Innovative Strategies for Organ Preservation in Heart Transplantation: Uniform Cooling Preservation and Ex-situ Normothermic Perfusion

Summary

Donor heart preservation is a major determinant of success in heart transplantation. Technological advances have led to optimizing the conditions of preservation, along with a more accurate assessment of the donor heart before transplantation. We herein describe two innovative technologies currently applied for cardiac preservation: uniform cooling preservation and normothermic ex-situ heart perfusion.

Abstract

Nearly 4,500 heart transplantations are performed annually worldwide. Given the current organ shortage, extended criteria are frequently accepted nowadays for the selection of donor hearts. There is therefore a need for optimized preservation technology to prevent the risk of primary graft dysfunction. The Uniform Cooling Preservation (UCP) is an FDA-approved and CE-marked approach applied in clinical practice since 2020. UCP provides stable cold storage for safe preservation of cardiac allografts, including those procured in donors with extended criteria. Decreased utilization of mechanical circulatory support, along with reduced hospital stay after transplant, has been associated with the use of UCP. Normothermic ex-situ heart perfusion (ESHP) has been developed to ensure safe and prolonged preservation of cardiac allografts. Thanks to ex-situ normothermic oxygenated blood perfusion, ESHP technology allows for continuous monitoring of the donor heart during transportation. Myocardial viability for transplant is characterized by a progressive decrease in lactate level in the perfusate. ESHP has recently been applied for the rehabilitation of cardiac allografts procured after controlled circulatory death. In the present report, we aim to describe technical features of UCP and ESHP preservation technologies. Early clinical outcomes will be discussed, focusing on the rate of severe primary graft dysfunction after transplant.

Introduction

Heart transplantation (HT) remains the treatment of choice for patients with advanced heart failure, despite advances in long-term mechanical circulatory support (MCS). Traditionally, donor heart preservation relies on ice-cold storage (ICS). In this method, the heart is first flushed with a crystalloid preservation solution, then stored in the same solution at 2-8 °C using a three-bag system placed in a specialized icebox for organ transport.

However, this approach has several limitations. Significant temperature fluctuations have been reported during ICS, particularly overcooling (below +2 °C), which may increase the risk of cold-induced graft injury. Additionally, ICS does not achieve complete hypothermic arrest of myocardial metabolism, which remains largely anaerobic. As a result, freeze-induced graft damage and subsequent ischemia-reperfusion injury are common. These injuries can contribute to primary graft dysfunction (PGD), especially when cold ischemic storage exceeds 4 h.

To minimize temperature fluctuations, uniform cooling preservation (UCP) using the SherpaPak Cardiac Transport System has been developed for the lungs, liver, and heart. Introduced in 2018, UCP provides consistent and controlled hypothermic preservation of the donor heart during transport, maintaining temperatures between 4 °C and  °C¹. This technology aims to reduce the risk of freeze-induced graft injury. UCP has seen increasing adoption in Europe and North America, with over 40% of donor hearts in the United States transported using this method in 2023. The Cardiac Transport System is a single-use device with an outer transport shipper containing an internal battery that requires no external power source. Three cold ribbons, stored in a -20 °C freezer for a minimum of 48 h, are then disposed of inside the outer transport shipper. A fourth cold ribbon is placed on the top of the outer canister. This device keeps the donor heart between 4 °C and 8 °C for a prolonged period of time (up to 8 h)^2,3. The Cardiac Transport System provides UCP but without the possibility of active temperature regulation. The temperature is constantly monitored and can be observed on a mobile phone application via a secure Bluetooth connection. Geolocation of the device is also available during organ transportation, except during airplane flights.

