Partial Heart Transplantation

Children with end-stage cardiomyopathy or uncorrectable congenital heart defects have been successfully treated with orthotopic heart transplantation for more than ۴۰ years. The current state-of-the-art operation for small children with critical semilunar valve defects, such as severe congenital aortic stenosis, truncus arteriosus, or pulmonary atresia, involves the implantation of cryopreserved, decellularized valved conduits from human cadavers (homograft). These homografts are extracellular matrices that permit native tissue ingrowth. However, they are prone to leaflet degeneration, which is especially rapid in infants and young children. The most important advantage of PHT is the growth of the transplanted tissue, which will theoretically minimize the morbidity and mortality rates associated with successive valve or other cardiac tissue replacements over a child's lifetime. The transplanted tissue may also be more physiologic than prosthetic devices and could potentially be durable without the need for anticoagulation. Another advantage of PHT is the versatility of the technique and the ability to tailor the donor allograft to the recipient's needs. There are also challenges associated with PHT that must be addressed. First, there is a limited supply of suitable donors. Fortunately, nearly ۴۰% of pediatric organ donors have hearts that are not allocated for full heart transplants, representing a potential source for partial heart grafts. Also, the use of living donor hearts from children receiving full heart transplants helps to expand the PHT donor pool in the so-called "domino partial heart transplant" model. Second, there are logistic challenges associated with the technique. Before more scientific insight is gathered about the viability of various partial heart allografts in cold storage, there remains a temporal constraint between donor allograft procurement and recipient PHT. Another challenge associated with the technique is the uncertainty about the long-term Effects of ABO matching and human leukocyte antigen tissue typing on PHT durability. Our center is currently using ABO compatible allografts for all patients except neonates, where we apply ABO-incompatible protocols used for full heart transplants.