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
