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									CME Cardiology                                                                         Clinical Medicine 2010, Vol 10, No 2: 188–91

Infective endocarditis                                                                         tion, abscesses, fistulae and leaflet perfo-
                                                                                               ration are all more reliably detected using
                                                                                               this technique.7
Wazir Baig, consultant cardiologist;          (now 17% of cases). Enterococci are the
Jonathan Sandoe, consultant                   third most frequent cause of IE and con-         Blood culture-negative
microbiologist                                sistently account for approximately 10%          endocarditis
Departments of Cardiology and                 of episodes.3
                                                 Further classification by type of car-        Depending on the patient group and type
Microbiology, Leeds General Infirmary,
                                              diac structure divides IE into:                  of structure affected, 5–12% of IE cases
                                                                                               are blood culture-negative. Negative cul-

Infective endocarditis (IE) is a non-con-
                                              •   native valve endocarditis                    tures are more frequent in prosthetic

tagious infection of intracardiac struc-
                                              •   prosthetic valve endocarditis, and           valve and cardiac device-related IE.3

tures which usually affects the valves of
                                              •   cardiac device-related IE – most             Contributing factors include the recent
                                                  commonly affecting permanent                 use of antibiotics, organisms that are dif-
the heart but, in contemporary practice,          pacemakers and implantable car-              ficult to culture and inadequate blood
may also involve infection of indwelling          dioverter-defibrillators.                    sampling. A novel technique in these
cardiac devices. Patients occasionally                                                         cases is broad-range 16S ribosomal RNA
present acutely with severe sepsis but                                                         gene polymerase chain reaction analysis
most still manifest with a non-specific       Diagnostic methods                               of tissue taken at the time of valve surgery
illness of insidious onset having been                                                         (where appropriate). The results can
symptomatic for several weeks or              The essential diagnostic methods for IE
                                              are blood cultures and echocardiog-              guide the appropriate choice of antimi-
months. IE remains a challenging disease                                                       crobial therapy. The technique is cur-
because of its variable presentation and      raphy. These investigations are needed to
                                              confirm continuing bacteraemia and to            rently limited to patients undergoing
frequent difficulty in securing the diag-                                                      valve surgery, but application to whole
nosis. Population-based studies are           demonstrate vegetations and/or new par-
                                              avalvular regurgitation of prosthetic            blood samples should soon be feasible.8
scarce, but US data indicate the incidence                                                     Consideration should also be given to
is currently 5–7/100,000 person years,1       valve(s). The synthesis of clinical and
                                              microbiological findings with echocar-           serological testing for Bartonella, Brucella,
but slowly rising2 as a result of:                                                             Q-Fever, Mycoplasma and Legionella
                                              diographic appearances is now known as
                                                                                               species when blood cultures are negative.
•   an ageing population who develop          the Duke criteria, first published in 1994.
    degenerative valve lesions                The original algorithm has been modi-
•   the increasing number of patients         fied and provides an objective frame-
                                                                                               Antimicrobial regimens
    who receive prosthetic heart valves       work to assist diagnosis (Table 1).4,5
    and other implantable cardiac devices     Definitions of positive echocardio-              Knowledge of the causative organism in IE
•   the rising number of patients who         graphic findings in IE are provided in           is key to the selection of appropriate
    receive renal replacement therapy via     Table 2.                                         antimicrobial therapy. Whether infection
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