Usefulness of thoracic radiological signs for the diagnosis and staging of severity in dogs with heartworm (Dirofilaria immitis).

Abstract

Dirofilaria immitis is a nematode that causes heartworm disease, which is a severe pathology that causes cardiopulmonary alterations in dogs. The purpose of this study was to determine whether specific thoracic radiography findings in dogs with heartworm disease are associated with some clinical variables (presence/severity of pulmonary hypertension (PH), parasitic burden or the presence of microfilariae), epidemiological variables (sex and age), as well as the presence of coagulation alterations. Dorsoventral and right lateral thoracic radiography projections were made in 49 heartworm-infected dogs, and the vertebral heart scale (VHS), the right cranial pulmonary artery at the level of the fourth rib (PA:4R) ratio, and the diameter of the right causal pulmonary artery at the level of the ninth rib (PA:9R) ratio were calculated. All the animals were subjected to an echocardiography examination to estimate the parasite burden and the presence of PH based on a right pulmonary artery distensibility index (RPADi). Additionally, blood samples were collected to assess the presence of microfilariae and Prothrombin Time (PT) and Activated Partial Thromboplastin Time (APTT) were determined. The results showed that there were 85.7% of dogs with some type of radiographic lung alteration and 67.3% presented anomalies within the cardiac silhouette. VHS was increased in 42.9% of dogs and PA:4R and PA:9R ratios were altered in 31.3% and 19.5%, respectively. VHS was not useful to evaluate the studied epidemiological and clinical parameters but the study of the PA:4R and PA:9R ratios may be useful to estimate PH and parasite burden in dogs infected by D. immitis. Results showed that thoracic radiography could be a useful and complementary important tool to assess cardiopulmonary alterations in canine heartworm disease.