Background and aims of the study: Prosthetic valve endocarditis (PVE) is an infrequent but serious complication of cardiac valve replacement. PVE is a foreign body infection predominantly based in the sewing cuff of a prosthetic heart valve leading to thromboembolism, ring abscess, paravalvular leakage, and eventual invasion of the myocardium. Mortality rates as high as 75% have been reported. A silver-coated sewing cuff is now available (St. Jude Medical mechanical heart valve SJMR Masters Series with Silzone coating) intended to inhibit the colonization and attachment to the sewing cuff of those microorganisms commonly associated with PVE. Silzone is a dense layer of metallic silver deposited on individual fiber surfaces of the valve cuff. Previously, Silzone coating was shown in vitro to decrease attachment and colonization of microorganisms with no adverse affect on biocompatibility. The present study was designed to assess the efficacy of Silzone-coated polyester fabric in vivo in a direct-contamination model. The organism chosen was a pathogenic strain of Staphylococcus epidermidis capable of producing biofilm.
Methods: Infection resistance of uncoated polyester and Silzone-coated polyester fabric was assessed by the acute inflammatory response in a guinea pig subdermal model. Fabric samples were implanted sterile or inoculated with S. epidermidis. The ability of the strain to produce biofilm was verified in vitro. Samples were explanted at one and two days postoperatively. Verification of the infecting bacteria was by colony morphology and Gram-staining properties of bacteria from the explanted samples. Inflammation was assessed histopathologically. Percent necrotic tissue within the fabric was determined by computer-assisted image analysis.
Results: Histopathology and image analysis of necrotic tissue showed significantly less inflammation within the Silzone-coated fabric than within uncoated polyester fabric.
Conclusions: The Silzone coating reduced inflammation in this direct-contamination model using a strain of S. epidermidis that is capable of producing biofilm. This indicates a concentration of silver ions sufficient for bacteriostatic or bactericidal activity within the fabric in vivo.