Hearts Donated After Circulatory Death and Reconditioned Using Normothermic Regional Perfusion Can Be Successfully Transplanted Following an Extended Period of Static Storage

Evaluation of target temperature on effectiveness of myocardial preservation during hypothermic machine perfusion

Background

Ex-situ heart perfusion (ESHP) has been proposed as an optimal method for preserving donated hearts prior to transplantation. Hypothermic oxygenated perfusion (HOP) is a simple method from a device design perspective, with enhanced safety compared to normothermic perfusion in the event of device failure. However, the optimal temperature for cardiac HOP has yet to be determined. We evaluated the effectiveness of 12-hour HOP using University of Wisconsin Machine Perfusion Solution (UWMPS) in different temperatures compared to static cold storage (SCS) for 6 hours followed by simulated transplantation. Additionally, we sought to determine the impact of oxygen supplementation in hypothermic ESHP in the heart function preservation.

Methods

Hearts were procured from Yorkshire pigs (n = 35) randomized into 3 preservation therapies: 6 hours-SCS; 12 hours-HOP and 12 hours hypothermic non-oxygenated perfusion (HNOP-without oxygen supplementation). For either HOP or HNOP groups, 3 temperatures were tested (5°C; 10°C; 15°C). After the preservation period, hearts had their function assessed in a normothermic perfusion machine capable of working mode, simulating transplantation.

Results

All perfusion parameters were stable throughout (mean ± SD): aortic flow 65 ± 5.57 ml/min, aortic pressure: 11.51 ± 3.17 mm Hg. All HOP hearts presented a better cardiac index than SCS (p < 0.05). The HNOP hearts presented similar cardiac function results compared to SCS.

Conclusions

HOP for 12 hours had better heart function preservation than SCS for 6 hours. Even HNOP had similar results compared to SCS. Greater edema formation in ESHP hearts did not affect heart function. Hypothermic ESHP safely enhances function preservation compared to SCS.

The role of a hemoadsorption filter on cytokine levels during 1 hour of thoraco-abdominal normothermic regional perfusion for donation after circulatory death heart donation in a porcine model

BACKGROUND

Both global ischemia caused by circulatory arrest and extracorporeal circulation circuits have been shown to trigger cytokine release. We hypothesized that inserting a hemoadsorption device during thoraco-abdominal normothermic regional perfusion (TA-NRP) in the donation after circulatory death setting would mitigate the inflammatory response, potentially resulting in improved cardiac allograft function.

METHODS

In 15 pigs, circulatory arrest was induced by hypoxia. After a 15-min no-touch-period, TA-NRP was performed for 60 min. Eight pigs had a hemoadsorption device incorporated in the ECC, while seven did not. Plasma concentrations of IFN-α, IFN-γ, TNF-α, IL-1β, IL-4, IL-6, IL-8, IL-10, and IL-12p40 were assessed by ELISA at baseline, immediately at start of TA-NRP, 60 min after start of TA-NRP (just before weaning from ECC), and at 30 and 60 min after weaning from ECC. Cardiac function was assessed with pressure-volume loop analysis.

RESULTS

Hemoadsorption had no relevant effects on systemic cytokine levels post TA-NRP. IL-6 plasma levels gradually rose throughout the procedure for both groups. Hemoadsorption did not affect systolic or diastolic left ventricular function, nor were global hemodynamics improved by hemoadsorption.

CONCLUSIONS

The insertion of a hemoadsorption device did not significantly affect plasma cytokine levels or cardiac function. Further research is necessary to assess the role of the inflammatory response in DCD heart transplantation and its modulation by TA-NRP.

Survival after heart transplants from circulatory-dead versus brain-dead donors: Meta-analysis of reconstructed time-to-event data

BACKGROUND

Heart transplantation (HTx) using donors after circulatory death (DCD) has the potential to significantly boost overall transplant rates. This study aims to reconstruct data from individual studies comparing survival between HTx from DCD recipients and donation after brain (DBD) recipients.

METHODS

MEDLINE, Embase, Scopus, were searched up to August 2024. We included studies that reported a Kaplan-Meier summary of survival comparing DCD and DBD HTx. Digitization of the Kaplan-Meier curves and reconstruction of individual patient data followed by survival analysis that was conducted using R software.

