Silver-coated prosthetic heart valve: a double-bladed weapon

Human T-Cell Responses to Metallic Ion-Doped Bioactive Glasses

Biomaterials are extensively used as replacements for damaged tissue with bioactive glasses standing out as bone substitutes for their intrinsic osteogenic properties. However, biomaterial implantation has the following risks: the development of implant-associated infections and adverse immune responses. Thus, incorporating metallic ions with known antimicrobial properties can prevent infection, but should also modulate the immune response. Therefore, we selected silver, copper and tellurium as doping for bioactive glasses and evaluated the immunophenotype and cytokine profile of human T-cells cultured on top of these discs. Results showed that silver significantly decreased cell viability, copper increased the T helper (Th)-1 cell percentage while decreasing that of Th17, while tellurium did not affect either cell viability or immune response, as evaluated via multiparametric flow cytometry. Multiplex cytokines assay showed that IL-5 levels were decreased in the copper-doped discs, compared with its undoped control, while IL-10 tended to be lower in the doped glass, compared with the control (plastic) while undoped condition showed lower expression of IL-13 and increased MCP-1 and MIP-1β secretion. Overall, we hypothesized that the Th1/Th17 shift, and specific cytokine expression indicated that T-cells might cross-activate other cell types, potentially macrophages and eosinophils, in response to the scaffolds.

Distribution, metabolism, excretion, and toxicity of implanted silver: a review

Some implantable medical devices contain silver. We aimed to assess at what amount implanted silver becomes toxic. Silver was elevated in bodily fluids and tissues surrounding silver-containing implants. Silver released from implants also distributes to blood and other tissues; there is evidence to suggest silver can pass the blood-brain-barrier. Silver can be deposited as nano-sized particles in various tissues. Such particles, in addition to silver, often contain other elements too, e.g., selenium and sulfur. Silver released from implants seems to stay in the body for long periods (years). Reported excretion pathways following implantation are urinary and fecal ones. Reported toxicological effects were virtually all local reactions surrounding the implants. Argyria is a blue-gray discoloration of the skin due to deposited silver granules. Localized argyria has been described after the implantation of acupuncture needles and silver-coated prostheses, although the presence of silver was tested only for and shown in the former. Other toxicological effects include local tissue reactivity and examples of neurotoxic and vascular effects. We did not include genotoxicity studies in the present publication as we recently evaluated silver to be genotoxic. Carcinogenicity studies were absent. We conclude that local toxicity of implanted silver can be foreseen in some situations.

Characterisation and in vitro activities of surface attached dihydropyrrol-2-ones against Gram-negative and Gram-positive bacteria

Bacterial infection of biomedical devices is still a major barrier to their use. This is compounded by increasing antibiotic resistance. Here, the specific covalent attachment of a series of dihydropyrrol-2-one (DHP), analogues of bacterial quorum sensing inhibitors, to surfaces via a Michael-type addition reaction is described. Differences in efficiency of attachment related to the substituent groups were found by X-ray photoelectron spectroscopy. The physical characteristics of the surfaces were further explored by atomic force microscopy and contact angle measurements. The ability of these coatings to prevent the formation of a biofilm by Pseudomonas aeruginosa and Staphylococcus aureus was examined using confocal laser scanning microscopy and image analysis. The DHP-treated surfaces showed significant reductions in bacterial adhesion without increased killing for both strains of bacteria (p < 0.001). 5-Methylene-1-(prop-2-enoyl)-4-phenyl-dihydropyrrol-2-one was identified as having broad spectrum activity and consequently represents an excellent candidate for the development of novel surfaces for the prevention of biomedical device infections.

Pathologic Analysis of 19 Heart Valves With Silver-Coated Sewing Rings

OBJECTIVE

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.

METHODS

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.

RESULTS

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.

CONCLUSION

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.

