribute to the development of transplant arteriosclerosis. This suggests that leukocyte-mediated inflammation may play a critical role in the progression of CLAD

Abstract

Purpose
Optimal immunosuppression after transplantation (Tx) aims to balance graft protection and avoid severe adverse effects. Standard protocols often don’t consider individual patient factors, like immune maturity. Our study investigated the impact of induction therapies—polyclonal depleting anti-thymocyte globulin (ATG) and transient blocking IL2 receptor antagonists (IL2RA, Basiliximab)— on lymphocyte composition, focusing on T and B cells with known or presumed regulatory capacity.

Methods
Children listed for heart, lung and kidney solid organ Tx enrolled in a national multicenter collaboration (CNTRP-POSITIVE) were included. Peripheral blood mononuclear cells (PBMCs) were isolated from pre-Tx, 3- and 12-month post-Tx blood samples. The adaptive immune system was characterized by flow cytometric deep phenotyping.

Results
Samples were analyzed from 115 children pre-Tx, 89 at 3 months, and 69 at 12 months. Heart (n=28) and liver (n=36) recipients were younger than kidney (n=51) recipients (median ages 1.6, 1.7, 10.3 years, respectively). IL2RA was used in 14%, 43%, and 46% and ATG in 39%, 3%, and 46% of heart, liver, and kidney recipients, respectively. All patients received steroids, and those without other induction served as a control group. Compared to pre-Tx samples, ATG use was associated with lower CD4+ T cell counts persistent to 12 months post-Tx, unlike IL2RA and controls. CD19+ B cell counts decreased after ATG and IL2RA treatment, persisting in 12 months samples, which was not observed in controls. No significant difference from baseline to 3 and 12 months post-Tx, by induction therapy, was observed for regulatory T cells (CD25hi, CD127low), which showed a transient increase early post-Tx, transitional B cells (CD24hi, CD38hi), regulatory B cells (CD5+, CD1dhi), and memory B cells. Effects on T cells were most pronounced in heart Tx children, while effects on B cells were more pronounced in infants and liver Tx recipients.

Conclusion
ATG induction resulted in a sustained reduction of T and B lymphocytes. IL2RA did not reduce T cells but surprisingly depleted B cells. Populations with regulatory capacity were not significantly affected by induction therapy. Potential long-term effects of lymphocyte subpopulation depletion must be considered when choosing an induction approach, especially in young and heart Tx children.

Abstract

Purpose
We identified interferon (IFN)-stimulated gene expressing TRAIL+CXCL10+ alveolar macrophages (ISG AM) in the bronchoalveolar lavage of lung transplant (LT) recipients with acute lung allograft dysfunction (ALAD) and lung tissue from patients with chronic lung allograft dysfunction (CLAD). Here, we tested the hypothesis that ISG AMs could be induced in human precision cut lung slices (PCLS) after treatment with IFN and LPS, enabling further study of their function in a lung microenvironment.

Methods
Tissue samples from four volume reduced and three rejected donor lungs were cut into 2.5cm² pieces. Tissue was insufflated with low melting point agarose. After solidification, the tissue was cut into 400um-thick slices on a Leica VT1200 vibratome. PCLS were cultured in media only (control), IFNg 50ng/mL, IFNb 50ng/mL or LPS 50-75ng/mL. After 7 days, PCLS were stained for confocal microscopy or underwent digestion and staining for flow cytometry.

Results
Light microscopy showed preserved lung structure and alveolar cells in PCLS (Fig a). Confocal microscopy revealed TRAIL+ CD163+ AMs in PCLS treated with 50 ng/mL LPS which were rare in control PCLS (Fig b). Among live cells in PCLS digests, there were 22.8±11.9% HLA-DR+ CD163+ AMs (Fig c). The percentage of TRAIL+CXCL10+ ISG AMs was 0.8±0.9% in control and 13.6±10.4% in IFNg-treated (50ng/mL) PCLS at day 7 (p=0.01, Fig c-e). The percentage of TRAIL-CXCL10+ AMs was 4.7±2.6% and 22.7±11.8% in control and IFNg-treated PCLS, respectively (p=0.01, Fig c-e). TRAIL+EPCAM+ epithelial cells increased by 8% (p=0.11) in IFNg PCLS (not shown). Minimal ISG induction was seen with IFNb (not shown).

