Effects of treatment type on vertebral heart size in dogs with myxomatous mitral valve disease.

The effect of treatment protocols including either pimobendan or ramipril on vertebral heart size (VHS) in dogs with class II-III (Scandinavian-modified NYHA system) congestive heart failure (CHF) due to myxomatous mitral valve disease (MMVD) was assessed. Radiographs from 42 dogs were analysed with 21 randomized to pimobendan and 21 to ramipril. VHS was measured prior to treatment at inclusion (Month 0) and at Months 1, 3, and 6. The least square means for the individual treatment groups showed that, for the pimobendan group, a reduction in VHS at Months 1 and 3 of treatment was observed with an increase at Month 6. In the ramipril group, an increase in VHS occurred at Months 1, 3, and 6. A difference in the treatment group least square means was demonstrable after 1 month of treatment and persisted for the remainder of the study period. Treatment with pimobendan led to lower VHS than treatment with ramipril. The clinical relevance of the changes observed in this study is as yet unclear and needs further investigation. However, it can be speculated that a reduction in VHS is a positive outcome and pimobendan would appear to be more beneficial than ramipril in this respect.