Heart transplant advances: Ex vivo organ-preservation systems

Enhancing outcomes in Langendorff-perfused rodent hearts through perfusion parameter optimization

Despite important advancements in addressing cardiovascular diseases (CVDs), there has been an overall lack of progress in the field, leading to a slower decline in the rate of CVDs related deaths, and even an increase for some risk groups (e.g. increase in stroke mortality) exacerbated by an aging and obese population. While a multi-faceted problem, this deceleration may be influenced by the preferred model systems utilized in translation research. Cardiac cell lines, although easier to handle, lack biological accuracy due to the unnatural modifications required for successful culture and may not recapitulate complex 3-dimensional structural and environmental factors. At the same time, whole animal experimentation provides unwanted complexity during initial scientific development. Alternatively, ex vivo perfusion of isolated rodent hearts provides the needed biological accuracy with decreased organismal complexity. This platform facilitates the evaluation of the isolated heart, without neuro-reflexes and/or humoral contributions, unveiling the direct effects of stimuli in heart function/homeostasis. This manuscript leverages the wide array of perfusion parameters (i.e. perfusate, flow rate, coronary pressures), to demonstrate the capability of ex vivo heart perfusion protocols to accommodate a large range of experimental needs. Through this work, it was determined that the use of physiological perfusion pressures leads to increased left ventricular (LV) pressures but results in a loss of function over time, making it ideal conditions for organ assessment. Conversely, lower-than-physiological perfusion pressures lead to decreased LV pressures but prevent loss of function over time, which is preferable when longer perfusion times are relevant to experimental needs. Similarly, the use of adenosine as a pharmacological intervention was found to decrease both edema formation and inflammatory responses. In contrast, the use of packed red blood cells as oxygen carriers appears to induce a pro-inflammatory response and cause greater cardiac damage, particularly when combined with low perfusion pressures.

Thoracoabdominal normothermic regional perfusion in donors with neurological determination of death extends organ donors pool

BackgroundHeart transplantation team of the Heart Institute of the Ministry of Health of Ukraine performs thoracoabdominal normothermic regional perfusion (TA-NRP) procedure for organ preconditioning in marginal donors. Martial law in Ukraine worsens preexisting shortage of donor organs since February 2022. The use of TA-NRP has been shown to be effective in rescucitating organs in donors with circulatory determination of death (CDD), and we hypothesize that TA-NRP can be used to perform in situ organ perfusion in donors with neurological determination of death (NDD) as well, thereby improve organ quality.MethodsA single centre, retrospective analysis of outcomes after heart transplantation using organs from donors with NDD who underwent TA-NRP for preconditioning from 2022 to 2024 year at the Heart Institute Ministry of Health of Ukraine. The indications for TA-NRP were hemodynamic instability of donors with NDD, characterized by the need for norepinephrine >1.0 μg/kg/h to maintain mean blood pressure >50 mm Hg.ResultsTA-NRP for donor preconditioning was performed in 12 cases (11.3%) of 106 heart transplantations between 2019 and 2023. The average duration of TA-NRP was 124.5 ± 10.1 minutes. Prior to TA-NRP initiation, all donors exhibited metabolic acidosis, hyperkalemia, and hyperlactatemia. The implementation of TA-NRP normalized the acid-base balance, demonstrated by a significant increase in pH (p < .001), correction of base excess (BE) (p < .001), and an increase in bicarbonate levels (HCO3-) (p < .001). TA-NRP also significantly reduced baseline lactate levels from 10.4 ± 2.91 mmol/L to 1.57 ± 0.33 mmol/L (p < .001) and decreased potassium levels (p = .003). Additionally, it led to a significant reduction in donor heart rate (p = .001) and an increase in mean arterial pressure (p = .012), accompanied by a 6.6-fold reduction in donor norepinephrine requirements (p = .003).ConclusionThe use of TA-NRP in donors with NDD improved organ quality which resulted in 30 days survival rate of 83% and 1-year survival rate of 75% in organ recipients.

