6.6.2 Diagnostic aids
In any animal in which endocarditis is suspected a thorough investigation is indicated in order to allow early diagnosis for there to be any chance of successful treatment. It is a good principle to perform clinical pathological tests in any horse which is unwell and in which a murmur of AR is detected, although other differential diagnoses need to be considered.
Haematology and biochemistry Haematological examination may show a neutrophilia, with or without a left shift. Toxic signs in the neutrophils are sometimes seen. These changes can be very variable. More consistent findings are a hypergammaglobulinaemia and a high plasma fibrinogen level. The latter is particularly useful; a fibrinogen assay should be requested in any animal in which endocarditis is considered a differential diagnosis. Very high fibrinogen levels of 8-13 gL are often found in animals with endocarditis. However, fibrinogen levels may be raised due to an inflammatory and/or infectious process in other organs and further diagnostic tests pertinent to these organs may be indicated. For example, animals with cardiogenic pulmonary oedema and secondary pneumonia may have high fibrinogen levels. Although the prognosis in the long-term is likely to be poor in these animals also, the pneumonia is more likely to respond to treatment than endocarditis.
Blood culture A wide variety of bacteria have been isolated from endocarditis lesions so the identity of the causative organism is unlikely to be known without successful blood culture. Scrupulous aseptic technique k needed to avoid connonetheless, the results of bacterial isolation and antibiotic sensitivity should be interpreted in the light of potential contaminants. If fever spikes are identified, it is theoretically advantageous to take a sample on a rising peak, although this is seldom practicable. At least three samples should be taken directly into blood culture media and cultured for aerobic and anaerobic organAlthough bacteria can usually be isolated from the lesion itself at PM, blood cultures are often negative. The best results are obtained when large quantities of culture medium and blood are used and when the samples are taken before any antibiotic treatment is given.
Ideally, echocardiography should be performed in any animal in which endois suspected, particularly those with a high plasma fibrinogen. It may also be helpful in any animal with a fever of unknown origin, whether a murmur is present or not. The purpose of the echocardiographic examination is to attempt to make a definitive diagnosis and to evaluate the effects of the valvular disease on cardiac function.
In order to make a definitive diagnosis of endocarditis, the location of the infective focus should be isolated to the heart valves or the walls of the ventricles. The lesions caused by endocarditis are usually large, florid and echogenic and are easily identified by echocardiography (Figure 4.20). Occasionally lesions are small and may be attributed to degenerative valvular disease. Serial echoexaminations are likely to show a change in the size or number of lesions with endocarditis. Measurement of any consequent volume overload may help to indicate the severity of valvular regurgitation. If severe, the prognosis is grave even if treatment of the infectious process is successful. It is therefore essential to judge the severity of volume overload before embarking on treat
In some animals, systemic disease related to an infectious process other than endocarditis may result in increased demands for cardiac output and may precipitate heart failure in animals with underlying degenerative valvular heart disease.
Clinical evaluation of horses with endocarditis is summarised in Table 6.5.