RESULTS

Six studies including a total of 3240 patients (2242 DBD and 998 DCD) were included in the final analysis. There was no significant difference in the overall survival rates between DCD and DBD patients (Hazard Ratio (HR): 1.01, 95 % CI [0.81-1.25], P = 0.91). However, the proportional hazard assumption was violated, deeming such results inconclusive. Time-varying flexible parametric model revealed a significantly declining survival in DCD recipients 3 years after surgery. Landmark analyses further suggest this declining trend in the DCD group at the two-year landmark (HR: 1.67, p = 0.021) and the four-year mark (HR: 2.78, p = 0.002). However, data beyond 6 years is limited. Evidence comparing direct procurement and normothermic regional perfusion is scarce, with no significant survival differences observed.

CONCLUSION

This meta-analysis shows that, despite similar early survival outcomes, DCD heart transplants showed a trend towards a lower long-term survival, with the difference becoming evident around three years post-transplantation. These findings highlight the need for enhanced monitoring and optimized post-transplant care in DCD recipients. Further studies with strict and long-term follow-up are warranted to confirm these results.

Ex vivo heart perfusion: an updated systematic review

Due to the discrepancy between patients awaiting a heart transplant and the availability of donor hearts, strategies to expand the donor pool and improve the transplant's success are crucial. This review aims to summarize current knowledge on the ex vivo heart preservation (EVHP) experience as an alternative to standard cold static storage (CSS). EVHP techniques can improve the preservation of the donor's heart before transplantation and allow for pre-transplant organ evaluation.

Considerations for the use of porcine organ donation models in preclinical organ donor intervention research

Use of animal models in preclinical transplant research is essential to the optimization of human allografts for clinical transplantation. Animal models of organ donation and preservation help to advance and improve technical elements of solid organ recovery and facilitate research of ischemia-reperfusion injury, organ preservation strategies, and future donor-based interventions. Important considerations include cost, public opinion regarding the conduct of animal research, translational value, and relevance of the animal model for clinical practice. We present an overview of two porcine models of organ donation: donation following brain death (DBD) and donation following circulatory death (DCD). The cardiovascular anatomy and physiology of pigs closely resembles those of humans, making this species the most appropriate for pre-clinical research. Pigs are also considered a potential source of organs for human heart and kidney xenotransplantation. It is imperative to minimize animal loss during procedures that are surgically complex. We present our experience with these models and describe in detail the use cases, procedural approach, challenges, alternatives, and limitations of each model.

Impact of normothermic regional perfusion during DCD recovery on lung allograft function: A preclinical study

Background

Normothermic regional perfusion (NRP) has been growing as a novel procurement strategy after circulatory death (donation after circulatory death (DCD)) in the context of heart transplantation. However, the impact of NRP on lung graft viability is largely unknown. We sought to determine lung function after thoraco-abdominal NRP (TA-NRP) in a clinically relevant porcine DCD model.

Methods

Donor domestic pigs underwent hypoxic cardiac arrest to simulate DCD procurement and were randomly allocated to either 1-hour resuscitation on TA-NRP (n = 4) or direct lung procurement (direct procurement and perfusion (DPP), n = 4). All lungs were placed on ex-vivo lung perfusion (EVLP) and evaluated for 3 hours to assess functional outcome parameters and suitability for transplantation.

Results

After 1 hour of TA-NRP, cardiopulmonary bypass was weaned, and mean systemic PaO2/fraction of inspired oxygen was 418 ± 76 mm Hg, which was comparable to baseline (467 ± 41, p = 0.41). No significant differences were seen between the groups during EVLP, except for a higher pulmonary artery pressure in the TA-NRP group at 3 hours of EVLP (19.7 ± 1.5 vs 14.7 ± 2.1 mm Hg, p = 0.02). Perfusate inflammatory cytokines levels of IL-6 and IL-8 were higher at the first hour of EVLP in the TA-NRP group; however, these differences were not sustained as levels were similar by the last hour of EVLP. There were no differences in histology, cytokines, or metabolic profile of the TA-NRP lungs compared to DPP.

