Wall-July PV-Review - VetLearn.com

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Compendium August 2002 Infective Endocarditis 619 or Holter recorded). Other less-common electrocardiographic abnormalities include bundle branch and atrioventricular blocks. Radiographic interpretation may reveal chamber enlargements or no abnormalities. Chamber enlargement (most commonly left atrial) is usually present when IE is chronic. 2–4,6,41 If overt or impending leftsided CHF is present, pulmonary edema and/or distention of the pulmonary veins will be present. 2–4,6,9,10,41 Echocardiography is the best diagnostic tool but is neither 100% sensitive nor 100% specific. 3,9–11 Modern, two-dimensional equipment can resolve 1-mm lesions in dogs. 10 Detection of an echogenic oscillating intracardiac mass on the aortic or mitral valve is a strong indication of the presence of IE. Both the M-mode and two-dimensional appearance of aortic valve vegetations are virtually pathognomonic (Figure 3). Echoes from vegetations on the mitral valve are usually on the cra- Figure 3—M-mode echocardiogram of a thickened aortic valve (AV). This echocardiographic image is typical of aortic valve vegetations. Figure 4—Two-dimensional echocardiogram in the right parasternal, long-axis plane demonstrating vegetative lesions on the cranial (anterior) mitral valve (arrowhead) and the aortic valve (arrow) leaflets during diastole. A = aorta; LA = left atrium; LV = left ventricle. www.VetLearn.com nial (anterior) leaflet but are not pathognomonic; in some cases, however, the lesion is so large that IE should be suspected (Figure 4). Operator skill and experience, as well as image quality, influence interpretation. Furthermore, results must be considered in the context of other clinical and laboratory findings. Falsepositive test interpretation is most commonly attributable to mitral valve myxomatous degeneration. 9,10 A clinician should always consider the signalment and history of the dog in question. The signalment associated with IE is largely different from that of dogs with advanced myxomatous degeneration. The presence of a new heart murmur is of special importance if the breed or age of the patient is not characteristic of dogs affected by myxomatous valvular degeneration. Chamber enlargements and altered contractility may be evident. 3,6,9,10 Decreased contractility is typical of the high-pressure volume overload of advanced aortic valve IE but not of the low-pressure volume overload of mitral valve IE. Decreased contractility may also be related to chronicity of volume overload. Diastolic fluttering of the anterior (cranial) mitral valve leaflet is indicative of aortic insufficiency and, therefore, suggestive of endocarditis. This fluttering is the result of the jet of aortic regurgitation striking the anterior mitral valve leaflet when it is open in diastole. Color-flow imaging is used to identify hemodynamic consequences of endocarditis, such as valvular regurgitation or left ventricular outflow tract turbulence (Figure 5). Doppler interrogation of aortic regurgitation is used to confirm the severity. The spectral display of severe aortic regurgitation is characterized by a rapid deceleration of regurgitant velocity during diastole. Severe aortic regurgitation is incompatible with survival. DIAGNOSIS The diagnosis of IE requires integration of clinical and laboratory data. The advent of echocardiography has greatly facilitated the diagnosis. Because the aortic valve is usually involved in IE, 2,3,6 ultrasonographic recognition is seldom difficult. Diagnosis of mitral valve IE is more difficult because the lesions of myxomatous degeneration can resemble those of IE. 3 It should be recognized that dogs with the highest incidence of myxomatous degeneration of the mitral valve (older, small-breed dogs) are seldom affected by IE. Signalment, clinical findings, femoral pulse characteristics, confirmation of bacteremia, and a murmur of recent onset (especially a diastolic murmur) are important to the diagnosis of IE if echocardiography is not available. Identification of Bacteremia Although blood cultures lack sensitivity and speci-
620 Small Animal/Exotics Compendium August 2002 Figure 5A Figure 5B Figure 5C Figure 5D Figure 5—(A) Two-dimensional echocardiogram in the left apical, long-axis, two-chamber imaging plane. During systole, an aortic valve leaflet thickened by vegetation (arrow) is opened into the aorta (A). There are also vegetations on the mitral valve leaflets (arrowhead). (B) In diastole, the vegetative aortic valve is closed, and a portion of the vegetation is protruding (arrowhead) into the left ventricle (LV). The open cranial (anterior) mitral valve leaflet is also thickened by vegetation (arrow). (C) Color-flow Doppler imaging in systole demonstrating the turbulent mitral regurgitation (arrowhead). (D) Color-flow Doppler imaging in diastole demonstrating the turbulent jet of aortic regurgitation (arrowhead). LA = left atrium. ficity, they should always be performed in an attempt to identify the offending organism. 10,12,14,42,43 Bacteremia may occur in other conditions, such as diskospondylitis, chronic wounds, prostate infections, and periodontal disease. 6,12–14 Performed properly, blood cultures often yield positive results (in our experience, approximately 30% to 50% of patients have positive results). 6,9–11,13,14 Decreased sensitivity may be explained by fastidious, slow-growing organisms; improper laboratory techniques; the failure to culture for anaerobes; low-blood bacterial concentrations; endogenous bactericidal factors (complement and phagocytes); intermittent shedding of the organism; chronic IE with encapsulated vegetative lesions; or infections with Bartonella. 13,31–33,42–44 Other variables affecting the yield of microorganisms include the volume of the blood sample, number of cultures performed, and incubation atmosphere of the culture. 14,44 www.VetLearn.com Two or three sets of blood samples should be taken aseptically, preferably before antibiotic administration. 6,13,14,43,44 Samples should be taken either from a freshly placed, meticulously maintained jugular catheter or from different veins. 14,42 Commercial vacuum bottles should be used. If the animal is receiving antibiotic therapy, collect the sample at the antibiotic trough level and use an antibiotic removal device. 14 Duration of antimicrobial therapy is an important factor in detecting bacteria. 45 Therapy for only 2 to 3 days may not interfere; however, longer courses of therapy require the use of antibiotic removal devices or discontinuation of therapy. Suppression of bacteremia often persists longer than antibiotic blood levels. Sterile technique should be practiced when collecting blood samples. The area must be clipped and disinfected, and sterile gloves should be worn. Samples (7 to 10 ml of whole blood) should be placed in two bottles:
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