C03 - Two- and Three-Dimensional Echocardiographic Assessment of Canine Left Ventricular Outflow Tract Velocity and Area

Abstract:
Background: Clinically, dogs are screened for subaortic stenosis (SAS) using 2-D and Doppler echocardiography. Distinguishing between mild SAS and unaffected can be difficult, and a more precise evaluation of the left ventricular outflow tract (LVOT) is desirable.

Hypothesis/Objectives: To determine the step-up in Doppler-derived peak velocity at different sites of the LVOT and ascending aorta, investigate associated factors, and determine the aortic orifice area using 2-D and 3-D echocardiography in dogs.

Animals: Sixty-nine healthy, privately-owned dogs.

Methods: Prospective study evaluating 2-D, spectral Doppler, and 3-D echocardiographic indices of the LVOT and aorta.

Results: Obtaining 3-D images and performing LVOT planimetry was feasible in all dogs (body weight: 4.8-56.6 kg). The mean (range) total step-up in velocity from LVOT to ascending aorta was 105 cm/s (65-168 cm/s) and 83 cm/s (34-128 cm/s) from subcostal and left apical (Lap) views, respectively. Subcostal-derived peak LVOT velocity was higher than Lap (p < 0.001), and peak velocities derived from both imaging planes were greater after behavioural stimulation (p < 0.001). Heart rate, left ventricular volume, and 3-D echocardiography-derived aortic valve (AoV) area were significantly associated with LVOT velocity. The 3-D planimetric AoV area was greater than the 2-D AoV annulus diameter-derived area (p < 0.001). The continuity equation underestimated 2-D and 3-D measures of LVOT area.

Conclusions and clinical importance: These results quantify the expected step-up in LVOT velocity and identify associated factors in apparently normal dogs. This information can be used for improving the accuracy of echocardiography in assessing dogs for SAS.