Outcomes of truncal valve replacement in neonates and infants: a meta-analysis

Partial Heart Transplantation: Early Experience With Pediatric Heart Valve Replacements That Grow

Heart valve replacement in children is fraught with long-term morbidity and mortality rates, largely because conventional implants lack the capacity to grow with the child. Partial heart transplantation presents a potential solution by transplanting only specific segments of a donor heart, thereby providing a living and growing heart valve implant. This approach harnesses the full spectrum of cardiac tissues, which, when freshly procured and supported by immunosuppression, can integrate as functional and potentially growth-capable tissue. This state-of-the-art review discusses the history and development of partial heart transplantation, its indications, recent clinical experiences, regulation, and future directions.

Domino partial heart transplantation

Heart valve replacement in pediatric cardiothoracic surgery poses problems because conventional heart valve implants do not have the ability to grow. This mandates serial reoperations for implant exchanges until an adult-size implant can fit. Partial heart transplantation eliminates these reoperations because the transplanted valves grow. However, partial heart transplantation competes with heart transplantation for a limited supply of donor hearts. This is a critical barrier to the progress of the field. Domino partial heart transplantation is a new surgical technique that overcomes this barrier by capitalizing cardiectomy hearts from heart transplant recipients for partial heart transplantation. This surgical technique has the potential to transform pediatric heart valve replacement by greatly expanding the cardiac donor pool, increasing the time available for matching donors with recipients and simplifying the logistics of donation. As a result, the number of domino partial heart transplants is expected to exceed the number of partial heart transplants from deceased donors.

Partial Heart Transplant Update: Where Are We In 2025?

Partial heart transplantation (PHT) creates a new and innovative approach to allow for patient and disease tailored intervention with the ability to treat a larger patient base. It offers the growth capacity of a heart transplantation without the need for high dose immunosuppression. The importance of a valve replacement with the potential of growth is imperative in the pediatric population as these patients will otherwise outgrow their new valves requiring repeat and high-risk interventions. Adaptive valve growth has been observed prior to PHT, in the case of orthotopic heart transplantation and Ross pulmonary autografts. The first human PHT was performed in April of 2022 at Duke. The recipient was a 17-day old infant with truncus arteriosus and severe truncal valve regurgitation. The operation was a success and the transplanted PHT conduit showed appropriate adaptive valve growth. Due to the low immunogenicity and recipient endothelialization of the transplanted PHT graft, the immunosuppressive requirements for PHT patients are low. One of the benefits of PHT is that it utilizes hearts which would otherwise not be suitable for orthotopic heart transplantation. Furthermore, the prospect of domino and split root PHT increases the potential of ethical and efficient organ stewardship. Currently PHT is regulated by the Food and Drug Administration, a ruling which was released in early 2024 as human cells, tissues, or cellular or tissue-based products (HCT/Ps). This means it does not compete with hearts suitable for orthotopic heart transplantation which are regulated as organs under the Organ Procurement and Transplantation Network (OPTN).

Indications and Practical Considerations for Partial Heart Transplantation

Partial heart transplantation is a new approach to deliver growing heart valve substitutes for children. The rationale for partial heart transplantation is that the valves contained in heart transplants grow. Partial heart transplants differ from heart transplants because only the part of the heart containing the necessary valve is transplanted, while the native ventricles are preserved. Preserving the native ventricles eliminates the risk of graft ventricular dysfunction and allows for utilization of donor hearts with ventricular dysfunction. Here we outline practical considerations for partial heart transplantation, including indications, sources for donor hearts, graft procurement, graft preservation, implantation, recipient immunosuppression, and reimbursement. This invited expert review is intended to help clinical teams implement partial heart transplantation.

Why partial heart transplantation could be regulated as organ transplantation

Partial heart transplant (PHT) is a recent clinical innovation involving the transplantation of a segment of the heart (valves) directly from the deceased donor into the recipient patient. This procedure holds out the possibility of significant benefit, especially for pediatric patients because these grafts show growth potential after transplant, reducing or eliminating the current need for repeat procedures. The clinical process for donation and transplant of partial heart (PH) grafts generally follows an organ clinical pathway; however, the Food and Drug Administration has recently stated its intent to regulate PH as tissues, raising a host of regulatory considerations. PHT requires donor testing and eligibility determinations within a short, clinically viable timeframe and, similar to organ transplant, involves donor-recipient matching. Waitlist allocation policies that are a regulatory focus of the Organ Procurement and Transplantation Network including equity and efficiency may become relevant. Oversight of PHT by the Organ Procurement and Transplantation Network could be accomplished through interpretation of the vascular composite allograft definition or through designation by the US Department of Health and Human Services of PH grafts as organs. While some clinical questions remain unanswered, it is important to carefully address these regulatory considerations to support the emergence of this innovation and ensure the continued trust of the donating public and the patients who may benefit from PHT.