Conclusion
Treatment of PCLS with IFNg resulted in the induction of TRAIL+CXCL10+ ISG AM seen in ALAD, as well as TRAIL-CXCL10+ AMs, which may be an ISG precursor. PCLS is a promising technique for studying AMs in a pulmonary microenvironment. Further experiments exploring ISG AM function, cell interactions, and spatial distribution in donor and explanted CLAD lungs are underway.

Abstract

Purpose
Though tolerance to kidney allografts can be consistently achieved using a mixed chimerism model, heart and lung allografts are much more resistant to tolerance induction. One possible reason may be that these allografts are more susceptible to a trained innate immune system. Lipoprotein-based nanobiologics loaded with a mammalian target of rapamycin inhibiting prodrug (mTOR inhibiting nanobiologics, mTORi-NBs) are designed to inhibit trained immunity in the hematopoietic organs and promote graft infiltrating regulatory macrophages that provide a favorable local immunologic milieu for tolerance induction. In this study, we evaluate the ability of mTORi-NBs to promote tolerance in tolerance-resistant NHP transplant models.

Methods
Four NHPs underwent heterotopic heart and delayed donor bone marrow transplantation (DBMT) (Group A) and two underwent orthotopic lung transplantation with simultaneous DBMT (Group B). Group A recipients (n=4) were maintained on standard immunosuppression after heart transplantation and later conditioned with 1.5Gy total body irradiation (TBI), 7Gy thymic irradiation (TI), venetoclax, Thymoglobulin®, anti-IL6R mAb, and anti-CD40L mAb. Group B recipients (n=2) were transplanted with an allolung and conditioned with 3Gy TBI, 7Gy TI, Thymoglobulin®, anti-CD40L mAb, and anti-IL6R mAb. Both groups were treated with cyclosporine for 28 days after DBMT, and both groups received mTORi-NBs at the time of solid organ transplant and DBMT. No further immunosuppression was given after the completion of their conditioning regimens.

Results
In group A, two recipients were lost to cytomegalovirus and post-transplant lymphoproliferative disorder, respectively. One recipient is still under immunosuppression, and one recipient is now nearly 300 days post-DBMT with no signs of rejection. In group B, one recipient is still under immunosuppression but the first recipient is now nearly 50 days post-DBMT with no signs of rejection. All recipients developed robust multilineage chimerism.

Conclusion
Preliminary studies suggest that mTORi-NBs, along with a clinically relevant conditioning protocol, can prolong the survival of tolerance-resistant heart and lung allografts in NHPs undergoing mixed chimerism conditioning.

Abstract

Purpose
The innate allogeneic immune response in lung transplantation contributes to both the development of primary graft dysfunction and the activation of the adaptive immune response, which can lead to rejection. Therefore, effectively targeting this innate immune response is crucial for better outcomes.

The current perioperative immunomodulatory treatment includes a corticosteroid injection administered to the recipient during surgery. However, the immunological benefit of extending this treatment to the donor, a practice that is not widely adopted, remains unknown.

Methods
To analyze the immune parameters affected by donor preconditioning, we used a porcine cross-circulation platform, consisting of an ex vivo donor lung (D) connected to the circulation of a recipient pig (R) whose leukocytes were fluorescently labeled. We compared 3 groups of pig pairs: i) untreated D and R, ii) treated R only, iii) treated D and R. Tissue samples from the ex vivo graft were collected during the first ten hours of reperfusion. The immune cell composition was analyzed by flow cytometry and immunohistochemistry. Gene expression was evaluated by RT-PCR.

Results
Recipient treatment, whether or not combined with donor treatment, similarly reduced the activation profile of recruited CD14pos and CD16pos monocyte subsets. Interestingly, we found that donor’s preconditioning reduced the representation of both donor- and recipient-derived CD3pos T cells in the graft and improved the anti-inflammatory profile of alveolar macrophages, at least during the first 10 hours of donor/recipient interaction. Donor preconditioning was associated with decreased expression of genes encoding T cell-attracting chemokines (CXCL9, CXCL10, and CXCL11) by alveolar macrophages.

Conclusion
These results indicate that preconditioning the donor lung with corticosteroids improves the early immunological status of lung grafts during LT and could have a positive impact on clinical outcomes.