Conclusions

TA-NRP porcine lungs met functional criteria to proceed to transplantation and demonstrated no significant histological, cytokine, and metabolic differences when compared to DPP porcine lungs. This study highlights the value of considering TA-NRP lungs for transplant with well-established protocols.

Utilization of Paragonix Sherpapak Cardiac Transport System for the Preservation of Donor Hearts After Circulatory Death

BACKGROUND

Donation after circulatory death (DCD) heart transplantation is being increasingly adopted by transplant centers. The optimal method of DCD heart preservation during transport after in situ thoracoabdominal normothermic regional perfusion (TA-NRP) is not known.

METHODS

We evaluated our experience with the Paragonix SherpaPak Cardiac Transport System (SCTS) for the transport of DCD cardiac allografts after TA-NRP recovery between January 2021 and December 2022. We collected and evaluated donor characteristics, allograft ischemic intervals, and recipient baseline demographic and clinical variables, and short-term outcomes.

RESULTS

Twelve recipients received DCD grafts recovered with TA-NRP and transported in SCTS during the study period. The median age of 10 male and 2 female donors was 32 years (min 15, max 38). The median duration of functional warm ischemia was 12 minutes (min 8, max 22). Hearts were preserved in SCTS for a median of 158 minutes (min 37, max 224). Median recipient age was 61 years (min 28, max 70). Ten recipients (83%) survived to hospital discharge, with one death attributable to graft dysfunction (8%). The median vasoactive-inotropic (VIS) score at 72 hours post-transplantation of the entire cohort was 6 (min 0, max 15). The median length of intensive care unit stay in hospital survivors was 5 days (min 3, max 17) days and hospital stay 17 days (min 9, max 37).

CONCLUSIONS

The Paragonix SCTS provides efficacious preservation of DCD grafts for ≥3.5 hours. Organs transported with this device showed satisfactory post-transplantation function.

Clamping of the Aortic Arch Vessels During Normothermic Regional Perfusion Does Not Negatively Affect Donor Cardiac Function in Donation After Circulatory Death

BACKGROUND

The hemodynamic effects of aortic arch vessel (AAV) clamping during normothermic regional perfusion (NRP) in donation after circulatory death is unknown. We investigated effects of AAV clamping during NRP compared with no clamping in a porcine model.

METHODS

In 16 pigs, hemodynamic parameters were recorded including biventricular pressure-volume measurements and invasive blood pressure. Additionally, blood gas parameters and inflammatory cytokines were used to assess the effect of AAV clamping. The animals were centrally cannulated for NRP, and baseline measurements were obtained before hypoxic circulatory arrest was induced by halting mechanical ventilation. During an 8-min asystole period, the animals were randomized to clamp (n = 8) or no-clamp (n = 8) of the AAV before commencement of NRP. During NRP, circulation was supported with norepinephrine (NE) and dobutamine. After 30 min of NRP, animals were weaned and observed for 180 min post-NRP.

RESULTS

All hearts were successfully reanimated and weaned from NRP. The nonclamp groups received significantly more NE to maintain a mean arterial pressure >60 mm Hg during and after NRP compared with the clamp group. There were no between group differences in blood pressure or cardiac output. Pressure-volume measurements demonstrated preserved cardiac function' including ejection fraction and diastolic and systolic function. No between group differences in inflammatory markers were observed.

CONCLUSIONS

AAV clamping did not negatively affect donor cardiac function or inflammation after circulatory death and NRP. Significantly less NE was used to support in the clamp group than in the nonclamp group.

Breaking barriers in cardiac donation after circulatory death

BACKGROUND

Heart transplant (HT) from controlled donation after circulatory death (cDCD) is an emerging strategy that is rapidly expanding and may help increase the heart donor pool.

MATERIALS AND METHODS

The use of thoracoabdominal normothermic regional perfusion with extracorporeal membrane oxygenation device has allowed to perform HT after cDCD in our country. We present a successful case of heart transplantation using a graft from cDCD with 201 min cold ischemia time.

DISCUSSION AND CONCLUSION

HT from cDCD could be a good alternative to brain dead donation. This experience suggests than nonlocal cardiac from cDCD could tolerate long periods of cold ischemia time and break the main barriers with this technique.