Animal models for partial heart transplantation

BACKGROUND

Partial heart transplantation delivers growing heart valve implants by transplanting the part of the heart containing the necessary heart valve only. In contrast to heart transplantation, partial heart transplantation spares the native ventricles. This has important implications for partial heart transplant biology, including the allowable ischemia time, optimal graft preservation, primary graft dysfunction, immune rejection, and optimal immunosuppression.

AIMS

Exploration of partial heart transplant biology will depend on suitable animal models. Here we review our experience with partial heart transplantation in rodents, piglets, and non-human primates.

MATERIALS & METHODS

This review is based on our experience with partial heart transplantation using over 100 rodents, over 50 piglets and one baboon.

RESULTS

Suitable animal models for partial heart transplantation include rodent heterotopic partial heart transplantation, piglet orthotopic partial heart transplantation, and non-human primate partial heart xenotransplantation.

DISCUSSION

Rodent models are relatively cheap and offer extensive availability of research tools. However, rodent open-heart surgery is technically not feasible. This limits rodents to heterotopic partial heart transplant models. Piglets are comparable in size to children. This allows for open-heart surgery using clinical grade equipment for orthoptic partial heart transplantation. Piglets also grow rapidly, which is useful for studying partial heart transplant growth. Finally, nonhuman primates are immunologically most closely related to humans. Therefore, nonhuman primates are most suitable for studying partial heart transplant immunobiology and xenotransplantation.

CONCLUSIONS

Animal research is a privilege that is contingent on utilitarian ethics and the 3R principles of replacement, reduction and refinement. This privilege allows the research community to seek fundamental knowledge about partial heart transplantation, and to apply this knowledge to enhance the health of children who require partial heart transplants.

Partial heart transplantation: Growing heart valve implants for children

Heart valves serve a vital hemodynamic function to ensure unidirectional blood flow. Additionally, native heart valves serve biological functions such as growth and self-repair. Heart valve implants mimic the hemodynamic function of native heart valves, but are unable to fulfill their biological functions. We developed partial heart transplantation to deliver heart valve implants that fulfill all functions of native heart valves. This is particularly advantageous for children, who require growing heart valve implants. This invited review outlines the past, present and future of partial heart transplantation.

Partial Heart Transplantation - How to Change the System

Partial heart transplantation is the first clinically successful approach to deliver growing heart valve implants. To date, 13 clinical partial heart transplants have been performed. However, turning partial heart transplantation into a routine procedure that is available to all children who would benefit from growing heart valve implants poses formidable logistical challenges. Firstly, a supply for partial heart transplant donor grafts needs to be developed. This challenge is complicated by the scarcity of donor organs. Importantly, the donor pools for orthotopic heart transplants, partial heart transplants and cadaver homografts overlap. Secondly, partial heart transplants need to be allocated. Factors relevant for equitable allocation include the indication, anatomical fit, recipient clinical status and time on the wait list. Finally, partial heart transplantation will require regulation and oversight, which only recently has been undertaken by the Food and Drug Administration, which regulates human cellular and tissue-based products. Overcoming these challenges will require a change in the system. Once this is achieved, partial heart transplantation could open new horizons for children who require growing tissue implants.

Partial Heart Transplant in a Neonate With Irreparable Truncal Valve Dysfunction

Importance

The treatment of neonates with irreparable heart valve dysfunction remains an unsolved problem because there are no heart valve implants that grow. Therefore, neonates with heart valve implants are committed to recurrent implant exchanges until an adult-sized valve can fit.

Objective

To deliver the first heart valve implant that grows.

Design, Setting, and Participants

Case report from a pediatric referral center, with follow-up for more than 1 year. Participants were a recipient neonate with persistent truncus arteriosus and irreparable truncal valve dysfunction and a donor neonate with hypoxic-ischemic brain injury.

Intervention

First-in-human transplant of the part of the heart containing the aortic and pulmonary valves.

Main Outcomes and Measures

Transplanted valve growth and hemodynamic function.

Results

Echocardiography demonstrated adaptive growth and excellent hemodynamic function of the partial heart transplant valves.

Conclusions and Relevance

In this child, partial heart transplant delivered growing heart valve implants with a good outcome at age 1 year. Partial heart transplants may improve the treatment of neonates with irreparable heart valve dysfunction.