Effect of mitral valve repair on outcomes in dogs with preclinical myxomatous mitral valve disease: a retrospective cohort study

INTRODUCTION/OBJECTIVES Mitral valve repair (MVR) for myxomatous mitral valve disease (MMVD) in dogs has favorable results, but its effectiveness compared with medical treatment in preclinical (stage B2) dogs remains unclear. This study investigated whether MVR improves survival in preclinical dogs with MMVD. ANIMALS, MATERIALS, AND METHODS Dogs diagnosed with stage B2 MMVD between October 2016 and September 2020 were divided into an MVR group and a control group receiving medical treatment. The primary outcome was a composite of all-cause mortality and the first onset of pulmonary edema. The waiting period between diagnosis and surgery in the MVR group was adjusted as a time-dependent exposure, and survival analysis was performed. RESULTS Overall, 91 and 171 dogs were enrolled in the MVR and control groups, respectively. The median observation period was 599.5 days (lower and upper quartiles: 374.0-1001.5). The primary outcome occurred in 10 dogs (11.0%) in the MVR group and 69 dogs (40.4%) in the control group. Cox proportional hazards analysis adjusted for time-dependent exposure yielded hazard ratios of 0.12 (95% confidence interval [CI]: 0.05-0.25, P < 0.001) for MVR and 2.85 (95% CI: 1.69-4.80, P < 0.001) for diuretic use. STUDY LIMITATIONS Limitations include potential selection bias, limited survey response rate, inter-observer variability in diagnostic assessment, and a short follow-up period. CONCLUSIONS Dogs undergoing MVR had a lower risk of reaching the composite endpoint than medically managed dogs. These findings may assist veterinarians and owners in decision-making regarding MVR for stage B2 dogs.