Early Outcomes of Heart Transplantation Using Donation After Circulatory Death Donors in the United States

BACKGROUND

Limited donor availability and evolution in procurement techniques have renewed interest in heart transplantation (HT) with donation after circulatory death (DCD). The aim of this study is to evaluate outcomes of HT using DCD in the United States.

METHODS

The United Network for Organ Sharing registry was used to identify adult HT recipients from 2019 to 2021. Recipients were stratified between DCD and donation after brain death. Propensity-score matching was performed. Cox proportional hazards was used to identify independent predictors of 1-year mortality. Kaplan-Meier analysis was used to estimate 1-year survival.

RESULTS

Of 7496 HTs, 229 DCD and 7267 donation after brain death recipients were analyzed. The frequency of DCD HT increased from 0.2% of all HT in 2019 to 6.4% in 2021 (P<0.001), and the number of centers performing DCD HT increased from 3 of 120 centers to 20 of 121 centers (P<0.001). DCD donors were more likely to be younger, male, and White. After propensity matching, 1-year survival was 92.5% for DCD versus 90.3% for donation after brain death (hazard ratio, 0.80 [95% CI, 0.44-1.43]; P=0.44). Among DCD HTs, increasing recipient age and waitlist time predicted 1-year mortality on univariable analysis.

CONCLUSIONS

Rates of DCD HT in the United States are increasing. This practice appears safe and feasible as mortality outcomes are comparable to donation after brain death. Although this study represents early adopting centers, outcomes of the experience for DCD HT in the United States is consistent with existing international data and encourages broader utilization of this practice.

Thoracoabdominal Normothermic Regional Perfusion for Cardiac Procurement

In donation after circulatory death donors, warm ischemia time is a significant threat to successful cardiac transplantation. The ability to perfuse these organs during the minutes after death, until cardiac evaluation is completed to satisfaction, is crucial in limiting total warm ischemic time. Thoracoabdominal normothermic regional perfusion (TANRP) has emerged as a promising strategy for recovering and monitoring these hearts. We propose a series of clinical practice pearls that we follow for all donation after circulatory death procurements to streamline the process of setting up a TANRP circuit and ensuring all team members present at time procurement are familiar with the procedure. Bicaval cannulation is achieved via the abdomen for aortic cannulation, and via the chest for right atrial cannulation, avoiding deairing maneuvers and providing the shortest possible duration from incision to initiation of cardiopulmonary bypass. Here, we describe a series of practice techniques which we have utilized in our early experience with TANRP.

Cardiac function unchanged following reanimation with normothermic regional perfusion in donation after circulatory death

Objectives

To determine whether hearts reanimated with normothermic regional perfusion (NRP) have clinically detectable changes in function using echocardiography comparing the prearrest and post-NRP imaging. As heart transplantation from donation after circulatory death (DCD) continues to increase, preliminary results suggest outcomes comparable with donation after brain death. It is unknown whether the obligatory period of warm ischemia experienced during DCD withdrawal process causes immediate changes in cardiac allograft function following in situ reanimation.

Methods

We retrospectively reviewed and compared predonation with postreanimation echocardiographic findings in all DCD donors at our institution from January to October 2021. All DCD donor organs were reanimated with in situ thoracoabdominal NRP after circulatory death. Echocardiographic assessment included (1) 2-dimensional and speckle-tracking measures of chamber size and function; (2) ejection fraction; (3) fractional area change; and (4) global longitudinal strain.

Results

Altogether, 4 DCD heart donations were performed during the study period. Basic demographics and withdrawal ischemic time periods are reported. There were no changes in left ventricular ejection fraction and right ventricular fractional area change when comparing the predonation and the postreanimation echocardiogram. There was a minimal, nonstatistically significant decrease in left ventricular global longitudinal strain and right ventricular free-wall systolic strain in 3 of the 4 donors following reanimation.

Conclusions

DCD cardiac allografts reanimated with NRP demonstrated no change in echocardiographic parameters used for a standard predonation donor heart evaluation. Findings suggest cardiac function of DCD allografts reanimated with thoracoabdominal NRP is not adversely impacted by limited period of warm ischemia following circulatory arrest.