Abstract

Purpose
Right ventricular failure (RVF) is a common complication after left ventricular assist devices (LVADs) and is associated with increased morbidity and mortality. Yet the cellular and molecular mechanisms underlying this condition remain poorly understood. This study aims to analyze the gene expression profile in LVAD patients with late-onset RVF.

Methods
We performed deep mRNA sequencing on the frozen right ventricle (RV) tissue from LVAD patients who underwent heart transplantation. Late-onset RVF, defined as occurring more than 30 days post-LVAD, followed the Mechanical Circulatory Support Academic Research Consortium criteria. Differential expression and Gene Set Enrichment Analyses (GSEA) were conducted, with a false discovery rate (FDR) threshold of < 0.05 for significance.

Results
We included 23 patients (median age 54 years [IQR 36, 61]; 3 women; 19 White; 7 with ischemic cardiomyopathy), of whom 7 had late-onset RVF. The top 5 genes significantly differentially expressed in late-onset RVF included activity-regulated cytoskeleton-associated protein (ARC), chloride intracellular channel 1 (CLIC1), C-C motif chemokine ligand 2 (CCL2), C-X-C motif chemokine ligand 3 (CXCL3), and low-density lipoprotein receptor (LDLR) (Fig A). GSEA showed upregulation of genes related to mitochondrial translation and localization, and downregulation of inflammatory genes, including those involved in humoral immune response and neutrophil migration (Fig B), in late-onset RVF compared to non-RVF counterparts.

Conclusion
This cross-sectional study identified unique gene expression in LVAD patients with late-onset RVF. Most differentially expressed genes were downregulated, except CLIC1. Counterintuitively, inflammation-related pathways were downregulated, while pathways related to mitochondrial localization were upregulated in patients with late-onset RVF. Further studies are needed to understand the molecular mechanisms of late-onset RVF.

Abstract

Purpose
The role of cell-free mitochondrial DNA (cf-mtDNA) in lung transplantation(LTx) is emerging as a critical focus of research, particularly regarding its potential to predict and monitor post-transplant complications such as chronic lung allograft dysfunction (CLAD) and acute rejection. This study aims to investigate the relationship between cf-mtDNA levels from brain-dead donors (DBD), controlled donors after circulatory death (cDCD), and the presence of donor-derived cf-mtDNA (dd-cf-mtDNA) with the incidence of primary graft dysfunction (PGD) following LTx.

Methods
This is a prospective, multicenter study conducted across four Spanish transplant centers. Blood samples were collected from donors at two time points: before (E0) and after organ retrieval (E1). Samples from recipients were taken before implantation (R-1), after graft reperfusion (R0), and 72 hours post-transplant (R72). Cf-mtDNA levels were quantified in serum by real-time qPCR. The mtDNA hypervariable region was deep-sequenced and the percentages of donor and recipient mtDNA were determined.at R0 and R72. The incidence of PGD, including grade 3 PGD at 72 hours (PGD3-72h), was analysed in relation to cf-mtDNA and dd-cf-mtDNA concentrations.

Results
The study included 40 DBD and 39 cDCD donors and their corresponding recipients. Demographic and procedural characteristics were comparable between the groups. No significant differences were observed in cf-mtDNA levels between DBD and cDCD at any time point; however, cf-mtDNA levels were significantly higher in cDCD recipients at R72 (13.35 vs 22.74, p=0.029). Among donors whose recipients developed PGD, cf-mtDNA levels were elevated at E0 (17.81 vs 27.95, p=0.010). Furthermore, recipients who developed PGD showed a significant increase in %dd-cf-mtDNA at R0.

Conclusion
cDCD donors did not exhibit increased cf-mtDNA levels prior to organ retrieval, but cDCD recipients demonstrated elevated cf-mtDNA levels at 72 hours post-transplant. Higher cf-mtDNA levels in donors were associated with the development of PGD in their recipients. The presence of dd-cf-mtDNA in recipients post-LTx could serve as a specific biomarker for graft damage and PGD, indicating its potential utility in monitoring transplant outcomes.

Abstract

Purpose
Acute ischemic stroke (AIS) is a devastating complication in advanced heart failure (AHF) patients with left ventricular assist devices (LVADs). We aimed to identify prognostic biomarkers of AIS risk in LVAD patients using untargeted plasma proteomics.

