Abstract
BACKGROUND: Some dogs with severe mitral valve regurgitation can have chronic cough, but its cause is unclear. Many of these dogs exhibit left principal (synonym mainstem) bronchial collapse or compression. Some clinicians believe that an enlarged heart, particularly the dilated left atrium, compresses the left principal bronchus, while others argue that a healthy bronchus cannot be compressed and that the cough is due to concurrent airway disease, such as bronchomalacia. In this study, we aimed to investigate the correlation between chronic cough and radiographic signs of bronchial narrowing in dogs with cardiomegaly secondary to primary mitral valve regurgitation. METHODS: Four radiologists independently evaluated 51 sets of thoracic radiographs from client-owned dogs with cardiomegaly due to severe mitral valve regurgitation, including 26 sets of radiographs belonging to dogs with chronic (>8 weeks) cough and 25 without cough. The presence or absence of bronchial narrowing was assessed while the radiologists were blinded to patient characteristics and each other's findings. RESULTS: Interobserver variability was high, and the radiologists could not reliably predict which dogs had a chronic cough. Dogs with left atrial enlargement and airway narrowing sometimes coughed and sometimes did not. Likewise, some dogs with left atrial enlargement but no signs of airway compression or collapse coughed, and some did not. It was impossible to distinguish the groups based on these features. CONCLUSIONS: Bronchial compression by an enlarged heart and left atrium is an unlikely cause of chronic cough in dogs with severe primary mitral valve regurgitation.