Pulmonary Arteriography and Hemodynamics During Feline Heartworm Disease

Abstract

The ability of aspirin to block arterial disease and thromboembolism of the pulmonary arteries was studied in heartworm‐infected cats. Three groups of cats were transplanted with four heartworms per cat and studied. One group of eight cats (aspirin group) received aspirin (97.5 mg, twice a week) for the five‐month infection and another group of eight cats served as the nontreated control group (nontreated group). Based upon the results of the first two groups, the third group (adjusted aspirin group) of six cats was studied in which the aspirin dosage was adjusted in order to maintain an inhibition of in vitro platelet aggregation. Cats were studied by nonselective pulmonary arteriograms before heartworm transplantation and by selective arteriograms, aortograms, and pulmonary hemodynamics five months after heartworm transplant. Pulmonary hypertension, (mean pulmonary artery pressures > 16 mmHg), was discovered in three cats with one cat in each group. There were no differences in the mean pulmonary artery pressure or vascular resistance between the groups. Many of the arterial diameters for the nontreated and aspirin groups were greater after the five‐month infection than before heartworm infection. All of the postinfection caudal arteries were tortuous and had aneurysms. Some of the caudal lung lobes had perfused areas that appeared to have a hypervascular microvasculature. The proportion of obstructed right and left distal caudal pulmonary arteries and the resulting nonperfused area of the caudal lung lobe in the nontreated and aspirin treated groups were each greater than in the adjusted aspirin group. Prominent bronchial arteries and arterial circulation were present in three of six of the nontreated cats, five of seven of the aspirin‐treated cats, and two of five adjusted aspirin cats, that had diagnostic aortograms. Aspirin given at a standard dosage of 97.5 mg twice a week did not reduce the arteriographically demonstrated arterial disease, the pulmonary hypertension, or the obstruction of caudal lobar arteries by thromboembolism and exuberant villiis proliferation. The adjusted aspirin dosage, which required daily administration in some cats, appeared to have limited benefits. Since this dosage was individualized for each cat and near the toxic dosage for cats, we are reluctant to recommend aspirin in cats with heartworm disease. Nonselective pulmonary arteriograms, as done in this study, can be useful in cats with suspected heartworm infection and radiographic signs, but which have negative test results for microfilaria and ELISA‐antigen.