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Eur J Cardiothorac Surg 2001;19:729-731
© 2001 Elsevier Science NL

Case report

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

Department of Cardiovascular Surgery, Sion Regional Hospital, Sion, Switzerland

Received 18 December 2000; received in revised form 2 March 2001; accepted 10 March 2001.

Corresponding author. Service de Chirurgie Cardiovasculaire – BH10, Centre Hospitalier Universitaire Vaudois, Rue du Bugnon 46, 1011 Lausanne, Switzerland. Tel.: +41-21-314-2280; fax: +41-21-314-2278
e-mail: tozzig{at}hotmail.com

	Abstract

Top Abstract 1. Introduction 2. Case report 3. Discussion 4. Conclusions References

 
A St. Jude Medical Silzone was implanted in a 72-year-old female, suffering from mitral valve disease. Four months later, the patient had acute cardiac failure due to partial detachment of the prosthetic valve. The mitral annulus was ulcerated and there were multiple erosions in the myocardial tissue in contact with the prosthetic valve. Histological examination revealed chronic inflammation with hemosiderine deposits and giant cells. No allergy to silver ions was found. The silver-coated sewing cuff had caused a chronic inflammatory reaction due to a toxic reaction to silver. The Silzone valve was withdrawn from the market on January 2000.

Key Words: Silver toxicity • Endocarditis • Prosthetic heart valve

	1. Introduction

Top Abstract 1. Introduction 2. Case report 3. Discussion 4. Conclusions References

 
Prosthetic valve endocarditis (PVE) is one of the complications of heart valve replacement and its treatment represents a challenge to the surgeon. The incidence of PVE ranges up to 0.5%/patient-year for mechanical mitral valves and up to 1%/patient-year for other mechanical valves [1]. PVE is a foreign body infection predominantly based in the sewing cuff of a prosthetic heart valve. The mortality rates are high: 75% for infection occurring up to 2 months (early PVE) and 43% for infection occurring thereafter (late PVE) [1].

Many techniques have been developed to reduce the incidence of PVE, such as antimicrobial treatment (topic and systemic) and also, the use of homographs. The newest and the most promising one consists of a silver-coated, sewing cuff heart valve (St. Jude Medical Silzone) [2]. The Silzone coating is a dense layer of metallic silver deposited on the surface of individual fabric fibrils (polyethylene tetraphthalate polyester) that acts as a source of silver ions that inhibit colonization and attachment of microorganisms to the sewing cuff [2]. Several animal and clinical studies [3–5] have proven the anti-infective efficacy of silver-coated prostheses. The Artificial Valve Endocarditis Reduction Trial (AVERT), a multicenter, randomized trial, was created to assess the clinical efficacy of Silzone in the prevention of PVE [6]. This report describes a patient enrolled in the AVERT that developed a type IV immune response in the periprosthetic tissue after mitral valve implantation.

	2. Case report

Top Abstract 1. Introduction 2. Case report 3. Discussion 4. Conclusions References

 
A 72-year-old female, suffered from mitral valve disease and chronic atrial fibrillation. She referred an allergic reaction (rash) after co-trimoxazole ingestion 10 years before. Echocardiography showed severe mitral regurgitation. The patient was enrolled in the AVERT and in August 1999, underwent mitral valve replacement. A St. Jude Medical Silzone, Ø 29 mm, was implanted using the interrupted suture technique (2/0 pledgetted Ticron sutures). Echocardiography showed no periprosthetic leakage and the patient was discharged 9 days after the operation.

Four months later, the patient was re-admitted because of progressive heart failure. Trans-esophageal echocardiography showed severe mitral insufficiency due to a partial detachment of the prosthetic valve, mostly on the interventricular septum side. Right basal pneumonia was diagnosed as well. An emergency prosthetic mitral valve replacement was necessary. At re-operation, the prosthetic valve was detached from the interventricular septum. All sutures and pledgets were in place, but on 1/3 of the circumference, sutures were detached from the mitral annulus. The annulus corresponding to the interventricular septum was ulcerated and there were multiple erosions in the myocardial tissue in contact with the prosthetic valve. No tissue covered the sewing cuff. We implanted a standard valve (St. Jude Medical Ø 31) with the same surgical technique. All bacteriological examinations were negative, except for the expectoration, in which we found Pseudomonas aeruginosa. Histological examination was carried out on three fragments of the mitral valve annulus of 0.7x0.3x0.2 cm, and revealed chronic inflammation with giant cells and hemosiderine deposits (Fig. 1). The patient was discharged 20 days after. A skin patch test carried out 3 months later, was negative for a type IV reaction to silver nitrate (maximal concentration, 0.7%). An international set of skin patch tests (24 classic allergens) was negative as well.

View larger version (160K): [in this window] [in a new window]   Fig. 1. Light micrograph of the mitral valve annulus 4 months after implantation of the silver-coated sewing cuff mitral valve. (A) Lymphocyte infiltration; (B), giant cells and hemosiderine deposits characterized the histological pattern.

