The outflow tract (OFT) of the heart carries blood away from the heart into the great arteries. During embryogenesis, the OFT divides to form the aorta and pulmonary trunk, creating the double circulation present in mammals. Defects in this area account for one-third of all congenital heart defect cases. Here, we present comprehensive transcriptomic data on the developing OFT at two distinct time points (embryonic and fetal) and its adult derivatives, the aortic valves, and use spatial transcriptomics to define the distribution of cell populations. We uncover that distinctive embryonic signatures persist in adult cells and can be used as labels to retrospectively attribute relationships between cells separated by a large timescale. Single-cell regulatory network inference identifies GATA6, a transcription factor linked to common arterial trunk and bicuspid aortic valve, as a key regulator of valve precursor cells. Its downstream network reveals candidate drivers of human cardiac defects and illuminates the molecular mechanisms of both normal and pathological valve development. Our findings define the cellular and molecular signatures of the human OFT and its distinct cell lineages, which is critical for understanding congenital heart defects and developing cardiac tissue for regenerative medicine.

Heart transplantation remains the gold standard treatment for selected patients with end-stage heart failure despite the best medical, interventional, and surgical treatment. However, the number of suitable hearts donated for transplantation remains far fewer than the number of patients who could benefit from this treatment. Consequently, many patients endure prolonged waiting time, either at home or in the hospital, and up to one-fifth die or become unsuitable for transplantation before a donor heart becomes available in the UK. Recipients of heart transplants require lifelong immunosuppression and remain vulnerable to complications, including rejection, infection, malignancy, and chronic allograft vasculopathy. Substantial research efforts have therefore focused on expanding the donor pool, improving donor heart preservation, reducing early graft dysfunction, and optimizing post-transplant care. This review outlines the contemporary landscape of heart transplantation, spanning donor and recipient selection through to long-term post-transplant management. It also highlights recent advances, including the use of donation after circulatory death hearts, ex situ heart preservation, and mechanical circulatory support.

Ex situ heart perfusion (ESHP) was first developed in the 19th century by the German physician Oskar Langendorff. In recent years, ESHP has been critical to the development of donation after circulatory determination of death (DCD) programmes around the globe. ESHP has potential uses that extend far beyond transplantation. Here, we argue that ESHP, and more broadly all ex situ organ perfusion, should be utilised to perform first-in-human studies using turned down donor hearts and explanted recipient hearts from transplantation. This model would enable significantly earlier testing of novel therapeutics in human hearts, with minimal risk to patients. Widespread adoption of this model could streamline drug discovery pipelines, by enabling inefficacious therapeutics to be abandoned earlier in the drug development process. This model is particularly attractive given the high proportion of medicines that fail in stage II and stage III clinical trials due to a lack of efficacy. Development of this model will be dependent on prolonging ex situ perfusion times. Collaboration between industry, academics and clinicians will be needed to ensure successful widespread adoption of this model.

This study sought to compare the morbidity and mortality of redo aortic valve replacement (redo-AVR) versus valve-in-valve trans-catheter aortic valve implantation (valve-in-valve TAVI) for patients with a failing bioprosthetic valve. A multicentre UK retrospective study of redo-AVR or valve-in-valve TAVI for patients referred for redo aortic valve intervention due to a degenerated aortic bioprosthesis. Propensity score matching was performed for confounding factors. From July 2005 to April 2021, 911 patients underwent redo-AVR and 411 patients valve-in-valve TAVI. There were 125 pairs for analysis after propensity score matching. Mean age was 75.2±8.5 years. In-hospital mortality was 7.2% (n=9) for redo-AVR vs 0 for valve-in-valve TAVI, p=0.002. Surgical patients suffered more post-operative complications, including IABP support (p=0.02), early re-operation (p<0.001), arrhythmias (p<0.001), respiratory and neurological complications (p=0.02 and p=0.03) and multi-organ failure (p=0.01). The valve-in-valve TAVI group had a shorter intensive care unit and hospital stay (p <0.001 for both). However, moderate aortic regurgitation at discharge and higher post-procedural gradients were more common after valve-in-valve TAVI (p<0.001 for both). Survival probabilities in patients who were successfully discharged from hospital were similar after valve-in-valve TAVI and redo-AVR over the 6-year follow-up (log-rank p=0.26). In elderly patients with a degenerated aortic bioprosthesis, valve-in-valve trans-catheter aortic valve implantation provides better early outcomes, as opposed to redo surgical aortic valve replacement, although there was no difference in mid-term survival in patients successfully discharged from hospital.

