Background: Right ventricular (RV) dysfunction independently predicts outcomes in human myxomatous mitral valve disease (MMVD). There is limited information regarding RV systolic function in dogs with MMVD. Hypothesis: Right ventricular systolic function differs among stages of disease, decreasing in decompensated MMVD. Animals: Thirty-sixclient-owned dogs with MMVD not receiving oral cardiovascular medications. Methods: Prospective clinical study. Dogs were categorized according to disease severity as ACVIM Stage B1, B2, or C. Seven echocardiographic indices of RV systolic function were measured. Groups were compared by 1-way ANOVA and Tukey's HSD test. Frequencies of cases with cardiac remodeling falling outside previously established reference intervals were compared using Fisher's exact test. Intra-and interobserver measurement variability was calculated for each RV function index. Results: The indices TAPSE (P = 0.029), RV St(L) (P = 0.012), and RV StR(L) (P = 0.041) were significantly different between groups. A greater proportion of B2 dogs (7 of 12) had TAPSE values above reference intervals compared with B1 (2 of 12) or C (2 of 12) dogs (P = 0.027). Measurement variability of TAPSE, RV S', and RV St(G) was clinically acceptable. Conclusions and Clinical Importance: Right ventricular systolic function differs between stages of MMVD, increasing in stage B2, and declining in stage C. The prognostic importance of RV function indices, particularly TAPSE, might be worth evaluating in dogs with MMVD.
