Histologic Findings in the Conduction System After Cardiac Transplantation and Correlation With Electrocardiographic Findings

There are very few histologic studies on the cardiac conduction system in the human transplanted heart. All agree that during acute cardiac rejection the conducting tissues are also affected. This involvement has been reported to have different degrees of severity. Before the advent of cyclosporine, Bieber et al 1 observed a greater inflammatory infiltration within the conduction system, when compared with the working myocardium. In contrast Stovin and Hewitt2 found a lesser degree of involvement of the conduction system in the cyclosporine era, whereas Chang et al3 suggested that acute cardiac rejection affected the conduction system at least to the same degree as observed in the myocardium. In rat cardiac allograft rejection, Kitamura et al4 demonstrated that mononuclear cell infiltrates of the conduction system produce prolongation of the refractory period of the specialized atrioventricular (AV) junction. Foerster5 reported cases of AV block after cardiac transplantation; one had almost exclusive cellular infiltrates of the AV conducting tissue. This study investigates, by serial histologic section technique, the conduction system in cardiac transplantation and correlates the pathologic substrates to electrocardiographic findings. ••• We studied 18 transplanted hearts obtained at necropsy. The cause of failure was acute rejection in 9, occurring early in 4 (mean survival 50 days) and late in 5 (mean survival 990 days); chronic rejection in 3 (mean survival 1,562 days); and other causes in 6 (infection, trauma, graft failure due to poor preservation; mean survival 214 days). In all the cases the traditional surgical technique (“atrioatrial anastomosis”) was performed, leaving the native atria in situ, which the donor heart is anastomosed to, thus resulting in the right atrium with 2 sinus nodes: the recipient’s sinus node and the donor one. Five donor agematched hearts from patients, who did not receive transplants and who died due to extracardiac causes, served as controls. From each heart specimen, 3 comprehensive blocks of the recipient sinoatrial junction, the donor sinoatrial junction, and the AV specialized junction (including AV node, His bundle, and bundle branches) were removed according to a previously described method.6 The entire blocks were serially sectioned at 7 mm. Two sections every 10 were mounted and stained with hematoxylin and eosin and trichrome Heidenhain, respectively. For each specimen nearly 400 sections were stained and microscopically examined. The severity of acute rejection was scored from 0 to 4 according to the International Society for Heart and Lung Transplantation formula, 7 which is currently used for biopsy grading, but is also considered worthwhile for evaluation of autopsy material. 3,4 The International Society for Heart and Lung