Tracheo-rachidian angle evaluation in 83 dogs affected with myxomatous mitral valve disease

Radiographic examination of thorax is recommended in all patients with myxomatous mitral valve disease (MMVD) to assess the hemodynamic significance of the murmur and the comorbidity of respiratory diseases. Cough in dogs with MMVD may be related to congestive heart failure (CHF), to respiratory disease and/or to compression of the left mainstem bronchus by an enlarged left atrium (LAE). The aim of the present study was to evaluate the tracheo-rachidian angle (TRA) and to assess its usefulness in dogs affected by MMVD, with and without cough. Eighty-three dogs affected by MMVD were included, and their thoracic radiographs (right lateral recumbency) were evaluated. TRA was assessed, and 3 clinical groups were detected. TRA1: trachea in the physiological position as compared with the spine (47 dogs)/ normal TRA TRA2: trachea dorsally displaced, but not more than parallel to the spine (31 dogs)/ intermediate TRA. TRA3: trachea dorsally displaced toward the spine (5 dogs)/ reduced TRA. In each TRA-group was then assessed the presence/absence of cough and the CHF-stage based on ACVIM consensus staging. The TRA1-group included 51% non-coughing dogs and 49% coughing dogs, TRA2-group 20% non-coughing and 80% coughing dogs and TRA3-group was entirely represented by coughing dogs (100%). In TRA1-group 43% dogs were in B1-stage of CHF, 17% in B2 and 40% in C. In TRA2-group 16% dogs were in B2-stage, 68% in C and 16% in D. In TRA3-group 40% dogs were in C-stage and 60% in D. TRA2 and TRA3-groups showed the highest percentage of coughing dogs. The B1-stage was represented exclusively in TRA1-group and not any B-stage dog was identified in the TRA3-group. These results evidenced that TRA3 is always associated with cough and CHF signs (C/D stage). The obtained data confirmed the important role of airways compression by LAE in cough pathogenesis of MMVD dogs, and the LAE significance in determining CHF. Otherwise not any strong correlation between cough and TRA1-group was found: coughing dogs and not resulted equal represented. The TRA1 coughing dogs belonging to B1-stage (100% TRA1-group) were probably animals with respiratory diseases and it would be interesting to investigate this hypothesis trough further diagnostic tests such as bronchoscopy. In conclusion TRA3 is always associated with cough and CHF. TRA1 and TRA2 additional tools to assess the hemodynamic state of a MMVD dog or to establish cough pathogenesis are necessary. These preliminary data indicate that a relationship exists, even if additional studies are required.