Methods
From an existing cohort of LVAD patients, we studied 8 patients who developed AIS within 90 days of implantation and 17 patients without AIS during that time. Untargeted plasma proteomics using LC-MS/MS was conducted on day 0 (pre-LVAD) and day 7 (post-LVAD). Intensity-based absolute quantitation (iBAQ) data were analyzed for differential enrichment of proteins, followed by principal component analysis (PCA) and network analysis.

Results
LC-MS identified 5,379 proteins, with 333 present in enough samples for imputation (Fig.A,B). Acute-phase reactants like SAA1 and CRP were upregulated post-LVAD, along with osteopontin (SPP1) (Fig.C). AIS was associated with the upregulation of myoglobin, hemoglobin, and SPP1, as well as the downregulation of serglycin (SGN) (Fig.D,E). In PCA, PC2 was correlated with AIS (p<0.01), and PC1 trended toward correlation (p=0.05) (Fig.F). PC1 was correlated with histones, ubiquitination, and peptidase regulation (Fig. G). PC2 was correlated with complement activation, iron ion transport, and SPP1 (Fig.H).

Conclusion
Plasma proteins seen as early as one week after LVAD implantation can predict stroke within the next 90 days. The post-LVAD proteome is enriched in inflammatory proteins such as complement and iron transporters. There is also an increase in SPP1, which is correlated with AIS. This exploratory study lays the groundwork for future validation studies for risk scores to predict post-LVAD stroke.

Abstract

Purpose
Inflammatory responses and cell death signals are commonly upregulated following reperfusion in ex vivo lung perfusion (EVLP) and human lung transplants. However, the specific type of programmed cell death (PCD) in across donor types, their interrelationships with inflammation, and their association with clinical outcome remain unclear. This study aimed to explore the transcriptomic signature of PCD types in donation after brain death (DBD) and donation after circulatory death (DCD) lungs, examining their changes after EVLP and potential clinical implications.

Methods
Transcriptomic analyses were performed on tissue biopsies collected pre- and post-EVLP from 49 pairs of DBD and 39 pairs of DCD donor lungs. Gene set enrichment analysis (GSEA) and single-sample GSEA (ssGSEA) were used to assess the activation of PCD pathways- including apoptosis, necroptosis, pyroptosis, ferroptosis, autophagy, and cuproptosis- and their interrelationships, and links with inflammatory pathways. The association between PCD pathways, donor characteristics and recipient outcomes were further analyzed.

Results
Prior to EVLP, DBD lungs exhibited higher levels of apoptosis, ferroptosis, and inflammatory pathways enrichment compared to DCD lungs. In both DBD and DCD lungs, the expression of apoptosis, necroptosis and pyroptosis genes were highly correlated with each other and with inflammation both pre- and post-EVLP, supporting the concept of PANoptosis. Moreover, the ferroptosis gene set became more strongly correlated with these three PCD pathways post-EVLP. The activation of PCD gene sets in DBD lungs before EVLP was associated with donor age, whereas smoking history was associated with PCD in DBD and DCD lungs post-EVLP. Notably, the levels of PCD in DCD donor lungs before EVLP were associated with the incidence of primary graft dysfunction in recipients.

Conclusion
This study provides insight into the differences of PCD types in DBD and DCD donor lungs, which are related to clinical outcomes. During EVLP, PANoptosis-related genes are co-regulated and may serve as a pre-condition for reducing reperfusion-induced injury. These findings underscore the potential for tailored EVLP strategies targeting donor type specific PCD to improve donor lung quality and enhance transplant outcomes.

Abstract

Purpose
Bronchial anastomotic complications after lung transplantation are plagued by several perioperative challenges including stenosis, necrosis, and dehiscence. The most common cause of bronchial anastomosis complications is microvascular disruption, resulting in hypoxia and ischemia. This causes the generation of inflammatory and profibrotic cytokines, which lead to delayed wound healing and additional anastomotic complications hampering patient recovery. The TNF-stimulated gene 6 protein (TSG-6) is secreted by stem cells and fibroblasts in response to inflammation and injury. It plays a major role in both suppressing inflammation and fibrosis. Despite recent studies on the role of TSG-6 in wound healing and tissue repair, little is known about its role in bronchial anastomotic complications. Studies have shown that IL-10/stem cell therapy enhances TSG-6 and promotes graft repair. Since IL-10/stem cell therapies face various challenges, a strong scientific rationale exists to investigate TSG-6's regulatory role in graft repair.

