Recently it has been all over the news that the first partial pediatric heart transplant was performed in the USA. This is a huge advancement for many reasons. There are many children born every year with unrepairable heart valve dysfunction (pulmonary atresia, truncus arteriosus, and aortic stenosis) and this is a huge problem because there are no growing heart valve implants outside of an entire heart transplant. There are mechanical valves for children, but most infants are too small for these. These mechanical valves also require lifelong anticoagulation which is not ideal in active children. Additionally, mechanical valves do not grow as the patient ages which necessitates reoperations as the child grows. There are also bioprosthetic valves (xenografts and homografts) but these too need to be replaced as the child grows and are not without other risks such as infection and calcifications. Heart transplantation is also an option, as the valves from a heart transplant do grow with the child and do not require replacement. But there is a lack of suitable donors for infants <1 year of age and the wait list mortality for this age group is high. This also requires life-long immunosuppression in a patient population with very naïve immune systems.
Researchers at Duke University and the Medical University of South Carolina have found an innovative solution. Partial heart transplantation is a new approach which involves transplantation of the heart valves only. Partial heart transplantation may offer the ability to use much lower immunosuppression as there is some immune privilege in this tissue. You might have heard of the concept of immune privilege in the past. This term was initially described by was coined by Sir Peter Medawar in the 1940s to describe parts of the body in which the introduction of foreign antigens does not elicit an inflammatory immune response. In fact, aortic homografts have been used since the early 1960s without the need for immunosuppression. There is some debate as to the actual immunogenicity of heart valves. Some studies have shown valves from transplanted hearts with severe rejection were spared 1, while others have shown the immunologic potential of these valves 2. Hill et al wrote a great review of the Immune Privilege of Heart Valves 3.
Partial heart transplantation can be performed using donor hearts with poor ventricular function and slow progression to donation after cardiac death that would normally be discarded making use of many more hearts. This amazing advancement could possibly ameliorate the need for donor hearts in children with unrepairable heart valve dysfunction and progression of these children to end-stage heart failure 4.
Dr. Tarak (Konrad) Rajab will be giving a plenary talk at IPTA’s 2023 Congress in Austin, Tx on his pivotal work on this advancement. This session will be on Monday, March 27th 14:45-15:15 CT. www.ipta2023.org/program/confirmed-speakers. Come join us to learn more!