Echocardiographic evaluation of regurgitant fraction in dogs with subclinical myxomatous mitral valve disease: Method comparison, effects of pimobendan, and reproducibility.

Abstract

INTRODUCTION/OBJECTIVES: To evaluate regurgitant fraction (RF) using Simpson's method of discs to estimate total stroke volume (RF) and using Motion-mode to estimate total stroke volume (RF) in dogs with subclinical myxomatous mitral valve disease (MMVD). We also sought to evaluate the effects of pimobendan on RF, and to determine the reproducibility of RFand RF. ANIMALS, MATERIALS, AND METHODS: Echocardiography was performed on 57 dogs with MMVD (30 stage B1 and 27 stage B2). Ten dogs received pimobendan for 7-10 days and had a second echocardiogram. Nine dogs underwent six repeated echocardiographic examinations by two operators on three nonconsecutive days within one week for reproducibility analysis. RESULTS: Both RFand RFexhibited a curvilinear relationship with left atrium-to-aortic root ratio. Both RFand RFvaried considerably within stage B1 (minimum-maximum: -9.1%-58.2% and -35.7%-66.2%, respectively) and B2 (13.6%-76.2% and 20.1%-85.7%, respectively). Method comparison showed RFand RFwere not interchangeable with proportional bias. Pimobendan significantly reduced RF(-32.0% ± 23.3%) and RF(-19.2% ± 10.9%) within the same dog and relative to controls. Good inter-day and between-operator reproducibility was observed for RFand RFbased on intraclass correlation coefficients 0.86-0.90 and 0.83-0.90, respectively. Reproducibility coefficients were 19.6%-24.1% and 24.1%-27.0%, respectively. CONCLUSIONS: Use of RF using the total stroke volume method to aid the assessment of dogs with subclinical MMVD might be of clinical value. However, further study is warranted. Based on response to pimobendan and reproducibility analysis, RFmight be a more reliable technique to quantify RF.