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The ideal prosthetic conduit for surgical repair of complex congenital heart disease has yet to be found. Twenty conduits were implanted between the right ventricle and pulmonary artery in growing sheep as follows: four Dacron porcine valve conduits (mean time in place, 142 days); four avalved glutaraldehyde-fixed bovine iliac veins (mean 132 days); and 12 glutaraldehyde-fixed bovine iliac veins containing a porcine valve (mean 180 days). Fifteen conduits were left in place from 167 to 244 days (mean 204 days), and five were explanted earlier (mean 54 days). Pathological study included gross, x-ray, histological, and ultrastructural investigation. Five conduits failed because of infective endocarditis. The valved Dacron conduits showed significant tissue ingrowth and calcification of the valve graft. The valved bovine iliac veins presented calcification at the valve level and vein wall, as well as a valvelike calcific fibrous ridge at the proximal anastomosis with the right ventricle. The avalved bovine iliac veins also presented calcific deposits along the wall and a valvelike calcific ridge at the ventricular anastomosis. Histological and ultrastructural studies of the vein tunica media revealed the phenomena of inflammatory rejection and foreign body reaction with loss of smooth muscle cells (medionecrosis) and fibrotic replacement. In conclusion, bovine iliac veins undergo inflammation with medionecrosis indicating that smooth muscle cell antigenicity is not attenuated by glutaraldehyde fixation.

The occurrence of stent post deformity was investigated in 38 consecutive, polypropylene flexible-stented Hancock porcine bioprostheses (PB) recovered from the mitral position because of early postoperative death or late tissue failure. The degree of deformity was assessed for each explant by calculating the triangular area obtained by projecting the apex of the stent posts on a plane and comparing it with the same area calculated for unimplanted PBs of comparable size. A significant stent deformity (reduction of the triangular area greater than 40%) was observed only in 6 PBs explanted because of tissue failure after a mean function time of 69.6 +/- 28 months. In these PBs, scanning electron microscopy of the bare surface of the stent at the point of maximal flexion showed cracks 0.7-1 microns large, which represent the morphological substrate of the so-called "creep" of polypropylene. Inward stent post bending may occur after implantation in mitral PBs and when severe, it corresponds to a definite ultrastructural plastic deformity of polypropylene.

Reoperation in porcine valve recipients is becoming increasingly frequent, owing to the limited durability of the valves. In reviewing our experience with first reoperation for porcine valve failure in 191 patients over a 17-year period, we found that following certain routine surgical steps can minimize complications and improve the surgical outcome. Extended dissection of the heart is useful during mitral bioprosthetic replacement to enhance visualization of the failing device while retracting the left atrium without undue tension on fragile structures such as the left innominate vein-superior vena cava junction. This maneuver can be avoided, however, when replacement of an aortic bioprosthesis is required. Excision of a porcine valve is performed by peeling off the fibrous tissue overgrown on the sewing ring, which exposes the underlying sutures, cutting each knot, and finding a plane between the stent and the native valve annulus by careful blunt dissection. Care is taken not to cut the Dacron cloth of the sewing ring to avoid the potential for embolization of the silicone sponge contained within it. The use of this technique helps to minimize postoperative complications such as paravalvular leak or atrioventricular block and to preserve the native annulus, which facilitates insertion of a new prosthesis. Our experience indicates that first reoperation in porcine valve recipients can be performed with low risk, particularly in elective cases, and with a low incidence of complications related to repeat median sternotomy.