Observed and expected reliability of echocardiographic volumetric methods and critical change values for quantification of mitral regurgitant fraction in dogs

Abstract Background Reliability of echocardiographic calculations for stroke volume and mitral regurgitant fraction (RFMR) are affected by observer variability and lack of a gold standard. Variability is used to calculate critical change values (CCVs) that are thresholds representing real change in a measure not associated with observer variability. Hypothesis Observed intra‐ and interobserver accuracy and variability in healthy dogs help model CCV for RFMR. Animals Reliability cohort of 34 healthy dogs; allometric scaling cohort of 99 dogs with heart disease and 25 healthy dogs. Methods Accuracy, variability, and CCV of 2 observers using geometric and flow‐based echocardiography were prospectively compared against a standard of RFMR = 0% and extrapolated across a range of expected RFMR values in the reliability cohort partly derived from cardiac dimensions predicted by the allometric cohort. Results Accuracy of methods to determine RFMR in descending order was 4‐chamber bullet (Bullet4CH), mitral inflow, cube formula, and Simpson's method of disks. Intraobserver variability was relatively high. The CCV for RFMR ranged from 28% to 88% and was inversely related to RFMR when extrapolated for use in affected dogs. For both observers, the Bullet4CH method had the lowest intraobserver CCV (Operator 1:28%, Operator 2:41%). Interobserver strength of agreement was low with intraclass correlation coefficients ranging from 0.210 to 0.413. Conclusions and Clinical Importance Echocardiographic volumetric methods used to calculate stroke volume and RFMR have low accuracy and high variability in healthy dogs. Extrapolation of observed CCV to a range of expected RFMR suggests observers and methods are not interchangeable and variability might hinder routine clinical usage. Individual observers should be aware of their own variability and CCV.