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

INTRODUCTION/

OBJECTIVES

Echocardiographic calculation of mitral regurgitant fraction (MR%) may complement variables used to assess myxomatous mitral valve disease (MMVD) severity. The geometric technique of calculating MR% uses four component variable measurements. Calculations using multiple measurements necessarily influence variability. The influence of disease severity on component measurements and MR% variability has not been explored. This study explored the contribution of component measurement variability and the markers of disease severity: left atrial-to-aortic ratio, R-R interval (RR) variability and heart rate on MR% variability.

ANIMALS, MATERIALS AND

METHODS

Echocardiographic studies from 109 dogs with MMVD were analysed. The co-efficient of variation (COV) was calculated from three measurements of each echocardiographic variable and calculated MR%. A multivariable linear regression model was devised modelling COV MR% as the outcome variable.

RESULTS

The COV of MR% correlated negatively with MR% severity and decreased with increasing American College of Veterinary Internal Medicine stages. Component variables of MR% generally had variability <10% in all American College of Veterinary Internal Medicine stages. In a multivariable model, of the component variables, only COV aortic diameter measured between the open aortic leaflets at mid-systole in a right parasternal long-axis view showed positive correlation with MR% variability (2.17, P=0.010). However, MR% variability showed clearest association with left atrial-to-aortic ratio (-16.89, P=0.001) and variation in R-R interval (COV RR: 1.47, P=0.002, COV RR2 = -0.04, P=0.013).

STUDY LIMITATIONS: Modelling of retrospective data is a limitation of the present study.

CONCLUSIONS

Variability of MR% is associated with disease severity. We propose beat-to-beat variation in component variables attributable to sinus arrhythmia is associated with variability of mitral regurgitation and echocardiographic calculation of MR% in dogs. These results provide insights into echocardiographic measurement variability in MMVD and assist interpretation of MR% at different disease stages.