Comparison of transducer placement sites for Doppler echocardiography in dogs with subaortic stenosis.

Effects of transducer placement site and various operators on Doppler echocardiographic measures were evaluated in 12 dogs with subaortic stenosis. Dogs sedated by IV administration of acepromazine and buprenorphine were examined by 2 observers. Maximal aortic velocity and aortic velocity time integral were determined from Doppler aortic velocity spectra recorded, using a 1.9-MHz continuous wave nonimaging transducer placed at 3 echocardiographic sites: left ventricular apex (LA), suprasternal notch (SSN), and subcostal (SC). Doppler-estimated left ventricular-to-aortic pressure gradients were calculated from the traced velocity spectra by application of the modified Bernoulli equation. Each observer recorded high-quality Doppler spectral signals in all dogs from the SC and LA transducer sites and in 83% of dogs from the SSN window. Mean values for maximal aortic velocity and velocity time integral differed among sites (P < 0.05), but not between observers. Maximal velocity and velocity time integral measured from the SC transducer site were higher than those measured from the SSN or LA positions. Presumably, SC transducer placement provided the highest aortic velocities because of optimal alignment with aortic outflow. The maximal pressure gradient estimated from SC velocities exceeded SSN values by 27 mm of Hg and LA measurements by 38 mm of Hg. In this study, the optimal site for the Doppler echocardiographic detection of subaortic stenosis and assessment of this lesion's hemodynamic importance in most affected dogs was the SC position.