Pathological study of infective endocarditis on Hancock porcine bioprostheses

A pathological study has been performed on 10 infected Hancock bioprostheses removed from nine patients who died of prosthetic endocarditis. The devices had been in place from 2 to 87 months (average 37.5), the interval between operation and onset of infection averaging 30 months. The offending organisms were Gram negative bacteria in three patients (Klebsiella pneumoniae, Enterobacter cloacae, and Serratia marcescens), Gram positive bacteria in two (Staphylococcus aureus and Streptococcus viridans), and fungi in four (Candida species in three and Aspergillus species in one). Gross examination of the explants revealed in most cases a vegetative endocarditis of one porcine valve leaflets. Septic embolization occurred in five cases owing to the high friability of the vegetations. Prosthetic valve incompetence was the commonest type to dysfunction observed because of tears, perforations, and even complete destruction of the cusps. Prosthetic valve stenosis following obstruction of the valve orifice by infected polypous masses was noted in two cases. Clumps of infective organisms were detected deep in the cusp tissue in most cases on histologic examination. Infection located on the paraprosthetic tissues, associated with ring abscess, valve detachment, and insufficiency, was observed only once. According to the results of investigation, endocarditis on porcine bioprostheses is associated with a better preserved native valvular ring as viewed at reoperation. Therefore surgical intervention appears appropriate in the presence of severe hemodynamic complications after adequate antibiotic treatment. However, infection of these particular prostheses still carries an extremely high mortality. In the present series, this poor outcome might be explained by the frequently associated septic and thromboembolic events.