Dynamic Metabolic Changes During Prolonged Ex Situ Heart Perfusion Are Associated With Myocardial Functional Decline

Ex situ heart perfusion (ESHP) was developed to preserve and evaluate donated hearts in a perfused beating state. However, myocardial function declines during ESHP, which limits the duration of perfusion and the potential to expand the donor pool. In this research, we combine a novel, minimally-invasive sampling approach with comparative global metabolite profiling to evaluate changes in the metabolomic patterns associated with declines in myocardial function during ESHP. Biocompatible solid-phase microextraction (SPME) microprobes serving as chemical biopsy were used to sample heart tissue and perfusate in a translational porcine ESHP model and a small cohort of clinical cases. In addition, six core-needle biopsies of the left ventricular wall were collected to compare the performance of our SPME sampling method against that of traditional tissue-collection. Our state-of-the-art metabolomics platform allowed us to identify a large number of significantly altered metabolites and lipid species that presented comparable profile of alterations to conventional biopsies. However, significant discrepancies in the pool of identified analytes using two sampling methods (SPME vs. biopsy) were also identified concerning mainly compounds susceptible to dynamic biotransformation and most likely being a result of low-invasive nature of SPME. Overall, our results revealed striking metabolic alterations during prolonged 8h-ESHP associated with uncontrolled inflammation not counterbalanced by resolution, endothelial injury, accelerated mitochondrial oxidative stress, the disruption of mitochondrial bioenergetics, and the accumulation of harmful lipid species. In conclusion, the combination of perfusion parameters and metabolomics can uncover various mechanisms of organ injury and recovery, which can help differentiate between donor hearts that are transplantable from those that should be discarded.

High Oxygenation During Normothermic Regional Perfusion After Circulatory Death Is Beneficial on Donor Cardiac Function in a Porcine Model

BACKGROUND

Thoracoabdominal normothermic regional perfusion (NRP) is a new method for in situ reperfusion and reanimation of potential donor organs in donation after circulatory death by reperfusion of the thoracic and abdominal organs with oxygenated blood. We investigated effects of high oxygenation (HOX) versus low oxygenation (LOX) during NRP on donor heart function in a porcine model.

METHODS

Pigs (80 kg) underwent a 15-min anoxic cardiac arrest followed by cardiac reanimation on NRP using a heart-lung bypass machine with subsequent assessment 180 minutes post-NRP. The animals were randomized to HOX (FiO2 1.0) or LOX (FiO2 0.21 increased to 0.40 during NRP). Hemodynamic data were obtained by invasive blood pressure and biventricular pressure-volume measurements. Blood gases, biomarkers of inflammation, and oxidative stress were measured.

RESULTS

Eight of 9 animals in the HOX group and 7 of 10 in the LOX group were successfully weaned from NRP. Right ventricular end-systole elastance was significantly improved in the HOX group compared with the LOX group, whereas left ventricular end-systole elastance was preserved at baseline levels. Post-NRP cardiac output, mean arterial, central venous, and pulmonary capillary wedge pressure were all comparable to baseline. Creatinine kinase-MB increased more in the LOX group than the HOX group, whereas proinflammatory cytokines increased more in the HOX group than the LOX group. No difference was found in oxidative stress between groups.

CONCLUSIONS

All hearts weaned from NRP showed acceptable hemodynamic function for transplantation. Hearts exposed to LOX showed more myocardial damage and showed poorer contractile performance than hearts reperfused with high oxygen.

Assessment of Machine Perfusion Conditions for the Donation After Circulatory Death Heart Preservation

Background

Donation after circulatory death (DCD) hearts requires machine perfusion preservation, the conditions of which are not well defined.

Methods

To achieve this, rat hearts were procured following a DCD or control beating‐heart donation (CBD) model, and perfused for 60 min with one of three machine perfusion solutions—St. Thomas (ST), University of Wisconsin (UW), or Polyethylene Glycol‐20k (PEG)—at one of two temperatures, 4°C or 15°C. At 15‐min intervals, perfusion pressure was measured as a marker of vascular resistance. Colored microspheres were added to capture the distribution of perfusate into the metabolically active sub‐endocardium, and the eluate was collected for troponin assays. Analyses compared groups using Wilcoxon rank‐sum and ANOVA.