A shortage of suitable donor hearts after brain death persists, despite the increasing use of marginal donors (e.g., age > 55, prolonged cardiac arrest, or cardiovascular comorbidities). Donation after controlled circulatory death (DCD) has emerged as a promising strategy to expand the donor pool and has recently been associated with a significant reduction in waiting times for patients with advanced heart failure^4,5,6. However, transplantations involving extended criteria donors (ECD) carry a higher risk of primary graft dysfunction (PGD), primarily due to prolonged warm ischemia and the potential for irreversible myocardial injury⁷. This underscores the need for improved preservation methods for ECD organs, as well as reliable assessment of myocardial viability prior to transplantation. Over the past decade, machine perfusion technology has emerged as an advanced modality for organ preservation. Normothermic ex-situ heart perfusion (ESHP) was initially developed to extend preservation times beyond the critical 4 h window associated with ice-cold storage (ICS)⁸. More recently, ESHP has demonstrated potential to expand the donor pool, particularly for ECD and DCD allografts^5,9. Early clinical outcomes are comparable to those achieved with heart transplants from standard brain-dead donors^5,10,11,12.

ESHP using oxygenated blood was first described in 1998¹³. The Organ Care System (OCS) is the only commercially available device validated (FDA- and CE-marked) for the transportation of donor hearts in a normothermic perfused state. Immediately after retrieval, the donor heart is reperfused and maintained in a warm, beating state until arrival at the recipient center. Complementary materials (defibrillator, external pacemaker, transportable blood gas analyzer) and accessories (heart perfusion module, 9 V batteries, epicardial pacing leads, left ventricular vent, spare leukocyte-depleting filter) are necessary to allow ESHP with the transportable OCS device. The procurement team should be composed of a senior cardiac surgeon (the procurement surgeon), an assistant cardiac surgeon, and an intensivist, perfusionist, or another cardiac surgeon dedicated to managing the ESHP console throughout the procedure at the donor center. The donor's hematocrit should be greater than 25% (or hemoglobin > 10 g/dL) to ensure optimal oxygen transport during ESHP.

The removable screen of the OCS console displays continuous values for mean aortic output and pressure, mean coronary flow, oxygen saturation, hematocrit, and temperature. Epinephrine infusion (diluted in 5% glucose solution) is used to maintain physiological levels of circulating catecholamines. This technology enables real-time visual and metabolic monitoring of the donor heart, allowing for assessment of its suitability for transplantation. A favorable ESHP is achieved when the arterial lactate trend is stable or decreasing, and this trend is consistent with a decreasing venous lactate concentration. A positive arterio-venous lactate difference confirms myocardial lactate extraction and serves as an accepted biomarker for optimal ESHP and donor heart eligibility for transplant^8,13.

ESHP may increase the utilization rate of ECD, a major issue in the current setting of organ shortage. A recent emphasis has been observed in the past decade on the use of ESHP in DCD heart transplantation^5,11,12,14. Indeed, Schroder et al. recently reported that 87% of donor hearts initially considered unsuitable for transplant (marginal donors) could finally be transplanted after ESHP⁶. Although promising, this technology is more complex than ICS and requires specialized technical skills that heart transplant teams must develop.

In our institution, we used exclusively ICS until 2019. We subsequently initiated an ESHP program for long-distance procurements and high-risk transplantations, particularly for recipients with preoperative mechanical circulatory support or a history of multiple open-heart surgeries. Since 2023, we have replaced ICS with uniform cooling preservation (UCP). The present protocol report aims to present a safe and reproducible methodology for implementing both ESHP and UCP. We also share our preliminary clinical experience in heart transplantation utilizing these two innovative technologies.

Protocol

All animals included in this video protocol (using porcine hearts) received humane care in accordance with the Principles of Laboratory Animal Care formulated by the National Society for Medical Research, as well as the Guide for the Care and Use of Laboratory Animals (NIH Publication No. 86-23, revised 1996). All procedures were conducted following approval for the use of animals in scientific research, granted by the French Ministry of Research (reference APAFiS#23716-2020012112432923v1). We obtained informed consent from the patients mentioned in this study to use and publish their data.

