Accessory heart graft as a surgical model in studies of transplantation immunology

The heterotopic heart graft was examined as a surgical model for in vivo studies of transplantation immunology. Two innovations previously described distinguish it from an orthotopic heart transplant; its heterotopic, superficial position in the neck, and the use of portex cuffs to facilitate anastomoses of donor aorta and pulmonary artery to recipient common carotid artery and external jugular vein respectively. In this study, few modifications to the original technique were required. However, to ensure a high technical success rate exceeding 95%, it was found that the use of small donors (less than 200 g) and large recipient rats (greater than 230 g) was required. The former minimised the risk of kinking of the venous anastomoses, and the latter ensured an adequate luminal diameter of the carotid artery to facilitate the cuff anastomosis. With the vena cava and pulmonary veins ligated, the transplant served purely as an indicator graft with rhythmic contractions discernible by inspection or palpation. This simplified monitoring of the graft, with no requirement for ECG or biochemical studies. The direction of blood flow was established by angiography as via the aorta to the coronary vessels, returned to the right atrium and ventricle and out through the pulmonary artery to the recipient circulation. As the accessory heart did not provide any life-sustaining function, it could be removed for histological studies once rejection had occurred without compromising the survival of the recipient animal. This allowed the use of the recipient for further studies on its immunological status, including the performance of second grafts.