	3. Discussion

Top Abstract 1. Introduction 2. Case report 3. Discussion 4. Conclusions References

PVE was our diagnostic hypothesis when the patient was re-admitted, but intraoperatory findings were very far from a classic PVE. The mitral valve annulus was partially destroyed and no abscess, fibrin deposits or vegetation were found. The periprosthetic tissue had multiple erosions and the interventricular septum near the valve was ulcerated. It looked like the valve burned the surrounding tissue. The histological examination of periprosthetic tissue showed a chronic inflammatory reaction with hemosiderine deposits and giant cells (Fig. 1). This histological pattern is unusual after the implantation of standard mechanic heart valves and it probably involves components of the immune system, such as T-cell lymphocytes (immune reaction type IV) [7]. No microorganisms were found in the sewing cuff, in the periprosthetic tissue or in the blood stream. Surgical, histological and bacteriological findings supported the hypothesis that this valve caused a chronic inflammatory reaction leading to its detachment. Assuming that the only difference between silver-coated sewing cuff valves and standard St. Jude Medical valves is the silver coating, there are two possible mechanisms that can produce the described histological pattern: allergy and toxic reaction to silver. Silver allergy is a well-known problem in oral pathology [8] as well as in jewelry manufacturing: 2–5% of the silver exposed population develops an allergic dermatitis [9]. Our patient had a negative silver nitrate patch test at a standard concentration of 0.7%, so we cannot evoke an allergic reaction as the mechanism behind the observed lesions. We can speculate that the lesions described are due to a direct toxic effect of silver ions on the myocarde. As Kraft et al. [10] demonstrated, pure silver implanted in striate muscle induces a persistent activation of leukocytes combined with a marked disruption of the microvascular endothelial integrity, massive leukocyte extravasation, and considerable venular dilation, probably due to the production of intracellular superoxide anions. A high silver concentration in the periprosthetic tissue could reasonably explain the described histological and clinical patterns.

The reported experience has played a major role in the interruption of the AVERT study and in the withdrawal of the Silzone valves from the market on January 2000.

Patients enrolled in the AVERT study need a more vigilant follow-up and greater attention to the signs and symptoms of paravalvular leak. Moreover, a reaction to the silver coating should be taken into account if PVE is suspected.

	4. Conclusions

Top Abstract 1. Introduction 2. Case report 3. Discussion 4. Conclusions References

 
The use of the silver-coated sewing cuff heart valve should be critically judged despite its bactericidal properties. The silver-coated sewing ring, in some patients, can be a potential source of chronic inflammation that could have clinical consequences as dramatic as PVE. The reported experience has played a major role in the interruption of the AVERT study and in the withdrawal of the Silzone valves from the market, awaiting more data concerning the safeness of silver-coated medical prostheses. We believe that patients enrolled in the AVERT study need special surveillance for early detection of potential inflammatory reactions to the silver-coated sewing ring.

	References

Top Abstract 1. Introduction 2. Case report 3. Discussion 4. Conclusions References

 

1. Vlessis A.A., Khaki A., Grunkemeier G.L., Li H., Starr A. Risk, diagnosis and management of prosthetic valve endocarditis: a review. J Heart Valve Dis 1997;6(5):443-465.[Medline]
2. Illingworth B.L., Tweden K., Schroeder R.F., Cameron J.D. In vivo efficacy of silver-coated (Silzone) infection-resistant polyester fabric against a biofilm-producing bacteria, Staphylococcus epidermidis. J Heart Valve Dis 1998;7(5):524-530.[Medline]
3. Brutel de la Riviere A., Dossche K.M., Birnbaum D.E., Hacker R. First clinical experience with a mechanical valve with silver coating. J Heart Valve Dis 2000;9(1):123-129.[Medline]
4. Bertrand S., Houel R., Vermes E., Soustelle C., Hillion M.L., Loisance L. Preliminary experience with Silzone-coated St. Jude Medical in acute infective endocarditis. J Heart Valve Dis 2000;9(1):131-134.[Medline]
5. Darouiche R.O. Anti-infective efficacy of silver-coated medical prostheses. Clin Infect Dis 1999;29:1371-1377.[Medline]
6. Schaff H., Carrel Th., Steckelberg J.M., Grunkemeier G.L., Holubkov R. Artificial Valve Endocarditis Reduction Trial (AVERT): protocol of a multicenter randomized trial. J Heart Valve Dis 1999;8(2):131-139.[Medline]
7. Sell S. Immunopathology. In: Rich R.R., Fleisher T.A., Schwartz B.D., Shearer W.T., Strober W., eds. Clinical immunology: principles and practice. St Louis, MO: Mosby, 1996:449-477.
8. Holmstrup P. Reaction of the oral mucosa related to silver amalgam: a review. J Oral Pathol Med 1991;20(1):1-7.[Medline]
9. Mc Kenna S.R., Latenser B.A., Jones L.M., Barrette R.R., Sherman H.F., Varcelotti J.R. Serious silver sulphadiazine and mafenide acetate dermatitis. Burns 1995;21(4):310-312.[Medline]
10. Kraft C.N., Hansis M., Arens S., Menger M.D., Vollmar B. Striated muscle microvascular response to silver implants: a comparative in vivo study with titanium and stainless steel. J Biomed Mater Res 2000;49:192-199.[Medline]

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