The conduction system in human cardiac allografts. A histological and immunopathological study

Twenty-five hearts were lost in the first 103 orthotopic human cardiac allografts in 100 recipients. Twenty-two patients died. The first nine recipients were treated with Cyclosporin A and high dose Prednisolone and the subsequent recipients were immunosuppressed with a triple regimen consisting of Azathioprine in addition to Cyclosporin A and low dose Prednisolone. Twenty grafts were examined at autopsy and three after retransplantation. Fourteen hearts with acute rejection and vascular pathology were investigated regarding the histological and immunopathological alterations due to cellular and vascular rejection. The recipient sinoatrial node was available for examination in 10, the donor node in 13 and the atrioventricular conductive tissue in all 14 grafts. The conduction system was involved in 8 out of 11 allografts attacked by acute cellular rejection. In one allograft in which the patient developed AV block, the cellular infiltrates were almost exclusively observed in the atrioventricular tissue. Most of the cells were T lymphocytes, while macrophages and B cells were present to a lesser extent. There was little evidence of permanent structural damage to the atrioventricular tissue after recurrent mild or moderate episodes of acute cellular rejection. In the sinus nodes, however, risk of traumatic damage to the recipient and donor sinus node was about half and a quarter respectively. Acute and chronic vascular rejection seemed to be equally distributed in the sinus node, atrioventricular arteries and in the intramural branches of the coronaries. No morphological differences were established between the two types of immunosuppressive regimes.