Mechanical heart valves

S. epidermidis is implicated in many medical implant infections. Mechanical heart valves, shunts, catheters and orthopedic devices are examples of implanted devices... 

Infective endocarditis (IE) is a serious infection affecting the lining and valves of the heart. While this disease is mostly associated with infection of the heart valves, the septal defects may become involved as well. Infections also occur in patients with prosthetic or mechanical devices, such as mechanical heart valves or who are intravenous drug users (IVDUs). Bacteria is the primary cause of IE however, fungi and atypical organisms also can be responsible pathogens. 

Ely JL, Emken MR, Accuntius JA, Wilde DS, Haubold AD, More RB, Bokros JC (1998) Pure pyrolytic carbon preparation and properties of a new material, On-X (R) carbon for mechanical heart valve prostheses. Journal of Heart Valve Disease 7 626-632. 

Among well-known medical devices are the mechanical heart valve and the pacemaker. Although medical devices are generally perceived as being either macroscopic or permanent, many, and in some cases all, of the effects (wanted and unwanted) of the devices are derived from interactions at the surface. Indeed, when the devices are made of metals, many, if not most, of the surface effects are electrochemical in nature. This fact is the main subject of this chapter whose role is to outline briefly the manner in which electrochemistry and thus electrochemical deposition are crucial to both the mechanical and materials stability of medical devices. In some cases, entirely new industries have been created around advances in our understanding of the electrochemical processes occurring at surfaces. An additional aim of this chapter is to touch on the ways in which electrochemistry can be used to modify surfaces actively to create a more amicable... 

Even so, synthetic polymers are important in replacing parts of our essential organs. Thus, silicon balls are used in the construction of mechanical heart valves. Many of these fail after sometime and they are being replaced by a flap valve made from pyrolytic carbon or POM. 

The increased risk of thromboembolism associated with atrial fibrillation and with the placement of mechanical heart valves has long been recognized. Similarly, prolonged bed rest, high-risk surgical procedures, and the presence of cancer are clearly associated with an increased incidence of deep venous thrombosis and embolism. Antiphospholipid antibody syndrome is another important acquired risk factor. Drugs may function as synergistic risk factors in concert with inherited risk factors. 

The risk of embolism associated with mechanical heart valves is 2 to 6% per patient per year despite anticoagulation and is highest with valves in the mitral position. Warfarin therapy (INR 2.5 to 3.5) is recommended in these patients. The addition of enteric-coated aspirin (100 mg/d) to warfarin (INR 3.0 to 4.5) in high-risk patients (preoperative atrial fibrillation, coronary artery disease, history of thromboembolism) with mechanical valves decreases the incidence of systemic embolism and death from vascular causes (1.9 vs. 8.5% per year), but increases the risk of bleeding. 

Suspected cardiac source at high risk of recurrent embolism prosthetic mechanical heart valve, endocarditis, aortic dissection, acute coronary syndrome, overt congestive heart failure... 

Vitale N, De Feo M, De Santo LS, Pollice A, Tedesco N, Cotrufo M. Dose-dependent fetal complications of warfarin in pregnant women with mechanical heart valves. J Am Coll Cardiol 1999 33(6) 1637-41. 

Polymer-based heart valves are widely used as replacements for diseased or damaged human heart valves. Most mechanical heart valves are made from metals, silicone, or polyesters, although some work has gone into incorporating biocompatible coatings such as PEO into these systems. 

Endocarditis is an inflammation of the endocardium, the membrane lining the chambers of the heart and covering the cusps of the heart valves. More commonly, endocarditis refers to infection of the heart valves by various microorganisms. Although it typically affects native valves, it also may involve nonvalvular areas or implanted mechanical devices (e.g., mechanical heart valves). Bacteria primarily cause endocarditis, but fungi and other atypical microorganisms can lead to the disease thus the more encompassing term infective endocarditis (IE) is preferred. 

A female patient with a mechanical heart valve who is taking warfarin informs you that she hopes to get pregnant in the near future. What advice do you give her regarding her antithrombotic medication during the anticipated pregnancy ... 

FIGURE 44.6 Photographs showing pitting on pyrolytic carbon surface of a mechanical heart valve. (Courtesy of Baxter Health Care, Irvine, CA.)... 

Chandran, K. B., Dexter, E. U., Aluri, S., and Richenbacher, WE. 1998. Negative pressure transients with mechanical heart-valve closure Correlation between in vitro and in vivo results. Ann. Biomed. Eng. 26 546-556. 

Kafesjian, R., Howanec, M., Ward, G.D., Diep, L., Wagstaff, L.S., and Rhee, R. 1994. Cavitation damage of pyrolytic carbon in mechanical heart valves. /. Heart Valve Dis. 3 (Suppl. 1) S 2-S 7. 

Lapeyre, D.M., Frazier, O.H., and Conger, J.L. 1994. In vivo evaluation of a trileaflet mechanical heart valve. ASAIO J. 40 M707-M713. 

Lee, C.S., Chandran, K.B., and Chen, L.D. 1994. Cavitation dynamics of mechanical heart valve prostheses. Artif Organs 18 758-767. 

Lee, C.S. and Chandran, K.B. 1995. Numerical simulation of instantaneous backflow through central clearance of bileaflet mechanical heart valves at the moment of closure shear stress and pressure fields within the clearance. Med. Biol. Eng. Comp. 33 257-263. 

Reul, H., Steinseifer, U., Knoch, M., and Rau, G. 1995. Development, manufacturing and validation of a single leaflet mechanical heart valve prosthesis. J. Heart Valve Dis. 4 513-519. 

N.L. De Campos, R.R. de Andrade, M.A. Silva, Oral anticoagulation in carriers of mechanical heart valve prostheses experience of ten years. Rev. Bras. Cir. Cardiovasc. 25 (2010) 457-465. 

V.L. Gott, D.E. Alejo, D.E. Cameron, Mechanical heart valves 50 years of evolution, Ann. Thorac. Surg. 76 (2003) S2230-S2239. 

For example, Pradaxa is contraindicated in patients with mechanical heart valves. With concerns over a suspected increase in the suicidality risk associated with antidepressant use in pediatric, adolescent, and young adult patients, close monitoring during the initial antidepressant treatment of these patients is recommended. This recommendation led the FDA to request a label change for all antidepressants on May 2, 2007 (http // www.fda.gOv/NewsEvents/Newsroom/PressAnnouncements/2007/ ucml08905.htm). 

Guidewires, mechanical heart-valve housings and struts, biologic heart-valve stents, vascular stents, vena cava umbrellas, artificial heart housings, pacemaker leads, leads for implantable electrical stimulators, surgical staples, supereleastic properties of some nickel-titanium formulations, shape memory properties of some Ni titanium formulation, radiopaque markers... 

Oxenham H, Bloomfield P, Wheatly DJ, et al. Twenty year comparison of a Bjork-ShUey mechanical heart valve with porcine bioprostheses. Heart 2003 89 715-21. 

Teoh, S.H., Lim, S.C., Yoon, E.T., and Goh, K.S. (1994a) A new method for in vitro wear assessment of materials used in mechanical heart valves, in Biomaterials Mechanical Properties, ASTM STP 1173, H.E. Kambic and A.T. Yokobori, Jr. (eds), American Society for Testing and Materials, Philadelphia, pp. 43-52. 

Fracture Fixation Devices Left Ventricular Apex Inlet Tubes Ligaments and Tendons Mechanical Heart Valve Components... 

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