Better Than Ice: Advancing the Technology of Donor Heart Storage With the Paragonix SherpaPak

The imbalance of supply and demand is a common theme in organ transplantation. For many years, it has been clear that transformative changes are needed to make organs available to the large number of patients who succumb to their end-stage organ failure while on the transplant waiting list. Efforts have focused on prioritizing patients who are most in need, expanding the donor pool, and improving the usability of donor organs. The implementation of a new heart allocation policy in 2018 by the Organ Procurement and Transplantation Network (OPTN) has led to a major shift in practice due to prioritization of patients with temporary mechanical circulatory support (MCS), resulting in fewer bridge-to-transplant durable left ventricular assist device (LVAD) implants. Despite that, the goal of improved geographic sharing of organs, reducing waitlist time, and better stratification of the most medically urgent patients appears to have been achieved.1–3 The opioid epidemic has led to an expanded donor pool,4 and additional expansion has occurred with the development of protocols for the use of hepatitis C positive organs5 and donation after cardiac death (DCD) hearts.6 Yet, organ preservation still remains a major issue limiting supply and geographic reach of donor hearts, and innovative technologies are emerging to address this issue.

According to the 2019 OPTN/SRTR data report,7 fewer than 4,000 patients received a donor heart, however approximately 70% of potential donor hearts (estimated to be over 80,000 hearts) were not utilized. The low utilization is predominately due to the limited ischemic time tolerated by the heart. In contrast to organs such as the kidney and liver, which can tolerate ischemic times upwards of 24 hours, the heart is only able to withstand 4–6 hours of ischemia. Prolonged ischemia is associated with more pronounced ischemia/reperfusion injury, creating substrate for the development of primary graft dysfunction (PGD) and cardiac allograft vasculopathy.8 Thus, optimizing preservation of the heart is critical to both graft and recipient survival.

In a recent publication in ASAIO Journal, Voigt et al. present encouraging results from the Global Utilization and Registry Database for Improved Heart Preservation (GUARDIAN), comparing clinical outcomes of heart transplant patients receiving donor hearts preserved in the Paragonix SherpaPak Cardiac Transport System (Paragonix Technologies, Cambridge, MA) versus conventional cold storage.9 The SherpaPak is a sterile, disposable unit with temperature monitoring, which in theory allows for uniform cooling of the organ submerged in preservation solution.10 The SherpaPak was designed to protect donor hearts from physical and thermal injury, with the intention of prolonging the ischemic time tolerated by donor hearts while also improving the outcomes of heart transplantation. Paragonix Technologies has reported temperature validity of the SherpaPak up to 40 hours, although the FDA approval from 2020 is for 4 hours of use. At the surface level, the SherpaPak may seem like a glorified cooler with an expensive price tag of $15,000–$20,000. It does not have a mechanism to actively regulate temperature once the organ has been packaged, and some investigators have found that it is necessary to cool the preservation solution to 4–8°C to ensure target organ temperatures of 4–8°C during storage.11 In comparison, conventional cold storage is simple and inexpensive. With the typical three-bag technique of cold storage, the donor organ is first placed in a plastic bag filled with preservation solution, then placed in a plastic bag filled with saline, covered with a third plastic bag, and then placed in a slush/ice-filled nonsterile cooler for transport. Yet, there is experimental evidence that cooling with conventional cold storage is non-uniform and that temperatures below 2°C are often achieved, which can lead to frost-bite injury and protein denaturation.12 Additionally, sterility may be more difficult to achieve than with the SherpaPak unit. Retrospective single-center experiences with Sherpapak technology have been reported by a small number of centers in recent years.13–17

Early results from the GUARDIAN Registry were presented at the 2022 annual meeting of the International Society of Heart and Lung Transplantation.18 At that time, the registry included data from 11 participating heart transplant centers in the United States, with a cohort of 156 patients receiving organs preserved with conventional cold storage (control), and 227 receiving organs preserved with the SherpaPak. GUARDIAN includes retrospective data on control as well as prospectively collected data on additional control and SherpaPak donor/recipient pairs. Nearly, all the SherpaPak cohorts (96.5%) were transplanted after the 2018 allocation change, compared to 55.8% of the control group. Not surprisingly, characteristics between the two groups differed, with lower rates of durable LVAD in the SherpaPak group (35.2% vs. 55.1% in the control), higher rates of pretransplant ECMO (17.2% vs. 7.8% in the control), longer distance to donor organ (463 vs. 274 miles), and longer ischemic time (217 vs. 195 minutes). The incidence of severe PGD was lower in the SherpaPak cohort (5.3% vs. 13% in the control), and 30-day and 1-year survival were similar between the groups.