1. Uniform cooling preservation

1. Retrieve the sterile nested canisters (the outer one protects the inner one) and place the inner one in a cup filled with ice. A "cold atmosphere" is therefore created around the inner canister.
2. Fill the inner canister with 3 L of cold preservation solution (the same as that used for cardioplegic arrest of the donor heart), after validation of the suitability of the graft for transplant (visual inspection), and just before retrieval.
3. Explant the donor heart conventionally with the longest possible ascending aorta to place the UCP-specific connector canula high enough to preserve sufficient length for the aortic anastomosis.
4. Choose the appropriate size for the UCP aortic connector corresponding to the inner diameter of the ascending aorta.
5. Secure the aortic canula into the aortic lumen with an external surgical loop.
6. Connect the aortic canula to the inner canister cover to suspend the donor heart in the preservation solution.
7. Deair the inner canister by slowly flushing the preservation solution through a dedicated port (fluid will exit from a second port located on the cover). Fill the canister with solution up to the top, then close it with its dedicated cap. Ensure the donor heart is completely submerged in the preservation solution.
8. Place the inner canister inside the outer canister and lock the outer canister with its dedicated cover.
9. Place the outer canister in the shipper and start temperature monitoring. Preservation temperature is visible on the anterior screen of the shipper and on the mobile phone application.
   NOTE: No temperature adjustment is possible during organ transportation using UCP.
10. Upon arrival of the procurement team at the recipient center, remove the donor heart from the inner canister (respecting sterile conditioning). Open the inner canister and gently disconnect the UCP aortic connector from the cover. Remove the connector from the ascending aorta.

2. Heart retrieval

1. Perform a median sternotomy.
2. Separate the ascending aorta from the pulmonary artery. Control the superior and inferior vena cava with a surgical loop.
3. Inject heparin (300 IU/kg, IV). Wait 3 min after heparin administration, then canulate the ascending aorta above the origin of the right coronary artery for cardioplegia injection.
   NOTE: Purge and connect the cardioplegia line to the aortic canula before blood collection. Blood collection may result in significant hemodynamic collapse with low pressure in the ascending aorta, making its canulation challenging. Another reason to secure the cardioplegia line to the aortic canula is to be ready for flushing after aortic cross-clamping as soon as blood collection is completed.
4. Canulate the right atrium with a 32-French double-staged canula.
5. Connect a sterile, heparinized bag (10,000 IU) to the right atrium cannula and collect 1,200 to 1,500 mL of blood. Allow 90-120 s for this process.
6. Prime the circuit of the heart perfusion module with the donor blood collected after leukocyte filtering using a dedicated filter. Add 500 mL of saline priming solution containing 10% albumin, insulin, steroids, and antibiotics.
7. Clamp the distal part of the ascending aorta and flush cold crystalloid cardioplegia solution to induce diastolic cardiac arrest.
8. Explant the donor heart with the longest possible ascending aorta to place the aortic canula high enough to avoid coronary artery obstruction.
9. Close the left atrial appendage if it was opened (in case of simultaneous lung procurement). Look for a patent foramen ovale and close it if present (one or two single stitches of 4.0 monofilament).

3. Heart instrumentation

1. Place the heart in a sterile cup with a 4 °C saline solution.
2. Place four pledgetted sutures of 4.0 monofilament on the cardinal points of the distal ascending aorta.
3. Choose the appropriate aortic cannula from the four available sizes to match the donor aorta diameter. Do not oversize the canula.
4. Secure the aortic canula with an external cable tie to prevent accidental detachment of the heart from the connector during transport.
5. Secure the malleable pulmonary cannula with a 4.0 monofilament running suture around the pulmonary trunk.
6. Create a purse-string suture with 4-0 monofilament on the left atrium to secure the left ventricular vent cannula. Insert a canula vent into the left ventricle through the left atrium for deairing during ESHP.
7. Close the superior vena cava with a 4.0 monofilament running suture.