Results

Perfusion pressure was significantly higher for DCD than CBD hearts at 15°C regardless of solutions. The lowest rise in perfusion pressure over time was observed with PEG at 15°C. Except for PEG at 15°C, ST and UW solutions at 4 or 15°C had decreased sub‐endocardial perfusion in DCD hearts. Troponin release from DCD hearts with UW and PEG solutions was comparable to CBD hearts but was significantly higher with ST solution at 15°C.

Conclusions

Optimal preservation conditions for DCD hearts were observed with PEG machine perfusion solution at 15°C.

Relationship of Laser-Doppler-Flow and coronary perfusion and a concise update on the importance of coronary microcirculation in donor heart machine perfusion

BACKGROUND

Machine perfusion (MP) is a novel method for donor heart preservation. The coronary microvascular function is important for the transplantation outcome. However, current research on MP in heart transplantation focuses mainly on contractile function.

OBJECTIVE

We aim to present the application of Laser-Doppler-Flowmetry to investigate coronary microvascular function during MP. Furthermore, we will discuss the importance of microcirculation monitoring for perfusion-associated studies in HTx research.

METHODS

Porcine hearts were cardioplegically arrested and harvested (Control group, N = 4). In an ischemia group (N = 5), we induced global ischemia of the animal by the termination of mechanical ventilation before harvesting. All hearts were mounted on an MP system for blood perfusion. After 90 minutes, we evaluated the effect of coronary perfusion pressures from 20 to 100 mmHg while coronary laser-doppler-flow (LDF) was measured.

RESULTS

Ischemic hearts showed a significantly decreased relative LDF compared to control hearts (1.07±0.06 vs. 1.47±0.15; p = 0.034). In the control group, the coronary flow was significantly lower at 100 mmHg of perfusion pressure than in the ischemia group (895±66 ml vs. 1112±32 ml; p = 0.016).

CONCLUSIONS

Laser-Doppler-Flowmetry is able to reveal coronary microvascular dysfunction during machine perfusion of hearts and is therefore of substantial interest for perfusion-associated research in heart transplantation.

Pathophysiology of severe primary graft dysfunction in orthotopic heart transplantation

BACKGROUND

A series of insults on the donor heart result in pathophysiological changes that manifest as primary graft dysfunction (PGD) post-orthotopic heart transplantation. The objectives of this study were: (i) describe the pathophysiology of severe PGD using an established cardiovascular model; and (ii) the evolution of the pathophysiology during recovery from severe PGD.

METHODS

Hemodynamic data from 20 consecutive patients with severe PGD (need for mechanical circulatory support, MCS) at baseline (T0), 6 h (T6) and "recovery" (explant of support), and 20 consecutive patients without severe PGD were used to model the pathophysiology using the cardiovascular model described by Burkhoff and Dickstein.

RESULTS

There was a progressive (from T0 to T6) up- and leftward shift in the diastolic pressure-volume relationship, especially of the right ventricle (RV), resulting in reduced capacitance. RV end-systolic elastance (Ees) was significantly elevated in severe PGD but preload-recruitable stroke work (PRSW) was significantly lower compared to patients without severe PGD. "Recovery" (after liberation from MCS) was associated with improvement in RV Ees, chamber capacitance and PRSW, although they remained significantly lower than patients without severe PGD.

CONCLUSION

Severe PGD of the dominant right heart failure phenotype is characterized by reduced chamber capacitance, increased "stiffness" and impaired contractility. Complete normalization was not required for successful weaning of MCS.

A state-of-the-art review of the current role of cardioprotective techniques in cardiac transplantation

OBJECTIVES

The use of 'extended criteria' donor hearts and reconditioned hearts from donation after circulatory death has corresponded with an increase in primary graft dysfunction, with ischaemia-reperfusion injury being a major contributing factor in its pathogenesis. Limiting ischaemia-reperfusion injury through optimising donor heart preservation may significantly improve outcomes. We sought to review the literature to evaluate the evidence for this.

METHODS

A review of the published literature was performed to assess the potential impact of organ preservation optimisation on cardiac transplantation outcomes.

RESULTS

Ischaemia-reperfusion injury is a major factor in myocardial injury during transplantation with multiple potential therapeutic targets. Innate survival pathways have been identified, which can be mimicked with pharmacological conditioning. Although incompletely understood, discoveries in this domain have yielded extremely encouraging results with one of the most exciting prospects being the synergistic effect of selected agents. Ex situ heart perfusion is an additional promising adjunct.