Corrosion of stainless steel sternal wire after long-term implantation

A variety of metallic components have been used in medical devices where lifelong durability and physical strength are demanded. To investigate the in vivo changes of implanted metallic medical devices in humans, stainless steel sternal wires removed from patients were evaluated. Stainless steel (316L) sternal wires removed from four patients after 10, 13, 22, and 30 years of implantation were evaluated using scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS). Macroscopically, the removed specimens maintained their metallic luster and color. Under SEM, small holes were observed sporadically at 10 years and they tended to connect in the drawing direction. The longer the implanted duration, the more numerous and deeper were the crevices observed. By EDS, sulfur, phosphorus, and calcium were identified in all areas at 10 years, in addition to the component elements of stainless steel, comprising iron, chromium, nickel, and manganese. Corrosion products observed at 30 years were identified as calcium phosphate. In conclusion, stainless steel sternal wires develop corroded pores that grow larger and deeper with time after implantation; however, the pores remain shallow even after decades of implantation and they may not be a cause of mechanical failure. An amount of metal ions equivalent to the corroded volume must have been released into the human body, but the effect of these metal ions on the body is not apparent.

Twenty-year experience with the St Jude Medical mechanical valve prosthesis

BACKGROUND

We have prospectively followed all adult St Jude Medical mechanical valve recipients at the Medical University of South Carolina since the initial implant in January 1979 and now present our 20-year experience.

METHODS

We prospectively followed 837 valve recipients (aortic valve replacement; n = 478; mitral valve replacement; n = 359) from January 1979 to December 2000 at 12-month intervals.

RESULTS

Ages ranged from 19 to 84 years. Follow-up averaged (mean +/- standard deviation) 7 +/- 5 years (98% complete). Patients were in New York Heart Association class III or IV in 77% (aortic valve replacement) and 89% (mitral valve replacement) preoperatively. A 19-mm valve was implanted in 15.5% of aortic valve replacement patients. Coronary bypass was required in 31% of aortic valve replacements and 20% of mitral valve replacements. Operative mortality was 17/478 (3.6%) in aortic valve replacement and 19/359 (5.3%) in mitral valve replacement, and multivariable predictors were 19-mm valve size, 3 or more coronary bypass grafts, and New York Heart Association class IV for aortic valve replacement and New York Heart Association class IV and age for mitral valve replacement. Actuarial survivorship at 10 and 20 years was 57% +/- 3% and 26% +/- 5% for aortic valve replacement and 61% +/- 3% and 39% +/- 4% for mitral valve replacement. Multivariable predictors of late death were African-American ethnicity, New York Heart Association class III or IV, coronary bypass, and age for aortic valve replacement and New York Heart Association class III or IV, coronary bypass, and age for mitral valve replacement. For aortic valve replacement, effective orifice area was univariately (P =.002) but not multivariately (P =.378) predictive of late death. Structural valve deterioration was not observed. For aortic valve replacement, actuarial freedom (at 10 and 20 years) from reoperation was 93% +/- 1% and 90% +/- 2%; thromboembolism, 82% +/- 3% and 68% +/- 8%; bleeding events, 77% +/- 3% and 66% +/- 6%; prosthetic valve endocarditis, 94% +/- 1% and 94% +/- 1%; valve-related mortality, 94% +/- 2% and 86% +/- 4%; and valve-related mortality or morbidity, 58% +/- 3% and 32% +/- 8%. For mitral valve replacement, actuarial freedom (at 10 and 20 years) from reoperation was 96% +/- 1% and 90% +/- 3%; thromboembolism, 77% +/- 3% and 59% +/- 7%; bleeding events, 86% +/- 2% and 65% +/- 8%; prosthetic valve endocarditis, 98% +/- 1% and 96% +/- 2%; valve-related mortality, 89% +/- 0.2% and 74% +/- 8%; and valve-related mortality or morbidity, 63% +/- 3% and 29% +/- 7%.

CONCLUSIONS

After 2 decades of observation with close follow-up, the St Jude Medical mechanical valve continues to be a reliable prosthesis.