Chapter 118. Infective Endocarditis (Part 6) docx

Infective Endocarditis Part 6 The roles of bacteremia and echocardiographic findings in the diagnosis of endocarditis are appropriately emphasized in the Duke criteria.. The requirement

Chapter 118 Infective Endocarditis

(Part 6)

The roles of bacteremia and echocardiographic findings in the diagnosis of endocarditis are appropriately emphasized in the Duke criteria The requirement for multiple positive blood cultures over time is consistent with the continuous low-density bacteremia characteristic of endocarditis (≤100 organisms/mL) Among patients with untreated endocarditis who ultimately have a positive blood culture, 95% of all blood cultures are positive; in 98% of these cases, one of the initial two sets of cultures yields the microorganism The diagnostic criteria attach significance to the species of organism isolated from blood cultures To fulfill a major criterion, the isolation of an organism that causes both endocarditis and

bacteremia in the absence of endocarditis (e.g., S aureus, enterococci) must take

place repeatedly (i.e., persistent bacteremia) and in the absence of a primary focus

of infection Organisms that rarely cause endocarditis but commonly contaminate blood cultures (e.g., diphtheroids, CoNS) must be isolated repeatedly if their isolation is to serve as a major criterion

Blood Cultures

Isolation of the causative microorganism from blood cultures is critical not only for diagnosis but also for determination of antimicrobial susceptibility and planning of treatment In the absence of prior antibiotic therapy, three blood culture sets (with two bottles per set), separated from each other by at least 1 h, should be obtained from different venipuncture sites over 24 h If the cultures remain negative after 48–72 h, two or three additional blood culture sets should be obtained, and the laboratory should be consulted for advice regarding optimal culture techniques Empirical antimicrobial therapy should not be administered initially to hemodynamically stable patients with subacute endocarditis, especially those who have received antibiotics within the preceding 2 weeks; thus, if necessary, additional blood culture sets can be obtained without the confounding effect of empirical treatment Patients with acute endocarditis or with deteriorating hemodynamics who may require urgent surgery should be treated empirically immediately after three sets of blood cultures are obtained over several hours

Non-Blood-Culture Tests

Serologic tests can be used to implicate causally some organisms that are

difficult to recover by blood culture: Brucella, Bartonella, Legionella, and C burnetii Pathogens can also be identified in surgically recovered vegetations or

emboli by culture, by microscopic examination with special stains (i.e., the

periodic acid–Schiff stain for T whipplei), and by use of polymerase chain

reaction (PCR) to recover unique microbial DNA or 16S rRNA that, when sequenced, allows identification of organisms

Echocardiography

Imaging with echocardiography allows anatomic confirmation of infective endocarditis, sizing of vegetations, detection of intracardiac complications, and assessment of cardiac function (Fig 118-3) Transthoracic echocardiography (TTE) is noninvasive and exceptionally specific; however, it cannot image vegetations <2 mm in diameter, and in 20% of patients it is technically inadequate because of emphysema or body habitus Thus, TTE detects vegetations in only 65% of patients with definite clinical endocarditis; i.e., it has a sensitivity of 65% Moreover, TTE is not adequate for evaluating prosthetic valves or detecting intracardiac complications TEE is safe and significantly more sensitive than TTE

It detects vegetations in >90% of patients with definite endocarditis; nevertheless, false-negative studies are noted in 6–18% of endocarditis patients TEE is the optimal method for the diagnosis of prosthetic endocarditis or the detection of myocardial abscess, valve perforation, or intracardiac fistulae

Figure 118-3

Imaging of a mitral valve infected with Staphylococcus aureus by

low-esophageal four-chamber-view translow-esophageal echocardiography (TEE) A

Two-dimensional echocardiogram showing a large vegetation with an adjacent

echolucent abscess cavity B Color-flow Doppler image showing severe mitral

regurgitation through both the abscess-fistula and the central valve orifice A, abscess; A-F, abscess-fistula; L, valve leaflets; LA, left atrium; LV, left ventricle;

MR, mitral central valve regurgitation; RV, right ventricle; veg, vegetation (With permission of Andrew Burger, M.D.)