Comparison of two echocardiographic views for evaluating the right pulmonary artery distensibility index in dogs.

Echocardiographic evaluation of the right pulmonary artery distensibility index (RPAD index) was recently described as a valuable method for early detection and severity evaluation of pulmonary arterial hypertension in dogs. RPAD index is calculated as the percentage change in diameter of the right pulmonary artery (RPA) between systole and diastole, obtained by M-mode echocardiography from the right parasternal long axis view. The aim of this study was to compare the RPAD index obtained by 2 different echocardiographic views in dogs. The study design was a prospective, multicenter, observational study. Forty-five clientowned dogs from different breeds were included: 31 dogs with heart disease and 14 healthy dogs. Two different right parasternal views, long axis (RPLA) and short axis (RPSA), were used to measure the RPAD index. From the RPLA view (method 1) and RPSA view (method 2) a short axis and a long axis image were respectively optimized for the right pulmonary artery. The RPAD index was calculated by M-mode as the percentage change in diameter of the right pulmonary artery: [(systolic diameter - diastolic diameter)/ systolic diameter]*100. Measurements were done off-line as an average of 5 consecutive cardiac cycles by a single investigator blinded to the dogs’ diagnosis. A Pearson and a Bland-Altman test were used to assess correlation and agreement between the 2 methods, respectively. Intra- and inter-observer measurement variability was quantified by average coefficient of variation (CV). Level of significance was set at P < 0.05. M-mode evaluation of the RPAD index was satisfactorily obtained by both methods in all dogs. Pearson test showed a strong positive linear correlation between the values of RPAD index obtained from both methods (r2 = 0.9346, P < 0.0001). Bland-Altman test showed a good agreement between the 2 methods in estimating RPAD index (bias = 0.51%, SD = 2.96%, 95% limits of agreement = 5.30, 6.33%). The mean difference between the 2 methods was 0.51% (95% confidence interval = 0.35; 1.35). Intra- and inter-observer measurement variability was clinically acceptable (CV<10%).The study showed a good agreement between short axis and long axis M-mode evaluation of RPA. Both methods can be used interchangeably to evaluate RPAD index. Further studies are needed to evaluate the RPAD index in a larger population of healthy dogs and the diagnostic and prognostic role of this echocardiographic parameter in dogs with different types of pulmonary hypertension.