Left and right-side echocardiographic measurement of pulmonary artery stiffness in thoroughbred racehorses

Background: Pulmonary Artery Stiffness (PAS) is a non-invasive echocardiographic index of pulmonary artery elasticity. In horses, PAS has been measured only from the right parasternal short-axis view, while the influence of alternative imaging windows remains unknown. Aims/objectives: To assess the repeatability and reproducibility of Acceleration Time (AT), Maximal Frequency Shift (MFS), and PAS measurements from the left parasternal angled view of the right ventricular inflow/outflow, and to compare these parameters with those obtained from the right parasternal short-axis view in Thoroughbred racehorses. Methods: Forty Thoroughbreds underwent pulsed-wave Doppler echocardiography from both right and left parasternal views. Measurements included AT, MFS, and PAS (MFS/AT). The intra-class correlation coefficient (ICC) and the coefficients of variation (CV) were used to assess intra-operator repeatability and inter-operator (three operators) reproducibility in 40 horses, day-to-day (two different days) repeatability in 5 horses, and inter-operator (two operators) reproducibility for image acquisition in 10 horses. The Wilcoxon signed-rank test was used to compare left and right parasternal measurements in 40 horses. Results: Intra-operator agreement was excellent for all parameters (AT: ICC=0.94; MFS: ICC=0.95; PAS: ICC=0.97). Inter-operator agreement ranged from moderate to excellent (AT: ICC=0.63-0.87; MFS: ICC=0.96-0.99; PAS: ICC=0.83-0.96). Day-to-day agreement was good for AT (ICC=0.80) and MFS (ICC=0.71), and excellent for PAS (ICC=0.98). Inter-observer agreement for image acquisition ranged from good to excellent (AT: ICC=0.97, MFS: ICC=0.86, PAS: ICC=0.94). Compared to the right view, the left parasternal view showed lower AT (110 vs. 151 ms), higher MFS (2.6 vs. 2.27 kHz), and higher PAS (23.8 vs. 15.6 kHz/s) (all p<0.001). Conclusion: PAS can be consistently measured from the left parasternal angled view in Thoroughbred racehorses. PAS was higher when measured from the left parasternal window, possibly due to a better alignment of the Doppler beam with the pulmonary artery flow.