CONCLUSIONS

Cardiac transplantation presents a unique opportunity to perfuse the whole heart before, or immediately after, the onset of ischaemia, thus maximising the potential for global cardioprotection while limiting possible systemic side effects. While clinical translation in the setting of myocardial infarction has often been disappointing, cardiac transplantation may afford the opportunity for cardioprotection to finally deliver on its preclinical promise.

Oxygen Therapy Lowers Right Ventricular Afterload in Experimental Acute Pulmonary Embolism

OBJECTIVES

To investigate if oxygen could unload the right ventricle and improve right ventricle function in a porcine model mimicking intermediate-high risk acute pulmonary embolism.

DESIGN

Controlled, blinded, animal study.

SETTING

Tertiary university hospital, animal research laboratory.

SUBJECTS

Female, Danish pigs (n = 16, approximately 60 kg).

INTERVENTIONS

Acute autologous pulmonary embolism was induced until doubling of baseline mean pulmonary arterial pressure. Group 1 animals (n = 8) received increasing Fio2 (40%, 60%, and 100%) for time intervals of 15 minutes returning to atmospheric air between each level of Fio2. In group 2 (n = 8), the effects of Fio2 40% maintained over 75 minutes were studied. In both groups, pulmonary vasodilatation from inhaled nitric oxide (40 parts per million) was used as a positive control.

MEASUREMENTS AND MAIN RESULTS

Effects were evaluated by biventricular pressure-volume loop recordings, right heart catheterization, and arterial and mixed venous blood gasses. Pulmonary embolism increased mean pulmonary arterial pressure from 15 ± 4 to 33 ± 6 mm Hg (p = 0.0002) and caused right ventricle dysfunction (p < 0.05) with troponin release (p < 0.0001). In group 1, increasing Fio2 lowered mean pulmonary arterial pressure (p < 0.0001) and pulmonary vascular resistance (p = 0.0056) and decreased right ventricle volumes (p = 0.0018) and right ventricle mechanical work (p = 0.034). Oxygenation was improved and pulmonary shunt was lowered (p < 0.0001). Maximal hemodynamic effects were seen at Fio2 40% with no additional benefit from higher fractions of oxygen. In group 2, the effects of Fio2 40% were persistent over 75 minutes. Supplemental oxygen showed the same pulmonary vasodilator efficacy as inhaled nitric oxide (40 parts per million). No adverse effects were observed.

CONCLUSIONS

In a porcine model mimicking intermediate-high risk pulmonary embolism, oxygen therapy reduced right ventricle afterload and lowered right ventricle mechanical work. The effects were immediately present and persistent and were similar to inhaled nitric oxide. The intervention is easy and safe. The study motivates extended clinical evaluation of supplemental oxygen in acute pulmonary embolism.

Heart donation and transplantation after circulatory determination of death: expert guidance from a Canadian consensus building process

Controlled donation after circulatory determination of death (DCD), where death is determined after cardiac arrest, has been responsible for the largest quantitative increase in Canadian organ donation and transplants, but not for heart transplants. Innovative international advances in DCD heart transplantation include direct procurement and perfusion (DPP) and normothermic regional perfusion (NRP). After death is determined, DPP involves removal and reanimation of the arrested heart on an ex situ organ perfusion system. Normothermic regional perfusion involves surgically interrupting (ligating the aortic arch vessels) brain blood flow after death determination, followed by restarting the heart and circulation in situ using extracorporeal membrane oxygenation. The objectives of this Canadian consensus building process by a multidisciplinary group of Canadian stakeholders were to review current evidence and international DCD heart experience, comparatively evaluate international protocols with existing Canadian medical, legal, and ethical practices, and to discuss implementation barriers. Review of current evidence and international experience of DCD heart donation (DPP and NRP) determined that DCD heart donation could be used to provide opportunities for more heart transplants in Canada, saving additional lives. Although candid discussion identified a number of potential barriers and challenges for implementing DCD heart donation in Canada, it was determined that DPP implementation is feasible (pending regulatory approval for the use of an ex situ perfusion device in humans) and in alignment with current medical guidelines for DCD. Nevertheless, further work is required to evaluate the consistency of NRP with current Canadian death determination policy and to ensure the absence of brain perfusion during this process.

