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

Background

Reliability of echocardiographic calculations for stroke volume and mitral regurgitant fraction (RF_MR) 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 RF_MR.

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 RF_MR = 0% and extrapolated across a range of expected RF_MR values in the reliability cohort partly derived from cardiac dimensions predicted by the allometric cohort.

Results

Accuracy of methods to determine RF_MR in descending order was 4-chamber bullet (Bullet_4CH), mitral inflow, cube formula, and Simpson's method of disks. Intraobserver variability was relatively high. The CCV for RF_MR ranged from 28% to 88% and was inversely related to RF_MR when extrapolated for use in affected dogs. For both observers, the Bullet_4CH 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 RF_MR have low accuracy and high variability in healthy dogs. Extrapolation of observed CCV to a range of expected RF_MR 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.