4. Heart reperfusion on ESHP

1. Reduce the pump flow to 1,000 mL/min and remove the shunt between the aortic and venous lines before positioning the heart.
2. Place the heart upside down with the posterior ventricular walls facing the operator.
3. De-air the ascending aorta and connect the aortic canula to the aortic line.
   NOTE: Blood flow is delivered into the aorta in a retrograde manner, enabling coronary artery perfusion.
4. Perform a gentle cardiac massage until the heart is warmed up.
5. Deliver a 30 J shock in case of ventricular fibrillation to obtain a sinus rhythm.
6. Place an epicardial pacing lead on the posterior wall of the right ventricle. Connect this lead to an external pacemaker and pace the heart at 80 beats/min.
7. Slowly increase the pump flow to reach an aortic pressure of 65 mmHg.
8. Close the inferior vena cava with a 4.0 monofilament running suture.
   NOTE: At this point, all the deoxygenated blood flowing from the coronary sinus goes into the right atrium and is ejected through the pulmonary artery since the right ventricle is beating.
9. De-air and connect the pulmonary cannula to the venous line. Place a flow probe on the venous line for continuous monitoring of the coronary blood flow.
   NOTE: Warm venous blood enters the reservoir and is then pumped by a centrifugal pump through the gas exchanger. Warm oxygenated blood then goes to the aortic line. Once connected to the perfusion module, the isolated heart thus receives a warm (34 °C), oxygenated, and nutrient-enriched perfusion.

5. Hemodynamic and metabolic monitoring during ESHP

1. Maintain the mean aortic pressure between 70 and 85 mmHg and mean coronary flow between 650 and 850 mL/min.
   NOTE: Coronary flow can be reduced by decreasing pump flow. Infusing a maintenance solution containing adenosine prevents coronary vasoconstriction and thus increases coronary flow. Increasing pump flow both leads to higher coronary flow and higher mean aortic pressure.
2. Perform metabolic monitoring during ESHP by repeatedly measuring arterial and venous lactate concentrations every 30 min (or every 15 min after adjusting the maintenance solution flow rate or changing the pump flow) using an automated transportable analyzer.
3. Optimize perfusion parameters and correct biochemical disorders (glycemia, Ca²⁺, K⁺, PO₂, PCO₂, pH) in response to an adverse lactate trend.
4. Disqualify the donor heart from transplantation in case of persistent arterial lactate increase despite all corrective measures.

6. Termination of ESHP

1. Connect the ESHP heart perfusion module to a water heater cooler via specific ports on the oxygenator membrane. Cool at 2 °C intervals.
2. Stop pacing the heart and disconnect the venous line when the heart rhythm drops below 50 bpm.
3. At 16 °C, stop the donor heart with the same crystalloid cardioplegia solution as the one used for initial cardiac arrest.
4. Decannulate the heart from the ESHP perfusion module. Place the heart in a bowl of cold saline solution until implantation.
   NOTE: ESHP using the OCS technology is not a platform for organ rehabilitation or repair. A poor-quality graft before organ procurement will remain an unsuitable heart for transplantation, even after several hours of ESHP. We would not recommend initiating an ESHP program using grafts from extended-criteria donors at the outset, as this may lead to unfavorable outcomes -- not due to the ESHP technology itself but because of the intrinsically poor quality of the grafts.

Results

All consecutive heart transplantations performed in our institution between January 2020 and July 2023 were reviewed. Three groups were compared considering the approach for organ preservation: ice cold storage (ICS, n = 37), normothermic ex-situ heart perfusion (ESHP, n = 7), and uniform cooling preservation using the Uniform Cooling Preservation (UCP, n = 7). PDG was defined by either left ventricular ejection fraction < 30%, and/or need for mechanical circulatory support (M...