Cardiac preservation using ex vivo organ perfusion: new therapies for the treatment of heart failure by harnessing the power of growth factors using BMP mimetics like THR-184

As heart transplantation continues to be the gold standard therapy for end-stage heart failure, the imbalance between the supply of hearts, and the demand for them, continues to get worse. In the US alone, with less than 4,000 hearts suitable for transplant and over 100,000 potential recipients, this therapy is only available to a very few. The use of hearts Donated after Circulatory Death (DCD) and Donation after Brain Death (DBD) using ex vivo machine perfusion (EVMP) is a promising approach that has already increased the availability of suitable organs for heart transplantation. EVMP offers the promise of enabling the expansion of the overall number of heart transplants and lower rates of early graft dysfunction. These are realized through (1) safe extension of the time between procurement and transplantation and (2) ex vivo assessment of preserved hearts. Notably, ex vivo perfusion has facilitated the donation of DCD hearts and improved the success of transplantation. Nevertheless, DCD hearts suffer from serious preharvest ischemia/reperfusion injury (IRI). Despite these developments, only 40% of hearts offered for transplantation can be utilized. These devices do offer an opportunity to evaluate donor hearts for transplantation, resuscitate organs previously deemed unsuitable for transplantation, and provide a platform for the development of novel therapeutics to limit cardiac injury. Bone Morphogenetic Protein (BMP) signaling is a new target which holds the potential for ameliorating myocardial IRI. Recent studies have demonstrated that BMP signaling has a significant role in blocking the deleterious effects of injury to the heart. We have designed novel small peptide BMP mimetics that act via activin receptor-like kinase (ALK3), a type I BMP receptor. They are capable of (1) inhibiting inflammation and apoptosis, (2) blocking/reversing the epithelial-mesenchymal transition (EMT) and fibrosis, and (3) promoting tissue regeneration. In this review, we explore the promise that novel therapeutics, including these BMP mimetics, offer for the protection of hearts against myocardial injury during ex vivo transportation for cardiac transplantation. This protection represents a significant advance and a promising ex vivo therapeutic approach to expanding the donor pool by increasing the number of transplantable hearts.

A Smart Computational Tool for Personalized Coronary Blood Flow Settings During Normothermic Ex Situ Heart Perfusion

Myocardial edema significantly develops during current subnormothermic ex situ heart perfusion (ESHP) procedures, resulting in myocardial function decline during prolonged perfusion. A relatively high coronary blood flow (CBF) during ESHP is thought to be responsible for this high degree of myocardial edema formation. In this study, we present a novel tool to calculate CBF based on individual donor (sex and body weight) and perfusate (hemoglobin concentration, oxygen saturation, partial pressure of oxygen [PO2]) characteristics. The tool continuously evaluates the balance between myocardial oxygen consumption (MVO2) and delivery to facilitate adequate and preventing excess perfusion. Taking this personalized approach, the CBF can potentially be lowered while still providing sufficient oxygen to the donor heart. Furthermore, the tool automatically calculates MVO2, ΔPO2, and coronary vascular resistance during ESHP, which aids in the qualitative assessment of the heart before transplantation.

Myocardial oxygen handling and metabolic function of ex-situ perfused human hearts from circulatory death donors

Background

This study investigated oxygen handling of human hearts donated after circulatory death (DCD) on normothermic ex-situ heart perfusion (ESHP) and evaluated oxygen handling markers as adjuncts to cardiac viability assessment.

Methods

This single-center retrospective study included human DCD heart transplantation procedures using ESHP. Lactate concentrations, blood gas, myocardial oxygen consumption (MVO2), delivery (MDO2), and extraction (MEO2), coronary blood flow (CBF), coronary vascular resistance (CVR), and adenosine infusion were reported over time. Correlation between parameters was assessed, and statistical testing compared patients who did and did not require extracorporeal membrane oxygenation (ECMO) support after transplantation.