Twenty-four-hour normothermic perfusion of isolated ex vivo hearts using plasma exchange

OBJECTIVE

Cross-circulation of plasma from a paracorporeal animal allows successful ex vivo heart perfusion (EVHP) for 3 days. Little is known about the feasibility of prolonged EVHP without a paracorporeal animal. These experiments evaluated plasma exchange (PX) that infuses fresh plasma, whereas an equal amount is removed to replace paracorporeal cross-circulation.

METHODS

Ten hearts were procured from 8 to 10 kg piglets and maintained with EVHP. The EVHP circuit was primed with platelet- and leukocyte-reduced blood. Plasma obtained from stored porcine blood (4°C for ≤7 days) was infused and removed with a plasma separator at 1 mL/h/g cardiac tissue (n = 5) in the PX group. Controls (n = 5) used the same EVHP without PX. Antegrade aortic perfusion was adjusted to reach physiologic coronary flow of 0.7 to 1.2 mL/min/g, normothermia (37°C), and hemoglobin ≥8 g/dL. Viability was assessed by hemodynamic metrics, metabolic assays, and histopathology.

RESULTS

All PX hearts remained viable for 24 hours compared with only 1 control (P = .015). Coronary resistance was higher in the PX versus controls (1.06 ± 0.06 mm Hg/mL/min; 0.58 ± 0.02 mm Hg/mL/min [P < .05]). Lactate levels were lower in PX (2.8-4.2 mmol/L) versus controls (3.6-7.6 mmol/L) (P < .05). PX demonstrated a trend toward preservation of left ventricle systolic pressure (63.0 ± 10.9 mm Hg) versus controls (37 ± 22.0 mm Hg) (P > .05). In mixed effect models, oxygen consumption was higher with PX (P < .05). Histopathologic evaluation confirmed extensive myocardial degeneration and worse interstitial edema in controls.

CONCLUSIONS

These results demonstrate that EVHP can be successfully maintained for at least 24 hours using continuous PX. This eliminates the need for a paracorporeal animal and provides an important step toward clinical application.

Comparing Donor Heart Assessment Strategies During Ex Situ Heart Perfusion to Better Estimate Posttransplant Cardiac Function

BACKGROUND

Ex situ heart perfusion (ESHP) limits ischemic periods and enables continuous monitoring of donated hearts; however, a validated assessment method to predict cardiac performance has yet to be established. We compare biventricular contractile and metabolic parameters measured during ESHP to determine the best evaluation strategy to estimate cardiac function following transplantation.

METHODS

Donor pigs were assigned to undergo beating-heart donation (n = 9) or donation after circulatory death (n = 8) induced by hypoxia. Hearts were preserved for 4 hours with ESHP while invasive and noninvasive (NI) biventricular contractile, and metabolic assessments were performed. Following transplantation, hearts were evaluated at 3 hours of reperfusion. Spearman correlation was used to determine the relationship between ESHP parameters and posttransplant function.

RESULTS

We performed 17 transplants; 14 successfully weaned from bypass (beating-heart donation versus donation after circulatory death; P = 0.580). Left ventricular invasive preload recruitable stroke work (PRSW) (r = 0.770; P = 0.009), NI PRSW (r = 0.730; P = 0.001), and NI maximum elastance (r = 0.706; P = 0.002) strongly correlated with cardiac index (CI) following transplantation. Right ventricular NI PRSW moderately correlated to CI following transplantation (r = 0.688; P = 0.003). Lactate levels were weakly correlated with CI following transplantation (r = -0.495; P = 0.043). None of the echocardiography measurements correlated with cardiac function following transplantation.

CONCLUSIONS

Left ventricular functional parameters, especially ventricular work and reserve, provided the best estimation of myocardial performance following transplantation. Furthermore, simple NI estimates of ventricular function proved useful in this setting. Right ventricular and metabolic measurements were limited in their ability to correlate with myocardial recovery. This emphasizes the need for an ESHP platform capable of assessing myocardial contractility and suggests that metabolic parameters alone do not provide a reliable evaluation.