Postimplantation leaflet cellularity of valve allografts: are donor cells beneficial or detrimental?

Background. The theory that “viable” valve grafts have superior durability because the donor cell population of the leaflets survives implantation and functions normally, thus maintaining leaflet integrity, is still not definitively proven. The postulate has been investigated for grafts produced and used at Green Lane Hospital by examining a series of 155 removed at reoperation following up to 21.3 years of implantation. Methods. Leaflet cellularity at explantation was assessed histologically. An additional 55 cases were also assessed by tissue culture. Cell origin for six positive cultures was determined by comparison of DNA of the culture with that of the recipient’s blood cells. Results. Grafts known to be nonviable at implantation lacked leaflet fibroblasts but sometimes showed ongrowth of fibrous tissue derived from the recipient’s aorta. Grafts potentially viable at implantation showed three main patterns of fibroblastic growth: (1) relatively sparse, scattered cells; (2) focal hyperplastic growth with intervening acellular tissue that was prone to rupture; and (3) widely disseminated, vigorous growth causing abnormal thickening. The first pattern was associated with recipient cells, and both the second and third patterns were associated with nonrecipient cells. Conclusions. Donor cells surviving implantation do not maintain a normal leaflet architecture and may lead to failure by producing loss of leaflet flexibility.