will have a poorer outcome with increased risk of congestive cardiac failure and premature death, but this has never been clearly demonstrated. This is in part due to lack of a validated gold standard technique with which to accurately quantify MR.Several studies have investigated the association of echocardiographic measures on survival or onset of congestive heart INTRODUCTIONMitral regurgitation (MR) associated with myxomatous mitral valve disease (MMVD) is highly prevalent in older small breed dogs (Whitney 1974, Thrusfield et al. 1985 and is the third most common cause of death in this species (Haggstrom et al. 2004). It is reasonable to suspect that dogs with worse MR RESULTS: Measurement of cardiac magnetic resonance imaging-derived mitral regurgitant fraction was attempted in 21 dogs. Twelve consecutive, complete studies were obtained and 10 dogs were included in the final analysis: vena contracta/aortic diameter (r=0·89, p=0·001) and E-wave velocity (r=0·86, p=0·001) had the strongest correlations with cardiac magnetic resonance imaging-derived mitral regurgitant fraction. E velocity had superior repeatability and could be measured in all dogs.The presence of multiple jets precluded vena contracta/aortic diameter measurement in one dog.CLINICAL SIGNIFICANCE: Measurement of cardiac magnetic resonance imaging-derived mitral regurgitant fraction is feasible but technically demanding. The echocardiographic measures that correlated most closely with cardiac magnetic resonance imaging-derived mitral regurgitant fraction were vena contracta/aortic diameter and E-wave velocity.

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