The outflow tract (OFT) of the heart carries blood away from the heart into the great arteries. During embryogenesis the OFT divides to the aorta and pulmonary trunk, which originate from the left and right ventricles, respectively, creating the double circulation present in mammals. Defects in this area account for one-third of all congenital heart disease cases. Although model systems have greatly enhanced our understanding of the cell lineages that contribute to the OFT, our knowledge of OFT development in humans remains limited. Here, we present comprehensive transcriptomic data on the developing OFT at two distinct timepoints (embryonic and fetal) and its adult derivatives, the aortic valves, providing a large reference framework of OFT cell repertoires and their gene expression profiles. Using spatial transcriptomics, we describe the distribution of cell populations. Our findings define the cellular and molecular signatures of the OFT and its distinct cell lineages, which is critical for understanding congenital heart defects and developing cardiac tissue for regenerative medicine.### Competing Interest StatementThe authors have declared no competing interest.

BACKGROUND:The association between interleukin-1β (IL-1β) concentrations during ex vivo lung perfusion (EVLP) with donor organ quality and post-lung transplant outcome has been demonstrated in several studies. The mechanism underlying IL-1β-mediated donor lung injury was investigated using a paired single-lung EVLP model. METHODS:Human lung pairs were dissected into individual lungs and perfused on identical separate EVLP circuits, with one lung from each pair receiving a bolus of IL-1β. Fluorescently labeled human neutrophils isolated from a healthy volunteer were infused into both circuits and quantified in perfusate at regular timepoints. Perfusates and tissues were subsequently analyzed, with perfusates also used in functional assays. RESULTS:Neutrophil numbers were significantly lower in perfusate samples collected from the IL-1β-stimulated lungs consistent with increased neutrophil adhesion ( P = 0.042). Stimulated lungs gained significantly more weight than controls ( P = 0.046), which correlated with soluble intercellular adhesion molecule-1 (R 2 = 0.71, P = 0.0043) and von-Willebrand factor (R 2 = 0.39, P = 0.040) in perfusate. RNA expression patterns for inflammatory genes were differentially regulated via IL-1β. Blockade of IL-1β significantly reduced neutrophil adhesion in vitro ( P = 0.025). CONCLUSION:These data illustrate the proinflammatory functions of IL-1β in the context of EVLP, suggesting this pathway may be susceptible to therapeutic modulation before transplantation.

The function of a cell is defined by its intrinsic characteristics and its niche: the tissue microenvironment in which it dwells. Here we combine single-cell and spatial transcriptomics data to discover cellular niches within eight regions of the human heart. We map cells to microanatomical locations and integrate knowledge-based and unsupervised structural annotations. We also profile the cells of the human cardiac conduction system1. The results revealed their distinctive repertoire of ion channels, G-protein-coupled receptors (GPCRs) and regulatory networks, and implicated FOXP2 in the pacemaker phenotype. We show that the sinoatrial node is compartmentalized, with a core of pacemaker cells, fibroblasts and glial cells supporting glutamatergic signalling. Using a custom CellPhoneDB.org module, we identify trans-synaptic pacemaker cell interactions with glia. We introduce a druggable target prediction tool, drug2cell, which leverages single-cell profiles and drug-target interactions to provide mechanistic insights into the chronotropic effects of drugs, including GLP-1 analogues. In the epicardium, we show enrichment of both IgG+ and IgA+ plasma cells forming immune niches that may contribute to infection defence. Overall, we provide new clarity to cardiac electro-anatomy and immunology, and our suite of computational approaches can be applied to other tissues and organs.

