Porcine aortic versus bovine pericardial valves: a comparative study of unimplanted and from patient explanted bioprostheses.

This extensive morphological study (macroscopy, x-ray, histology, histochemistry and electron microscopy) compares two types of bioprosthetic valves, porcine aortic (PAV) and bovine pericardial (BPV) of various models, both unimplanted (five) and explanted (229). There were 197 PAV and 32 BPV explanted from the mitral, aortic and tricuspid positions, with a mean duration of implantation of 70.3 and 13.5 months, respectively. Within that material, a smaller, rather homogeneous, series of 11 Carpentier-Edwards PAV (CE) and 11 Ionescu-Shiley BPV (IS) explants (mean implantation period 53 and 49, mean patient-age 45 and 47 years) made the comparison of clinical and macroscopic features more valid. In the total series, the leading causes of failure were cuspal tear/perforation with calcification in the PAV group (64 per cent); non-calcified leaflet rupture (27 per cent) and infective endocarditis (27 per cent) in the BPV group. In the small series of CE PAV and IS PAV, the characteristic modes of failure were calcified juxta-commissural cusp rupture for CE and non-calcified leaflet rupture at the suture for IS. The most characteristic x-ray features were calcification of fibrous cords irradiating from the commissures and calcific nodules in the centre in PAV and large plaques extending from the commissures and leaflet base in all directions in BPV. The main microscopic features of leaflet degradation were: the soaked sponge phenomenon (loosening and plasma and fat insudation) and the nodular, protein-rich calcification, both centred in the spongiosa, in PAV explants; important macrophagic activity and destruction of collagenous structures at the outflow layer and along the suture of the leaflets, with preservation of the middle layer, and the intrinsic calcification of the deep collagenous bundles, in BPV explants. Those alterations and other features are discussed with reference to leaflet structure and design, haemodynamics and possible causal mechanisms.