Use of echocardiography for the diagnosis of heartworm disease in cats: 43 cases (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 examinations at 2 veterinary teaching hospitals between 1985 and 1997. Twenty-two of these 43 cats also underwent radiography of the thorax and heartworm antibody and heartworm antigen testing. Procedure-Cats were determined to be infected with Dirofilaria immitis infection on the basis of 1 or more of the following findings: positive modified Knott or antigen test result, echocardiographic evidence of heartworm disease. or confirmation of the disease on postmortem examination. The percentage of echocardiographs in which heartworms were evident was compared with the percentage of radiographs in which pulmonary artery enlargement was evident and results of antigen or antibody tests in cats in which all tests were performed. Results-Overall, heartworms were detectable by use of echocardiography in 17 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, antigen test results were positive in 12, and pulmonary artery enlargement was evident radiographically and heartworms were identifiable echocardiographically in 14. Heartworm infection was diagnosed exclusively by use of echocardiography in 5 cats in which the antigen test result was negative. Conclusions and Clinical Relevance-Although echocardiography was less sensitive 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 the likelihood of detection of heartworms echocardiographically.