Intracardiac heartworms in dogs: Clinical and echocardiographic characteristics in 72 cases (2010-2019)

Abstract

Background: Heartworms, a cause of pulmonary hypertension (PH) in dogs, can migrate from the pulmonary arteries into the heart resulting in life-threatening caval syndrome (CS).

Objectives: To describe clinical and echocardiographic characteristics in dogs with intracardiac heartworms including estimated heartworm burden and frequency of PH and pigmenturia.

Animals: Seventy-two client-owned dogs with heartworms.

Methods: Retrospective study. Data collected from an electronic medical records search for dogs with intracardiac heartworms included clinicopathologic, echocardiographic, and procedural findings. Dogs with heartworms isolated to the pulmonary arteries were excluded.

Results: Estimated intracardiac heartworm burden was low in 14 of 72 (19%) and high in 58 of 72 (81%) dogs. The majority were small breed (54/72; 75%; 29/72; 40% Chihuahuas) and had a high likelihood of PH (67/72; 93%). Pigmenturia was the second most common clinical finding (31/72; 43%) after lethargy (32/72; 44%). Anemia (37/55; 36%), pigmenturia (30/58; 52%), and bilirubinuria (28/36; 78%) were significantly more common in dogs with a high worm burden (P < .05). Based on the presence of anemia, pigmenturia, and clinical signs, 18 of 72 dogs (25%) were considered to have CS.

Conclusions and clinical importance: Although the majority of dogs with intracardiac heartworms had a high worm burden and high likelihood of PH, only 25% had clinical evidence of CS. Echocardiography is a useful tool to identify intracardiac heartworms, detect likelihood of PH, and could be useful for staging heartworm positive small breed dogs for intracardiac heartworm migration.

Keywords: Dirofilaria immitis; canine; caval syndrome; hemolysis; pigmenturia; pulmonary hypertension.

FIGURE 1

Echocardiographic images of the heart from a right parasternal long‐axis 4 chamber view in 2 dogs with intracardiac heartworms that appear as parallel hyperechoic lines (arrows). Panel A is an example of an estimated low worm burden (a few worms present in the right atrium; estimated < 5). Panel B is an example of an estimated high worm burden (more than a few worms and fills the right atrium). LA, left atrium; LV, left ventricle; PA, pulmonary artery; RA, right atrium

FIGURE 2

Frequency distribution of 72 dogs with (47) and without (25) heartworm extraction performed grouped by month of year at the time of presentation. Number of extractions performed was equally distributed between seasons (Winter = December, January, February; Spring = March, April, May; Summer = June, July, August; Fall = September, October, November)