Association of component measurement variability and disease severity with variability of calculated mitral regurgitant fraction in dogs with myxomatous mitral valve disease.

MR% variability is greatest in early MMVD, driven primarily by sinus arrhythmia and lower LA:Ao ratios.

This study investigated the variability of echocardiographically calculated mitral regurgitant fraction (MR%) in 109 dogs with myxomatous mitral valve disease (MMVD), focusing on how component measurement variability and disease severity markers influence overall MR% variability. The geometric technique for calculating MR% relies on four component variables, each introducing potential measurement error. Using coefficient of variation (COV) calculated from three repeated measurements, the authors employed multivariable linear regression to identify predictors of MR% variability. Key findings revealed that MR% variability correlated negatively with disease severity—meaning measurements became more consistent as disease progressed—and decreased across advancing ACVIM stages. Component variables individually demonstrated acceptable variability (<10% COV) across all disease stages. In the multivariable model, COV of aortic diameter measured at mid-systole in the right parasternal long-axis view was the only component variable significantly associated with MR% variability. Notably, left atrial-to-aortic ratio (LA:Ao) showed the strongest inverse association with MR% variability, while R-R interval variability showed a positive association, implicating sinus arrhythmia-driven beat-to-beat variation as a significant contributor to MR% measurement inconsistency. The authors propose that physiological variation from sinus arrhythmia—common in dogs—substantially influences echocardiographic MR% calculations. These findings are clinically relevant because MR% may be less reliable in early-stage MMVD patients, where sinus arrhythmia is more prevalent and disease-related hemodynamic changes are subtler. The retrospective nature of the data is acknowledged as a study limitation.

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