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

INTRODUCTION/OBJECTIVES: To evaluate regurgitant fraction (RF) using Simpson's method of discs to estimate total stroke volume (RFSMOD_TSV) and using Motion-mode to estimate total stroke volume (RFM-modeTSV) 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 RFSMOD_TSV and RFM-modeTSV. 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 RFSMOD_TSV and RFM-modeTSV exhibited a curvilinear relationship with left atrium-to-aortic root ratio. Both RFSMOD_TSV and RFM-modeTSV varied 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 RFSMOD_TSV and RFM-modeTSV were not interchangeable with proportional bias. Pimobendan significantly reduced RFSMOD_TSV (-32.0% ± 23.3%) and RFM-modeTSV (-19.2% ± 10.9%) within the same dog and relative to controls. Good inter-day and between-operator reproducibility was observed for RFSMOD_TSV and RFM-modeTSV based 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, RF SMOD_TSV might be a more reliable technique to quantify RF.