Capillary and myofiber ultrastructure in endomyocardial biopsies from cyclosporine-treated heart transplant patients.

This study focuses on the ultrastructure of microvessels and myofibers in 54 endomyocardial biopsy specimens from 16 patients treated with cyclosporine after heart transplantation. Although the capillary and myofiber pathologic condition was significantly correlated with the degree of rejection, ultrastructural changes sometimes occurred in biopsy specimens with little or no histologic cellular infiltration. Immunocytochemical studies of some biopsy specimens showed that all microvessels were positive for IgM, whereas concentrations of IgG, complement, and fibrin varied. The microvascular and myofiber changes appeared to be reversible and correlated (Pearson's coefficient of correlation of myofiber vacuoles and microangiopathy, R = 0.67, p less than 0.00001). The vacuoles in myofibers resembled those in subendocardial regions of ischemic myocardium. They could, however, be related to cyclosporine toxicity because similar vacuoles have been described in kidneys of transplant patients receiving cyclosporine. We conclude that in cases of unclear graft failure in the absence of classic signs of rejection, electron microscopy could be helpful in detecting microvascular and myofiber pathologic situations that may influence myocardial function.