Voigt et al.’s work offers additional insight into the potential advantages of SherpaPak storage versus conventional cold storage.9 They compared hospital costs and posttransplant outcomes in 87 propensity matched pairs from the GUARDIAN Registry. Eligible subjects were those with no prior history of organ transplantation who received a heart transplant at 12 designated transplant hospitals between August 2015 and November 2021. Of 490 eligible subjects, 174 were matched. The study used Medicare cost reports and hospital specific cost/charge ratios from hospital chargemaster reports to quantify costs. The SherpaPak cohort had lower incidence of severe PGD (5.7% vs. 16.1% in control, p = 0.03), as well as lower postoperative use of MCS (21.8% vs. 40.2% in control, p = 0.009). This was associated with an overall lower cost of hospitalization. Among recipients who did develop PGD, the severity of PGD and mortality associated with PGD was significantly reduced in the Sherpapak group compared to control.

The reported improvement in posttransplant outcomes with SherpaPak donor heart storage compared to conventional cold storage should certainly garner the attention of heart transplant clinicians. When compared to other emerging preservation strategies for donor hearts, including hypothermic and normothermic machine perfusion, the SherpaPak device offers ease of use, relative freedom from mechanical failure, and significantly lower cost. That said, this particular study9 has important limitations that must be considered, including (1) absence of randomization, (2) exclusion of donor procurement costs (including the cost of the SherpaPak unit) from the cost analysis, and (3) reliance upon Medicare cost reporting which may be incomplete or inaccurate. Future randomized studies will undoubtedly be important to quantify the clinical and economic impact of SherpaPak technology.

1. Bradbook K, Goff RR, Lindblad K, Daly RC, Hall S: A national assessment of one-year heart outcomes after the 2018 adult heart allocation change. J Heart Lung Transplant 42: 196–205, 2023. 2. Goff RR, Uccellini K, Lindblad K, et al.: A change of heart: preliminary results of the US 2018 adult heart allocation revision. Am J Transplant 20: 2781–2790, 2020. 3. Colvin M, Smith JM, Ahn Y, et al.: OPTN/SRTR 2020 annual data report: Heart. Am J Transplant 22: 350–437, 2022. 4. Durand CM, Bowring MG, Thomas AG, et al.: The drug overdose epidemic and deceased-donor transplantation in the United States. Ann Intern Med 168: 702–711, 2018. 5. Villegas-Galaviz J, Anderson E, Guglin M: Clinical outcomes of heart transplantation using hepatitis c-viremic donors: A systematic review with meta-analysis. J Heart Lung Transplant 41: 538–549, 2022. 6. Kwon JH, Ghannam AD, Shorbaji K, et al.: Early outcomes of heart transplantation using donation after circulatory death donors in the United States. Circ Heart Failure 15: e009844, 2022. 7. Israni AK, Zaun D, Rosendale JD, Schaffhausen C, McKinney W, Snyder JJ: OPTN/SRTR 2019 annual data report: deceased organ donors. Am J Transplant 21: 521–558, 2021. 8. Del Rizzo DF, Menkis AH, Pfugfelder PW, et al.: The role of donor age and ischemic time on survival following orthotopic heart transplantation. J Heart Lung Transplant 18: 310–319, 1999. 9. Voigt JD, Leacche M, Copeland H, et al.: Multicenter registry using propensity score analysis to compare a novel transport/preservation system to traditional means on postoperative hospital outcomes and costs for heart transplant patients. ASAIO J 69: 345–349, 2023. 10. Michel SG, LaMuraglia GM, Madariaga MLL, Anderson LM: Innovative cold storage of donor organs using the Paragonix SherpaPak devices. Heart Lung Vessel 7: 246–255, 2015. 11. Kawabori M, Posawatz DA, Chen FY, Couper GS: A simple technique for reliable donor organ temperature management with the SherpaPak system. ASAIO J 68: e134–e135, 2022. 12. Hendry PJ, Walley VM, Koshal A, Masters RG, Keon WJ: Are temperatures attained by donor hearts during transport too cold? J Thorac Cardiovasc Surg 98: 517–522, 1989. 13. Schmiady MO, Graf T, Ouda A, et al.: An innovative cold storage system for donor heart transportation- lessons learned from the first experience in Switzerland. J Thorac Dis 13: 6790–6799, 2021. 14. Bitargil M, Haddad O, Pham SM, et al.: Controlled temperatures in cold preservation provides safe heart transplantation results. J Card Surg 37: 732–738, 2022. 15. Bitargil M, Haddad O, Pham SM, et al.: Packing the donor heart: Is SherpaPak cold preservation technique safer compared to ice cold storage. Clin Transplant 36: e14707, 2022. 16. Zhu Y, Shudo Y, He H, et al.: Outcomes of heart transplantation using a temperature-controlled Hypothermic storage system. Transplantation, 2022. doi:10.1097/TP0000000000004416. 17. Radakovic D, Karimli S, Penov K, et al.: First clinical experience with the novel cold storage SherpaPak system for donor heart transportation. J Thorac Dis 12: 7227–7235, 2020. 18. Leacche M, Philpott J, Pham S, et al.: US Multi-center analysis of the Global Utilization and Registry Database for Improved Heart Preservation (GUARDIAN) Registry: 1-Year transplant survival analysis. J Heart Lung Transplant 41: S30–S31, 2022.

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