Results

Lactate concentrations decreased during ESHP in all transplanted hearts (n = 25) and increased in 1 rejected heart. Arterial partial pressure of oxygen (PO2) was 75.2 ± 2.9 kPa, with an arteriovenous ΔPO2 of 44.8 ± 10.4 kPa. Oxygen saturation was 100% in most arterial and venous samples. Average MVO2 was 2.7 ± 0.6 ml/min/100 g myocardium, MDO2 98.5 ± 20.4 ml/min, and MEO2 8.6 ± 1.8%. Average CVR was 0.025 ± 0.006 mm Hg min/ml/100 g and increased over time. ΔPO2 correlated strongly with MVO2 (R = 0.797, p < 0.001) and lactate trend (R = 0.799, p < 0.001) in transplanted hearts, without differences compared to the rejected heart with increasing lactate. Adenosine infusion on ESHP was significantly higher in patients requiring ECMO post-transplantation vs non-ECMO cases (11.7 (4.5-21.0) vs 2.2 (1.5-6.7) ml/h, p = 0.039).

Conclusions

Hearts on normothermic ESHP receive excessive MDO2, due to high PO2 and CBF, while the MVO2 is relatively low. Thus, CBF and PO2 can potentially be lowered. Furthermore, ΔPO2 could serve as additional marker of metabolic function under these hyperoxic circumstances. The adenosine infusion rate might predict post-transplantation ECMO requirement.

Cardiac Loading using Passive Left Atrial Pressurization and Passive Afterload for Graft Assessment

Ex vivo machine perfusion or normothermic machine perfusion is a preservation method that has gained great importance in the transplantation field. Despite the immense opportunity for assessment due to the beating state of the heart, current clinical practice depends on limited metabolic trends for graft evaluation. Hemodynamic measurements obtained from left ventricular loading have garnered significant attention within the field due to their potential as objective assessment parameters. In effect, this protocol provides an easy and effective manner of incorporating loading capabilities to established Langendorff perfusion systems through the simple addition of an extra reservoir. Furthermore, it demonstrates the feasibility of employing passive left atrial pressurization for loading, an approach that, to our knowledge, has not been previously demonstrated. This approach is complemented by a passive Windkessel base afterload, which acts as a compliance chamber to maximize myocardial perfusion during diastole. Lastly, it highlights the capability of capturing functional metrics during cardiac loading, including left ventricular pulse pressure, contractility, and relaxation, to uncover deficiencies in cardiac graft function after extended periods of preservation times (˃6 h).

Ex vivo lung perfusion and the Organ Care System: a review

With the increasing prevalence of heart failure and end-stage lung disease, there is a sustained interest in expanding the donor pool to alleviate the thoracic organ shortage crisis. Efforts to extend the standard donor criteria and to include donation after circulatory death have been made to increase the availability of suitable organs. Studies have demonstrated that outcomes with extended-criteria donors are comparable to those with standard-criteria donors. Another promising approach to augment the donor pool is the improvement of organ preservation techniques. Both ex vivo lung perfusion (EVLP) for the lungs and the Organ Care System (OCS, TransMedics) for the heart have shown encouraging results in preserving organs and extending ischemia time through the application of normothermic regional perfusion. EVLP has been effective in improving marginal or borderline lungs by preserving and reconditioning them. The use of OCS is associated with excellent short-term outcomes for cardiac allografts and has improved utilization rates of hearts from extended-criteria donors. While both EVLP and OCS have successfully transitioned from research to clinical practice, the costs associated with commercially available systems and consumables must be considered. The ex vivo perfusion platform, which includes both EVLP and OCS, holds the potential for diverse and innovative therapies, thereby transforming the landscape of thoracic organ transplantation.