Discussion

Hypothermia has been the gold standard for decades to achieve safe organ preservation. The optimal temperature for static cold storage ranges between 4 °C and 8 °C to prevent cellular damage. In experimental conditions, UCP can maintain a heart within this temperature range up to 30 h⁹. In our preliminary clinical experience, the longest ischemic time associated with UCP preservation was 286 min in a patient transplanted in emergency for post cardiotomy refractory heart failure. A severe...

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
Equipment for OCS
4-0 polypropylene suture	Peters, bobigny, France	20S15B	sutures
5-0 polypropylene suture	Peters, bobigny, France	20S10B	sutures
Adrenaline 0.25 mg/L	Laboratoire Renaudin, Itxassou, France		Drugs for the Epinephrine infusion
Albumin 25% 100 mL	CSL Behring AG, Bern, Switzerland	44206-251-10	Drugs for the priming solution
Cefotaxime 1 g	Panpharma, Luitre, France	3400955083139	Drugs for the priming solution
Ciprofloxacin 200 mg	Panpharma, Luitre, France	3400893163542	Drugs for the priming solution
DLP Aortic Root Cannula	Medtronic Inc. Minneapolis, Minneapolis, USA	ref. 11012, 12.5 inch	Aortic Root Cannula
EKG epicardial electrodes	Cardinal Health LLC, Waukegan, Illinois, USA	31050522	EKG detection electrodes
External pacemaker	Medtronic Inc. Minneapolis, Minneapolis, USA	5392	Pacemaker device
Glucose 5%	B.Braun Melsungen AG, Melsungen, Germany	3400891780017	Drugs for the Epinephrine infusion
Heart Perfusion Set, Organ Care System	Transmedics, Andover, MA, USA	Ref#1200	Normothermic ex-vivo heart perfusion device
Insulin	Novo Nordisk, Puteaux, France	34009 352 590 9 7	Additive for the maintenance Solution
Intracardial sump	Medtronic Inc. Minneapolis, Minneapolis, USA	12112	intracardial sump for left ventricle venting
Istat 1	Abbott, Chicago, Ill, USA	714336-03O	Blood Analyzer machine
Methylprednisolone	Mylan S.A.S, Saint Priest, France	400005623	Drugs for the priming solution
Multivitamin Cernevit	BAXTER S.A.S, Guyancourt, France	34009 356 571 9 0	Drugs for the priming solution
OCS Aortic cannula	TransMedics, Andover, USA	NA	Ex-situ heart perfusion aortic cannula
OCS Pulmonary artery cannula	TransMedics, Andover, USA	NA	Ex-situ heart perfusion pulmonary artery cannula
Plegisol 1000 mL	Pfizer, Paris, France	34009 555 976 9 8	Cardioplegia
Sodium Bicarbonate	Laboratoire Renaudin, itxassou, France	3701447	Drugs for the priming solution
Sodium chloride	Aguettant, Lyon, France	606726	Drugs for the priming solution
Two staged Venous Cannula (32 Fr)	Medtronic Inc. Minneapolis, Minneapolis, USA	91240, 32 french	Venous Cannula
Equipment for SHERPAPAK
4-0 polypropylene suture	Peters, bobigny, France	20S15B	sutures
5-0 polypropylene suture	Peters, bobigny, France	20S10B	sutures
Perisoc 6 Litres	Serb laboratory, Paris, France	34009 550 712 1 1	Cardioplegia
Sherpapak Aortic cannula	Paragonix Technologies, Inc, Cambridge, Massachusetts, USA	NA	Static cold storage device
Sherpapak nested canister system	Paragonix Technologies, Inc, Cambridge, Massachusetts, USA	NA	Static cold storage device
Sherpapak Rigid Outer Shell	Paragonix Technologies, Inc, Cambridge, Massachusetts, USA	NA	Static cold storage device
Surgical Loop (coton)	B. BRAUN SURGICAL SA, Rubi (Barcelone), Spain	B1095668	sutures