Table 3.

Glossary of Heart Transplantation Procedures and Applications for Xenotransplantation

Procedural Definitions
Technique	Description	Utility
Heterotopic	Vascularized, extra-anatomic	Evaluate biology and histology
Abdomen or neck location		Evaluate immunosuppression
Right thorax, auxiliary parallel circuit		Provide partial hemodynamic support
Orthotopic	Replace native heart	Evaluate full hemodynamic support

The heterotopic (“other place,” not placed in its normal anatomic position) heart transplantation model was originally developed in rodents and later adapted to large animal models for preclinical allotransplantation and xenotransplantation research. The coronary arterial circulation to the unloaded, nonworking heart graft is supported by the recipient’s circulation, with coronary sinus blood returned via the donor pulmonary artery to the recipient inferior vena cava, effectively creating a parasitic arteriovenous shunt. The heterotopic technique permits efficient study of xenograft injury mechanisms and immunosuppressive drug efficacy. The auxiliary chest piggy-back heterotopic technique supports recipient circulation by pumping blood in parallel with and supplemental to the retained native heart and was used by Barnard in his first 2 clinical cases. Because of the operative complexity and a high incidence of pulmonary and thromboembolic complications, current clinical use is limited to patients with elevated pulmonary vascular resistance. Replacing the native heart with the graft, the orthotopic (“same place”) technique pioneered by Lower and Shumway is used in most clinical circumstances. Orthotopic transplantation allows rigorous preclinical evaluation of heart xenograft performance and the best available prediction of the clinical efficacy and safety of candidate therapeutic strategies.