Mitral regurgitation (MR) is a common finding in dogs, most often secondary to degenerative mitral valve disease. This overwhelmingly affects either the anterior leaflet alone, or both leaflets together (Terzo et al., 2009).
The 2D clip below gives some hints as to the underlying pathology. The left atrium appears dilated, the point of coaptation of the mitral valve leaflets appears to be behind the level of the annulus, suggestive of bileaflet prolapse.
Notice how the body of the leaflets bow back behind the annular plane:
To be sure that regurgitation is present, however, we would have to visualise a regurgitant jet, especially as there were no other supportive signs such as evidence of pulmonary hypertension secondary to left-sided valve disease. The easiest way to detect regurgitation is usually with colour Doppler, but this little dog’s heart rate was so fast that it presented a real challenge for the colour frame rate of the ultrasound machine. The flash of turbulence of the colour flow in the left atrium during systole is perhaps the only clue that something is amiss in the clip below:
In the clip below, the flow of blood back into the left atrium during systole is a little more readily appreciated (but still tricky!). Freezing the image and going back through the frames using the trackball can also help to check timings.
In this case, Continuous Wave (CW) Doppler was used to confirm the presence of the MR without doubt. Even without parallel alignment (an apical view would have been better), the mitral regurgitation (MR) trace shown below is dense. The sound coming from the speakers was loud and harsh, and likely similar to the murmur heard on auscultation. Qualitatively, therefore, this dog appears to have at least moderate mitral regurgitation due to bileaflet mitral valve prolapse.
Terzo, E., Di Marcello, M., McAllister, H. et al. (2009). Echocardiographic assessment of 537 dogs with mitral valve prolapse and leaflet involvement. Vet Radiol Ultrasound, Jul-Aug, 50(4):416-22.