Approach to Infective Endocarditis at Surgery or Autopsy

At surgery or autopsy examination of hearts, valves, and vascular prostheses, clinical suspicion that the patient has IE may or may not be present. The presence of unexpected but suspicious valvular lesions should prompt a proper workup for IE. Before immersion of the heart or resected valve in fixative, a thorough examination should be made to visualize all the valves and perivalvular structures. Sterile instruments should be used if a suspicious lesion is encountered (Figure 2.1). Since the proper approach is to assume that all valvular thrombi are infected until proven otherwise (this is the author's personal practice), portions of the thrombus should be submitted for culture. Swabs of the lesions are not recommended. Cultures should never be interpreted in isolation. Pre-mortem or pre-operative blood cultures should be consulted. Microscopy of the valve or thrombus to confirm the presence of microorganisms is essential [18].

Special stains are useful to detect microorganisms; however, treatment with antimicrobial agents has changed the utility of these stains. Gram stain is useful to detect bacteria, but after a few weeks of antimicrobial treatment the organisms may not stain (Figures 2.2, 2.3) [2]. Therefore silver stains should always be performed not only to detect fungi but also to

Figure 2.1. Gross photograph of excised three cusp aortic valve with infective endo-carditis.The left cusp has adherent infected thrombus (vegetation).The middle cusp has a small nonruptured acquired aneurysm (windsock lesion) related to the infection. Ruler = 1 cm.

Figure 2.1. Gross photograph of excised three cusp aortic valve with infective endo-carditis.The left cusp has adherent infected thrombus (vegetation).The middle cusp has a small nonruptured acquired aneurysm (windsock lesion) related to the infection. Ruler = 1 cm.

detect bacteria that have lost their positive Gram staining, yet still can be detected with silver stain of their cell walls (Figure 2.4). Care must be exercised with silver stain interpretation as this stain also highlights cellular debris and some intracellular organelles. Giemsa stain is useful to detect rickettsial organisms, which may not stain with the other stains.

Correlating the blood culture result with cultures of the tissues and vegetation is essen tial. Communication with the clinicians may save much frustration if the special stains are negative and the organism is known from prior cultures. This is common in patients who have received prior antimicrobial agents. In culture-negative IE, the common culprit organisms include Eikenella, Brucella, Neisseria, fungi, Chlamydia, acid-fast bacilli, or right-sided endocarditis, where the lungs filter out the organisms. HACEK (Hemophilus,

Figure 2.2. Photomicrograph of valve cusp with infective endocarditis. The valve cusp tissue is heavily infiltrated by acute inflammatory cells and there is inflamed thrombus (left). (hematoxylin phloxine saffron, x200).

Figure 2.2. Photomicrograph of valve cusp with infective endocarditis. The valve cusp tissue is heavily infiltrated by acute inflammatory cells and there is inflamed thrombus (left). (hematoxylin phloxine saffron, x200).

Figure 2.3. Photomicrograph of valve cusp. This is a Gram stain demonstrating large clusters of blue-staining Gram-positive cocci bacteria (Gram stain, x200).
Figure 2.4. Photomicrograph of valve cusp. This is a silver (Grocott) stain demonstrating degenerating clusters of cocci bacte-ria.This is an excellent stain for fungi, but it is also useful to detect degenerating or dying bacteria after antibiotic treatment (Grocott, x200).

Actinobacillus, Cardiobacterium, Eikenella, Kingella) organisms may be particularly difficult to grow [19,20]. Clinical history and history of treatment and exposures may be very relevant [21]. Electron microscopy, immunofluorescence, polymerase chain reaction (PCR), or other molecular techniques may be contributory in the search for these often culture negative organisms [18,21-23]. Studies have suggested that PCR may be a better diagnostic tool than culture, especially after antimicrobial therapy, but there remains concern about false positives and background contamination [18,23,24].

Pathological diagnosis of healed IE can be difficult, as the findings may be nonspecific and organisms frequently cannot be found. The diagnosis can only be made with confidence when the gross and microscopic features are typical, and there are collaborative clinical findings. This is quite common in patients with adequate pre-operative antibiotic treatment.

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