Methods
Here, we investigated the effects of TSG-6 mediated immunosuppression on graft epithelial and microvascular repair in a mouse model of orthotopic tracheal transplantation, which mimics clinical bronchial anastomosis. An effective immunosuppression was achieved by administering 5 μg of recombinant TSG-6/transplant intranasally on days -1, 2, 5, and 8 post-transplantation. All treated and control groups were monitored for four weeks for immunotolerance, microvascular flow, fibrosis, and epithelial repair.

Results
Preliminary results show that non-rejected syngrafts have higher TSG-6/FOXP3/IL-10 levels than rejected allografts. TSG-6 mediated immunosuppression downregulated total CD4⁺ T cells and M1 macrophages while upregulating Tregs and M2 macrophages, and preserved microvascular blood flow as compared to untreated allografts. In addition, TSG-6 mediated immunosuppression facilitates epithelial repair while reducing collagen deposition at day 28.

Conclusion
We conclude that TSG-6 administration effectively fosters immune tolerance and facilitates tracheal microvascular and epithelial repair while reducing tracheal narrowing and subepithelial fibrosis, suggesting that it could be an effective therapeutic option for treating bronchial anastomotic complications.

Abstract

Purpose
Targeting cell death might be a promising strategy during ex vivo lung perfusion (EVLP) to reduce ischemia-reperfusion injury (IRI) prior to transplantation. Ferroptosis is an iron-dependent type of regulated cell death characterized by excessive phospholipid membrane peroxidation. We hypothesized that blocking ferroptosis with a third generation ferroptosis inhibitor (UAMC-3203) during EVLP would reduce lung IRI in a model of prolonged warm ischemia.

Methods
Porcine donor lungs were divided in 3 groups. In group 1 (VEH; n=5) and 2 (UAMC-3203; n=5), the grafts underwent 3 hours of warm ischemia in the donor animal. In group 3 (CON; n=5), lungs were cold flushed without warm ischemia. All lungs were mounted on our EVLP system for 8 hours (closed atrium, whole blood added to induce ferroptosis). Vehicle (NaCl 0,9%) or UAMC-3203 (10mg/kg), was added to the perfusate in VEH and UAMC-3203, respectively, while CON received no treatment. Assessment was based on physiological parameters, wet-to-dry ratio (W/D; gold standard for lung injury during EVLP), computed tomography (CT) measured density, cytokine profile and histology. Statistics: Mann-Whitney U, two-way ANOVA.

Results
3 hours of warm ischemia induced significant lung injury in VEH compared to CON (p=0.008; Fig 1A). Ferroptosis inhibition resulted in significantly reduced edema formation with lower W/D in UAMC-3203 compared to VEH (p=0.03; Fig 1A). Physiological variables did not differ between VEH and UAMC-3203 (Fig 1B-D). The mechanisms will be further analyzed on molecular biology and histology.

Conclusion
We demonstrated that ferroptosis inhibition is a promising tool to reduce IRI during EVLP for lungs with prolonged warm ischemic intervals. As ferroptosis is an ancient cellular mechanism, preserved in many organisms and organ systems, UAMC-3203 may have gre

Abstract

Purpose
Retrograde cardioplegia via current catheters is known to frequently provide inadequate protection for the right heart. We aimed to develop a novel retrograde catheter design to better deliver cardioplegia to both sides of the heart.

Methods
We hypothesize that the inadequacy of right-sided protection using current cannulas is caused by perfusion only distal to the occlusive balloon, which may obstruct cardiac vein branches and impair retrograde perfusion (Fig 1A). We developed two novel catheter designs to address this problem. Using ex vivo hearts, perfusion to the right heart was qualitatively assessed using an infrared thermal camera and compared between cannulas.

