An Assessment of Thoracic Inlet Heart Score in Maltese Dogs with ACVIM Stage B Myxomatous Mitral Valve Disease

Myxomatous mitral valve disease (MMVD) is the most common cardiac disease in dogs. Vertebral heart score (VHS) is used for the diagnosis, treatment, and monitoring of MMVD, and it is one of the criteria used to distinguish between stages B1 and B2 according to the American College of Veterinary Internal Medicine (ACVIM) guidelines. The thoracic inlet heart score (TIHS) method is simple to perform and provides practitioners with an additional tool for evaluating dogs with clinical signs compatible with MMVD stage B. Previous studies have evaluated TIHS. In our study, we assessed correlations of TIHS with other radiographic and echocardiographic indices in Maltese dogs with MMVD stages B1 and B2. Eighty-seven Maltese dogs with MMVD stage B1 or B2, which visited Chungnam National University Veterinary Medicine Teaching Hospital, were included in this study. Each dog was diagnosed with MMVD ACVIM stage B1 or B2 through physical examination, cardiac auscultation, thoracic radiography, and echocardiography, with evaluation of TIHS, VHS, vertebral left atrial size (VLAS), left atrial to the aotic root ratio (LA:Ao ratio), and left ventricular internal diameter in diastole, normalized for body weight (LVIDDn). TIHS increased as the disease progressed and showed a significant difference between stages B1 and B2. Furthermore, TIHS positively correlated with VHS, LA:Ao ratio, and LVIDDn. The correlation coefficients revealed the strongest significant correlations between TIHS and VHS. In conclusion, TIHS can help diagnose and monitor MMVD in Maltese dogs, in addition to measuring VHS.