Structure of bovine parietal pericardium and of unimplanted Ionescu-Shiley pericardial valvular bioprostheses.

To obtain a basis for the evaluation of postimplantation changes in bioprostheses made of parietal pericardium, we conducted comparative histologic, scanning and transmission electron microscopic studies of the structure of (1) normal bovine parietal pericardium, (2) glutaraldehyde-treated pericardial patches to be used for repair of cardiac defects, and (3) pericardial tissue cusps of unimplanted Ionescu-Shiley valves. Bovine parietal pericardium has three layers: (1) the serosa, or mesothelial cell layer; (2) the fibrosa, formed by diversely oriented, wavy bundles of collagen and by elastic fibers, and (3) the epipericardial connective tissue layer, which is partly continuous with the pericardiosternal ligaments. Pericardial patches and pericardial bioprosthetic cusps differ from normal pericardium by being denuded of mesothelium but they have normal degrees of waviness in their collagen. In Ionescu-Shiley valves, the inflow and outflow surfaces of each cusp correspond to the epipericardial and serosal surfaces of parietal pericardium, respectively. The inflow surfaces have a coarse texture, characterized by large bundles of collagen, and the outflow surfaces have numerous grooves, 10 to 30 mu in width and 20 mu in depth, which probably result from pressure exerted on the cuspidal surfaces by cotton material either during manufacturing or packing of the valves. Comparisons of the structure of bioprosthetic pericardial cusps and porcine aortic valve cusps show that the latter have reduced degrees of collagen waviness and a different layered structure: A layer similar to the spongiosa of aortic valve cusps is not present in pericardium. The functional implications of these observations are discussed in detail.