Results
Two novel retrograde cardioplegia cannulas were tested. The first design consists of fenestrations in a self-inflating balloon so that if any fenestration aligns with a branch vein it will be perfused (Fig 1B). The second consists of two balloons - the distal balloon is placed in the great cardiac vein and a more proximal balloon is secured directly outside and abutting the ostium (Fig 1C). In addition to the distal perfusion port, there are perfusion ports between the balloons to ensure perfusion to the middle and small cardiac veins. Qualitative assessment of the perfusion distribution of each cannula design suggests the new catheters achieve increased perfusion to the right heart (Fig 2).

Conclusion
These novel retrograde cardioplegia catheters may better perfuse the right heart. Further study is warranted to substantiate these results and determine if there is a clinical effect of increased direct retrograde cardioplegia delivery.

Abstract

Purpose
Static cold storage (SCS) has been a mainstay of heart transplantation (HTx), however the temperature variation during organ preservation and transplantation is unknown and underexplored. The purpose of this study was to elucidate the temperature distribution within the organ during each stage of HTx to assess thermal heterogeneity and time for the organ to cool and warm.

Methods
We used high-fidelity in silico Multiphysics biothermal modeling of temperature evolution within an anatomically accurate cardiac model that included key structures such as chambers, interventricular septum and variations in thicknesses for the left and right cardiac walls. Time-varying temperature evolution was modeled in COMSOL Multiphysics using physiological thermal properties of cardiac tissue including thermal conductivity, density and specific heat capacity. The HTx process was modeled in five stages including cardioplegic cooling, back table prep, SCS preservation and transport and implantation into recipient. The model was validated using published experimental data, and rigorous quantitative analyses was performed using detailed thermal distributions and virtual probes.

Results
For each stage, the temperature variation is highly heterogeneous, with the left heart taking longer to cool down and warm up, compared to the right heart due to increased tissue thickness. During cardioplegic cooling, the heart experienced a rapid cool down to below 10° C within 15 minutes with a maximum cooling rate of 5° C/min. Temperatures dropped below 2° C during SCS icebox transport within 1 hour and below 0.4° C beyond 4 hours, increasing chances of cold injury. During implantation, the heart warms up very quickly to over 30° C in ~10 minutes, with the right heart warming approximately 2x faster compared to the left heart, up to a rate of ~ 4° C/min.

Conclusion
Our assessments indicate that the heart undergoes a roller-coaster like temperature variation during its journey from the donor to the recipient. This study quantitatively answered the questions of (1) how long does it take for the heart to warm/cool and (2) if the temperature distribution was uniform within the heart. The rapid and heterogeneous temperature changes throughout the heart and extended duration of sub-2° C during SCS transport have implications for frostbite injury and viability, necessitating detailed in-depth studies.

Abstract

Purpose
Stroke is a critical complication that affects patient quality of life and survival, especially in children with ventricular assist devices (VAD). The Advanced Cardiac Therapies Improving Outcomes Network (ACTION) conducts monthly discussions on stroke events to establish a standardized approach to addressing adverse events.

Methods
Multi-institutional meetings involve cardiologists, neurologists, radiologists, ICU specialists, surgeons, nurses, and VAD coordinators. Every month, all ACTION sites enter data on pediatric VAD patients into the registry. Centers reporting stroke or neurological events are asked to provide follow-up data via standardized presentations. De-identified stroke data are reviewed to identify structural or personnel-related issues, with findings driving interventions to prevent future strokes.

Results
Between 2021 and 2023, 26 sites reported stroke events at monthly telehealth meetings, with 59 sites represented worldwide. On average, 33 participants attended the 50 presentations. Along with the data in Figure 1, the discussion identified 7 standard VAD management deviations, 18 cases that did not relate stroke events to anticoagulation, blood pressure, or communication, and 35 reflections on practices to reduce the risk of stroke. Providers attributed these events to VAD implantation timing and device availability in 12 cases, infection, inflammation, antiplatelet and steroid use in 9 cases, periprocedural antithrombosis management in 4 cases, and known intracardiac thrombosis risk in 2 cases.

Conclusion
The cross-disciplinary data discussions aim to improve pediatric stroke care globally. The findings offer valuable insights for educating medical centers and guiding future clinical trials and quality improvement initiatives. The program holds the potential to revolutionize stroke care worldwide by fostering a culture of continuous learning, data sharing, and collaboration to enhance patient outcomes and management practices.