INTRODUCTION:Normothermic machine perfusion (NMP) provides a platform for drug-delivery. However, pharmacological considerations for therapeutics delivered during NMP are scarcely reported. We aimed to demonstrate the ability of NMP as a platform for pharmacological testing, using a drug which increases metabolism (2,4-dinitrophenol; DNP) as an example therapeutic. METHODS:We performed 25 h of NMP on human livers which had been declined for transplant due to steatosis (n = 7). Three livers received a DNP bolus, three were controls, and one received a DNP infusion. RESULTS:Toxicity studies revealed DNP delivery was safe, without hepatotoxic effects. The liver surface temperature was increased in the DNP group (p = 0.046), but no livers suffered hyperthermia-the mechanism of DNP toxicity in vivo. Pharmacokinetic studies revealed DNP elimination with first-order kinetics and 7.7 h half-life (95% CI = 5.1-15.9 hrs). The clearance of DNP in bile was negligible. As expected, DNP significantly increased oxygen consumption (p = 0.023); this increase was closely correlated with perfusate DNP concentration (r2  = 0.975; p = 0.002) and the effect was lost as DNP was eliminated by the liver. A DNP infusion rate, calculated using our pharmacokinetic data, successfully maintained perfusate DNP concentration. DISCUSSION:Detailed pharmacological testing can be performed during NMP. Our therapeutic (DNP) is rapidly eliminated by the ex vivo liver, meaning the drug effect of increased metabolism is only transient. This demonstrates the importance of assessing pharmacokinetics when delivering therapeutics during NMP, especially for prolonged perfusion of organs with established roles in drug elimination. Rigorous pharmacological testing is needed to unlock the potential of NMP as a clinical drug-delivery platform.

Preventing SARS-CoV-2 infection by modulating viral host receptors, such as angiotensin-converting enzyme 2 (ACE2) 1 , could represent a new chemoprophylactic approach for COVID-19 that complements vaccination 2,3 . However, the mechanisms that control the expression of ACE2 remain unclear. Here we show that the farnesoid X receptor (FXR) is a direct regulator of ACE2 transcription in several tissues affected by COVID-19, including the gastrointestinal and respiratory systems. We then use the over-the-counter compound z-guggulsterone and the off-patent drug ursodeoxycholic acid (UDCA) to reduce FXR signalling and downregulate ACE2 in human lung, cholangiocyte and intestinal organoids and in the corresponding tissues in mice and hamsters. We show that the UDCA-mediated downregulation of ACE2 reduces susceptibility to SARS-CoV-2 infection in vitro, in vivo and in human lungs and livers perfused ex situ. Furthermore, we reveal that UDCA reduces the expression of ACE2 in the nasal epithelium in humans. Finally, we identify a correlation between UDCA treatment and positive clinical outcomes after SARS-CoV-2 infection using retrospective registry data, and confirm these findings in an independent validation cohort of recipients of liver transplants. In conclusion, we show that FXR has a role in controlling ACE2 expression and provide evidence that modulation of this pathway could be beneficial for reducing SARS-CoV-2 infection, paving the way for future clinical trials.

The success of pig-to-baboon life-supporting cardiac xenotransplantation reported by Längin and colleagues1 in Nature was a notable milestone toward turning xenotransplantation into clinical reality. However, the authors observed left ventricular hypertrophy, which led to life-limiting diastolic heart failure around 1 month post-transplant. Although the cardiac overgrowth could be controlled with antihypertensive therapy and temsirolimus, it poses a significant obstacle to clinical translation. The current study, conducted by Goerlich and colleagues,2 demonstrated that cardiac xenografts from genetically engineered pigs with growth hormone receptor (GHR) knockout (KO) underwent minimal growth with preserved function for more than 6 months without adjunctive therapies.

