Dog panting uncontrollably with heart murmur and no clear cause

Abstract

A 9.5-year-old 20.8-kg (45.8-lb) spayed female Border Collie was referred to the Washington State University Veterinary Teaching Hospital for evaluation of excessive and uncontrollable panting. According to the owner, the panting had begun suddenly 2 nights before with no obvious cause. The dog had had a heart murmur for 2 years for which it had been prescribed enalapril (10 mg, PO, q 24 h). The referring veterinarian obtained 2 radiographic views of the thorax to rule out congestive heart failure, but did not notice any radiographic abnormalities, and the dog was subsequently referred to the cardiology service at the Washington State University Veterinary Teaching Hospital for further evaluation of the heart murmur and excessive panting. The owner reported that the dog had been very restless and was unable to sleep or eat properly because of the nonstop panting and was drinking an excessive amount of water. The dog had a littermate that had died suddenly of an unknown cause, but a heart murmur had been identified prior to the dog’s death. On initial physical examination at the Veterinary Teaching Hospital, the dog was alert and responsive. Body condition score was 5 on a scale from 1 to 9. The dog’s mucous membranes were pink and moist, and capillary refill time was < 2 seconds. The dog had a rectal temperature of 38.2°C (100.7°F) and pulse rate of 76 beats/min and was panting excessively. No crackles or wheezes were identified during thoracic auscultation, but a grade III/VI heart murmur loudest at the left apex was heard. Results of abdominal palpation were unremarkable, and no peripheral lymphadenopathy was noted. Neurologic and musculoskeletal examinations did not reveal any abnormalities. No abnormalities were detected on a CBC, but serum biochemical analyses revealed slightly high alanine aminotransferase activity (307 U/L; reference range, 0 to 112 U/L), high SUN concentration (34 mg/dL; reference range, 9 to 26 mg/dL), and slightly low total protein concentration (5.1 g/dL; reference range, 5.5 to 7.5 g/dL). Serum D-dimer concentration was unremarkable (< 250 ng/mL; reference range, < 250 ng/mL), and prothrombin time (7.3 seconds; reference range, 6.4 to 8.2 seconds) and activated partial thromboplastin time (10.8 seconds; reference range, 8.4 to 14.8 sec-