Determinants of survival following heart transplantation in adults with congenital heart disease

BACKGROUND

Adult patients surviving with congenital heart disease (ACHD) is growing. We examine the factors associated with heart transplant outcomes in this challenging population with complex anatomy requiring redo-surgeries.

METHODS

We reviewed the United Network for Organ Sharing-Standard Transplant Analysis and Research database and analyzed 35,952 heart transplants from January 1st, 2000, to September 30th, 2018. We compared transplant characteristics for ischemic cardiomyopathy (ICM) (n = 14,236), nonischemic cardiomyopathy (NICM) (n = 20,676), and ACHD (n = 1040). Mean follow-up was 6.20 ± 4.84 years. Kaplan-Meier survival curves and Cox-proportional hazards analysis were used to analyze survival data.

RESULTS

Multivariable analysis confirmed that ACHD was associated greater in-hospital death compared to ICM (HR = 0.54, P < 0.001) and NICM (HR = 0.46, P < 0.001). Notable factors associated with increased mortality were history of cerebrovascular disease (HR = 1.11, P = 0.026), prior history of malignancy (HR = 1.12, P = 0.006), pre-transplant biventricular support (HR = 1.12, P = 0.069), postoperative stroke (HR = 1.47, P < 0.001) and postoperative dialysis (HR = 1.71, P < 0.001). ACHD transplants had a longer donor heart ischemic time (P < 0.001) and trend towards more deaths from primary graft dysfunction (P = 0.07). In-hospital deaths were more likely with ACHD and use of mechanical support such as use of right ventricular assist device (HR = 2.20, P = 0.049), biventricular support (HR = 1.62, P < 0.001) and extracorporeal membrane oxygenation (HR = 2.36, P < 0.001). Conditional survival after censoring hospital deaths was significantly higher in ACHD (P < 0.001).

CONCLUSION

Heart transplant in ACHD is associated with a higher post-operative mortality given anatomical complexity but a better long-term conditional survival. Normothermic donor heart perfusion may improve outcomes in the ACHD population by reducing the impact of longer ischemic times.

Donor Heart Preservation: Current Knowledge and the New Era of Machine Perfusion

Heart transplantation remains the conventional treatment in end-stage heart failure, with static cold storage (SCS) being the standard technique used for donor preservation. Nevertheless, prolonged cold ischemic storage is associated with the increased risk of early graft dysfunction attributed to residual ischemia, reperfusion, and rewarming damage. In addition, the demand for the use of marginal grafts requires the development of new methods for organ preservation and repair. In this review, we focus on current knowledge and novel methods of donor preservation in heart transplantation. Hypothermic or normothermic machine perfusion may be a promising novel method of donor preservation based on the administration of cardioprotective agents. Machine perfusion seems to be comparable to cold cardioplegia regarding donor preservation and allows potential repair treatments to be employed and the assessment of graft function before implantation. It is also a promising platform for using marginal organs and increasing donor pool. New pharmacological cardiac repair treatments, as well as cardioprotective interventions have emerged and could allow for the optimization of this modality, making it more practical and cost-effective for the real world of transplantation. Recently, the use of triiodothyronine during normothermic perfusion has shown a favorable profile on cardiac function and microvascular dysfunction, likely by suppressing pro-apoptotic signaling and increasing the expression of cardioprotective molecules.

The Year in Cardiothoracic Transplant Anesthesia: Selected Highlights From 2021 Part II: Cardiac Transplantation

This article spotlights the research highlights of this year that specifically pertain to the specialty of anesthesia for heart transplantation. This includes the research on recent developments in the selection and optimization of donors and recipients, including the use of donation after cardiorespiratory death and extended criteria donors, the use of mechanical circulatory support and nonmechanical circulatory support as bridges to transplantation, the effect of COVID-19 on heart transplantation candidates and recipients, and new advances in the perioperative management of these patients, including the use of echocardiography and postoperative outcomes, focusing on renal and cerebral outcomes.