Despite the advancements in medical treatment, mechanical support, and stem cell therapy, heart transplantation remains the most effective treatment for selected patients with advanced heart failure. However, with an increase in heart failure prevalence worldwide, the gap between donor hearts and patients on the transplant waiting list keeps widening. Ex situ machine perfusion has played a key role in augmenting heart transplant activities in recent years by enabling the usage of donation after circulatory death hearts, allowing longer interval between procurement and implantation, and permitting the safe use of some extended-criteria donation after brain-stem death hearts. This exciting field is at a hinge point, with 1 commercially available heart perfusion machine, which has been used in hundreds of heart transplantations, and a number of devices being tested in the pre-clinical and Phase 1 clinical trial stage. However, no consensus has been reached over the optimal preservation temperature, perfusate composition, and perfusion parameters. In addition, there is a lack of objective measurement for allograft quality and viability. This review aims to comprehensively summarize the lessons about ex situ heart perfusion as a platform to preserve, assess, and repair donor hearts, which we have learned from the pre-clinical studies and clinical applications, and explore its exciting potential of revolutionizing heart transplantation. (C) 2020 International Society for Heart and Lung Transplantation. All rights reserved.

BACKGROUND: Left ventricular assist devices (LVADs) mechanically unload the heart and coupled with neurohormonal therapy can promote reverse cardiac remodeling and myocardial recovery. Minimally invasive LVAD decommissioning with the device left in place has been reported to be safe over short-term follow-up. Whether device retention reduces long-term safety, or sustainability of recovery is unknown. METHODS: This is a dual-center retrospective analysis of patients who had achieved responder status (left ventricular ejection fraction, LVEF >= 40% and left ventricular internal diastolic diameter, LVIDd <= 6.0 cm) and underwent elective LVAD decommissioning for myocardial recovery from May 2010 to January 2020. All patients had outflow graft closure and driveline resection with the LVAD left in place. Emergent LVAD decommissioning for an infection or device thrombosis was excluded. Patients were followed with serial echocardiography for up to 3-years. The primary clinical outcome was survival free of heart failure hospitalization, LVAD reimplantation, or transplant. RESULTS: During the study period 515 patients received an LVAD and 29 (5.6%) achieved myocardial recovery, 12 patients underwent total device explantation or urgent device decommissioning, 17 patients underwent elective LVAD decommissioning, and were included in the analysis. Median age of patients at LVAD implantation was 42 years (interquartile range, IQR: 25-54 years), all had a noni-schemic cardiomyopathy, and 5 (29%) were female. At LVAD implantation, median LVEF was 10% (IQR: 5%-15%), and LVIDd 6.6 cm (IQR: 5.8-7.1 cm). There were 11 hydrodynamically levitated centrifugal-flow (65%), and 6 axial-flow LVADs (35%). The median duration of LVAD support before decommissioning was 28.7 months (range 13.5-36.2 months). As compared to the turndown study parameters, 1-month post-decommissioning, median LVEF decreased from 55% to 48% (p = 0.03), and LVIDd increased from 4.8 cm to 5.2 cm (p = 0.10). There was gradual remodeling until 6 months, after which there was no statistical difference on follow-up through 3-years (LVEF 42%, LVIDd 5.6 cm). Recurrent infections affected 41% of patients leading to 3 deaths and 1 complete device explant. Recurrent HF occurred in 1 patient who required a transplant. Probability of survival free of HF, LVAD, or transplant was 94% at 1-year, and 78% at 3-years. CONCLUSIONS: LVAD decommissioning for myocardial recovery was associated with excellent long-term survival free from recurrent heart failure and preservation of ventricular size and function up to 3-years. Reducing the risk of recurrent infections, remains an important therapeutic goal for this management strategy. (C) 2021 International Society for Heart and Lung Transplantation. All rights reserved.

Pulmonary sequestration is a congenital abnormality of a non-functional pulmonary mass with anomalous systemic arterial supply. Surgical resection is the gold standard treatment, but it carries a risk of life-threatening haemorrhage from accidental injury of the anomalous artery. Endovascular embolisation has been introduced as a safe alternative, but does not eliminate the possibility of symptom recurrence. We report a case of a 61-year old woman with intralobar pulmonary sequestration treated with a combination of endovascular coil embolisation and surgical resection.

