Calcification of valve bioprostheses: the cardiac surgeon's nightmare

Pericarbon is a last-generation bovine pericardial valve bioprosthesis, which was designed [I], experimentally tested [2], and introduced into clinical practice [3] in the late 1980’s with the aim of overcoming the main drawback of the Ionescu-Shiley and Vascor Hancock devices, namely mechanical tearing at the commissural level even in the absence of calcification [4-61. The early and medium-term failures observed in these first-generation pericardial valve bioprostheses were unanimously ascribed to limitations of valve design and structural properties, namely poor tissue preservation, the use of the three-leaflet model requiring excessive stitch anchorage to the commissure and tissue wear owing to friction between the leaflet and the Dacron-covered stent. To solve these problems, a single-cusp pericardial device was designed by Gabbay, which consisted of a single leaflet of glutaraldehyde-fixed bovine pericardium mounted on a flexible Delrin stent, covered by a second pericardial sheet [7]. The aims were to reduce the number of leaflet commissures at risk of tearing, to prevent contact between cloth and tissue, and to obtain the largest possible orifice area. However, despite this unquestionable rationale and promising results, both in the experimental models and initial clinical experience [8], subsequent animal [9] and clinico-pathological studies [IO] demonstrated failure of the single-cusp principle: cusp redundancy, primary commissural tears and dystrophic calcification occurred early, which suggests that this device is unsuitable as a cardiac valve substitute. Alternative solutions designed to prolong mechanical resistence at the commissures were attempted with the Carpentier-Edwards and Pericarbon pericardial bioprostheses [12], which incorporated many improvements. The Pericarbon device is characterized by a single, three-cuspal shaped pericardium sheet, which is sutured to a second sheet lining the inner surface of a low-profile, Dacron-covered Delrin frame. The two pericardial sheets are cross-sutured internally to the stents. A coating of hemocompatible Carbotilm covers all the exposed, nonbiological surfaces. The use of two pericardial sheets should allow the creation of a linkages chain with smoothly decreasing elasticity (pericardial leaflet-pericardium lining-Dacron-Delrin stent), with the aim of optimizing the stress reduction. Moreover, pericardiumto- pericardium contact should avoid leaflet abrasion.