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

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.