The most common acquired cardiovascular disease in dogs is chronic degenerative mitral valve disease as a result of myxomatous degeneration; that is, myxomatous mitral valve disease (MMVD). In general, MMVD has a long preclinical period before heart failure develops. The records of 256 dogs with stage B1 (n = 136) or B2 (n = 120) MMVD were reviewed retrospectively. Long-term outcome was assessed by follow-up telephone interview; if the dog was alive, the client was asked to bring it in for reevaluation. Thirty-four different breeds were represented; the majority weighed <20 kg. Clinical signs included cough (21%), syncope (9%), and systolic murmur (65%). No murmur was auscultated in 26% of dogs. Median survival time regardless of cause of death was 588 days (range, 75–1668 days). Of the 13 variables evaluated, only presence of murmur showed a negative prognostic effect on survival. Seventy dogs died between the time of initial examination and telephone interview; 30 deaths were considered cardiac related. Reevaluation was possible for 83 of the remaining dogs; 32 had progressed to more advanced stages of MMVD. Two variables were associated with significantly increased risk for progression to a more advanced stage of disease: cough and peak E-wave velocity (Emax) >1.2.

Commentary
An important finding in this study is that early-stage MMVD seems relatively benign, with only a small percentage of patients progressing to heart failure during the observation period. However, the population studied was diverse and the survival time documented demonstrated a wide range. In addition, a significant amount of variability and uncertainty reflected the retrospective nature of the study and missing patient data. Therefore, prospective evaluation of early MMVD with established criteria for evaluation and treatment (eg, presence and intensity of heart murmur, thoracic radiographic measurements, echocardiographic variables, medications) might minimize the variability.—Jennifer Ginn, DVM,MS, DACVIM

Source
Survival characteristics and prognostic variables of dogs with preclinical chronic degenerative mitral valve disease attributable to myxomatous degeneration. Borgarelli M, Crosara S, Lamb K, et al. J VET INTERNMED 26:69-75, 2012.