Severe acute kidney injury (AKI), defined as requiring renal replacement therapy (RRT), is associated with higher mortality postheart transplantation, but its long-term renal consequences are not known. Anonymized data of 3365 patients, who underwent heart transplantation between 1995 and 2017, were retrieved from the UK Transplant Registry. Multivariable binary logistic regression was performed to identify risk factors for severe AKI requiring RRT, Kaplan-Meier analysis to compare survival and renal function deterioration of the RRT and non-RRT groups, and multivariable Cox regression model to identify predicting factors of mortality and end-stage renal disease (ESRD). 26.0% of heart recipients received RRT post-transplant. The RRT group has lower survival rates at all time points, especially in the immediate post-transplant period. However, conditional on 3 months survival, older age, diabetes and coronary heart disease, but not post-transplant RRT, were the risk factors for long-term survival. The predicting factors for ESRD were insulin-dependent diabetes, renal function at transplantation, eGFR decline in the first 3 months post-transplant, post-transplant severe AKI and transplantation era. Severe AKI requiring RRT post-transplant is associated with worse short-term survival, but has no impact on long-term mortality. It also accelerates recipients' renal function deterioration in the long term.

<h2>Abstract</h2> Heart transplantation is the definitive treatment for selected patients with end-stage heart failure refractory to medical, interventional and surgical treatment. However, due to limited number of donor organs, most patients wait a long time for heart transplantation and a significant proportion die or become unsuitable for transplantation while waiting. Although post-transplant survival outcomes continue improving, a fifth of recipients die within 1 year after transplantation. In addition, recipients face constant threats from infection, rejection, malignancy and chronic allograft vasculopathy. Therefore, it is imperative to increase donor heart utilization to reduce waiting list mortality, and maintain allograft quality during transportation and optimize post-transplant care to improve outcomes. This review summarizes the process of heart transplantation from recipient and donor selection and matching to post-transplant management with a focus on the surgical aspects, and highlights the recent advancement, including donation after circulatory death programme, mechanical circulatory support, and <i>ex-vivo</i> heart perfusion.

Heart transplantation is the definitive treatment for selected patients with end-stage heart failure refractory to medical, interventional and surgical treatment. However, due to limited number of donor organs, most patients wait a long time for heart transplantation and a significant proportion die or become unsuitable for transplantation while waiting. Although post-transplant survival outcomes continue improving, a fifth of recipients die within 1 year after transplantation. In addition, recipients face constant threats from infection, rejection, malignancy and chronic allograft vasculopathy. Therefore, it is imperative to increase donor heart utilization to reduce waiting list mortality, and maintain allograft quality during transportation and optimize post-transplant care to improve outcomes. This review summarizes the process of heart transplantation from recipient and donor selection and matching to post-transplant management with a focus on the surgical aspects, and highlights the recent advancement, including donation after circulatory death programme, mechanical circulatory support, and ex-vivo heart perfusion.

Heart transplantation is the definitive treatment for selected patients with end-stage heart failure refractory to medical, interventional and surgical treatment. However, due to limited number of donor organs, most patients wait a long time for heart transplantation and a significant proportion die or become unsuitable for transplantation while waiting. Although post-transplant survival outcomes continue improving, a fifth of recipients die within 1 year after transplantation. In addition, recipients face constant threats from infection, rejection, malignancy and chronic allograft vasculopathy. Therefore, it is imperative to increase donor heart utilization to reduce waiting list mortality, and maintain allograft quality during transportation and optimize post-transplant care to improve outcomes. This review summarizes the process of heart transplantation from recipient and donor selection and matching to post-transplant management with a focus on the surgical aspects, and highlights the recent advancement, including donation after circulatory death programme, mechanical circulatory support, and ex-vivo heart perfusion.