Myxomatous mitral valve disease is the most common cause of cardiac-related morbidity and mortality in dogs. The effective regurgitant orifice area (EROA) is a measure of mitral regurgitant severity that can aid in earlier identification and intervention prior to significant disease progression. This echocardiographic metric is calculated via the proximal isovelocity surface area (PISA) or the stroke volume (SV) method, which are typically applied on single plane images that may not accurately reflect true three-dimensional shape.

The objective of this study is to ascertain the interchangeability of EROAs calculated from monoplane and multiplane approaches. The specific aims are to: 1) determine the level of agreement between, and the respective interoperator reproducibilities of, monoplane and real-time triplane measures of EROA using the PISA and SV methods; and 2) establish whether the agreement between biplane and real-time triplane measures of EROA exceeds that between monoplane and real-time triplane measures. We hypothesize that the monoplane- and real-time triplane-derived EROAs will have a low level of agreement, that the biplane-derived EROA will generate higher agreement with real-time triplane EROA, and that interoperator reproducibility will be good to excellent amongst all the approaches.

Sixty dogs with preclinical myxomatous mitral valve disease will be prospectively recruited over 10 months to undergo two echocardiograms by two operators in random consecutive order. The monoplane PISA and SV methods will be used to calculate EROAs from routine single plane images. A three-dimensional probe will also be used to obtain real-time triplane images; the triplane PISA method will be applied on simultaneous two long-axis views and one short-axis view of the mitral valve, while the triplane SV method will be applied on three simultaneous long-axis views of the left ventricle. Additionally, non-simultaneous images from both the left apical 4-chamber and 2-chamber views will be acquired for calculations using the biplane methods. All monoplane, biplane, and real-time triplane EROA measurements will be performed separately offline and in a blinded fashion. Their agreements will be assessed by the mean difference (paired t-test), Bland-Altman analysis, and concordance correlation coefficients. The interoperator reproducibility will be assessed by intraclass correlation coefficients and reproducibility coefficients. Data analysis will be completed within 2 months of case recruitment.

The results of this study will allow veterinary cardiologists to more accurately stratify higher risk dogs with preclinical myxomatous mitral valve disease for earlier intervention, as well as understand the limitations and degree of bias that each method possesses.