Echocardiographic assessment of mitral regurgitation severity in dogs

Mitral regurgitation (MR) is the most important cardiovascular problem affecting dogs. Transthoracic echocardiography is the most practical imaging modality to characterize the fundamental features of MR, including an assessment of MR severity. The diversity of MR severity in subclinical dogs and advancements in treatments directed at the cause of MR have (re)ignited interest in more comprehensive and quantitative methods of assessing MR severity. This review focuses on evaluating the severity of chronic MR in dogs. It discusses when a comprehensive assessment of MR severity is indicated. It highlights the strengths, limitations and challenges associated with the numerous structural, qualitative, semiquantitative and quantitative variables available to assess MR severity. The methods involved in determining the important quantitative variables of MR severity such as effective orifice area, regurgitant volume and regurgitant fraction are reviewed in detail. This paper advocates for an integrative approach, ideally from guidelines generated by an expert panel, where multiple echocardiographic variables from multiple categories are incorporated to assess MR severity and grade the MR as mild, moderate or severe. It summarizes the work on assessing MR severity in dogs to date and highlights shortcomings where there is much work to be done.