Experimental orthotopic and heterotopic canine heart allografts : the problem of the heart transplantation model

Two heart transplantation models have been developed, one orthotopic and the other heterotopic, but the respective value of these models for human heart transplantation is still unknown despite the explosive growth in the field of experimental and clinical transplantation since 1960. Although great advances have been made, the rejection phenomenon continues to challenge all transplantation research workers. Over the past years and in many widely separated countries, almost 277 human hearts have been implanted. The experience gained from these operations has not only confirmed the surgical feasibility of the procedure, but has also shown that transpLnted hearts can function adequately until rejection occurs. Since this rejection precludes complete success of the procedure in man, cardiac transplantation research must proceed in animals until the problem of rejection is solved. The oldest of the two research models we have at our disposal today was originated by Carrel and Guthrie in 1905 (Carrel 1907). This is the heterotopic model. The experimental animal receives an accessory heart. Survival remains independent of the functioning of the graft. Many investigators have employed a technique in which the aorta of the graft is anastomosed to a systemic artery and the pulmonary artery to a systemic vein of the recipient, use being made of the neck vessels, the main abdominal vessels, and the inguinal vessels. The adjective heterotopic (Gr. heteros topos = other place) was chosen to distinguish this heart transplantation research model from the orthotopic model, in which a graft is substituted for the recipient's heart.