Prosthetic valves

Hea.rt Va.Ives. Since the early 1960s nearly 50 different heart valves have been developed. The most commonly used valves as of the mid-1990s include mechanical prostheses and tissue valves. Nearly 75,000 of these prosthetic valves are implanted aimually worldwide, and about 30,000 in the United States alone. Caged-baH, caged disk, and til ting-disk heart valves are the types most widely used. 

Gram-negative coverage is indicated for patients with diabetes, HIV infection, prosthetic valves, or those receiving immunosuppressive agents (gentamicin 2 mg/kg intravenously with serum concentration monitoring). 

Echocardiogram positive for IE [TEE recommended in patients with prosthetic valves, rated at least "possible IE" by clinical criteria, or complicated IE (paravalvular abscess) TTE as first test in other patients], defined as follows ... 

Other gram-negative organisms, such as Pseudomonas spp., have been noted to cause IE, especially in IVDUs and patients with prosthetic valves. Additionally, IE caused by Salmonella spp., Escherichia coli, Citrobacter spp., Klebsiella spp., Enterobacter spp., Serratia marcescens, Proteus spp. and Providencia spp. also has been reported.1... 

It is important to determine (1) whether the isolate is methicillin-susceptible or methicillin-resistant and (2) whether the patient has a prosthetic valve. For patients with no prosthetic material, methicillin-susceptible staphylococci treatment should consist of a penicillinase-resistant penicillin (e.g., nafcillin or oxacillin) with or without gentamicin, and for methicillin-resistant strains, therapy should consist of vancomycin (see Table 71-4). Combination therapy with aminoglycosides, when used in these patients, typically is given only during the first 3 to 5 days of therapy. In the absence of prosthetic material, some treatment guidelines do not recommend combination therapy against MRSA. However, many clinicians may combine either gentamicin or rifampin with vancomycin if the patient is unresponsive to monotherapy. 

TABLE 71-5. Therapy for Prosthetic Valve Endocarditis Caused by Staphylococci... 

Therapy for Native-Valve or Prosthetic-Valve Enterococcal Endocarditis Caused by Strains Susceptible to Penicillin, Gentamicin, and Vancomycin... 

Aqueous 1 8-30 million 4-6 IA Prosthetic valve or other prosthetic cardiac... 

Cardiac conditions in which prophylaxis is recommended include presence of prosthetic valves, prior infective endocarditis, congenital cardiac abnormalities, rheumatic heart disease or any other valvular dysfunction, hypertrophic... 

Prosthetic-valve endocarditis Endocarditis that occurs in patients with bioprosthetic or synthetic implanted heart valves. 

Most types of structural heart disease resulting in turbulence of blood flow will increase the risk for IE. Some of the most important risk factors include / Presence of a prosthetic valve (highest risk)... 

Left-sided endocarditis caused by Staphylococcus aureus / Prosthetic valve endocarditis (PVE)... 

In patients with endocarditis of prosthetic valves or other prosthetic material caused by viridans streptococci and Streptococcus bovis, treatment courses are extended to 6 weeks (Table 37-5). 

Therapy for Endocarditis of Prosthetic Valves or Other Prosthetic Material Caused by Viridans Group Streptococci and Streptococcus bovis... 

Aqueous crystalline pen idllin C sodium plus 18-30 million units/24 hours IV either continuously or in six equally divided doses 4-6 IA recommended for patients with symptoms greater than 3 months Prosthetic valve or other prosthetic cardiac material minimum... 

Diphtheroid-yancomyan is effective for diphtheroid endocarditis, and has been used successfully with rifampin, an aminoglycoside, or both in early onset prosthetic valve endocarditis caused by Staphylococcus epidermidls or diphtheroids. 

In developed countries endocarditis is present in 1/1000 hospital admissions or 1-2 cases per million population. An increasing number of endocarditis cases are associated with intravascular device infections and the placement of prosthetic valves thus, endocarditis can be acquired during hospital stay. Men are afflicted more often than females, and most patients are >50 years of age. Pre-existing heart lesions predispose to bacterial endocarditis if they are accompanied by (thrombotic) alterations of the endocardial surface or blood flow such that bacteria... 

Rifampin is a first-line antitubercular drug used in the treatment of all forms of pulmonary and extrapul-monary tuberculosis. Rifampin is an alternative to isoniazid in the treatment of latent tuberculosis infection. Rifampin also may be combined with an antileprosy agent for the treatment of leprosy and to protect those in close contact with patients having H. influenza type b and N. meningitidis infection rifampin is also used in methicillin-resistant staphylococcal infections, such as osteomyelitis and prosthetic valve endocarditis. 

Rifampin combined with a second agent is used to eradicate staphylococcal carriage. Rifampin combination therapy is also indicated for treatment of serious staphylococcal infections such as osteomyelitis and prosthetic valve endocarditis. 

Rifampin is used in a variety of other clinical situations. An oral dosage of 600 mg twice daily for 2 days can eliminate meningococcal carriage. Rifampin, 20 mg/kg/d for 4 days, is used as prophylaxis in contacts of children with Haemophilus influenzae type b disease. Rifampin combined with a second agent is used to eradicate staphylococcal carriage. Rifampin combination therapy is also indicated for treatment of serious staphylococcal infections such as osteomyelitis and prosthetic valve endocarditis. Rifampin has been recommended also for use in combination with ceftriaxone or vancomycin in treatment of meningitis caused by highly penicillin-resistant strains of pneumococci. 

Non-bacterial thrombotic or marantic endocarditis Rheumatic disease Prosthetic valve Calcification and/or sclerosis... 

Prosthetic valves, particularly mechanical ones, are associated with thrombosis and embolism, and infective endocarditis. The overall risk of clinically evident embolism is 1-2% per annum in those taking anticoagulants (Vongpatanasin et al. 1996), with mitral valve prostheses being the most prone to thrombosis. 

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