Pathologic analysis of 19 heart valves with silver-coated sewing rings

The St. Jude Medical Silzone (Silzone) mechanical heart valve was voluntarily recalled (January 2000) due to an unusually high incidence of paravalvular leaks. We present the first series of human morphological data on the failure of these valves.

Nineteen Silzone valves were evaluated from the 176 Silzone valves implanted in 147 patients at our institution between 1997 and 1999. Explanted prostheses were fixed in 10% formalin, photographed, and X-rayed. Histological sections were collected from the sewing cuff, accompanying tissues, and thrombus. For comparison, six age-matched SJM-standard valves were similarly analyzed.

Nineteen Silzone valves from 16 patients (10 male, six female, 52.0 +/- 15.2 years) were examined. Significantly more mitral (15/95) prostheses were removed than aortic (4/81) despite the nearly equal number implanted (p = 0.027). Fifteen of the Silzone valves (13/16 patients) were explanted in the early postoperative period (within six months of implantation), although collection continued for eight years after our institution stopped implanting them. The common indications for surgical explantation were paravalvular leak (8/12) and clinically suspected infective endocarditis (IE) (four patients, five valves). IE was not confirmed by histology or culture in any valve. The sewing cuffs of many Silzone valves showed large regions of pannus, granulation tissue, and purulent exudate. Polymorphonuclear leukocytes were more common in the sewing cuff of Silzone valves; however, the cellular infiltrate was superficial when compared to SJM-standard valves.

This is the largest morphologically analyzed series of Silzone explants. It demonstrates a consistent pattern of atypical tissue incorporation into the silver-coated sewing ring particularly in the mitral position. Clinical and morphologic features of IE (sterile) are seen in the early postimplant period. Prosthesis-related problems were almost wholly seen at the mitral site, in our group. Our current data indicate that although early failure due to dehiscence and paravalvular leak is a problem, Silzone valves that "survive" past six months will likely function as well as the SJM-standard prosthesis.