Use of echocardiography for the diagnosis of heartworm disease in cats: 43cases (1985-1997)

Objective-To determine the usefulness of echocardiography in the diagnosis of heartworm disease in cats and to compare this modality with other tests. Design-Retrospective study. Animals-43 cats with heartworm infection that had echocardiographic examina tions at 2 veterinary teaching hospitals between 1985 and 1997. Twenty-two of these 43 cats also underwent radiography of the thorax and heartworm ant ibody and heartworm antigen testing. Procedure-Cats were determined to be infected with Dirofilaria immitis infe ction on the basis of 1 or more of the following findings: positive modifie d Knott or antigen test result, echocardiographic evidence of heartworm dis ease. or confirmation of the disease on postmortem examination. The percent age of echocardiographs in which heartworms were evident was compared with the percentage of radiographs in which pulmonary artery enlargement was evi dent and results of antigen or antibody tests in cats in which all tests we re performed. Results-Overall, heartworms were detectable by use of echocardiography in 1 7 of 43 cats, most often in the pulmonary arteries. in the 22 cats in which all tests were performed, antibody test results were positive In 18, antig en test results were positive in 12, and pulmonary artery enlargement was e vident radiographically and heartworms were identifiable echocardiographica lly in 14. Heartworm infection was diagnosed exclusively by use of echocard iography in 5 cats in which the antigen test result was negative. Conclusions and Clinical Relevance-Although echocardiography was less sensi tive than antigen testing, it was a useful adjunctive test in cats that had negative antigen test results in which there was a suspicion of heartworm disease. The pulmonary arteries should be evaluated carefully to increase t he likelihood of detection of heartworms echocardiographically.