A body weight-based formula of the canine aortic valve diameter for use in echocardiographic stroke volume and cardiac output calculations.

OBJECTIVE

To generate and test a formula to predict the echocardiographic aortic valve (AV) diameter (AVd) for use in echo-hemodynamic evaluations.

METHODS

Echocardiograms of hemodynamically stable dogs more than 1 year old that included images of the AV in the right parasternal inflow-outflow view with concurrent ECG were included. Exclusions included AV pathology, congestive heart failure, systolic dysfunction, sustained arrhythmias, congenital heart diseases, hypovolemia, systemic hypertension, and pericardial and pleural space diseases. The AVd was measured in centimeters in triplicate using digital calipers. A linear regression examined the relationship between weight and AVd, generating a predictive formula. Next, 20 dogs had their AVd measured and predicted, and stroke volumes were calculated using each method. These were compared using the paired Student t test, intraclass correlation coefficients, coefficients of variation, and Bland-Altman plots.

RESULTS

Data from 176 unique dogs included 64 (34.7%) normal hearts and 109 (61.9%) with preclinical myxomatous mitral and/or tricuspid valve disease. The median (range) age was 8 (1 to 16) years; weight was 9.6 (1.7 to 73) kg. The median (range) AVd was 1.20 (0.60 to 2.45) cm. The formula derived was AVd = 0.545 X (weight)0.347 (r2 = 0.875). Despite moderate agreement and low variation between the predicted and measured AVd, differences occurred due to mild systematic underestimation (-0.1 ± 0.13 cm), with consequent underestimation of stroke volumes.

CONCLUSIONS

The formula allowed calculation of AVd, although underestimation resulted in differences between measured and predicted stroke volumes.

CLINICAL RELEVANCE: Using a formula can reduce acquisition and measurement error; however, it must be validated with a larger sample.